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Optimization Guidance Manual
for
Drinking Water Systems
2014
Ministry of the Environment
ISBN 978-1-4606-3734-0
Optimization Guidance Manual
for
Drinking Water Systems
2014
Ministry of the Environment
PIBS 9649e
DISCLAIMER i
Optimization Guidance Manual for Drinking Water Systems 2014
DISLAIMER
This optimization Guidance manual for drinking water systems (“Optimization Manual”) was
prepared by XCG Consultants Ltd. in collaboration with Her Majesty the Queen in right of
Ontario as represented by the Minister of the Environment (“Ministry”) and is intended to be a
representative compilation and assessment of the current state of knowledge on optimization
measures for drinking water systems in Ontario. The views and ideas expressed in this
Optimization Manual are solely those of the XCG Consultants Ltd.
The contents of the Optimization Manual were prepared in accordance with generally recognized
engineering principles and practices existing at the time of its preparation and are for general
information purposes only. In preparing the Optimization Manual, third party data and
information has been provided and relied upon which has not been independently verified and
which due to the nature or source of the data, is assumed to be accurate, complete, timely, non-
infringing and fit for the intended purpose. The Optimization Manual is a technical document and
is not a legal representation or interpretation of any environmental laws, rules, regulations, or
policies of the Ministry or any governmental agencies. All findings stated in the Optimization
Manual are based on facts and circumstances as they existed during the time period that the
Optimization Manual was prepared. Any changes in fact or circumstances which may have
occurred subsequent to the time of preparation of the Optimization Manual may change the
findings in the Optimization Manual.
XCG Consultants Ltd. and the Ministry make no representation or warranty of any kind
whatsoever with respect to the completeness or accuracy of the information contained in the
Optimization Manual. Readers are advised to obtain competent advice prior to relying on or using
any information contained in the Optimization Manual with respect to its suitability for general or
specific application.
XCG Consultants Ltd. and the Ministry and their respective officers, employees, servants or
agents expressly disclaim all liability for damages of any kind (including without limitation,
damages for loss of profits, business interruption, loss of information, or direct, indirect,
incidental, special, consequential or punitive damages) arising out of the use of, reference to, or
reliance on the information contained herein whether under contract, in tort or under any other
basis of liability.
Cette publication hautement spécialisée n’est disponible qu’en anglais en vertu du
règlement 441/97, qui en exempte l’application de la Loi sur les services en français.
Pour obtenir de l’aide en français, veuillez communiquer avec le ministère de
l’Environnement au (416) 327- 6949
ACKNOWLEDGEMENTS ii
Optimization Guidance Manual for Drinking Water Systems 2014
ACKNOWLEDGEMENTS
The Optimization Guidance Manual for Drinking Water Systems was prepared by XCG
Consultants Ltd. under the guidance of the Technical Working Group identified below. This
document underwent review by various branches of the Ontario Ministry of the Environment
(MOE) and the following stakeholders and reviewers.
Technical Working Group
Robert Dumancic, M.A.Sc., P.Eng., Standards Development Branch, MOE
George Lai, M.Eng., P.Eng., Standards Development Branch, MOE
Xibo Liu, Ph.D., P.Eng., Safe Drinking Water Branch, MOE
Ranee Mahalingam, M.Eng., P.Eng., Safe Drinking Water Branch, MOE
Mirek Tybinkowski, M.Eng., P.Eng., Land and Water Policy Branch, MOE
The following stakeholders and reviewers reviewed and provided valuable input to the
Optimization Manual.
Stakeholders and Reviewers
Dr. William B. Anderson, Ph.D., Academia (University of Waterloo)
Dr. Susan Andrews, Ph.D., P.Eng., Academia (University of Toronto)
Jane Bonsteel, Ontario Water Works Association (Peel Region)
Steve Burns, P.Eng., Engineering Practitioner ( B.M. Ross and Associates Ltd.)
Ian Douglas, P.Eng., Drinking Water Quality Professionals (City of Ottawa)
Andrew Farr, P.Eng., Ontario Water Works Association (Peel Region)
Martin Gravel, P.Eng., Ontario Water Works Association (Genivar Ontario Inc.)
Patrick Halevy, M. Sc., Drinking Water Quality Professionals (City of Brantford)
Dr. William Hargrave, Ph.D., P.Eng., Engineering Practitioner (W.J. Hargrave &
Company Inc.)
Andrew J. Henry, P.Eng., Ontario Municipal Water Association (Lake Huron & Elgin
Area Primary Water Supply System)
Brian Jobb, Walkerton Clean Water Centre
Asim Massaud, P.Eng., Ontario Clean Water Agency
Judith Patrick, Standards Development Branch, MOE
Thom Sloley, P.Eng., Municipal Engineers Association (Durham Region)
Alex Vukosavljevic, B.A., Water Treatment Operators (City of Toronto)
Tim Walton, Ontario Water Works Association (Waterloo Region)
PREAMBLE iii
Optimization Guidance Manual for Drinking Water Systems 2014
PREAMBLE
This Ministry of the Environment (MOE) Optimization Guidance Manual for Drinking Water
Systems is developed in response to the increasing need to improve performance, increase
capacity and/or reduce the operating costs associated with existing Ontario drinking water
systems. The selection and design of specific unit processes is beyond the scope of this manual.
Optimization is an important aspect in the protection of public health. Many outbreaks of
waterborne illnesses have occurred because the operation of unit processes or system components
were not optimized (e.g. North Battleford, Saskatchewan and Milwaukee, Wisconsin).
Drinking water treatment plants (WTPs) represent a significant capital investment for most
municipalities and their efficient operation and maintenance is critical to ensuring a safe and
adequate supply of drinking water. The combination of population growth and increasingly
stringent drinking water quality standards has prompted the need for increased treatment capacity
via upgrades and/or expansion, as well as addressing water quality issues for existing facilities. In
many cases, optimization of the treatment processes may meet the increased production demands,
improve performance and treated water quality, and can reduce the costs of upgrades and/or
expansion if additional treatment units are required. Optimization techniques are important for the
delivery of high quality water in the most efficient manner.
The intended users of this Manual are operating authorities, consultants, regulatory personnel and
others with the responsibility of achieving compliance or more consistent and efficient
performance from existing water treatment plants and distribution systems.
The users of this Manual should determine which statutes and regulations apply to a proposed
drinking water system optimization program and ensure that the users are familiar with treatment
requirements and approval/permits needed to carry out the optimization work. The
municipality/owner should contact the Safe Drinking Water Branch for information regarding
applicability of statutes/regulations and applications for approvals/permits.
TABLE OF CONTENTS iv
Optimization Guidance Manual for Drinking Water Systems 2014
TABLE OF CONTENTS
DISLAIMER ........................................................................................................................ i
ACKNOWLEDGEMENTS ................................................................................................ ii
PREAMBLE ...................................................................................................................... iii
TABLE OF CONTENTS ................................................................................................... iv
ACRONYMS & ABBREVIATIONS............................................................................... vii
CHAPTER 1 INTRODUCTION ..................................................................................... 1-1
1.1 Purpose and Objectives of the Manual ................................................................... 1-1
1.2 Using the Manual ................................................................................................... 1-1
1.3 Regulatory Requirements ....................................................................................... 1-2
1.4 What is Optimization? ............................................................................................ 1-2
1.5 When Should an Owner/Operator Optimize?......................................................... 1-6
1.6 What are the Benefits of Optimization? ................................................................. 1-7
1.7 What Does Optimization Cost and How Long Does it Take?................................ 1-9
1.8 Who Should Conduct the Optimization? .............................................................. 1-10
1.9 What are the General Approaches to Optimization? ............................................ 1-10
1.10 References ............................................................................................................ 1-12
CHAPTER 2 QUALITY MANAGEMENT SYSTEMS ................................................. 2-1
2.1 Introduction ............................................................................................................ 2-1
2.2 Quality Management Systems ................................................................................ 2-1
2.3 Operational Plans and Operations Manuals ........................................................... 2-3
2.4 Role of Water Operations Staff in Water System Optimization ............................ 2-4
2.5 Training of Operations Staff ................................................................................... 2-4
2.6 References .............................................................................................................. 2-5
CHAPTER 3 COMPOSITE CORRECTION PROGRAM ............................................. 3-1
3.1 Introduction ............................................................................................................ 3-1
3.2 CPE Methodology .................................................................................................. 3-1
3.3 Carrying Out a CPE .............................................................................................. 3-13
3.4 CTA Methodology................................................................................................ 3-25
3.5 How to Conduct a CTA ........................................................................................ 3-35
3.6 Required Personnel Capabilities for Conducting a CTA ..................................... 3-39
3.7 References ............................................................................................................ 3-40
CHAPTER 4 GENERAL OPTIMIZATION TECHNIQUES ......................................... 4-1
4.1 Introduction ............................................................................................................ 4-1
4.2 Field Evaluations .................................................................................................... 4-1
4.3 Modelling and Simulation ...................................................................................... 4-7
4.4 Case Histories ....................................................................................................... 4-11
4.5 References ............................................................................................................ 4-15
CHAPTER 5 INTAKE STRUCTURES AND SCREENING ......................................... 5-1
5.1 Introduction ............................................................................................................ 5-1
5.2 Sources of Supply ................................................................................................... 5-1
5.3 Intake Structures ..................................................................................................... 5-6
5.4 Screens .................................................................................................................... 5-9
5.5 Low-Lift (Raw Water) Pumping .......................................................................... 5-11
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Optimization Guidance Manual for Drinking Water Systems 2014
5.6 Pre-Chlorination/Oxidation and Zebra Mussel Control ....................................... 5-15
5.7 Case Histories ....................................................................................................... 5-16
5.8 References ............................................................................................................ 5-19
CHAPTER 6 COAGULATION AND FLOCCULATION ............................................. 6-1
6.1 Introduction ............................................................................................................ 6-1
6.2 Coagulation and Flocculation ................................................................................. 6-1
6.3 Optimization Techniques........................................................................................ 6-7
6.4 Case Histories ....................................................................................................... 6-12
6.5 References ............................................................................................................ 6-19
CHAPTER 7 CLARIFICATION ..................................................................................... 7-1
7.1 Introduction ............................................................................................................ 7-1
7.2 Clarification ............................................................................................................ 7-1
7.3 Optimization Techniques........................................................................................ 7-6
7.4 Case Histories ......................................................................................................... 7-8
7.5 References ............................................................................................................ 7-11
CHAPTER 8 FILTRATION ............................................................................................ 8-1
8.1 Introduction ............................................................................................................ 8-1
8.2 Granular Media Depth Filters ................................................................................. 8-1
8.3 Slow Sand Filters .................................................................................................. 8-13
8.4 Membrane Filters.................................................................................................. 8-17
8.5 Case Histories ....................................................................................................... 8-24
8.6 References ............................................................................................................ 8-27
CHAPTER 9 DISINFECTION ........................................................................................ 9-1
9.1 Introduction ............................................................................................................ 9-1
9.2 Chemical Inactivation ............................................................................................. 9-1
9.3 Ultraviolet (UV) Irradiation ................................................................................. 9-15
9.4 Case Histories ....................................................................................................... 9-21
9.5 References ............................................................................................................ 9-25
CHAPTER 10 OTHER TREATMENT PROCESSES .................................................. 10-1
10.1 Introduction .......................................................................................................... 10-1
10.2 Aeration and Air Stripping ................................................................................... 10-1
10.3 Ion Exchange ........................................................................................................ 10-4
10.4 Biologically Active Filtration ............................................................................... 10-5
10.5 Iron and Manganese Control ................................................................................ 10-6
10.6 Taste and Odour Control .................................................................................... 10-11
10.7 Natural Organic Matter Removal ....................................................................... 10-16
10.8 Internal Corrosion Control ................................................................................. 10-20
10.9 Case Histories ..................................................................................................... 10-25
10.10 References .......................................................................................................... 10-27
CHAPTER 11 DISTRIBUTION SYSTEMS ................................................................ 11-1
11.1 Introduction .......................................................................................................... 11-1
11.2 Treated Water Pumping Stations .......................................................................... 11-1
11.3 Treated Water Storage .......................................................................................... 11-4
11.4 Distribution System Piping and Appurtenances ................................................... 11-8
11.5 Case Histories ..................................................................................................... 11-20
11.6 References .......................................................................................................... 11-22
TABLE OF CONTENTS vi
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 12 RESIDUALS AND RECYCLE STREAMS ......................................... 12-1
12.1 Introduction .......................................................................................................... 12-1
12.2 Water Treatment Process Residuals ..................................................................... 12-1
12.3 Residuals Treatment Processes............................................................................. 12-3
12.4 Case Histories ..................................................................................................... 12-11
12.5 References .......................................................................................................... 12-14
CHAPTER 13 REPORTING RESULTS....................................................................... 13-1
13.1 Introduction .......................................................................................................... 13-1
13.2 Interim Reports – Technical Memoranda ............................................................. 13-1
13.3 Workshops ............................................................................................................ 13-2
13.4 Final Report .......................................................................................................... 13-3
13.5 Implementation of Recommendations and Follow-up ......................................... 13-5
APPENDICES
APPENDIX A: Classification System, Factor Checklist and Definitions ...................... A-1
APPENDIX B: Data Collection Forms........................................................................... B-1
APPENDIX C: Example CPE Report............................................................................. C-1
APPENDIX D: Example CPE Scheduling Letter and Letter to MOE Regarding
Project Approval ................................................................................... D-1
APPENDIX E: Example Special Study ........................................................................... E-1
APPENDIX F: Example CTA Summary Report ............................................................. F-1
APPENDIX G: Equations and Calculations ................................................................... G-1
A. Coagulation and Flocculation Calculations
B. Disinfection Calculations
ACRONYMS AND ABBREVIATIONS vii
Optimization Guidance Manual for Drinking Water Systems 2014
ACRONYMS & ABBREVIATIONS
Abbreviation Definition
1-D one-dimensional
2-D two-dimensional
3-D three-dimensional
AOA Ammonia oxidizing archaea
AOB Ammonia oxidizing bacteria
AOC Assimilable organic carbon
AOP Advanced oxidation process
AWWA American Water Works Association
AwwaRF American Water Works Association Research Foundation
(now known as the Water Research Foundation or WaterRF)
BDOC Biodegradable organic carbon
CCP Composite Correction Program
CFD Computational fluid dynamics
C of A Certificate of Approval
CPE Comprehensive Performance Evaluation
CSMR Chloride to sulphate mass ratio
CT Disinfectant concentration (C) x contact time (T)
CTA Comprehensive Technical Assistance
CWA Clean Water Act, 2006
DAF Dissolved air flotation
DBP Disinfection by-product
DO Dissolved oxygen
DOC Dissolved organic carbon
DWQMS Drinking Water Quality Management Standard
ACRONYMS AND ABBREVIATIONS viii
Optimization Guidance Manual for Drinking Water Systems 2014
Abbreviation Definition
DWS Drinking water system
DWSP Drinking Water Surveillance Program
DWWP Drinking Water Works Permit
EAA Environmental Assessment Act
EBCT Empty bed contact time
EBR Environmental Bill of Rights
EMS Environmental management system
EPA Environmental Protection Act
G Velocity gradient
GAC Granular activated carbon
GBT Gravity belt thickener
GCDWQ Guidelines for Canadian Drinking Water Quality
Gt Mixing intensity x detention time
GUDI Groundwater under the direct influence of surface water
HAA Haloacetic acid
HACCP Hazard Analysis and Critical Control Points
HDT Hydraulic detention time
HPC Heterotrophic plate count
HVAC Heating, ventilating and air conditioning
IDDF Integrated Disinfection Design Framework
IPZ Intake protection zone
ISO International Organization for Standardization
LPHO Low pressure high output
MAC Maximum acceptable concentration
MDWL Municipal Drinking Water License
ACRONYMS AND ABBREVIATIONS ix
Optimization Guidance Manual for Drinking Water Systems 2014
Abbreviation Definition
MF Microfiltration
MIB Methylisoborneol
MOE Ministry of the Environment
MP Medium pressure
MSDS Material safety data sheet
NF Nanofiltration
NMA Nutrient Management Act, 2002
NOM Natural organic matter
NP Number of particles
NTU Nephelometric turbidity unit
O & M Operations and Maintenance
OWRA Ontario Water Resources Act
PAC Powdered activated carbon
PACl Polyaluminum chloride
PASS Polyaluminum silicate sulphate
PLC Programmable logic controller
Q Flow rate
QMS Quality management system
RDT Rotating drum thickener
RO Reverse osmosis
rpm Rotations per minute
RTD Residence time distribution
SCADA Supervisory control and data acquisition
SCD or SCM Streaming current detector or monitor
SDWA Safe Drinking Water Act, 2002
ACRONYMS AND ABBREVIATIONS x
Optimization Guidance Manual for Drinking Water Systems 2014
Abbreviation Definition
SDWB Safe Drinking Water Branch
SOP Standard operating procedure
SOR Surface overflow rate
STP Sewage treatment plant
SVI Sludge volume index
TCU True colour units
THM Trihalomethane
THMFP Trihalomethane formation potential
TM Technical memorandum
TMP Transmembrane pressure
TOC Total organic carbon
TON Threshold odour number
TOT Time of travel
TS Total solids
TSS Total suspended solids
UF Ultrafiltration
UFRV Unit Filter Run Volume
USEPA United States Environmental Protection Agency
UV Ultraviolet
UVT Ultraviolet transmittance
VE Value Engineering
VFD Variable frequency drive
VOC Volatile organic compound
WHPA Wellhead protection area
WQA Water Quality Analyst
ACRONYMS AND ABBREVIATIONS xi
Optimization Guidance Manual for Drinking Water Systems 2014
Abbreviation Definition
WTP Water treatment plant
WTR Water treatment residuals
zp Zeta potential
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 1 INTRODUCTION
INTRODUCTION
1.1 Purpose and Objectives of the Manual ................................................................... 1-1
1.2 Using the Manual ................................................................................................... 1-1
1.3 Regulatory Requirements ....................................................................................... 1-2
1.3.1 Applicable Legislation Administered by the Ministry ............................ 1-2
1.3.2 Drinking Water Regulations and Support Documents ............................ 1-2
1.4 What is Optimization? ............................................................................................ 1-2
1.4.1 Overview of Optimization ....................................................................... 1-2
1.4.2 Total System Optimization including Unit Process Optimization ........... 1-5
1.4.3 Value Engineering and Optimization ...................................................... 1-6
1.5 When Should an Owner/Operator Optimize? ........................................................ 1-6
1.6 What are the Benefits of Optimization? ................................................................. 1-7
1.6.1 Reduce the Capital Cost of Expansion or Upgrading .............................. 1-7
1.6.2 Achieve Stricter Standards ....................................................................... 1-8
1.6.3 Improve Performance .............................................................................. 1-8
1.6.4 Reduce Operating Cost ............................................................................ 1-9
1.7 What Does Optimization Cost and How Long Does it Take? ............................... 1-9
1.8 Who Should Conduct the Optimization? .............................................................. 1-10
1.9 What are the General Approaches to Optimization? ............................................ 1-10
1.9.1 Operator Training .................................................................................. 1-11
1.9.2 Composite Correction Program (CCP) .................................................. 1-11
1.9.3 Modelling and Simulation ..................................................................... 1-11
1.10 References ............................................................................................................ 1-12
CHAPTER 1. Introduction 1-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 1
INTRODUCTION
1.1 PURPOSE AND OBJECTIVES OF THE MANUAL
The previous ministry optimization manual titled “Guidance Manual for the Optimization of
Ontario Water Treatment Plants using the Composite Correction Program (CCP) Approach”
(MOE, 1998) was aimed at improving the performance of conventional or direct-filtration
surface WTPs and was based on the United States Environmental Protection Agency
(USEPA) Handbook entitled “Optimizing Water Treatment Plant Performance Using the
Composite Correction Program” (USEPA, 1998).
Although the CCP approach is applicable to all sizes of systems, the MOE experience is that
smaller systems are those most in need of optimization. The previous MOE Manual mainly
addressed activities directed at achieving improved particulate removal and disinfection to
meet regulations. This Manual has been expanded to consolidate optimization methodologies,
techniques and practices, as applicable to Ontario, which had not been covered in the
previous manual, including optimization of: pumping; slow sand filtration; membrane
filtration and manganese greensand filtration; optimization to reduce disinfection by-product
(DBP) formation; and optimization of distribution systems to meet drinking water quality
standards.
The purpose of this revised MOE Manual is to present procedures for identifying factors that
cause poor performance in both surface water and groundwater treatment plants, and outlines
techniques used to address these factors and improve performance. The methodology
presented in this Manual is based on the CCP’s two-step approach of combining
Comprehensive Performance Evaluation (CPE) and Comprehensive Technical Assistance
(CTA). The approach has been adapted to identify performance limiting factors on an
individual unit process or component basis, and evaluate the system components. In addition,
this Manual targets a variety of monitoring or regulated parameters rather than focusing
solely on particulate removal and disinfection.
1.2 USING THE MANUAL
The CCP approach described in this Manual emphasizes modifying existing facilities to meet
desired performance at existing water demands. Even though these procedures may identify
design shortcomings, this MOE Manual is not a detailed process audit document to be used
for studying facility expansion. If existing facilities are inadequate, the reader should refer to
the MOE Design Guidelines for Drinking Water Systems (MOE, 2008) to assess the need for
increased capacity as well as improved performance.
This Manual provides an overview of some of the general approaches to drinking water
system optimization, including the use of modelling and simulation, Quality Management
Systems (Chapter 2) and the CCP approach (Chapter 3).
In subsequent chapters (Chapters 4 to 12), optimization approaches that could be applied to
individual unit processes or components are discussed and described. Generally, each chapter
describes the purpose and expected performance of the unit process or component, provides a
summary of some of the typical design or operational problems that may be encountered, and
CHAPTER 1. Introduction 1-2
Optimization Guidance Manual for Drinking Water Systems 2014
describes techniques that could be used to diagnose the cause of poor performance, improve
performance, increase capacity or reduce costs.
Each of the chapters can be used independently or with other chapters depending on the
scope of the drinking water system optimization program. If the objective is to troubleshoot
or optimize a specific unit process or component within the drinking water system, then
reference should be made to the contents of the chapter dealing with that unit process or
component. If a system-wide optimization program is undertaken, reference should be made
to the overview chapters and to unit process chapters that are relevant to the drinking water
system being optimized. In all cases, the references included in each chapter should be
reviewed to provide additional information.
1.3 REGULATORY REQUIREMENTS
1.3.1 Applicable Legislation Administered by the Ministry
The Environmental Assessment Act (EAA), the Safe Drinking Water Act, 2002 (SDWA), the
Ontario Water Resources Act (OWRA), the Clean Water Act, 2006 (CWA), the
Environmental Protection Act (EPA) and the Environmental Bill of Rights (EBR) are statutes
administered by the MOE that have application to drinking water systems. All can be
accessed from the Ontario e-Laws website http://www.e-laws.gov.on.ca or the ministry
website http://www.ene.gov.on.ca.
1.3.2 Drinking Water Regulations and Support Documents
The Drinking Water Systems regulation (O. Reg. 170/03) under the SDWA outlines
minimum requirements for treatment, sampling and monitoring, and other matters which
must be considered during the optimization of drinking water systems. The designer should
refer to O. Reg. 170/03 and to the latest edition of the Procedure for Disinfection of Drinking
Water in Ontario (Disinfection Procedure; MOE, 2006a), which is adopted by reference by
O. Reg. 170/03 under the SDWA, for more information.
For drinking water systems that are not governed by O. Reg. 170/03, refer to O. Reg. 319/08
and other applicable regulation(s).
Treated water must meet the Ontario Drinking Water Quality Standards regulation (O. Reg.
169/03) under the SDWA and should meet the aesthetic objectives and operational goals
described in the latest edition of Technical Support Document for Ontario Drinking Water
Standards, Objectives and Guidelines (Technical Support Document; MOE, 2006b).
1.4 WHAT IS OPTIMIZATION?
1.4.1 Overview of Optimization
In the 1980s and 1990s, designers, owners and operators of drinking water systems
recognized that there were opportunities to optimize water treatment facilities in order to
reduce capital cost of expansions, improve water quality, and reduce the cost of energy,
chemicals and other operational requirements. Over the past 20 years, the concept of WTP
optimization has evolved from a single study undertaken prior to an expansion of the system
to a process of continuous improvement or an operational philosophy that is championed by
the operating authority at all levels.
CHAPTER 1. Introduction 1-3
Optimization Guidance Manual for Drinking Water Systems 2014
Optimization of WTPs is an iterative process that includes the following four major steps as
illustrated in Figure 1-1:
Step 1: Clearly define the objectives of the optimization program;
Step 2: Evaluate specific components of the drinking water system to establish the
baseline conditions and the processes or factors that limit the capacity or the
performance of the existing system;
Step 3: Develop and implement a study program aimed at mitigating the capacity or
performance limiting factors; and
Step 4: Conduct follow-up monitoring after upgrades or process changes have been
implemented to assess and document the results.
Figure 1-1 – Interactive Approach to Optimization of Drinking Water Systems
Adapted from National Guide to Sustainable Municipal Infrastructure (2003)
The specific details of the study program will depend on the optimization objectives.
Objectives can be broadly-based, covering all aspects of the design and operation of the
drinking water system, or can be focused on mitigating a specific problem. Optimization
objectives might include the following, among others:
Improving treated water quality to reduce the potential for adverse public health
effects;
Increasing the capacity of the system to service growth in the community;
Upgrading the performance of the water treatment plant to meet more stringent
regulatory requirements;
Improving the reliability, flexibility and robustness of the system;
Reducing the operating cost associated with energy, chemicals and labour;
Reducing water treatment process waste residuals production and management cost;
and/or
Improving water treatment plant performance to minimize problems associated with
aesthetic parameters.
Document Benefits
Establish Objectives
Identify Limiting Factors
Identify and Implement Changes
CHAPTER 1. Introduction 1-4
Optimization Guidance Manual for Drinking Water Systems 2014
Often optimization of a drinking water system to achieve one goal can result in
improvements in other areas. For example, optimization to achieve lower chemical use and
lower chemical cost for particulate removal (e.g. coagulation/flocculation) will also result in
lower waste residuals (sludge) production and lower sludge management costs. Similarly,
improving the reliability and flexibility of the system can also result in improvements in
treated water quality.
Depending on the objectives of the optimization program, different approaches may be
applicable. Table 1-1 (Nutt and Ross, 1995) presents some of the investigations that might be
undertaken as part of an optimization project to address specific optimization objectives.
Table 1-1 – Activity and Objectives Matrix
ACTIVITY
OBJECTIVE
Performance
Improvement
Operating
Cost Savings
Increased
Capacity
Capital Cost
Savings
Hydraulic Analysis
Individual Process
Capacity Evaluation
Process Design
Modifications
Process Control
Modifications
Energy Audit
Operator Training
Activities
Optimization methods will vary from system to system depending on program objectives and
facility design; however, some steps are common. The following is a brief discussion of the
optimization methodology described in this Manual. Detailed guidance is provided in
Chapter 3.
After the optimization objectives have been defined, the next step is to establish the baseline
condition of the existing system or those components of the system that are of interest based
on the objectives. This usually involves a desk-top analysis of historic data for a period of
time that is representative of the design and operation of the existing system; usually a
minimum of three to five years will be considered.
A site visit is conducted in the accompaniment of operational and management staff. The key
objectives of the site inspection are:
To familiarize the optimization team with the physical facilities, including the water
treatment plant and distribution system layout; identify the locations of significant
CHAPTER 1. Introduction 1-5
Optimization Guidance Manual for Drinking Water Systems 2014
sampling and monitoring stations; make a preliminary assessment of operational
flexibility of the existing processes or components;
To obtain input from plant operations staff regarding equipment, hydraulic or process
limitations in the plant based on their operating experience; and
To discuss standard operating procedures for major unit processes or system
components.
The design of the existing system is compared to standard design practices and guidelines
from references such as Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008),
“Ten State Standards” (Recommended Standards for Water Works, Great Lakes-Upper
Mississippi River Board of State Public Health and Environmental Managers, 2007), Water
Treatment Principles and Design (MWH, 2005), and Water Quality and Treatment (AWWA,
1999).
A process capacity chart should be developed that identifies the capacity and capability of
each unit process or the unit processes under investigation. This establishes the unit process,
or processes, that limit the capacity or performance of the overall system. It will also serve to
identify unit processes that would benefit from optimization and the field investigations that
may be warranted.
Field investigations can then be undertaken to confirm the findings of the desk-top analysis
and to identify the preferred method of optimizing the component of the drinking water
system that is of interest. The specific field investigations undertaken will vary depending on
the size of the facilities, the design of the system and the specific objectives of the
optimization program.
The design or operational improvements are implemented and follow-up monitoring is
undertaken to confirm the benefits.
A more detailed discussion of the historic data analysis and desk-top investigation is provided
in Section 3.2 of this Manual. Specific field investigations that might be undertaken to
confirm the findings of the desk-top study or to identify preferred optimization approaches
are described in subsequent chapters of the Manual.
1.4.2 Total System Optimization including Unit Process Optimization
This Manual provides a description of optimization approaches that could be applied to all
components of a drinking water system from source to tap, including treatment unit processes
and distribution systems.
In this regard, this Manual recognizes that all parts of the system should be optimized before
the performance, capacity and capability of the drinking water system can be considered to be
fully optimized. It is also important to recognize that optimization of one component of the
treatment system may adversely or beneficially impact the performance of other components.
Therefore the possible implications of optimization steps applied to part of the drinking water
system on other unit processes should be considered.
CHAPTER 1. Introduction 1-6
Optimization Guidance Manual for Drinking Water Systems 2014
1.4.3 Value Engineering and Optimization
Value engineering (VE) is a systematic approach used to evaluate an engineering project with
the objective of improving its value. Normally, VEs are undertaken at various stages of a
design project to determine if the value of the project can be improved by using alternative
design approaches. VEs will typically involve a team of experts with expertise in a variety of
relevant engineering disciplines, construction and costing in a multi-day workshop
environment. VEs have been shown to successfully reduce project construction costs while
ensuring that the basic objectives of the project are preserved.
VEs can add value to optimization projects either at the planning stage or during the project
execution by serving as a forum for peer review of the work plan, the results and the
recommendations. The workshops described in Chapter 13 of this Manual could be
conducted using the principles of value engineering and involving a VE facilitator and a team
of experts knowledgeable in drinking water system design, operation and optimization.
1.5 WHEN SHOULD AN OWNER/OPERATOR OPTIMIZE?
In the United States, optimization of sewage treatment plants (STPs) became a priority when
the USEPA recognized that many new or expanded facilities that had been constructed in the
1970s with federal funding assistance were not performing as intended (USEPA, 1979;
USEPA, 1980). To address this issue, the U.S. supported the development of the CCP as a
means of evaluating STPs to determine the underlying cause(s) of poor performance
(USEPA, 1984; USEPA, 1985).
The success of the CCP in improving performance of STP led to the development of a similar
approach for surface water treatment facilities. The experience gained from a number of
optimization studies conducted in the U.S. and Ontario formed the basis for the development
of the previous MOE optimization manual.
Over time, optimization of drinking water systems (and other municipal infrastructure) has
become more common and, in some instances, has been adopted by municipalities with
multiple facilities, both water and sewage works, as a routine part of their operation (Wilson,
2009; Wheeler, 2009). Optimization as a tool to achieve continuous improvement is now
widely accepted; however, the following activities may warrant a more detailed optimization
study of a specific component or process:
Implementation of more stringent regulatory requirements (e.g. reduction of
trihalomethane levels in the distribution system);
Recurring non-compliance or poor performance, particularly when corrective action
is required by a Provincial Officer’s Order (e.g. filtration process not meeting
monthly performance criteria);
A need to increase rated capacity due to growth in the service area;
A requirement or desire to achieve a higher level of performance in terms of treated
water quality; or
A need to reduce operating cost due to escalating cost for energy, chemicals or other
operational requirements.
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Case histories presented elsewhere in the Manual document performance improvements as
well as operating and capital cost savings that have been realized by the successful
optimization of drinking water systems (note: costs presented in case histories are as per the
date of publication). Realizing some of these benefits is ample reason to implement an on-
going program of drinking water system optimization.
1.6 WHAT ARE THE BENEFITS OF OPTIMIZATION?
Optimization of drinking water systems in Ontario, across Canada and internationally has
been shown to deliver benefits to the owner/operator, ranging from capital cost savings
during plant expansions, improvements in performance and reliability, and/or operating and
maintenance cost reductions. Numerous example case histories are presented in this Manual.
Some select examples are summarized briefly below.
It is important to recognize that when a drinking water process or system is optimized to
increase capacity or meet more stringent regulatory requirements than the system was
originally designed to achieve, the optimization should ensure that the overall robustness and
reliability of the system is maintained. This may include enhancement of the multiple
barriers, such as additional monitoring and/or implementation of control technologies, as well
as specific training for operational staff. Vigilance with respect to the operating conditions is
required to ensure that the optimized system continues to consistently achieve the new
requirements.
1.6.1 Reduce the Capital Cost of Expansion or Upgrading
Design guidelines for drinking water systems are, by necessity, conservative as they are
intended to ensure that the components or processes are capable of achieving an appropriate
level of performance on a consistent basis by providing a margin of safety in the design,
particularly when adequate historic data are lacking.
Some of the tools described in the Manual, such as Stress Tests, can be effectively used to
document that a unit process can achieve the required performance level at hydraulic loading
higher than typically stated in design guidelines. If such is the case, significant capital cost
savings can be realized when the facility is expanded or if an expansion could be deferred. In
some cases, the facility could be re-rated to a higher rated capacity with no or minimal
construction of new facilities.
The Regional Municipality of Wood Buffalo, Alberta, undertook a number of studies
to define potential options and costs for upgrading the water treatment plant in the
City of Fort McMurray. A combination of optimization measures and minor capital
improvements was used to expand the plant capacity from 40 to 50 ML/d while
ensuring compliance with water quality standards. The optimization of the existing
system allowed the municipality to defer additional plant expansions and conversion
to membrane filtration (Suthaker, 2007).
A filter re-rating study was conducted by the Southern Nevada Water Authority
(SNWA) to determine if filters could be operated safely at increased loading rates
while maintaining filter effluent water quality requirements. One year of full-scale
filter stress testing was conducted to determine if the hydraulic loading rate on the
filters could be increased from a rated capacity of 6 gpm/ft2 (15 m/h) to 7.5 gpm/ft
2
(18 m/h). The success of the trials allowed both of SNWA’s treatment facilities to
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gain the operational flexibility to run at full production with several filters offline,
and one WTP gained an additional 100 mgd (380 ML/d) of capacity. SNWA
estimates the filter re-rating saved the utility more than $10 million in construction
costs alone for the additional capacity gained (Lew et. al., 2010).
1.6.2 Achieve Stricter Standards
Optimization approaches have been used to demonstrate that new or more stringent
regulatory requirements can be achieved at some facilities without costly capital works.
CPEs were conducted at four surface water treatment plants following revisions to
the Disinfection Procedure (MOE, 2006a), changing the performance criterion for
filter effluent turbidity from ≤ 0.5 NTU to ≤ 0.3 NTU in 95% of measurements each
month. The study results indicated that three of the four WTPs were able to produce
filtered water meeting the MOE’s turbidity criterion at the current average daily
flows (XCG, 2006a, b; MacViro, 2006; MMM, 2006).
Optimization studies were conducted at three Ontario drinking water treatment plants
with the goal of minimizing the formation of trihalomethanes (THMs) and haloacetic
acids (HAAs) to below 80 µg/L without major capital investment. Bench- and full-
scale trials were conducted to evaluate DBP formation strategies. Based on the
results of the study, enhanced coagulation was observed to reduce THM and HAA
formation in both the treated water leaving the plant and in the distribution system
(AH&A and RVA, 2009).
1.6.3 Improve Performance
Improvements in performance through operational improvements or improved process control
can often bring a drinking water system into compliance with its regulatory requirements or
improve the reliability of the system. The USEPA’s CCP approach was developed specifically to
address sewage plants that were unable to achieve their regulatory requirements (USEPA, 1984)
and this same approach has been widely used in Ontario (Wheeler et. al., 1994). There are many
successful examples of the usefulness of this approach in WTPs where the design of the system
was shown to be appropriate, but performance requirements were not consistently being met.
A Comprehensive Performance Evaluation was conducted at a small GUDI treatment
plant to identify operational procedures that were contributing to non-compliance
problems with respect to turbidity. The results of the CPE indicated that backwashing
and other maintenance procedures were the main cause of the non-compliance issues.
Changes to Standard Operating Practices (SOPs) and increased operator training
were implemented to improve plant performance (Wetzel, 2007).
The Ministry of Environment and Energy completed the Water Plant Optimization
Study in the early 1990s to document and review conditions at 44 drinking water
systems in Ontario to determine an optimum treatment strategy with emphasis on
disinfection and particulate removal processes. Several of the treatment facilities
included in the study had demonstrated problems with treated water turbidity levels
and residual aluminum concentrations. The study findings were used to provide
short- and long-term recommendations for physical improvements and operational
changes leading to improved performance (MOE, 1995).
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1.6.4 Reduce Operating Cost
Optimization can identify opportunities to reduce chemical cost and/or improve energy use
efficiency.
The City of Ottawa conducted numerous bench- and pilot-scale studies to determine
the optimum alum dosage and pH conditions for the removal of organic matter,
colour and turbidity. Implementation of the optimum chemical combinations and
dosages at full-scale resulted in a $150,000 savings per year and reduced the
production of residual aluminum sludge (Douglas et. al., 2008).
The Region of Niagara conducted a pilot program applying OPIR® software to
optimize water treatment plant production and balance storage in the Grimsby
drinking water system. By pumping at average day rates rather than peak production
rates, water treatment plant performance was improved and an energy cost savings of
10 to 15 percent was expected (Tracy, 2009).
1.7 WHAT DOES OPTIMIZATION COST AND HOW LONG DOES IT
TAKE?
The cost and duration of a drinking water system optimization program depends on a number
of variables, including:
The project scope and objectives;
Plant location, size, complexity and configuration;
Maintenance and construction activities underway at the facility that affect the
availability of unit processes or equipment for testing;
Type and duration of field investigations;
Level of support provided by the owner/operator;
Equipment required to execute the field program;
Sampling and analytical cost;
Approval requirements; and
Reporting requirements.
It should be recognized in considering the time required to complete an optimization program
that optimization is an iterative and on-going process that involves continuous review of the
performance, cost, capacity and capability of the drinking water system. When a specific
optimization project is completed, further opportunities for optimization of the system may
be identified.
In 2010 dollars, the cost of an optimization program can range from about $20,000 to conduct
the CPE phase of the CCP at a small to medium-sized WTP, to about $50,000 to $100,000
for a full CCP including the CTA phase. Stress testing and other field testing activities to re-
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rate a small or medium-sized WTP, including multi-season testing, can range in cost from
about $80,000 to $120,000. A comprehensive performance evaluation of all treatment
processes, including clarifier or filter stress testing, tracer testing, hydraulic modelling,
evaluation of flow instrumentation, and other activities at a large WTP can cost up to
$500,000, inclusive of analytical cost.
These cost ranges are a guide to the cost to undertake an optimization program, but should
not be used for detailed budgetary purposes. A detailed Terms of Reference should be
developed with specific tasks and activities identified and used as the basis for estimating the
cost of a proposed optimization program.
As shown by the case histories presented in this Manual, the cost for optimization are often
recovered in the form of reduced capital cost for plant expansions and/or reduced operating cost.
Also, there are often non-monetary benefits, such as improved operation, improved performance
and enhanced plant reliability.
1.8 WHO SHOULD CONDUCT THE OPTIMIZATION?
Optimization of a drinking water system should involve active participation of the owner and
the operating authority, if different from the owner. The owner should establish the objectives
of the optimization program and maintain an involvement throughout the process. Operating
staff play a critical role in identifying performance limitations or capacity restrictions in the
facility based on their hands-on experience in operating the system. They also can assist with
conducting specific testing or sampling during the field test program. This can result in an
enhanced level of process and system knowledge and a better understanding of process and
system control options and outcomes, with a resulting benefit in ongoing optimization
through a continuous improvement program. As described in Chapter 3, operating staff
should be involved in the development and implementation of Standard Operating Practices
(SOPs) related to the system that they operate.
Some elements of system optimization are best undertaken by an engineering professional
experienced in the specific area. Some of the test methods described in this Manual utilize
specialized equipment and training. In addition, the interpretation of the resulting information
often is best accomplished by an experienced drinking water process engineer.
It is often prudent to include representatives from the regulator, which in Ontario is the MOE.
This might include representatives of the Safe Drinking Water Branch (SDWB) and
Standards Development Branch (SDB). Any approvals necessary to undertake the
optimization program should be discussed with SDWB and the MOE Drinking Water
Inspector for that drinking water system, and appropriate contingency plans should be in
place in the event that there are any unexpected short term impacts on treated water quality
during field testing. Pre-consultation with MOE will ensure that the optimization program
planning is sufficient to support any future approval applications.
1.9 WHAT ARE THE GENERAL APPROACHES TO OPTIMIZATION?
This section of the Manual provides a brief introduction to some of the more common
approaches used for drinking water system optimization. These approaches are not mutually
exclusive but rather are complementary and are often used concurrently depending on the
program objectives.
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Optimization Guidance Manual for Drinking Water Systems 2014
More detailed discussions are provided in subsequent chapters as referenced herein.
1.9.1 Operator Training
It is recognized that a well-trained operating staff with process control skills and an
understanding of drinking water treatment processes and distribution system can produce
high quality finished water from a marginal facility and deliver it safely to the consumer.
When supported by a management team that encourages optimization and ensures that
adequate resources are available to operating staff, an optimized drinking water system will
be realized. The development of an empowered operating staff is the focus of the CTA phase
of the CCP, which is discussed in detail in Chapter 3.
1.9.2 Composite Correction Program (CCP)
As noted previously, the CCP was originally developed by the USEPA to identify factors that
limit the performance of sewage works. The CCP has been demonstrated in Ontario to be an
effective tool for assessing and optimizing WTPs and versions of the procedure have been
developed for use in both water and sewage treatment plants in Ontario (XCG Consultants
Ltd., 1992; Wastewater Technology Centre and Process Applications Inc., 1994).
The CCP is a two-step process. The first step, the CPE, evaluates the operation, design,
maintenance and administration of the water treatment plant and distribution system to
determine which factors are affecting system performance and their relative importance. If
the CPE determines that the design of the drinking water system should be adequate to allow
the performance requirements to be met consistently, then the next step in the CCP process,
the CTA, is initiated.
In the CTA, the performance limiting factors identified in the CPE are addressed with the
goal of achieving the desired performance. The emphasis of the CTA is on providing operator
assistance with process control to ensure that the performance achieved when the CTA is
complete can be maintained by a well-trained operating staff.
More detailed discussion of the role of the CCP in optimization of drinking water systems is
provided in Chapter 3 of the Manual.
The reader is also referred to the AWWA Partnership for Safe Drinking Water program,
which has adopted a similar methodology to the CCP, for additional information.
1.9.3 Modelling and Simulation
Numerical models can be used as tools to support the assessment of plant performance and
capacity as well as a means of predicting the impact of design or process changes on
performance and capacity. There are several areas where modelling and simulation can be
used to support drinking water system optimization.
Hydraulic models of the water treatment plant and/or distribution system can be used
to identify hydraulic bottlenecks in the drinking water system that may limit the
ability to treat peak flows.
Clarifier models can be used to estimate the effects of baffling or other clarifier
modifications on clarifier performance or capacity.
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Optimization Guidance Manual for Drinking Water Systems 2014
Mixing models, such as Computational Fluid Dynamics (CFD) models, can be used
to assess the degree of short-circuiting or dead-space in chlorine contact tanks, or the
effectiveness of mixing devices at various flow rates.
Water treatment models can be used to simulate operating conditions and predict
treated water quality based on raw water characteristics and/or automatically adjust
chemical dosages to ensure satisfactory or optimal performance (e.g. chlorine
dosages to ensure compliance with CT requirements).
More detailed discussion of the role of modelling and simulation in optimization of drinking
water systems is provided in the Chapter 4.
1.10 REFERENCES
American Water Works Association (1999). Water Quality and Treatment: A Handbook of
Community Water Supplies, 5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
Andrews, Hofmann & Associates Inc. and R.V. Anderson Associates Ltd (2009).
Optimization Study to Control the Formation of THMs and HAAs, report for the Ontario
Ministry of the Environment.
Douglas, I., A. Campbell and J. Van Den Oever (2008). 25 Things You Probably Didn’t
Know About Drinking Water Treatment: Findings From 15 Years of Research and
Optimization, presented at the OWWA/OMWA Joint Annual Conference, London, Ontario.
Graef, S.P., C.S. Zickefoose, P.T. Karney, M.C. Mulbarger and T.M. Regan (1985). EPA
Handbook for Improving POTW Performance, Water Pollution Control Federation, ISBN 0-
9432244-76-5.
Great Lakes-Upper Mississippi River Board of State Public Health and Environmental
Managers (2007). Recommended Standards for Water Works, (known as the “Ten State
Standards”).
Lew, J., T. Pickle, D. Johnson and E. Wert (2010). Filter Rerating Increases Production.
American Water Works Association. Opflow Volume 36, No. 3, March 2010.
MacViro Consultants Inc. (2006). Optimization of Drinking Water Systems Utilizing
Chemically Assisted Filtration to Meet Lower Turbidity Levels – Draft Optimization Report,
report for the Ontario Ministry of the Environment.
Marshall Macklin Monaghan Ltd (2006). Longlac Water Treatment Facility Comprehensive
Performance Evaluation – Final Optimization Report, report for the Ontario Ministry of
Environment.
MOEE (1995). Water Plant Optimization Study: Plant Study Summary Report. ISBN 0-7778-
3906-7.
MOE (2006a). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.
MOE (2006b). Technical Support Document for Ontario Drinking Water Standards,
Objectives and Guidelines. PIBS 4449e01.
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Optimization Guidance Manual for Drinking Water Systems 2014
MOE (2008). Design Guidelines for Drinking Water Systems. ISBN 978-1-4249-8517-3.
MWH (2005). Water Treatment: Principles and Design, 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
National Guide to Sustainable Municipal Infrastructure (2003). Wastewater Treatment Plant
Optimization, Federation of Canadian Municipalities and National Research Council.
Nutt, S.G. and D. Ross (1995). “What is Optimization and Why Optimize,” presented at the
24th Annual Water Environment Association of Ontario Conference, Toronto, Ontario.
Suthaker, S. and G.E. Drachenberg (2007). “Modified Deep Bed Filtration: Low-cost Option
for Increasing Capacity and Improving Quality Within Existing Filter Cells”, presented at the
American Water Works Association Annual Conference & Exposition, Toronto, Ontario.
Tracy, H. (2009). “Water System Optimization & Energy Savings Using Predictive Control”,
presented at the OWWA/OMWA Joint Annual Conference, Toronto, Ontario.
USEPA (1979). Evaluation of Operation and Maintenance Factors Limiting Biological
Wastewater Treatment Plant Performance, EPA-600/2-79-078.
USEPA (1980). Evaluation of Operation and Maintenance Factors Limiting Municipal
Wastewater Treatment Plant Performance, Phase II, EPA-600/2-80-129.
USEPA (1984). Handbook: Improving POTW Performance Using the Composite Correction
Program, EPA/625/6-84-008.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program, EPA/625/6-91-027.
Wastewater Technology Centre and Process Applications Inc. (1994). The Ontario
Composite Correction Program Manual for Optimization of Sewage Treatment Plants
(draft), Ontario Ministry of Environment and Energy, Environment Canada and Municipal
Engineers Association.
Wetzel, M. (2007). “Improving Water System Operations Using Comprehensive Performance
Evaluation Methodology”, presented at the American Water Works Association Annual
Conference & Exposition, Toronto, Ontario.
Wheeler, G. (1994). Assessment of the Comprehensive Performance Evaluation Technique
for Ontario Sewage Treatment Plants, prepared for the Ontario Ministry of Environment and
Energy.
Wheeler, G.W. (2009). City of Guelph, Personal Communication.
Wilson, P. (2009). Haldimand County, Personal Communication.
XCG Consultants Ltd. (1992). Assessment of Factors Affecting the Performance of Ontario
Sewage Treatment Facilities, report for the Ontario Ministry of Environment and Energy,
Environment Canada and the Municipal Engineers Association.
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Optimization Guidance Manual for Drinking Water Systems 2014
XCG Consultants Ltd. (2006a). Performance Evaluation Report – Alexandria Water
Treatment Plant, report for the Ontario Ministry of Environment.
XCG Consultants Ltd. (2006b). Performance Evaluation Report – Dunnville Water
Treatment Plant, report for the Ontario Ministry of Environment.
Optimization Guidance Manual of Drinking Water Systems 2014
CHAPTER 2QUALITY MANAGEMENT SYSTEMS
QUALITY MANAGEMENT SYSTEMS
2.1 Introduction ............................................................................................................ 2-1
2.2 Quality Management Systems ................................................................................ 2-1
2.2.1 What is a Quality Management System? ................................................. 2-1
2.2.2 What is the Drinking Water Quality Management Standard? ................. 2-2
2.3 Operational Plans and Operations Manuals ........................................................... 2-3
2.4 Role of Water Operations Staff in Water System Optimization ............................ 2-4
2.5 Training of Operations Staff ................................................................................... 2-4
2.6 References .............................................................................................................. 2-5
CHAPTER 2. Quality Management Systems 2-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 2
QUALITY MANAGEMENT SYSTEMS
2.1 INTRODUCTION
Part Two of the Report of the Walkerton Inquiry (O’Connor, 2002), recommended the
adoption of a quality management system (QMS) for drinking water systems. It was also
recommended that a quality management standard, specifically designed for drinking water
systems, be developed and implemented in Ontario. This resulted in the Drinking Water
Quality Management Standard (DWQMS).
Ontario has established a strong regulatory framework for drinking water systems. This
framework under the SDWA and related regulations focuses on compliance-based results that
are verified through the MOE’s compliance and inspection programs.
The DWQMS complements this legislative and regulatory framework by endorsing a
proactive and preventative approach to drinking water quality management. The Report of
the Walkerton Inquiry recommendations stated that:
“The purpose of the quality management approach in the context of drinking
water is to protect public health by achieving consistent good practice in
managing and operating a water system.
An important assumption of quality management is that, in evaluating or
improving a management system, one should look at the process by which
something is produced as well as the end product (O’Connor, 2002).”
This recommendation to adopt a QMS approach has been mandated by the provincial
government through the SDWA. As such, the requirement to implement the DWQMS is
applicable to the owners and operating authorities for all municipal residential drinking water
systems, including treatment, transmission and/or distribution systems.
Although the continuous improvement component of the DWQMS is directly related to the
improvement of the effectiveness of the QMS, the approach used to initiate corrective actions
and monitor improvement can be applied to optimization activities; for example, correcting
performance limiting factors as part of a CTA program.
2.2 QUALITY MANAGEMENT SYSTEMS
2.2.1 What is a Quality Management System?
A QMS is a system to: a) establish policy and objectives and achieve those objectives, and b)
direct and control an organization with regard to quality.
Quality management systems and management system standards are not new. They have
been around since the early 1950s. In 1987, the International Organization for
Standardization (ISO) released the first version of the ISO 9001 Quality Management System
Standard. Organizations can become certified to ISO 9001 to demonstrate their compliance to
the standard. The standard includes a requirement for continual improvement.
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Similar to the ISO 9000 series, the ISO 14000 series of international standards is a set of
policies and procedures related specifically to Environmental Management Systems (EMS).
The aim of this standard is to reduce the environmental footprint of a business and to
decrease the amount of pollution or waste that the business generates. As with ISO 9001, a
business can become certified to demonstrate their compliance to the standard. In Ontario,
some water and sewage works owners and operators, such as the Lake Huron Primary Water
Supply System, the Region of York and the Region of Durham, have had their water and/or
sewage works certified to the ISO 14001 standard with the goal of improving performance
and compliance.
Most management system standards are generic. They can be applied to any type or size of
organization. They have been developed for the implementation of quality-based or
environmentally-based management systems in any type of organization.
Management system standards have also been developed for specific industries or product
sectors. For example, the Hazard Analysis and Critical Control Point (HACCP) standard is an
internationally recognized, science-based, food safety standard that was developed to help
ensure the manufacture of safe food products.
Quality management for Ontario’s municipal drinking water systems occurs through the
development and implementation of a QMS for each drinking water system based on
Ontario’s DWQMS.
The complexity of a QMS for a drinking water system will depend, to some degree, on the
size of the drinking water system and its processes. For a small drinking water system (e.g.
consisting of a well with chlorination), the QMS can be relatively simple. For a system with a
large number of staff, several connected surface water treatment plants, a complex
distribution system, and interconnections to other systems, the QMS will be larger and more
comprehensive.
2.2.2 What is the Drinking Water Quality Management Standard?
The DWQMS is a “Made-in-Ontario” management system standard required by the MOE’s
Municipal Drinking Water Licensing Program under O. Reg. 188/07 for municipal residential
drinking water systems. Its requirements are similar to ISO-based quality management
standards but not equivalent.
The DWQMS sets out a framework for the operating authority and the owner of a drinking
water system to develop a QMS that is relevant and appropriate for their specific system.
The DWQMS contains elements of both the ISO 9001 standard with respect to management
systems and the HACCP standard with respect to product safety. The DWQMS also
incorporates the HACCP approach to risk assessment and reflects the multi-barrier approach
for drinking water safety.
In general, the concepts outlined in the DWQMS reflect, for the most part, how owners and
operating authorities currently manage and operate their drinking water systems. The
DWQMS, however, requires that these concepts be formalized and documented in an
operational plan, and that there is a documented commitment throughout an organization to
continuously review and improve quality management practices.
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The DWQMS approach emphasizes the importance of:
Proactive and preventative rather than strictly reactive management strategies to
identify and manage risks to public health;
The establishment and documentation of management procedures;
Meeting the management procedures; and
Continuous improvement of the management system.
The definition of QMS in the DWQMS refers to the establishment of policies and objectives.
The DWQMS has explicit requirements for policies but does not make specific reference to
objectives. Objectives are, however, embedded or implicit in most of the DWQMS elements.
The DWQMS is based on a “PLAN, DO, CHECK and IMPROVE” methodology that is
similar to that found in some international standards.
Additional information on the DWQMS is provided in the MOE guidance document entitled
Implementing Quality Management: A Guide for Ontario’s Drinking Water Systems (MOE,
2007).
2.3 OPERATIONAL PLANS AND OPERATIONS MANUALS
An operational plan is the documentation of a QMS. It is not an Operations and Maintenance
Manual. The PLAN requirements of the DWQMS identify the policies and procedures that
must be documented in the Operational Plan.
Additional information regarding the preparation and contents of operational plans is
provided in the MOE DWQMS Guidance Document (MOE, 2007).
An operations manual is generally supplied to the water works as an essential part of the
design and commissioning of a facility. The operations manual should include detailed
descriptions and explanations of the treatment process and operational strategies for meeting
the requirements of O. Reg. 170/03 and the Disinfection Procedure (MOE, 2006). All
standard operating procedures (SOPs) developed for the plant should be included in the
operations manual. The manual should cover the following topics:
A plant overview and process control philosophy statement;
Detailed unit operations and chemical dosing for normal operation and emergency
situations;
Simplified system schematics that take into account the spatial relationships
involved;
Storage and transmission descriptions and operational procedures;
Descriptions and operational procedures for facility utilities (HVAC, plant service
water, security, etc.);
General safety information, including Material Safety Data Sheets (MSDS);
Spill containment and emergency procedures;
Emergency power systems and electrical system operation;
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Security of infrastructure, treated water, electronic files and/or programs and
response procedures to breaches or intrusions;
Applicable regulations;
Monitoring, reporting and documentation procedures;
Disinfection procedures for bringing equipment on-line after maintenance;
Reliability and redundancy analysis of system components;
Detailed routine maintenance procedures;
Alarm notifications and response procedures;
A list of emergency contacts and locations of contingency plans;
A list of major equipment suppliers with specifications, maintenance requirements
and spare parts lists for major equipment; and
A list of chemical suppliers (and alternates if possible) with emergency contact
names and phone numbers.
It is important to note that any changes to operating conditions or procedures that are the
result of optimization activities must be reflected in the documentation contained in the
Operations Manual and the Operational Plan, where applicable.
2.4 ROLE OF WATER OPERATIONS STAFF IN WATER SYSTEM
OPTIMIZATION
The quality of water leaving a water treatment plant and passing through the distribution
system has the potential to directly impact the health of its consumers. All staff associated
with the drinking water system, from the operator to the highest level administrator, have an
important role in protecting public health and a responsibility to provide drinking water that
minimizes the possibility of a disease outbreak.
Experience gained from implementing CCP optimization activities at plants has demonstrated
that, in most situations, once utility staff become aware of the importance of achieving
optimized performance goals, they have enthusiastically pursued these goals through a
variety of activities (USEPA, 1998). The subsequent chapters of this Manual present
comprehensive procedures for assessing and achieving optimum levels of performance.
2.5 TRAINING OF OPERATIONS STAFF
Optimization of a drinking water system should involve increasing the capabilities and
knowledge of the operations and management staff of the works and improving the
performance of the equipment and the treatment processes to be effective and sustainable.
Developing a capable and empowered operating staff with supportive management and
appropriate operating and maintenance procedures and practices is critical to achieving and
maintaining a high level of performance in the drinking water system. The success of the
CCP approach (Chapter 3) is, to a large extent, due to the transfer of skills and knowledge to
the operations and management staff during the CTA phase.
Training of operators and water quality analysts (WQA) as part of or as a result of a CCP or
optimization program should not be confused with operator/WQA certification or licensing,
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which is regulated under O. Reg. 128/04 – Certification of Drinking Water System Operators and
Water Quality Analysts. The objective of the certification program is to ensure that drinking water
system operators and WQAs have the necessary education, training, knowledge and experience to
operate the works. Certification is based on passing certification exams and meeting the minimum
requirements for professional development or training per year.
CCPs undertaken in Ontario (XCG, 2006a, b; MacViro, 2006; MMM, 2006) and elsewhere
(USEPA, 1998) have shown that the lack of appropriate process control techniques and the
misapplication of process control concepts are among the most common performance
limiting factors in drinking water systems.
Providing operations staff with the knowledge, ability and tools needed to achieve a
consistent level of process control for the drinking water system should involve a
combination of classroom and hands-on training. The classroom training is aimed at
explaining the fundamental concepts of drinking water treatment, process control, and
distribution system management and operation. The hands-on training is intended to
demonstrate how the concepts apply to the specific works that are being operated.
There are numerous sources of classroom training available. Acquiring the requisite hands-on
training in monitoring and process control techniques is more difficult and expensive than
classroom training, particularly for smaller works that may not have in-house staff capable of
providing hands-on training. A regional approach to delivery of hands-on training can reduce
the high costs of this type of training for small facilities.
2.6 REFERENCES
MacViro Consultants Inc. (2006). Optimization of Drinking Water Systems Utilizing
Chemically Assisted Filtration to Meet Lower Turbidity Levels – Draft Optimization Report,
report for the Ontario Ministry of the Environment.
Marshall Macklin Monaghan Ltd (2006). Longlac Water Treatment Facility Comprehensive
Performance Evaluation – Final Optimization Report, report for the Ontario Ministry of
Environment.
MOE (2006). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.
MOE (2007). Implementing Quality Management: A Guide for Ontario’s Drinking Water
Systems. PIBS 6320e.
O’Connor, D. R. (2002). Part Two Report of the Walkerton Inquiry: A Strategy for Safe
Drinking Water. Toronto: Publications Ontario. ISBN: 0-7794-2621-5.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program. United States Environmental Protection Agency. Office of
Ground Water and Drinking Water. Cincinnati, OH. EPA/625/6-91-027.
XCG Consultants Ltd. (2006a). Performance Evaluation Report – Alexandria Water
Treatment Plant, report for the Ontario Ministry of Environment.
XCG Consultants Ltd. (2006b). Performance Evaluation Report – Dunnville Water
Treatment Plant, report for the Ontario Ministry of Environment.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 3COMPOSITE CORRECTION PROGRAM
COMPOSITE CORRECTION PROGRAM
3.1 Introduction ............................................................................................................ 3-1
3.2 CPE Methodology .................................................................................................. 3-1
3.2.1 Evaluation of Major DWS Components .................................................. 3-1
3.2.2 Conducting Performance Assessment ..................................................... 3-5
3.2.3 Identification and Prioritization of Performance Limiting Factors ......... 3-6
3.2.4 Assessment of Applicability of a CTA .................................................. 3-12
3.2.5 CPE Report ............................................................................................ 3-13
3.3 Carrying Out a CPE .............................................................................................. 3-13
3.3.1 Personnel Capabilities ............................................................................ 3-14
3.3.2 Initial Activities ..................................................................................... 3-15
3.3.3 On-Site Activities .................................................................................. 3-16
3.3.4 CPE Report ............................................................................................ 3-24
3.4 CTA Methodology ............................................................................................... 3-25
3.4.1 CPE Results ........................................................................................... 3-25
3.4.2 Process Control Priority Setting ............................................................ 3-26
3.4.3 Long Term Involvement ........................................................................ 3-27
3.4.4 Facilitator Tools ..................................................................................... 3-27
3.4.5 Correcting Performance Limiting Factors ............................................. 3-31
3.5 How to Conduct a CTA ........................................................................................ 3-35
3.5.1 Initial Site Visit ...................................................................................... 3-35
3.5.2 Off-Site Activities .................................................................................. 3-37
3.5.3 CTA Results ........................................................................................... 3-37
3.5.4 CTA Summary Report ........................................................................... 3-38
3.6 Required Personnel Capabilities for Conducting a CTA ..................................... 3-39
3.7 References ............................................................................................................ 3-40
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CHAPTER 3
COMPOSITE CORRECTION PROGRAM
3.1 INTRODUCTION
This chapter provides information on the two phases of the CCP approach used to improve
the performance of existing drinking water systems (DWS). The first evaluation phase of the
CCP, called the Comprehensive Performance Evaluation (CPE), is a thorough review and
analysis of a facility’s capabilities as designed and associated administrative, operational and
maintenance practices as they relate to the performance requirements for the water treatment
plant and/or distribution system. A primary objective is to determine if significant
improvements in performance can be achieved without major capital expenditures. The
objective of the second phase of the CCP, the Comprehensive Technical Assistance (CTA), is
to achieve a desired level of performance from an existing DWS without major
modifications.
In this chapter, the term “DWS component” will be used to refer to treatment unit processes,
such as sedimentation and filtration, as well as other major works included in the DWS, such
as: intake structures; distribution system piping; pumping stations; and storage facilities.
3.2 CPE METHODOLOGY
A CPE is a comprehensive evaluation of the administration, design, operation and
maintenance of a DWS. Although the evaluation focuses on the current condition of the
system (i.e. “a snapshot in time”), consideration is given to seasonal variations in raw water
quality and operating conditions. A CPE involves several activities:
Evaluation of the DWS components;
Assessment of DWS performance;
Identification and prioritization of performance limiting factors;
Assessment of applicability of follow-up CTA; and
Reporting results of the evaluation.
Although these are distinct activities, some are conducted concurrently. For example,
evaluation of DWS components and identification of performance-limiting factors are
generally conducted simultaneously. A more detailed discussion of these activities follows.
3.2.1 Evaluation of Major DWS Components
3.2.1.1 Overview
The evaluation of major DWS components is used to establish the potential of existing
components to achieve desired performance levels. If the CPE indicates that the major DWS
components are adequate, a major upgrade or expansion is probably not necessary, and a
properly conducted CTA should be implemented to optimize performance. If, on the other
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hand, the CPE shows that major DWS components are inadequate, utilities should consider
modification of these components as the initial focus for achieving desired performance.
A rating system is used that allows the evaluator to rate each DWS component and the
overall system as either Type 1, 2 or 3. This evaluation approach is illustrated in Figure 3-1.
Type 1 systems are those where a CPE shows that current performance difficulties are not
caused by limitations in the size or capability of existing DWS components. In these cases,
problems are likely related to system operation, maintenance, aging infrastructure or
administration. Type 1 systems are projected to be most likely to achieve desired
performance through implementation of non-construction oriented follow-up assistance (e.g.,
a CTA as described later in this chapter).
Figure 3-1 – Major DWS Component Evaluation Approach
The Type 2 category is used to represent a situation where marginal capacity of DWS
components could potentially prohibit a DWS from achieving the desired performance level.
For Type 2 systems, it is expected that implementation of a CTA would lead to improved
Administrators or Regulators Recognize the Need to Evaluate or Improve System Performance
CPE Evaluation of Major DWS Components
TYPE 2 Major DWS Components
Are Marginal
TYPE 1 Major DWS Components
Are Adequate
TYPE 3 Major DWS Components
are Inadequate
Implement CTA to Optimize Existing
Facilities Before Initiating Any Facility Modifications
Implement CTA to Achieve Desired
Performance from Existing Facilities
Do Not Implement CTA Evaluate Options for Facility Modifications
Facility Modifications
Facility Modifications
Construct New
Facilities to Meet Demand
Desired Performance Achieved
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performance, but might not achieve the required performance level without facility
modifications to the major DWS components.
Type 3 systems are those in which major DWS components are considered to be inadequate
to provide required capacity for existing water demands. For Type 3 systems, major
modifications are felt to be required to achieve the desired level of performance. Although
other performance-limiting factors may exist, such as the operators’ lack of process control
capability or the administration's unfamiliarity with DWS needs, consistent acceptable
performance cannot be expected to be achieved until any physical limitations of major DWS
components are eliminated. If severe public health problems exist with present system
performance, officials may conduct activities to improve system performance as much as
possible until major modifications can be completed. A Boil Water Advisory (which can only
be issued by the Medical Officer of Health) or water use restrictions may have to be
implemented until modifications are completed and performance is improved. The owners of
a Type 3 system could meet their performance requirements by pursuing modifications of
existing water treatment and/or distribution facilities. However, depending on future water
demands, more detailed study of feasible alternatives may be warranted. CPEs that identify
Type 3 systems are still of benefit to system administrators in that the need for construction is
clearly defined. Additionally, the CPE provides an understanding of the capabilities and
weaknesses of existing operation and maintenance practices, and administrative policies.
3.2.1.2 Approach
When using the CCP approach, major DWS components are generally evaluated based on
their capability to handle current peak instantaneous flow requirements. The evaluator should
use judgement in assessing the peak instantaneous flow rate, and anomalous operating
conditions should not be included in the data evaluation. When assessing DWS components
that have not been traditionally included in a CPE, such as distribution system piping or
storage facilities, the use of a different flow requirement (e.g. maximum day demand or fire
flow) may be more appropriate. It should be noted that for any DWS component, nominal
flow metering inaccuracies should be taken into account.
All major DWS components should be included in the evaluation; typically these are
flocculation, sedimentation, filtration and disinfection. These processes are selected for
evaluation based on the concept of determining if the "concrete" (e.g., basin size) is adequate.
The potential capacity of a major DWS component is not increased if "minor modifications",
such as providing chemical feeders or installing baffles, could be accomplished by the staff.
This approach is in line with the CPE intent of assessing adequacy of existing facilities to
determine the potential of non-construction alternatives and can be applied to other DWS
components, including distribution system components. Other components or plant
processes, such as rapid mix or pumping facilities, are not included in the major DWS
component evaluation but rather are evaluated separately as factors that may be limiting
performance. These components can most often be addressed through "minor modifications".
An approach using a "performance potential graph" has been developed to evaluate the major
DWS components. As an initial step in the performance potential graph approach, the CPE
evaluators are required to use their judgment to estimate the peak treatment or hydraulic
capacity for each of the major DWS components. It is important to note that the ratings are
based on achieving optimum performance from each of the major DWS components such
that each process maintains its integrity as a "barrier" to the passage of particulate matter,
microorganisms or other parameters targeted for optimization (e.g. colour, iron and
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manganese, etc.). The projected capacity rating is then compared to the peak instantaneous
operating flow rate (or other flow rate, as determined by the evaluator) experienced by the
DWS during the most recent twelve months of operation. If the most recent twelve months is
not indicative of typical flow rates, the evaluator may choose to review a time period
considered to be more representative. The peak instantaneous operating flow is utilized for
the comparison because it is necessary that high quality finished water be produced and
delivered to consumers on a continuous basis.
The comparison of estimated DWS component capacity to peak instantaneous operating flow
rate is made using a performance potential graph, as shown in Figure 3-2. The components
evaluated are shown on the left of the graph and the flow rate units are shown on the "x"
scale across the top. Horizontal bars on the graph depict the estimated capacity for each DWS
component, and the vertical line represents the actual peak operating flow experienced at the
plant or in the distribution system. Footnotes are used to explain the conditions used to rate
the DWS components.
The approach to determine whether a DWS component is Type 1, Type 2 or Type 3 is based
on the relationship of the horizontal bars to the peak instantaneous operating flow rate. As
presented in Figure 3-2, a DWS component would be rated Type 1 if its projected capacity
exceeds the actual peak demand, Type 2 if its projected capacity was 90 to 100 percent of
actual peak demand, or Type 3 if its projected capacity is less than 90 percent of actual peak
demand.
Figure 3-2 – Example Performance Potential Graph
When rating the capability of a DWS component, it is important to consider several options
that are available for the operation of the DWS. For example, if a DWS components receives
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a Type 3 rating, it may be able to achieve Type 2 or Type 1 status by reducing demand or by
extending the operating time and operating at a lower rate (e.g., if the peak instantaneous
operating flow rate of a plant is only occurring over a 12-hour period, the plant may be able
to be operated at half the flow rate for a 24-hour period). In addition, it may be possible for a
community to take steps to reduce demand by activities such as increasing water rates, water
rationing, or leak detection and repair. In these instances, the potential to decrease peak
instantaneous operating flow rate needs to be carefully assessed by the evaluator in order to
justify a change in the DWS component rating (see Section 3.2.1.3).
3.2.1.3 Rating Individual DWS Components
Typical assessment criteria to be used as a basis to rate individual DWS components are
presented in the individual DWS component chapters (Chapters 5 to 12). There is a wide
range in the criteria which can translate into large differences in estimated DWS component
capabilities. As such, using the performance potential graph approach requires a great deal of
judgment from an experienced water system evaluator to properly estimate the capacity of a
major DWS component.
These criteria are based on experience gained from CPEs and other sources including the
Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008). The evaluator should use
judgement in selecting evaluation criteria and should consider the original design of the
component, changes in raw water characteristics and operating conditions in the evaluation of
the component rating.
Major DWS component performance is assessed both with respect to the capability of
consistently contributing to overall treated water quality and with respect to providing
consistent individual DWS component performance. DWS component performance
capability is important to ensure that multiple barriers are maintained on a continuous basis.
3.2.2 Conducting Performance Assessment
The performance assessment step uses existing and on-site data evaluations to determine if
DWS component and total system performance have already been optimized. The
performance of each DWS component is assessed to ensure that multiple barriers are in place,
such that continuous optimum performance is achieved.
3.2.2.1 Data Analysis and Data Confidence
The evaluator should be confident in the accuracy and representativeness of the data to be
used in the component evaluation. Judgement is therefore required in analyzing and
potentially eliminating unusual or atypical data. This includes assessment of the presence of
short periodic breakdowns in the system caused, for example, by "bumping a filter" which
releases previously trapped particles. Such a practice could have a significant health effect if
the particles are Giardia or Cryptosporidium cysts and therefore represents a poorly
performing facility. Using these criteria, it is possible to identify poorly performing DWS
components and thus poorly performing systems even though these facilities may have
reported compliance with regulatory standards.
With the advancement of instrumentation and control in drinking water systems application,
data must be fully understood in terms of what it represents and how it has been acquired
from the field device or devices.
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It is important to confirm that data generated by a field device is fully understood with
respect to how the measured parameter is analyzed, converted to a signal output, and
conveyed to devices such as programmable logic controllers (PLC) and supervisory control
and data acquisition (SCADA) systems. Such output signals may be conditioned by the
measuring device itself or set with variable dead-bands or scan rates that may impact the
understanding of the data. It should not be assumed that the instrument sends out an
instantaneous signal to the PLC and SCADA system; for example, some analyzers have built-
in calibration check cycles where the on-line measurement of a parameter is interrupted for a
period of time.
Confirmation that ranges, spans and signals from field devices correlate correctly for all
PLCs and SCADA systems acquiring such information is recommended. It is important that
data read at the device be identical to the data presented on charts, HMIs and databases
archiving such information. Analog to digital conversions from field devices to PLCs should
also be confirmed.
PLC scan rates should be set to the appropriate levels according to the criticality of the
measured parameter. Data archiving may or may not align with the defined device and PLC
scan rate setting. Retrieval of data from the SCADA historian or database on a granularity
lower than the scan rate must be understood to confirm such information is not modified by
arithmetic functions such as averaging, minimum or maximum functions. As an example, a
5-second turbidity scan rate provides 720 distinct parameter values into a database. Retrieval
of such information on an hourly granularity would likely result in a value that is the average
of 720 values. This must be known since other arithmetic functions could also be applied to
the data rolled up to an hourly value.
Once understood, data acquired from field devices can be used to safely develop conclusions
regarding process optimization initiatives.
3.2.3 Identification and Prioritization of Performance Limiting Factors
3.2.3.1 Identification of Performance Limiting Factors
A significant aspect of any CPE is the identification of factors that limit the existing system's
performance. This step is critical in defining the focus of follow-up efforts. To assist in factor
identification, a list of 65 different factors that could potentially limit DWS performance is
provided in Appendix A. These factors are divided into broad categories of administration,
maintenance, design and operation. Definitions of each factor are provided. This list and
definitions have been updated and modified based on the results of water treatment plant
CPEs that have been conducted in the U.S. and Ontario, and is provided for convenience and
reference. If alternate names or definitions provide a clearer understanding to those
conducting the CPE, they can be used. However, if different terms are used, each factor
should be defined and these definitions should be readily available to those conducting the
CPE and interpreting the results. It is desirable to adopt a consistent list to allow comparison
from system to system. Note that the list includes factors related to the capacity of major
DWS components. If the evaluation of major DWS component results in a Type 2 or 3
classification, these results can then be documented in the overall list of factors identified as
limiting an existing system’s performance.
A factor should only be identified if it impacts performance. As such, an observation that a
factor does not meet a particular "industry standard" (e.g., a documented preventive
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maintenance program or good housekeeping practices) does not necessarily indicate a
performance limiting problem. An actual link between poor performance and the identified
factor must exist. Properly identifying a system's unique list of factors requires very careful
analysis because the actual problems in a system are often masked. This concept is illustrated
in the following example:
A review of plant records revealed that a conventional water treatment plant was
periodically producing finished water with turbidity greater than 0.5 NTU. The
utility, assuming that the plant was operating beyond its capability, was beginning to
make plans to expand both the sedimentation and filtration unit processes. Field
evaluations conducted as part of a CPE revealed that settled water and finished water
turbidities averaged about 5 NTU and 0.6 NTU respectively. Filtered water
turbidities peaked at 1.2 NTU for short periods following a filter backwash. Initial
observations could lead to the conclusion that the plant's sedimentation and filtration
facilities were inadequately sized. However, further investigation revealed the poor
performance was caused by the operator adding coagulants at dosages 200 percent higher
than required, leading to formation of a pinpoint floc that would not settle or filter, and
operating the plant at its peak capacity for only 8 hours each day, resulting in the washout
of solids from the sedimentation basins. It was determined that implementing proper
process control of the plant and operating the plant at a lower flow rate for 16 hours each
day would allow the plant to continuously achieve acceptable finished water quality. It was
further determined that the reason the plant was not operated for longer periods of time was
an administrative policy that limited plant staff to one person, which made both 16-hour
and weekend coverage difficult. Staffing with one operator would not allow continuous
successful operation of the plant because there would be periods of time when necessary
process control adjustments could not be made.
It was concluded that four factors contributed to the poor performance of the plant:
1. Operator Application of Concepts and Testing to Process Control – Inadequate
operator knowledge to determine proper coagulant doses and to set chemical feed
pumps to apply the correct chemical dose.
2. Administrative Policies – Restrictive administrative policy that prohibited hiring
an additional operator to allow reduced plant operating flow rate by increasing
operating time.
3. Process Control Testing – Inadequate test equipment and sampling program to
provide process control information.
4. Administrative Familiarity With Plant Needs – Poor administrative guidance that
resulted in a rate structure that would not support the needs of the plant.
Given the above observations, plant expansion was not required.
The above discussion illustrates that a comprehensive analysis of a performance problem is
essential to identify the actual performance limiting factors. If the initial conclusions regarding
sedimentation and filtration capacity had been pursued, improper corrective actions in the form of
unnecessary expenditures would probably have occurred. As well, the issues associated with
process control and administrative guidance would likely have been ongoing even with the
planned expansion giving continued poor performance. Instead, addressing the operational and
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administrative factors identified would allow the plant to produce acceptable finished water on a
continuous basis without major expenditures for construction.
3.2.3.2 Prioritization of Performance Limiting Factors
After all performance limiting factors are identified, they are prioritized in order of their
adverse effect on allowing desired system performance to be achieved. This prioritization
establishes the sequence and/or emphasis of follow-up activities necessary to optimize system
performance. For example, if the highest ranking factors (i.e., those having the most negative
impact on performance) are related to physical limitations in DWS component capacity,
initial corrective actions are directed toward defining system modifications and obtaining
administrative funding for their implementation. If the highest ranking factors are process
control-oriented, initial emphasis of follow-up activities would be directed toward site-
specific operator training.
Prioritization of factors is accomplished by a two-step process. First, all factors that have
been identified are individually assessed with regard to adverse impact on system
performance and assigned an "A", "B" or "C" rating (Table 3-1). The checklist of factors in
Appendix A includes a column to enter this rating. The second step of prioritizing factors is
to list those receiving an "A" rating in order of severity, followed by listing those receiving
"B" rating in order of severity. "C" factors are not prioritized.
Table 3-1 – Classification System for Prioritizing Performance Limiting Factors
Rating
Impact On System Performance
A Major effect on long-term repetitive basis
B Minimum effect on routine basis or major effect on a periodic basis
C Minor effect
"A" factors are major sources of a performance deficiency and are the central focus of any
subsequent improvement program. An example "A" factor would be sedimentation facilities
that are inadequate to reduce the suspended solids loading to the filters at all times of the
year, such that desired finished water quality cannot be achieved.
Factors are assigned a "B" rating if they fall in one of two categories:
Those that routinely contribute to poor performance but are not the major problem.
An example would be insufficient plant process control testing where the primary
problem is that the staff does not have a good understanding of coagulation
chemistry, how to run or interpret jar tests, or the need for additional process control
testing.
Those that cause a major degradation of system performance, but only on a periodic
basis. A typical example is sedimentation basins that cause periodic serious problems
during spring run-off.
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Factors receive a "C" rating if they contribute to a performance problem, but have minor
effect. For example, if raw water was being sampled from the rapid mix after chemical feed,
it could indirectly contribute to poor performance since raw water testing would not be
representative of actual conditions. The problem could be easily corrected and would not be a
major focus during follow-up correction activities.
As a comparison of the different ratings, the example of a factor with a rating of "A" above
(sedimentation) would receive a "B" rating if the basin was only inadequate periodically, for
example, during a run-off event. The factor would receive a "C" rating if the basin size and
volume were adequate, but minor baffling was required to improve its performance.
Typically, 5 to 15 factors are identified during a CPE. The remaining 50 to 60 factors that are
not identified as performance limiting represent a significant finding. For example, in the
example presented in Section 3.2.3.1, neither sedimentation nor filtration was identified as a
performance limiting factor. Since they were not identified, plant personnel need not focus on
the sedimentation basins or filters as a problem, which would preclude spending large
amounts of capital to upgrade these facilities. Factors that are not identified are also a source
for providing recognition to personnel for adequately addressing these potential sources of
problems.
Once each identified factor is assigned an "A", "B", or "C" rating, those receiving "A" or "B"
ratings are listed on a one page summary sheet (see Appendix A) in order of assessed severity
on system performance. The prioritized summary list of factors provides a valuable reference
for the next step of the CPE, assessing the ability to improve performance, and serves as the
foundation for implementing correction activities if they are deemed appropriate.
All factors limiting system performance typically may not be identified during the CPE
phase. It is often necessary to later modify the original corrective steps as new and additional
information becomes available during conduct of the performance improvement (CTA)
phase.
3.2.3.3 Evaluation of Performance Limiting Factors
Evaluation of administration, maintenance, design and operation factors occurs throughout
the conduct of a CPE. The following are some useful observations in identifying factors in
these areas.
Administration Factors
The evaluation of administrative performance limiting factors is a subjective effort, primarily
based on management and staff interviews. In small systems the entire staff, budgetary
personnel and administrators, including one or two elected officials, should be interviewed.
These interviews are more effective after the evaluator has been on a system tour and has
completed enough of the data development activities (including the major DWS component
and performance assessment evaluations) to become familiar with system capabilities and
past performance. With this information, the evaluator is better equipped to ask insightful
questions about the existing DWS. To accurately identify administrative factors requires
aggressive but non-threatening interview skills. The evaluator must always be aware of this
delicate balance when pursuing the identification of administrative factors.
Budgeting and financial planning are the mechanisms that system owners/administrators
generally use to implement their objectives. Therefore, evaluation of these aspects is an
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integral part of efforts to identify the presence of administrative performance limiting factors.
Smaller utilities often have financial information combined with other utilities, such as
wastewater treatment, street repairs, and parks and recreation. Additionally, nearly every
utility's financial information is set up differently. Therefore, it is necessary to review
information with the assistance of operations and/or budgetary personnel to rearrange the line
items into categories understood by the evaluator. Forms for comprehensively collecting
DWS information, including financial information, have been developed and are presented in
Appendix B. These forms allow a consistency in development of financial information.
Reference should be made to the Financial Plans Regulation (O. Reg. 453/07) made under
the SDWA.
When reviewing financial information, it is important to determine whether the rate structure
creates sufficient revenue to adequately support the DWS. Water system revenues should
provide an adequate number of fairly paid staff and exceed expenditures sufficiently to allow
establishment of a reserve fund for future system modifications.
Typically, all administrators verbally support goals of low costs, safe working conditions,
good plant performance, and high employee morale. An important question that the evaluator
must ask is, "Where does treated water quality fit in?". An ideal situation is one in which the
administrators function with the awareness that they want to achieve high quality finished
water as the end product of their water treatment efforts. Administrators who are not
supportive of these objectives are typically identified as contributing to inadequate
performance during factor identification activities. The requirements of Section 19 of the
SDWA, Statutory Standard of Care, should be discussed with administrators to ensure they
are aware of their legal duties and responsibilities with regard to the protection and safety of
the users of municipal drinking water.
Technical problems identified by operating staff or the CPE evaluator, and the potential costs
associated with these problems, often serve as the basis for assessing administrative
performance limiting factors. For example, the water staff may have correctly identified
minor modifications needed for the facility and presented these needs to the utility manager,
but had their requests declined. The evaluator must solicit the other side of the story from the
administrators, to see if the administration is indeed non-supportive in correcting the
problem. There have been numerous instances in which operators or superintendents have
convinced administrators to spend money to "correct" problems that resulted in no
improvement in system performance.
Administrators can directly impact performance of a DWS by failing to provide adequate
staffing levels required for the efficient operation of a WTP. Inadequate staff coverage (e.g.
no one is on-site to adjust chemical dosages relative to raw water quality changes) often
results in poor performance. Another area in which administrators can indirectly affect
system performance is through personnel motivation. A positive influence exists if
administrators encourage personal and professional growth through support of training,
tangible awards for upgrading of certification levels, etc. If, however, administrators
eliminate or skimp on essential operator training, downgrade operator positions through
substandard salaries, require operators to perform too wide a range of duties not related to
water treatment or distribution, or otherwise provide a negative influence on operator morale,
administrators can have a significant detrimental effect on system performance.
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Design Factors
Data gathered during a system tour, review of plant and distribution system drawings and
specifications, completion of design information forms in Appendix B, and the completed
evaluation of major DWS component capabilities, including the performance potential graph,
provide the basic information needed to assess design-related performance limiting factors.
Often, to complete the evaluation, the evaluator must make field investigations of the various
DWS components.
Field evaluations or special studies should be completed in cooperation with operations staff.
The evaluator must not make any changes in equipment operation unilaterally. Any field
testing desired should be discussed with the operator, whose cooperation should be obtained
in making any needed changes. This approach is essential since the evaluator may wish to
make changes that could improve system performance but could be detrimental to equipment.
The operator has worked with the equipment, repaired past failures, and read the
manufacturer's literature, and is in the best position to ascertain any adverse impact of
proposed changes. Field evaluations are discussed in more detail in Section 3.3.3.5.
Operational Factors
Operational factors are those that relate to the process control functions. Significant
performance limiting factors often exist in these areas (USEPA, 1998). The approach and
methods used in maintaining process control can significantly affect performance of DWS
that have adequate physical facilities.
A system tour provides an opportunity to initially assess process control efforts. For example,
the process control capability of an operator can be subjectively assessed during a plant tour
by noting if the operator recognizes the unit process functions and their relative influences on
plant performance. A good grasp of process control is indicated if this capability exists.
The heart of the operational factors assessment is the process control testing, data
interpretation, and process adjustment techniques utilized by operating staff. The primary
controls available to a water treatment plant operator are flow rate; chemical selection and
dosage; and filter backwash frequency. Other controls include flocculation energy input and
sedimentation sludge removal. Controls at the system level may include distribution system
pressure and storage tank levels. Process control testing is necessary to gain information to
make decisions regarding these available controls. It should be noted, however, that
instrument devices can have filtering and damping capabilities that condition the actual
parameter value. Data should be interpreted with a full understanding of the instrument
device output conditioning, if applicable. It is also important to fully understand how
parameter values are interpreted and presented in SCADA databases given that arithmetic
functions may be applied (e.g. average, minimum, maximum, etc.) to such raw parameter
values. Additional information on data confidence and analysis is provided in Section 3.2.2.1.
Information to assist in evaluating process control testing, data interpretation and process
adjustment efforts is presented in the individual component chapters.
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Maintenance Factors
Maintenance performance limiting factors are evaluated throughout the CPE by data
collection, observations and questions concerning reliability and service requirements of
pieces of equipment critical to system performance. If units are out of service routinely or for
extended periods of time, maintenance practices may be a significant contributing cause to a
performance problem. However, equipment breakdowns are often used as excuses for
performance problems. For example, one operator blamed excessive turbidity levels from the
sedimentation basin on the periodic breakdown of the primary alum feeder. However, the
backup feeder, while of greater capacity, could have provided an acceptable alum dose. The
real cause of the poor sedimentation basin performance was a lack of understanding by the
operator of the importance of maintaining the chemical feed rate.
It is important that maintenance activities be evaluated with respect to their impact on system
performance and process criticality, and not on the basis of comparison to the availability of a
documented preventive maintenance program. As such, maintenance would not be identified
as a performance limiting factor of a system that is exhibiting a high degree of performance
but has no documented routine maintenance system.
3.2.4 Assessment of Applicability of a CTA
Proper interpretation of the CPE findings is necessary to provide the basis for a
recommendation to pursue the performance improvement phase (e.g., CTA described in
Section 3.4). It is at this assessment phase that the maximum application of the evaluator's
judgment and experience is required. The initial step in assessment of CTA applicability is to
determine if improved performance can be achieved by evaluating the capability of major
DWS components. A CTA is recommended if DWS components receive a Type 1 or Type 2
rating. However, if major DWS components are deficient in capacity, acceptable
performance from each "barrier" may not be achievable, and the focus of follow-up efforts
must include a more detailed evaluation of options for upgrades or expansion.
Although all performance limiting factors can theoretically be eliminated, the ultimate
decision to conduct a CTA may depend on the factors that are identified during the CPE. An
assessment of the list of prioritized factors helps assure that all factors can realistically be
addressed given the unique set of factors noted. There may be reasons why a factor cannot be
approached in a straightforward manner. Examples of issues that may not be feasible to
address directly are replacement of key personnel, increases in rate structures or training of
uncooperative administrators to support DWS needs. In the case of reluctant administrators
who do not take water quality seriously, regulatory pressure may be necessary before a
decision is made to implement a CTA.
For systems where a decision is made to implement a CTA, all performance limiting factors
must be considered as feasible to correct. These are typically corrected with adequate
"training" of the appropriate personnel. The training is addressed toward the operational staff
for improvements in process control and maintenance, toward the system administrators for
improvements in administrative policies and budget limitations, and toward operators and
administrators to achieve minor facility modifications. Training, as used in this context,
describes activities whereby information is provided to facilitate understanding and
implementation of corrective actions.
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3.2.5 CPE Report
Results of a CPE are summarized in a brief written report to provide guidance for facility
administrators and operators and, if applicable, regulatory personnel. It is important that the
report be kept brief so that the maximum amount of resources is used for the evaluation
rather than preparing an all-inclusive report. The report should present enough information to
allow the decision-making official to initiate efforts toward achieving desired performance
from their system. It should not provide a list of specific recommendations for correcting
individual performance limiting factors. Making specific recommendations often leads to a
piecemeal approach to corrective actions, and the goal of improved performance is not
achieved. For Type 1 and Type 2 systems, the necessity of comprehensively addressing the
combination of factors identified by the CPE through a CTA should be stressed. For Type 3
systems, a recommendation for a more detailed study (e.g. process audit) may be warranted.
Appendix C includes a sample CPE report.
3.3 CARRYING OUT A CPE
A CPE involves conducting several activities within a structured framework to determine if
significant improvements in system performance can be achieved without major capital
improvements. A schematic of CPE activities is shown in Figure 3-3.
Initial activities are conducted prior to on-site efforts and involve notifying appropriate utility
personnel to ensure that they will be available. The kickoff meeting, conducted on-site,
allows the evaluators to describe on-site activities, to coordinate schedules, and to notify
personnel of the materials that will be required. Following the kickoff meeting, a system tour
is conducted by the superintendent or process control supervisor. During the tour, the
evaluators ask questions regarding the drinking water system and notice items that may
require additional attention during data collection activities. For example, an evaluator might
make a note to investigate more thoroughly the flow splitting arrangement prior to
flocculation basins.
Following the system tour, data collection activities begin. Depending on team size, the
evaluators split into groups to facilitate simultaneous collection of the administrative, design,
operations, maintenance and performance data. After data are collected, the major DWS
component evaluation and performance assessment are conducted. Completing these
activities prior to the interviews provides the evaluators with an understanding of DWS
component capability and current performance, which allows interview questions to be
focused on possible factors limiting system performance. Interviews and special studies are
then conducted which allow additional insight to be gained regarding actual system
performance and what factors are contributing to the level of performance observed.
After all information is collected, the evaluation team meets at a location away from the
utility personnel to review findings. At this meeting, factors limiting performance of the
system are identified and prioritized. The prioritized list of factors, performance data, and
major DWS component evaluation data are then compiled and copied for use as handouts
during the exit meeting. An exit meeting is held with appropriate operating and
administrative personnel where all evaluation findings are presented. Off-site activities
include assessing the applicability of a follow-up CTA and completing the written report. A
more detailed discussion of each of these activities follows.
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Figure 3-3 – Schematic of CPE Activities
3.3.1 Personnel Capabilities
A CPE is typically conducted over a three to five day period by a team composed of a
minimum of two people. The team approach allows a system to be evaluated in a reasonable
time frame and for personnel to share impressions. Shared impressions are especially
important when identifying and prioritizing performance limiting factors and in assessing
major DWS component capability since these efforts require a significant amount of
Initial Activities
Kick-off Meeting
System Tour
Data Collection Activities
Administration Data
Design Data
Operations Data
Maintenance Data
Performance Data
Conduct Performance Assessment
Evaluate Major DWS
Components
Conduct Interviews
Conduct Special Studies
Identify and Prioritize Factors
Exit Meeting
Assess Applicability of a
CTA
CPE Report
Off-Site
Off-Site
On-Site
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judgment. Persons responsible for conducting CPEs should have significant knowledge and
skills in the areas identified in Table 3-2.
Table 3-2 – Personnel Capabilities for Conducting a CPE
Technical Skills
Leadership Skills
Water treatment plant and distribution
system design
Communication (presenting, listening, interviewing)
Water treatment and distribution system
operation and process control
Organization (scheduling, prioritizing)
Regulatory requirements Motivation (involving people, recognizing staff abilities)
Maintenance Decisiveness (completing CPE within timeframe
allowed)
Utility management (rates, budgeting,
planning)
Interpretation (assessing multiple inputs, making
judgments)
Regulatory agency personnel with experience in evaluating drinking water systems and
consulting engineers who routinely work with system evaluation, process design and start-up
represent the types of personnel with adequate backgrounds to conduct CPEs.
Utilities/municipalities are encouraged to use the services of a consultant with specialized
expertise in drinking water treatment process and distribution system design and
troubleshooting, as opposed to a consultant whose focus is designing and building plants. It
may be beneficial to consult with the design engineer to discuss the original intent of the
design and how the facility was meant to be operated.
3.3.2 Initial Activities
To determine the magnitude of the field work required and to make the on-site activities most
productive, specific initial information should be gathered. This information includes basic
data on the system and sources for any additional information. If a person associated directly
with the system is the evaluator conducting the CPE, some of the steps may not be necessary.
The following is a list of items that the CPE team should bring during site visits. These items
will aid in the collection and handling of data and other information.
MOE Manual entitled Optimization Guidance Manual for Drinking Water Systems
(this document) and other reference materials (e.g. USEPA, 1998);
Bench-top or hand-held instruments/devices (e.g. turbidimeter, chlorine residual
analyzer, pH meter, filter media probe, etc.);
Lap-top computer with spread-sheet capability for analysis/presentation of data;
Tape measure; and
Camera.
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3.3.2.1 Identify Key People
It is necessary to have key people available during the CPE. Therefore, these people should
be identified and their availability determined. The superintendent, manager or other person
in charge of the DWS must be available. If different persons are responsible for maintenance
and process control, their presence should also be required. These persons should be available
throughout the field activities. A person knowledgeable about details of the utility budget
must also be available. A one- to two-hour meeting with this person will typically be required
during the field work to assess the financial aspects of the utility. In many small
communities, this person is most often the Clerk. In larger communities, the Manager or
Superintendent can usually provide the best information.
Availability of key administrative personnel is required. In many small communities, an
operator or superintendent may report directly to the local Council or Chair of Council. In
larger communities, the key administrative person is often the Director of Public Works or
other non-elected administrator. In all cases the administrator(s) as well as representative
elected officials who have the authority to effect a change in policy or budget for the DWS
should be available.
If a consulting engineer is currently involved with the system, that individual should be
informed of the CPE and provided with a copy of the report. Normally, the consulting
engineer will not be directly involved in the conduct of the CPE. An exception may occur if
there is an area of the evaluation that could be supplemented by the expertise available
through the consultant.
3.3.2.2 Scheduling
When initiating a CPE, a letter should be sent to the utility describing the schedule of
activities that will take place and outlining the commitment required of operat ions and
administrative staff. An example letter is presented in Appendix D. Interviews of
personnel associated with the system are a key component of a CPE. As such, the major
criterion for scheduling the time for a CPE should be local personnel availabil ity. If the
CPE is conducted by personnel not associated with a regulatory agency, it may be
beneficial to inform regulatory personnel of the CPE schedule. Responsibility for this
task should be clearly identified by the evaluator and local personnel during the
scheduling of activities.
3.3.2.3 Pre-Meeting
It may be beneficial for the municipality/utility to hold a meeting with its operational staff at
some time prior to the CPE kickoff meeting. This will familiarize staff with the intent of the
CPE and allows them to be better prepared when the CPE begins. By including operators at
the earliest stages, they will be more likely to "buy-in" to the CPE process.
3.3.3 On-Site Activities
On-site CPE activities are largely devoted to collection and evaluation of data. As a
courtesy to the system owner and to promote efficient data collection, the field work is
initiated with a kickoff meeting. This activity is followed by a system tour (conducted by
senior operations staff) and a period of time where detailed data on the system are
gathered and analyzed.
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3.3.3.1 Kickoff Meeting
A short (less than 30 minutes) meeting between key operations and administrative staff
and the evaluators should be held to initiate the field work. The major purposes of this
meeting are to present the objectives of the CPE effort, to coordinate and establish the
schedule, and to initiate the administrative evaluation activities. Each of the specific
activities that will be conducted during the on-site effort should be described. Meeting
times for interviews with non-operations and operations personnel should be scheduled.
A sign-up sheet (see Appendix B) may be used to record attendance and as a means of
assisting with recall of names.
Information and resource requirements should be established. Specific items that are required
and may not be readily available are: budget information to provide a complete overview of
costs associated with water treatment and distribution; a water rate schedule; historical
monitoring data for a period of at least one year; O & M Manuals, if available; and any
facility drawings and specifications or other engineering studies available for the existing
facilities.
Administrative factors that may affect system performance should be noted during this
meeting, such as the priority of high quality finished water, familiarity with system needs,
communication between administration and operations staff, and policies on funding. These
initial perceptions often prove valuable when formally evaluating administrative factors later
in the CPE effort.
3.3.3.2 System Tour
A system tour should follow the kickoff meeting. The objectives of the tour are to familiarize
the evaluator with the physical works of the water treatment plant and distribution system,
make a preliminary assessment of operational flexibility of the existing processes and
chemical feed systems, and provide an initial basis for discussions on performance, process
control and maintenance.
The evaluator should also consider other elements of the system, which may not be physical
work, that contribute to the delivery of safe drinking water. For example, the system tour may
include activities or discussions related to source control measures and/or programs targeted
directly at the end-users of water (e.g. backflow and cross-connection prevention).
For the water treatment facility, a walk-through tour following the flow from the raw water
source through the plant to the clearwell is suggested. It is then appropriate to tour backwash
and sludge treatment and disposal facilities, distribution system facilities, followed by the
support facilities, such as the laboratory and maintenance areas. The evaluator should note
the sampling points and chemical feed locations throughout the plant.
Pre-treatment
Pre-treatment facilities consist of raw water intake structures, screening equipment, raw water
pumps, pre-sedimentation basins and flow measurement equipment. Intake structures and
screening equipment can have a direct impact on plant performance. For example, if the
intake configuration is such that screens become clogged with plant growth or the intake
becomes clogged with silt, consistent supply of water may be a problem. While at the raw
water source, questions should be asked regarding variability of the raw water quality,
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potential upstream pollutant sources, seasonal problems with taste and odours, raw water
quantity limitations and algae blooms.
Raw water pumping should be evaluated regarding the ability to provide a consistent water
supply and with respect to how many pumps are operated at a time. Frequent changing of
high volume constant speed pumps can cause significant hydraulic surges to downstream unit
processes, degrading plant performance. In addition, operational practices as they relate to
peak flow rates, peak daily water production, and plant operating hours should be discussed
to assist in defining the peak instantaneous operating flow rate.
Pre-sedimentation facilities are primarily found at water treatment plants where raw water
turbidities exceed several hundred NTUs. If plants are equipped with pre-sedimentation
capability, basin inlet and outlet configurations should be noted and the ability to feed
coagulant chemicals should be evaluated. Typically, most pre-sedimentation configurations
lower turbidities sufficiently to allow conventional water treatment plants to perform
adequately. If pre-sedimentation facilities do not exist, the evaluator must assess the
capability of existing water treatment unit processes to remove peak raw water turbidities.
Flow measurement facilities are important to accurately establish chemical feed rates,
backwash water rates and unit process loadings. The system tour should be used to observe
the location of flow measurement equipment and to ask questions regarding various plant
flows. Questions should be asked concerning maintenance and calibration of flow
measurement devices, the age of devices, ranges (device and PLC), telemetry, meter accuracy
ranges, data logging, etc.
Mixing/Flocculation/Sedimentation
Rapid mixing is utilized to provide a complete instantaneous mix of coagulant chemicals to
the water. The coagulants neutralize the negative charges on the colloidal particles allowing
them to agglomerate into larger particles during the gentle mixing of flocculation. These
heavier particles are then removed by settling in the quiescent area of the sedimentation
basin. These facilities, if properly designed and operated, provide the primary barrier to
pathogens, lowers the concentration of NOM and reduce the particulate load to the filters,
allowing them to "polish" the water. During the tour, observations should be made to
determine if the mixing, flocculation and sedimentation processes are designed and operated
to achieve this goal. The evaluator should also observe flow splitting facilities and determine
if parallel basins are receiving equal flow distribution.
Rapid mix facilities should be observed to determine if adequate mixing of chemicals is
occurring. The operator should be asked what coagulant chemicals are being added and what
process controls are employed to determine their dosage. Observations should be made as to
the types of chemicals that are being added together in the mixing process. For example, the
addition of alum and lime at the same location may be counter productive if no consideration
is given to maintaining the optimum pH for alum coagulation. If coagulant chemicals are
added without mixing, observations should be made as to possible alternate feed locations,
such as prior to valves, orifice plates or hydraulic jumps, where acceptable mixing might be
achieved.
When touring flocculation facilities, the evaluator should note inlet and outlet conditions,
number of stages and the availability of variable energy input. Flocculation facilities should
be baffled to provide even distribution of flow across the basin and to prevent velocity
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currents from disrupting settling conditions in adjacent sedimentation basins. If multiple
stages are not available, the capability to baffle a basin to create additional staging should be
observed. The ability to feed flocculation aids to the gentle mixing portion of the basin
should be noted. The operator should be asked how often flocculation energy levels are
adjusted or if a special study was conducted to determine the existing levels. In the case of
hydraulic flocculation, the number of stages, the turbulence of the water, and the condition of
the floc should be noted to determine if the unit process appears to be producing an
acceptable floc.
Sedimentation basin characteristics that should be observed during the tour are visual
observations of performance and observations of physical characteristics such as
configuration and depth. Performance observations include clarity of settled water, size and
appearance of floc, occurrence of floc carryover, and presence of flow or density currents.
The general configuration, including shape, inlet conditions, outlet conditions, and
availability of a sludge removal mechanism should be observed. The operator should be
asked what process control measures are utilized to optimize sedimentation including sludge
removal.
Filtration
Filters are utilized to remove the particles that are too small to be removed in sedimentation
basins by gravity settling. The number and configuration of filters should be noted, including
the type of filter media. The filter rate control equipment should be observed and discussed to
ensure that it regulates filter flow in an even, consistent manner without rapid fluctuations.
The flow patterns onto each filter should be noted to see if there is an indication of uneven
flow to individual filters.
Backwash equipment including pumps, air compressors, and surface washers should be
noted. The availability of back-up backwash pumping is desirable to avoid interruptions in
treatment if a breakdown occurs. The operator should be asked how frequently filters are
backwashed and what process control procedures are used to determine when a filter should
be washed. Preferably turbidity, rather than head loss or filter run duration, should be the
parameter utilized since it relates to water quality. The operator's response to these inquiries
helps to demonstrate his understanding and priorities concerning water quality. The operators
should also be questioned concerning the backwash procedure and if all operators follow the
same technique.
Disinfection
The evaluator should tour disinfection facilities to become familiar with the equipment feed
points and type of contact facilities. Special attention should be given to the configuration
and baffling of clearwells and finished water reservoirs that provide contact time for final
disinfection. Observation of the in-line contact time availability should be made by noting the
proximity of the first consumer, which is often the water treatment plant.
The availability of back-up disinfection equipment should be observed to assess the
capability of providing an uninterrupted application of disinfectant. The addition of a
disinfectant prior to filtration, either as an oxidizing agent or disinfectant should also be
noted. The capability to automatically control the disinfection systems should be determined.
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Water Treatment Process Residuals Handling and Disposal
During the tour, the evaluator should become familiar with the facilities available to handle
filter backwash water and sedimentation basin sludge. If backwash water and sludge are
discharged to the storm sewer system or a waterway, questions should be asked to determine
if the discharge is permitted and in compliance with Certificate of Approval (C of A) or
Drinking Water Works Permit (DWWP)/Municipal Drinking Water Licence (Licence)
requirements.
The location of any recycle streams should be identified during the tour. Recycle of
backwash water should be assessed relative to the feasibility of returning a potentially high
concentration of cysts to the plant raw water stream. Cysts are primarily removed by the
filters so that the recycle of backwash water in a plant where the raw water has a high
potential for substantial numbers of cysts may compound the health risk, depending on
washwater treatment.
Laboratory
The laboratory facilities should be included as part of the plant tour. Performance monitoring,
process control testing, instrumentation calibration and frequency, and quality control
procedures should be discussed with laboratory personnel. It is especially important to
determine if turbidity measurements represent actual plant performance. Available analytical
capability for other parameters (e.g. pH, chlorine residual) should also be noted.
Distribution System
For large distribution systems, the layout may be best ascertained by reviewing
distribution system drawings or schematics. Visits to major distribution system
components, such as major pumping stations or storage facilities, should be conducted.
The evaluator should note the location of sampling stations throughout the distribution
system as well as any interconnections with other drinking water systems (i.e.
neighbouring municipalities). The evaluator should review backflow and cross-
connection control programs or by-laws, and discuss their implementation and/or
enforcement.
Maintenance
Maintenance facilities should be included as part of the plant tour. Tools, spare parts
availability, storage, filing systems for equipment catalogs, general plant appearance and
condition of equipment should be observed. Questions on the preventive maintenance
program, including methods of initiating work (e.g., work orders), are appropriate.
During the conduct of a system tour the evaluator must be sensitive to the personnel
conducting the tour. Questions that challenge current operational practices or that put
operations personnel on the defensive should be avoided. The evaluator should maintain an
information gathering posture at all times. It is not appropriate to recommend changes in
facilities or operational practices during the tour although the evaluator will often be asked
for an opinion. A suggested response is to state that observations will be presented at the
conclusion of the on-site activities and after additional information is collected and analyzed.
Most of the questions asked on the tour will be asked again during formal data collection
activities. The staff should be informed that this repetitiveness will occur. The system tour
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also provides an excellent opportunity for the evaluator to observe intangible items that may
contribute to the identification of factors limiting performance (i.e., operator knowledge of
the system operation and facilities, relationship of process control testing to process
adjustments, etc.). Suggestions to help the evaluator meet the objectives of the system tour
are provided in subsequent chapters.
3.3.3.3 Detailed Data Gathering
Following the system tour, formalized data collection procedures are initiated. Information is
collected through conducting interviews with operations and administrative staff; reviewing
operating records, drawings, specifications, process control data sheets, etc., and conducting
field evaluations.
3.3.3.4 Drinking Water System Records
A variety of drinking water system records including budgets, drawings and specifications,
MOE Drinking Water Surveillance Program (DWSP) reports, MOE Drinking Water System
Inspection Program reports, operational logs, O & M Manuals, and manufacturers' literature
are required for the formal data collection efforts. The forms in Appendix B have proven to
be valuable in compiling information from these multiple sources in a consistent manner.
Categories covered by these forms are listed below:
Kickoff Meeting
Administration Data
Design Data
Operations Data
Maintenance Data
Performance Data
Interview Data
Exit Meeting
When collecting information, the evaluator should be aware that the data are to be used to
evaluate the performance capability of the existing facilities. The evaluator should
continuously be asking "How does this information affect plant performance?". If the area of
inquiry is directly related to system performance, such as filter design or an indication of an
administrative policy to cut costs by reducing chemical addition, the evaluator should spend
sufficient time to fully develop the perceived effect of the information on system
performance.
3.3.3.5 Field Evaluations
Field evaluations are an important means of identifying performance problems. Typically,
field evaluations should be conducted to verify the accuracy of monitoring and flow records,
chemical dosages, drawings, and other operating conditions. Specific field evaluations that
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could be conducted for major DWS components are discussed in the individual component
chapters.
Record drawings may have to be field verified by measuring basin dimensions with a tape
measure if there is doubt as to their accuracy. If no drawings are available, all basin
dimensions should be measured.
3.3.3.6 Evaluation of Major DWS Components
An evaluation of the system’s major DWS components is conducted to determine the
performance potential of existing facilities at peak instantaneous operating flow (or other
flow rate, as deemed applicable by the evaluator; see Section 3.2.1.2). This is accomplished
by developing a performance potential graph and rating the major DWS components as Type
1, 2, or 3, as discussed in Section 3.2.1. It is important that the major DWS component
evaluation be conducted early in the on-site activities since this assessment provides the
evaluator with the knowledge of the system's capability. If a poorly performing system’s
major components are determined to be Type 1 or 2, then typically factors in the areas of
administration, operation or maintenance are primarily contributing to the performance
problems. The completed major DWS component assessment allows the evaluator to focus
later interviews and data gathering to identify those performance limiting factors.
3.3.3.7 Performance Assessment
An assessment of the system's performance is made by evaluating existing recorded data and
by conducting on-site evaluations to determine if DWS component and total system
performance have been optimized. Typically, the previous twelve months of existing process
control data is evaluated and graphs are developed to assess performance of the system. Other
periods of process control data can be evaluated if they are more representative of system
operating conditions. Field evaluations are also conducted to determine if existing operating
records accurately reflect actual treated water quality. A detailed discussion of the methods
utilized in the performance assessment of individual DWS components is presented in
subsequent chapters.
3.3.3.8 Interviews
It is beneficial to complete the data collection forms and to complete the major DWS
component evaluation and performance assessment before initiating the formalized
interviews, since this background information allows the evaluator to better focus interview
questions. Interviews should be conducted with all of the operations staff, including the
superintendent and other key administrative personnel. Key administrators typically include a
Council or Board member (especially from a Water Committee), and the Utility
Director/Manager. The interviews should be conducted privately with each individual.
Approximately 30 minutes should be allowed for each interview.
Interviews are conducted to clarify information obtained from operating records and to
ascertain differences between real or perceived problems. Intangible items such as
communications, administrative support, morale, and work attitudes are also assessed during
the interview process. Administrative and operations staff are both interviewed to ensure that
a balanced opinion is obtained. The performance focus of the CPE process must be
maintained in the interviews. For example, an adamantly stated concern regarding
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supervision or communication is only of significance if it can be directly related to system
performance.
3.3.3.9 Evaluation of Performance Limiting Factors
After all data have been gathered, the major DWS component evaluations have been
completed, system performance has been assessed, and formal interviews have been
completed, identification and prioritization of performance limiting factors should be
conducted. The identification of factors should be completed at a location that allows open
and objective discussions to occur (i.e. away from operations staff). Prior to the discussion, a
debriefing session should be held that allows the evaluators to discuss pertinent findings from
their respective efforts. This step is especially important if more than two evaluators are
involved in the CPE because, with larger evaluation teams, not all members can be exposed
to every aspect of the comprehensive evaluation. All data compiled during the evaluations
should be readily available to support the factor identification efforts.
The checklist of performance limiting factors presented in Appendix A, as well as the factor
definitions, provides the structure for an organized review of problems in the subject system.
The intent is to identify, as clearly as possible, the factors that most accurately describe the
causes of limited performance. Often a great deal of discussion is generated in this phase of
the CPE effort. Several hours should be allocated to complete this step and all opinions and
perceptions should be solicited. It is particularly important to maintain the performance focus
during the activity in order to avoid identifying factors that do not have this emphasis.
Each factor identified as limiting performance should be assigned an "A", "B", or "C" rating.
Further prioritization is accomplished by completing the Summary Sheet presented in
Appendix A. Only those factors receiving either an "A" or "B" rating are prioritized on this
sheet.
3.3.3.10 Exit Meeting
Once the evaluation team has completed the field work for the CPE, an exit meeting should
be held with the system administrators and staff. A presentation of preliminary CPE results
should include brief descriptions of the following:
System performance assessment;
Evaluation of major DWS components;
Prioritized performance limiting factors; and
System performance potential.
Handouts summarizing these topics can be utilized to assist in the exit meeting presentation.
Examples of handouts typically utilized to present performance assessment findings include
time versus turbidity plots (one year of data) and percentile plots for raw, settled and finished
water, and results of field evaluations such as turbidity profiles following a filter backwash.
The performance potential graph and factor summary sheet can be utilized to present
information regarding the major DWS component evaluation and performance limiting
factors, respectively.
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If the CPE reveals that the system performance represents a significant health risk, this
should be carefully explained to the system owner and/or operating authority. System
administrators should be advised to be in contact with regulatory and public health officials.
If a utility is operating within applicable regulatory requirements, but not optimizing treated
water quality, a presentation can be made as to the potential health advantage of setting more
aggressive goals, such as a filtered water turbidity of less than 0.1 NTU. A brief presentation
on the function of each water treatment and distribution system component and the effort
required to produce and deliver acceptable finished water quality can also be made to
enhance understanding for the administrators.
It is important to present all findings at the exit meeting with local officials. This approach
eliminates surprises when the CPE report is received and lays the foundation for the approach
necessary for any follow-up activities. In situations where administrative or operating staff
shortcomings are difficult to present, the evaluator must be sensitive and use communication
skills to successfully present the results. Throughout the discussions, the evaluator must
remember that the purpose of the CPE is to identify and describe facts to be used to improve
the current situation, not to place blame for any past or current problems.
It is emphasized that findings, and not recommendations, be presented at the exit meeting.
The CPE, while comprehensive, is conducted over a short time and is not a detailed
engineering design study. Recommendations made without appropriate follow-up could
confuse operators and administrators, and lead to inappropriate or incorrect actions on the
part of the utility staff (e.g., improper technical guidance). For example, a recommendation to
set coagulant dosages at a specific level could be followed literally to the extent that the next
time the evaluator is at the plant, coagulant dosages may still be the same as that
recommended even though time has passed and raw water conditions have changed.
It should also be made clear at the exit meeting that other factors are likely to surface during
the conduct of any follow-up activities. These factors will also have to be addressed to
achieve the desired performance. This understanding of the short term CPE evaluation
capabilities is often missed by local and regulatory officials, and efforts may be developed to
address only the items prioritized during the CPE. The evaluator should stress that a
commitment must be made to achieve the desired improved performance, not to addressing a
"laundry list" of currently identified problems. An ideal conclusion for an exit meeting is that
the facility owners fully recognize their responsibility to provide a high quality finished water
and that, armed with the findings from the CPE, they are enthusiastic to achieve that goal.
3.3.4 CPE Report
At the conclusion of the field activities, a CPE report is prepared. The objective of a CPE
report is to summarize findings and conclusions (see Section 3.2.5). Eight to twelve typed
pages are generally sufficient for the text of the report. An example report is presented in
Appendix C. Typical contents are:
Introduction
System Information
Major DWS Component Evaluation
Performance Assessment
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Performance Limiting Factors
Projected Impact of a CTA
As a minimum, the CPE report should be distributed to system administrators and all
operations personnel. Further distribution of the report (e.g., to the design engineer) depends
on the circumstances of the CPE, but should be done at the direction or with the awareness of
local administrators.
3.4 CTA METHODOLOGY
The methodology for conducting CTA is a combination of 1) utilizing CPE results as a basis
for follow-up, 2) implementing process control priority setting techniques and 3) maintaining
long term involvement to systematically train staff and administrators responsible for water
treatment and distribution.
If the results of a CPE indicate a Type 1 system (see Figure 3-1), then existing major DWS
components have been assessed to be adequate to meet current performance requirements.
For Type 1 facilities, major system modifications are not indicated and the CTA can focus on
systematically addressing identified performance limiting factors to achieve the desired
finished water quality.
For Type 2 facilities, existing major DWS components have been determined to be marginal.
Improved performance is likely through the use of CTA; however, the system may or may not
meet performance objectives without major facility modifications. For these systems, the CTA
focuses on obtaining optimum capability of existing facilities. If the CTA does not achieve the
desired finished water quality, DWS component deficiencies will be clearly identified and the
owner/operator can be confident in pursuing the indicated facility modifications.
For Type 3 systems, major DWS components have been assessed to be inadequate to meet
performance objectives. For these facilities, major construction is indicated and a
comprehensive study that focuses on alternatives to achieve these construction needs is
warranted. A study of this type should look at long term water needs, raw water source or
treatment alternatives, distribution or storage requirements, and financing mechanisms. Such
a study may be subject to the requirements of the Municipal Class Environmental Assessment
(MEA, 2007) process under the Environmental Assessment Act.
If existing system performance has the potential to cause a serious public health risk, officials
may want to address the most serious operating problems to reduce the risk until
modifications can be implemented.
3.4.1 CPE Results
Implementation of a CTA initially focuses on addressing the prioritized list of performance
limiting factors that was developed during the CPE. This list provides a system-specific
outline of those items that must be addressed if desired performance is to be achieved. A
combination of activities such as training, minor modifications, and process control
adjustments may all be used by the person implementing the CTA to address identified
factors. It is important to note that additional performance limiting factors, not identified in
the short duration of the CPE, often become apparent during the CTA. These factors must
also be addressed to achieve the desired level of performance.
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3.4.2 Process Control Priority Setting
The areas in which performance limiting factors have been broadly grouped (administration,
maintenance, design and operation) are all important in that a factor in any one of these areas
can individually cause poor performance. However, when implementing the CTA the
relationship of these categories to achieving the goal of desired delivered water quality must
be understood. Administration, design and maintenance activities all lead to a DWS
physically capable of achieving desired performance. It is the operation, or more specifically
the process control activities, that enables a physically capable system to produce and deliver
drinking water of acceptable quality. This concept is illustrated graphically in Figure 3-4.
Figure 3-4 – Relationship of Performance Limiting Factors to Achieving a Performance
Goal
Focusing on process control efforts when implementing the CTA allows priorities to be
developed for making the required changes to achieve improved performance. In this way the
most direct approach to improve performance is implemented. For example, if filtered water
turbidities cannot be consistently maintained at required levels because operating staff are not
at the plant to make chemical feed adjustments in response to changing raw water quality,
then improved performance will require better staff coverage. In this case, identified
limitations in meeting process needs (e.g., limitations in making chemical feed adjustments)
establish the priority for improving staff coverage (e.g., an administrative policy) at the plant.
Additional staff would alleviate the identified deficiency (e.g., provide a capable system) and
allow process adjustments to be made, so that progress toward the performance goal can be
continued. Conversely, non-performance related improvements can be justifiably delayed
utilizing the same process control emphasis.
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3.4.3 Long Term Involvement
To be effective, implementation of the CTA must constitute a long term effort, typically
involving several months, for several reasons:
Greater Effectiveness of Repetitive Training Techniques: Operator and administrator training
can be conducted under a variety of actual operating conditions (e.g., seasonal water quality
or demand changes). This approach allows development of observation, interpretation and
implementation skills necessary to maintain desired finished water quality during periods of
variable raw water quality.
Time Required to Make Minor Facility/System Modifications: For changes requiring
financial expenditures, both time and a multiple step approach are typically required to gain
administrative (e.g. Local Council) approval. First, the need for minor modifications must be
demonstrated through process control efforts. Then council/administrators must be shown the
need and ultimately convinced to approve the funds necessary for the modifications. These
activities normally take several months before the identified modification is implemented and
operational. In addition, depending on the nature of the modifications, an amendment to the
plant's C of A or DWWP/Licence may be required.
Time Required to Make Administrative Changes: Administrative factors can prolong CTA
efforts. For example, if the utility rate structure is inadequate to support system performance,
extensive time can be spent implementing required changes in the rate structure. Communication
barriers between administrative and operational staff may have to be addressed for improved
performance. If the staff is not capable, personnel changes may have to be made for the CTA to
be successful.
Time Required to Address Additional Performance Limiting Factors That May Be Found
During the CTA: During the conduct of a CTA, new problems are often encountered that
were not apparent during the CPE, or arise as a result of actions taken early in the CTA.
3.4.4 Facilitator Tools
Experience has shown that no single approach can address the unique combination of factors
at every DWS; therefore, actual details of implementation must be site specific and should be
left to the individual implementing the CTA. However, general techniques that have been
successfully used in implementing CTAs are presented.
The individual who implements a CTA is called a facilitator. This individual is typically an
"outsider" and accomplishes the objectives utilizing periods of on-site involvement (e.g. site
visits) interspersed with off-site limited involvement (e.g. phone calls). This approach is
graphically illustrated in Figure 3-5.
Site visits are used by the facilitator to verify or clarify system status, initiate major process
control changes, test completed facility/system modifications, provide on-site operator or
administrative training, and report progress to utility staff. Dates for site visits should be
scheduled as indicated by the system status and training requirements and not necessarily be
established at specific intervals. As shown in Figure 3-5, fewer site visits and telephone calls
will typically be necessary as the CTA progresses. This is in line with the transfer of
responsibility to the operations staff that occurs during the CTA. The number of site visits
required by a CTA facilitator is dependent on system size and on the specific performance
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limiting factors. For example, some administrative (e.g., staffing and rate changes) and
design factors could significantly increase the number of site visits required to complete a
CTA. Typically two to four days are spent touring the DWS facilities during site visits. A
final site visit is conducted to present a report.
Figure 3-5 – Typical Scheduling of CTA Activities
Telephone calls are used to routinely monitor CTA progress. Routine phone contact is used to
train and encourage operations personnel concerning system observations, data interpretation,
and follow-up implementation activities. Telephone calls are limited in effectiveness in that
the CTA facilitator must completely rely on observations of the operations staff. To enhance
communication, the CTA facilitator should always summarize important points, describe
decisions that have been reached, and identify actions to be taken. Further, both the CTA
facilitator and operations personnel should maintain written phone logs. Typically, two to
four hours each week are spent on phone calls and data development and interpretation.
Specific tools have been used to increase the effectiveness of site visits and telephone calls,
and to enhance the transfer of capability for achieving and maintaining desired finished water
quality to plant administrators and staff. These are further described below.
Contingency plans should be prepared for the occasions where a CTA is initiated at a DWS
that is producing unacceptable finished water quality, or where a CTA is being conducted and
finished water quality deteriorates to an unacceptable level. The contingency plan should
include actions such as reducing plant flow rate to improve performance, shutting down the
plant, isolating portions of the distribution system, initiating public notification and/or
initiating a boil water advisory. If finished water exceeds a health-based objective, the
regulatory agency (Ministry of Health/Ministry of the Environment) must be immediately
informed and public notification procedures mandated by the SDWA followed. To minimize
the chance of producing unacceptable finished water while conducting a CTA, all
experimentation with treatment processes, such as chemical doses and different coagulant
products, should be done at bench scale (e.g. jar test) before implementing changes at full
scale.
Action-implementation plans should be developed and updated by the facilitator throughout
the CTA to ensure progressive implementation of performance improvement activities. The
"Action" plan lists items to be completed, including the name of the person that is assigned a
particular task and the projected due date. The plan is normally updated and distributed to
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administrators and operations personnel after a site visit. Phone calls are used to encourage
and monitor progress on the assigned action items. An example format for an "Action" plan is
shown in Table 3-3.
Table 3-3 – Example Action/Implementation Plan
Item
Action Person
Responsible Due Date
1 Develop calibration curve for polymer feed
pump Phil 12/05/2011
2
Draft special study procedure to study impact
on performance of reducing plant flow to 300
m3/h
Phil 19/05/2011
3
Process control:
a) develop daily process data sheet
b) develop routine sampling plan
c) calibrate on-line instruments and
telemetry
Jane
Jane
Jane
12/05/2011
18/05/2011
31/05/2011
Special studies can be used to evaluate and optimize DWS components, to document past
performance, to modify process control activities, or to justify administrative or design
changes necessary to improve system performance. They are a structured, systematic
approach of evaluating operating conditions. The format, which is shown in Table 3-4,
consists of a one page write-up that defines the hypothesis, approach, duration of the study,
expected results, documentation/conclusions and implementation plan. The hypothesis should
be narrow in scope and should clearly define the study that is to be conducted. The approach
should provide a detailed procedure of how the study is to be conducted, including when and
where samples are to be collected, who is to collect the samples, what analyses are to be
conducted, and how the results are to be tabulated. This approach should be developed in
conjunction with the operations staff to obtain staff commitment and to eliminate "bugs" on
paper prior to beginning the study. It is important that the study results be documented using
tools such as graphs, figures or tables. This allows the findings to be presented to the
operations staff, administrators, regulatory officials, or other "observers" as a basis for a
change in operations, design, maintenance or administration leading to improved system
performance. An implementation plan in conjunction with documentation addresses the
procedural changes and support required to implement special study results. If all of the steps
are followed, the special study approach ensures involvement by the operations staff, serves
as a basis for ongoing training, and increases confidence in system capabilities. An example
special study is presented in Appendix E.
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Table 3-4 – Example Special Study Format
Special Study Name:
Hypothesis: Narrow in scope. Try to show definite cause/effect relationship.
Approach: Detailed procedure of conducting study. Involve operations staff in
development.
Duration of Study: Important to define limits of the study since "extra work" is typically required.
Expected Results: Projections of results focus attention on interim measurements and define
success or limitations of effort.
Conclusions: Documented impact of study allows the effort to be used as a training tool for
all interested parties. Allows credit to be given for trying an approach.
Implementation: Changes or justifies current operating procedures. Formalizes the mechanisms
to improve system performance.
Operating procedures can be used to formalize activities that are essential to ensure
consistent system performance. Examples of procedures that can be developed include: jar
testing, chemical feed calculations, filter backwashing and distribution system flushing.
Procedures are most effective if they are developed by the operations staff. Through the
staff's participation, operator training is enhanced and operator familiarity with equipment
manuals and operating procedures is obtained. Also, when operators are able to prepare a
procedure, it indicates that they have gained a thorough understanding of the DWS
component that was discussed.
Process control data sheets are used to formalize the recording of results of process control
testing that is initiated. Typically, a daily sheet is used to record results of tests, flow data,
chemical use, etc. These data are transferred to a monthly sheet that allows observation and
trending of the data.
Graphs or trend charts can be used to enhance the interpretation of process control results.
The data developed can be plotted over long periods to show seasonal trends, changes in
water demand, etc., or over shorter periods to show instantaneous performance.
Letter reports are recommended to promote clarity and continuity. Since a CTA is an action-
oriented program, only concise status reports are recommended. Short (one-page) written
summaries should be prepared after each site visit and for each facility modification. Initially
reports should be prepared by the CTA facilitator, but the responsibility should ultimately be
transferred to the operations staff.
A final CTA report should be prepared to summarize activities. Since all major
recommendations should have been implemented during the CTA, current status of the
system performance should be the main focus of this report.
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3.4.5 Correcting Performance Limiting Factors
The major emphasis of a CTA is addressing factors identified as limiting performance.
Correcting these factors provides a capable system and allows improved process control to
move the DWS to continuous compliance with desired water quality objectives. Activities
that can be conducted to address factors in the areas of design, administration, maintenance
and operation are discussed below.
3.4.5.1 Design Performance Limiting Factors
The performance of Type 2 and 3 systems may be limited by design factors that require
major modifications to correct. Major modifications require the development of engineered
drawings and specifications, and hiring a construction company to complete the
improvements. Examples include improvements such as adding a sedimentation basin or
filter. Major modifications can often be avoided, for example, by operating a WTP at a lower
flow rate for longer periods of time, thereby reducing the hydraulic loading rate to a range
that allows adequate performance to be achieved.
The performance of Type 1 and Type 2 systems can often be improved by making minor
modifications or additions to the DWS. A minor modification is defined as a modification
that can be completed by the operations staff without major construction. Minor
modifications include improvements such as adding a chemical feeder, developing additional
chemical feed points, or installing baffles in a sedimentation basin.
Ideally, the CTA facilitator and operations personnel should be able to justify each proposed
DWS design modification based on the resulting increased performance capability that the
modification will provide. A sound basis is to relate design modifications to the need to
provide a capable system such that process control objectives can be met (see Figure 3-4).
The degree of justification required usually varies with the associated costs and system-
specific circumstances. For example, little justification may be required to add a sampling tap
to a filter effluent line, whereas, justification for adding baffles to a flocculation basin would
require much more effort. Additionally, extensive justification may be required for a facility
where water rates are high and have recently been raised, yet there is no money available for
an identified modification.
The CTA facilitator should transfer to the operations staff the capability to formally
document the need for minor modifications. This documentation is valuable in terms of
presenting a request to supervisory personnel and in providing a basis for the operations staff
to continue such requests after the CTA has been completed. For many requests, the special
study format can be used as the approach for documenting the change (see Section 3.4.4). For
modifications with a larger cost the following items may have to be added to the special
study format:
Purpose of the proposed change (e.g., how does the change relate to the development
of a capable system so that process control can be used to improve performance?).
Detailed description of the change and an associated cost estimate.
Modifications to the DWS, other than repair and maintenance items, such as temporary
changes to operation for experimental purposes (e.g. alternate chemicals, alternate feed
points, changing flocculator speed, changing flow splits etc.) may require an amendment to
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the C of A or DWWP/Licence. If there is any doubt as to whether an amendment for either a
temporary or permanent change is needed, the facilitator should recommend contacting the
local MOE District Office.
Once the proposed modification has been approved by system administrators and the MOE,
the CTA facilitator should serve as a technical and managerial reference throughout the
implementation of the modification. Following completion of a modification, the CTA
facilitator should ensure that a formal presentation of the improved system capability is given
to the administration. This feedback is necessary to build rapport with the system
administrators and to ensure support for future requests. The intent of the presentation should
be to identify the benefits in performance obtained from the resources expended.
3.4.5.2 Maintenance Performance Limiting Factors
Maintenance can be improved in nearly all DWSs, but it is a significant performance limiting
factor in only a small percentage of systems (Renner, 1989; Renner, 1990). The first step in
addressing maintenance factors is to document any undesirable results of the current
maintenance effort. If system performance is degraded as a result of maintenance-related
equipment breakdowns, the problem is easily documented. Likewise, if extensive emergency
maintenance events are experienced, a need for improved preventive maintenance is easily
recognized. Ideally, maintenance factors should have been previously identified and
prioritized during a CPE. However, most DWSs do not have such obvious evidence directly
correlating poor maintenance practices with poor performance; therefore, maintenance
factors often do not become apparent until the CTA is conducted.
Simply formalizing record keeping will generally improve maintenance practices to an
acceptable level in many DWSs, particularly smaller ones. A suggested four-step procedure
for developing a maintenance record keeping system is to:
List all equipment;
Gather manufacturers' literature on all equipment;
Complete equipment information summary sheets for all equipment; and
Develop time-based preventive maintenance schedules, advanced forms of predictive
maintenance, reliability centered maintenance, etc.
Equipment lists can be developed by touring the system and by reviewing available
equipment manuals. As new equipment is purchased, it can be added to the list. Existing
manufacturers' literature should be inventoried to identify missing but needed materials.
Maintenance literature can be obtained from the manufacturer or from local equipment
representatives. Once sheets are completed for each piece of equipment, a time-based
schedule can be developed. This schedule typically includes daily, weekly, monthly,
quarterly, semi-annual and annual check-off lists of required maintenance tasks.
The above method for developing a maintenance record keeping system has worked
successfully at numerous DWSs. However, there are many other good maintenance systems,
including computer-based systems. The important concept to remember is that adequate
maintenance is essential to achieve consistent delivered water quality.
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3.4.5.3 Administrative Performance Limiting Factors
Changes to drinking water legislation and regulations in Ontario, as well as the
implementation of the DWQMS, has greatly enhanced the awareness that administrators have
with regards to the importance of the delivery of safe drinking water and the reliability of
drinking water systems. However, experience gained in CCP studies in the U.S. and Ontario
have shown that administrators who are unfamiliar with system needs, and thus implement
policies that conflict with system performance, are a commonly identified factor. For
example, such items as implementing minor modifications, purchasing testing equipment, or
expanding operator coverage may be recognized by operations personnel as needed
performance improvement steps, but changes cannot be pursued due to lack of support by
non-technical administrators.
Administrative support and understanding are essential to the successful implementation of a
CTA. The following techniques have proved useful in addressing identified administrative
factors limiting performance:
Build a rapport with administrators such that candid discussions concerning physical
and personnel resources can take place.
Involve administrators from the start. Initial visits should include time with key
administrators to explain the process and possibly include a joint DWS tour to
increase their understanding of processes and problems.
Focus administrators on their responsibility to deliver a "product" that not only meets
but exceeds regulatory requirements on a continuous basis. Section 19 of the SDWA,
Statutory Standard of Care, should be discussed with administrators. Often
administrators are reluctant to pursue actions aimed at improving performance
because of a lack of understanding of both the health implications associated with
operating a water treatment plant and/or distribution system and of their
responsibilities in producing safe drinking water. Administrators must be informed
that even momentary excursions in water quality must be avoided to prevent
pathogenic organisms from passing through the treatment plant and into the
distribution system. Such a breakdown in the system could result in sickness of
numerous consumers. Administrators must understand that to minimize the exposure
of consumers to pathogenic organisms in their drinking water that all DWS
components must be performing optimally on a continuous basis. This provides a
"multiple barrier" to prevent passage of pathogenic organisms through the DWS.
Establishment and continuous achievement of high quality treated water goals
minimizes the risk that pathogenic organisms will reach consumers. As such,
administrators should be convinced to establish goals for high quality treated water
that exceed current objectives, and to emphasize to the operating staff the importance
of achieving these goals.
Listen carefully to the concerns of administrators so that they can be addressed.
Some of their concerns or ideas may be technically unimportant, but are very
important "politically." Political influence as well as technical requirements must be
addressed and are considered to be an integral part of the activities of a CTA
facilitator.
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Use technical data based on process needs to convince administrators to take
appropriate actions; do not rely on "authority". Alternatives should be presented,
when possible, and the administrators left with the decision.
Solicit support for involvement of operations staff in the budgeting process. Budget
involvement has been effective in encouraging more effective communication and in
motivating operations staff.
Encourage development of a "self-sustaining utility" attitude. This requires financial
planning for modification and replacement of equipment and structures, which
encourages communication between administrators and operations staff concerning
the need to accomplish both short- and long-term planning. It also requires
development of a fair and equitable rate structure that requires each water user
(domestic, commercial, and industrial) to pay their fair share. The revenues generated
should be sufficient to support long-term as well as short-term modification and
replacement costs plus provide for ongoing items such as proper staffing, training
and chemical supplies. Reference materials are available to assist the CTA facilitator
in guiding activities in this area (AWWA, 2000).
Encourage long-term planning for future water supplies and facility improvements
necessary to meet more stringent water quality requirements.
3.4.5.4 Operational Performance Limiting Factors
Improvement of system performance is ultimately achieved by providing process control
procedures tailored for the particular DWS that can be used to move a capable system to the
desired finished water quality goal. Initial efforts should be directed toward the training of the
key process control decision makers. In most small systems (e.g. flows less than 2,000 m3/d),
one person typically makes and implements all major process control decisions. In these
cases, on-the-job training is usually more effective than classroom training and is
recommended. If possible, in systems of this size, a qualified "back-up" person should also be
trained. As the number of operators to be trained increases with system size, the need for and
effectiveness of combining classroom training with on-the-job training also increases. Since
on-the-job training or site-specific training greatly enhances the operators' capability to apply
knowledge, this "hands-on" approach must be an integral part of the CTA.
Process Sampling and Testing
Successful process control of a DWS involves producing and delivering a consistent, high
quality treated water from an often highly variable raw water surface source and under a
variety of operating conditions. To accomplish this goal, it is necessary that the performance
of each DWS component be optimized. This is important because a breakdown in any one
DWS component places a greater burden on the remaining processes and increases the
chance of viable pathogenic organisms reaching the distribution system and consumers’ taps.
By optimizing each DWS component, the benefit of providing multiple barriers prior to
delivery to consumers is realized.
To optimize each DWS component, information must be routinely obtained and recorded on
raw water quality and on the performance of the various unit processes in the plant so that
appropriate controls can be exercised to maintain consistent treated water quality. The term
“routinely” is stressed because it is advantageous to have the plant staffed at all times it is in
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operation to allow information to be gathered and for process control adjustments to be made
whenever water quality conditions dictate. The gathering of information in an organized and
structured format involves development of a process control sampling and testing schedule.
Recommendations for process-specific sampling and testing are provided in the subsequent
individual DWS component chapters.
The process control data should be recorded on daily sheets, and these data should be
transferred to monthly sheets to allow observation of water quality trends. The daily sheets
should include space for recording actual chemical feed rates and the conversion of these
values to a mg/L dosage so that dosage and water quality can be correlated. This database can
then be used by the operator to better predict chemical feed requirements when raw water
quality characteristics change suddenly. Graphs and trend charts greatly enhance these
correlation efforts.
3.5 HOW TO CONDUCT A CTA
3.5.1 Initial Site Visit
A good working relationship between the CTA facilitator and the operations staff and
administration should be established during the initial site visit. Such a relationship is based
on mutual respect and good communication. Understanding the objective of the CTA greatly
enhances the potential for success. During the initial site visit, CPE results are used to
prioritize follow-up activities. Ideally, activities for addressing all major performance
limiting factors (rated "A" or "B" in the CPE) should be initiated.
Before implementing any major changes, the facilitator must carefully consider the potential
adverse impact on system performance and public health. Contingency plans should be
prepared for the case where a CTA is initiated for a system that is producing unacceptable
finished water quality (see Section 3.4.4). Actions could include plant shutdown, lowering
plant flow rate, isolating areas of a distribution system or initiating an order to boil water. In
all cases, contact with appropriate health/regulatory officials to notify them of the problem
must be made. If process adjustments are grossly out of line, corrective actions should be
initiated to minimize the adverse effect of the treated water. Jar tests or other bench scale
testing should be done prior to initiating a process adjustment in order to avoid full-scale
experimentation that could actually result in a further deterioration in treated water quality.
After a contingency plan has been developed to ensure protection of public health, the CTA
facilitator can begin directing the implementation of process control adjustments to optimize
system performance. Changes in process control direction must be made with consideration
of the operators' morale and traditional approaches to chemical dosing (such as more
disinfectant is "safer"). All recommendations for process control changes should be
thoroughly explained prior to implementation. Even with this approach, a CTA facilitator
should not expect to obtain immediate enthusiastic support from operations personnel. A
response such as "well let’s try it and see" is often the best that can be expected. Some
changes may have to be made with only the degree of consensus expressed with the
statement, "I don't think it will work, but we can try it."
If operations factors are top ranking, the initial site visit should be used to introduce the staff
to proper process control activities, such as conducting jar tests and chemical feed
calculations (see Section 3.4.4). Existing chemicals and dosages should be utilized in initial
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adjustments. Special studies can be initiated later in the CTA to determine the effectiveness
or necessity of alternative chemicals.
Understanding how to determine correct chemical dosages and how to set the chemical
feeders is extremely important in achieving optimum system performance. Procedures that
clearly describe these activities should be reviewed, or developed if they don't exist, during
the initial visit. The operations staff then has a written description that can be consistently
followed.
Existing process control testing should also be reviewed and modified so that all necessary
process control elements are adequately monitored. Sampling frequency and location,
collection procedures, and laboratory analyses should be reviewed and, if necessary,
standardized so that data collected can be used for evaluating progress. New or modified
sampling and analysis procedures should be demonstrated and documented.
The necessary process control equipment is not always available to operators. Any needed
sampling or testing equipment should be noted and the purchasing process should be
implemented as quickly as possible. Provisions may be made for loaner equipment for
essential items.
Data sheets, which summarize process control parameters and performance monitoring
results, should be developed. It is important that a common understanding of information on
the summary sheets be reached during the initial site visit since they will be used by
operations staff to provide data to the CTA facilitator throughout the CTA. The CTA
facilitator reviews the data, sets operating targets and makes process control decisions in
conjunction with the operations staff. Often, weekly summaries of data are used. However, if
computer capability is available, electronic transfer of data can be used to allow daily data
exchange.
System performance is often limited by the performance goals established by utility
personnel. For example, many plants only try to achieve a finished water quality as required
by the regulatory standard. This attitude negatively affects the attainment of optimum unit
process performance (multiple barriers) and continuous finished water quality that minimizes
public exposure to pathogenic organisms. It is essential that the facilitator work with
operations staff and administrators to establish aggressive treatment goals during the initial
site visit and to instil in the operators and administrators the tenacity to achieve those goals.
The change in attitude to support these goals often does not occur until it is demonstrated that
the DWS, given more intense process control, can consistently achieve a very high quality
delivered water. However, once this is experienced, the administrators and operators are
driven by pride to maintain consistent, high quality delivered water. With this pride comes
the willingness of administrators to provide adequate budgets and staffing to support
optimum delivered water quality.
Activities to implement any minor design changes identified as necessary during the CPE and
confirmed by the CTA facilitator should be initiated during the site visit. Some design
changes often require significant amounts of time for approvals, delivery of equipment or
construction. It is important to have the upgraded facilities in place with the desired capacity
when the CTA is undertaken.
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Efforts to address administrative factors are also appropriate to be implemented during the
initial site visit. Administrative changes such as increasing rates, changing personnel, or long
range planning activities require significant time and diplomacy to address. The sensitivity of
these issues may require that significant background information be obtained before action is
taken.
3.5.2 Off-Site Activities
The CTA facilitator should provide a short letter summarizing activities during the first site
visit and include an implementation plan. Any procedures or process control sheets that were
developed in conjunction with the operations staff should also be formalized and returned to
the utility. Phone calls should be made at least weekly to obtain operating information and to
make certain that action items are being accomplished in a satisfactory manner. A return or
intermediate site visit should be made when operating conditions dictate or when process
control equipment (e.g., jar testing equipment, instrumentation, etc.) or minor design
modifications that were determined necessary for future CTA activity are implemented.
3.5.2.1 Follow-Up Site Visits
During intermediate site visits, follow-up training should be presented to the operations staff
on chemical feed calculations, jar testing and other procedures initiated during the initial site
visit. Repetitive training in this manner is effective in transferring capability to the operating
staff. Typically, the concept of special studies (Section 3.4.4) is also introduced at the first
follow-up site visit and a prioritized list of special studies is developed in conjunction with
the utility staff. During remaining site visits the facilitator should follow up on special study
activities and set additional direction as required.
The facilitator should present graphs depicting performance improvement achieved during
the CTA. This, coupled with additional discussion on the necessity of achieving continuous
high quality water and praise regarding improved performance obtained to date, provides the
operators with the incentive to continue striving to produce the highest quality water possible.
During site visits, discussions must also be held with administrators to inform them of
progress made and to convince them to continue supporting optimum performance through
adequate budgeting and staffing. During the final site visit, the results of the CTA should be
presented to administrators and operations staff.
3.5.3 CTA Results
The success of conducting CTA activities can be measured by a variety of parameters, such
as improved operator capability, cost savings, improved maintenance, etc. However, the true
success of a CTA should be documented improved performance to the degree that the DWS
has achieved the desired performance goals, which should consist of, as a minimum, meeting
or exceeding the Ontario Drinking Water Quality Standards and Objectives. Given this
objective, the results of a successful effort can be easily depicted in graphical form.
Results from an actual CTA conducted at a conventional filtration plant are presented in
Figure 3-6. As shown, plant performance was inconsistent as depicted by the variations in
finished water turbidity. After CTA activities had been implemented the treated water quality
remained consistent at about 0.3 NTU. It is recommended that CTA results be presented in
this format.
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Figure 3-6 – Example Treated Water Quality Achieved During Conduct of a CTA
3.5.4 CTA Summary Report
A CTA summary report should be prepared and presented to utility personnel upon
completion of the CTA. The objective is to summarize the conclusions and document
achievement of improved system performance. The report should be brief and outline
activities that were implemented to address the factors limiting system performance. Graphs
documenting the improvement in system performance should also be presented. If other
benefits were achieved these should also be documented. Eight to twelve pages are typically
sufficient for the text of the report. An example CTA report is shown in Appendix F.
Typical contents are:
Introduction (reasons for the CTA);
CPE Results (briefly summarize information from the CPE report);
CTA Significant Events (chronological summary of activities conducted);
CTA Results (graph of system performance plus other CTA benefits); and
Conclusions (efforts required to maintain improved performance).
As a minimum, the CTA report should be distributed to administrators and key operating
personnel. Further distribution of the report, for example to the design engineer or regulatory
agency(ies), depends on the circumstances of the CTA, but should be done at the direction or
with the awareness of local administrators.
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3.6 REQUIRED PERSONNEL CAPABILITIES FOR CONDUCTING A CTA
Persons responsible for conducting a CTA must have a comprehensive understanding of
water treatment and distribution principles and practices, extensive hands-on experience in
drinking water system operations, and strong capabilities in personnel motivation.
Comprehensive understanding of water treatment is necessary because current state-of-the-art
in water treatment leaves room for individual judgment in both design and process control.
The CTA facilitator must be familiar with all types of unit processes, raw water quality
characteristics and chemical products available for successful water treatment. In addition,
those responsible for implementing a CTA must have sufficient process experience to
determine appropriate application of a strategy to the personnel capabilities of the plant in
question.
Experience in distribution system operations and understanding of the factors that affect
water quality in distribution systems are also key assets. Leadership and motivational skills
are required to fill the multi-faceted "facilitator" role required of individuals responsible for
implementing a CTA.
Individuals who routinely work in the area of improving water treatment plant performance
and distribution system water quality likely will be best qualified to be CTA facilitators.
These people are typically engineers or operators who have focused their careers on drinking
water system troubleshooting and have gained experience in correcting deficiencies in
systems of various types. It is important that CTA facilitators have experience in a variety of
systems because the ability to recognize true causes of limited performance is a skill
primarily developed through experience. Similarly, the successful implementation of a cost-
effective CTA is greatly enhanced by experience.
By the very nature of the approach, the CTA facilitator must often address improved
operation, maintenance and minor design modifications with personnel already responsible
for these functions. A "worst case situation" is one in which the operations staff is trying to
prove that "the facilitator can't make it work either". The CTA facilitator must be able to deal
with this personnel issue in such a manner that allows all parties involved to focus on the
common goal of achieving system performance.
A CTA facilitator must be able to conduct training in both formal and on-the-job situations.
Training capabilities must also be developed so that they are effective with both operating as
well as administrative personnel. When addressing process control limitations, training must
be geared to the specific capabilities of the process control decision makers. Some may be
inexperienced; others may have considerable experience and credentials. "Administrative"
training is often a matter of clearly providing information to justify or support CTA activities.
Although many administrators are competent, some may not know what their facilities
require in terms of staffing, minor modifications or specific funding needs.
CTA facilitators include consultants, regulatory personnel or utility employees. However, the
desired "existing facility" focus of a facilitator must be maintained, since a substantial
construction cost can be incurred if an inexperienced facilitator is not able to bring a capable
DWS to the desired level of performance. For example, a consultant, involved primarily with
facility design, may not have the operational experience to utilize the capability of existing
DWS components to their fullest extent and may be biased toward designing and constructing
new facilities.
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If utilities/municipalities decide to conduct a CTA with people closely associated with the
system, they should recognize that some inherent problems may exist. The individuals
implementing the CTA, for example, often find it difficult to provide an unbiased assessment
of the area in which they normally work. Operating personnel tend to look at design and
administration as problem areas while administrators typically feel that operating personnel
should be able to do better with what they have. In addition, the engineer who approved a
facility’s design is often reluctant to admit design limitations. These biases should be
considered before personnel closely associated with the facilities initiate a CTA.
3.7 REFERENCES
American Water Works Association (2000). AWWA Manual M1: Principles of Water Rates,
Fees, and Charges. 5th Ed. ISBN 1-58321-069-5.
Municipal Engineers Association (2007), Municipal Class Environmental Assessment.
October 2000, as amended 2007.
MOE (2008). Design Guidelines for Drinking Water Systems. ISBN 978-1-4249-8517-3.
Renner, R.C., B.A. Hegg and D.L. Fraser (1989). “Demonstration of the Comprehensive
Performance Evaluation Technique to Assess Montana Surface Water Treatment Plants”,
presented at the 4th Annual ASDWA Conference, Tucson, Arizona.
Renner, R.C., B.A. Hegg and J.H. Bender (1990). EPA Summary Report: Optimizing Water
Treatment Plant Performance with the Composite Correction Program. U.S EPA Centre for
Environmental Research Information. EPA 625/8-90/017.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program, EPA/625/6-91-027.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 4GENERAL OPTIMIZATION TECHNIQUES
GENERAL OPTIMIZATION TECHNIQUES
4.1 Introduction ............................................................................................................ 4-1
4.2 Field Evaluations .................................................................................................... 4-1
4.2.1 Performance Monitoring and Verification ............................................... 4-1
4.2.2 Controlling Plant Flow Rate .................................................................... 4-2
4.2.3 Control of Chemical Dosages .................................................................. 4-2
4.2.4 Filter Investigations ................................................................................. 4-3
4.2.5 Tracer Testing .......................................................................................... 4-3
4.2.6 Stress Testing ........................................................................................... 4-6
4.2.7 Pilot Plants ............................................................................................... 4-7
4.3 Modelling and Simulation ...................................................................................... 4-7
4.3.1 Applications of Modelling and Simulation .............................................. 4-8
4.3.2 Clarifier Modelling .................................................................................. 4-8
4.3.3 Modelling Reactor Flow Characteristics ................................................. 4-9
4.3.4 Mixing Modelling .................................................................................. 4-10
4.3.5 Distribution System Modelling .............................................................. 4-10
4.3.6 Limitations of Modelling and Simulation .............................................. 4-11
4.4 Case Histories ....................................................................................................... 4-11
4.4.1 Peterborough Utilities Commission – Distribution System Tracer
Study ...................................................................................................... 4-11
4.4.2 City of Toronto – CFD Modelling of Flocculation Mixing
Performance ........................................................................................... 4-14
4.5 References ............................................................................................................ 4-15
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CHAPTER 4
GENERAL OPTIMIZATION TECHNIQUES
4.1 INTRODUCTION
A number of general techniques are available to improve the operation and performance of a
drinking water system (DWS) that are not specific to a particular unit process. The objective
of this chapter is to present an overview of these techniques that can be applied as part of a
DWS optimization study, such as field investigation, modelling and simulation.
4.2 FIELD EVALUATIONS
Field evaluations are an important aspect of the on-site activities conducted as part of an
optimization study. Typically, field evaluations are conducted to verify the accuracy of
monitoring and flow records, chemical dosages, record drawings, filter integrity and
backwash capability. A discussion of various field activities is provided in the following
subsections.
4.2.1 Performance Monitoring and Verification
Performance monitoring records can be verified, for example, by utilizing a properly
calibrated continuous recording instrument to assess process performance over a 24-hour
period. It is important that the field evaluation team acquire or have made available to them
properly calibrated instruments to support field efforts. If recording on-line instruments are
not available, an instrument that allows individual analysis of grab samples can be used. If
the evaluation team does not have access to a specific instrument, the plant’s instruments can
be used providing they are calibrated prior to the sampling and testing activities.
Treated water quality obtained during the field evaluation can be compared with plant
recorded data to make a determination whether the performance monitoring records
accurately represent treated water quality. Differences in actual versus recorded finished
water quality can be caused by sampling location, sampling time, sampling procedures and
testing variations. The evaluation team’s instrument can also be used to assess the plant’s
instrument accuracy and calibration techniques.
The accuracy of flow records can be verified by assessing the calibration of flow
measurement equipment. It may also be helpful to assess upstream and downstream meter
flows in order to assess the overall flow consistency within meter effort ranges, where
applicable. This is often difficult because of the type of meter utilized (e.g. propeller, venturi,
magnetic). If these types of meters are utilized, it may be necessary to conduct a timed fill-
and-draw test to check the accuracy of the flow metering equipment.
If accuracy of metering equipment is difficult to field-verify, the frequency of calibration of
the equipment by the plant staff or outside instrumentation technicians can be evaluated;
however, it is important to recognize that calibration of flow metering equipment often
involves only the secondary element (the pressure differential measurement device, for
example) and does not include calibration of the primary measurement device. In such cases,
it is important to review the flow meter installation to ensure that it meets the manufacturer’s
specifications or follows good engineering principles. Ideally, a full station calibration
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(primary and secondary elements) should be undertaken to confirm the accuracy of flow
metering equipment.
Throughout the document, recommendations are provided for monitoring DWS component
performance. These recommendations are in addition to required regulatory monitoring, and
should in no way compromise sampling or monitoring activities related to regulatory
compliance. It should be noted that the results of additional monitoring are required to be
reported under the applicable drinking water regulations. Additional information on sampling
parameters, frequency, etc., for performance monitoring is provided in Kirmeyer (1999);
AwwaRF (2002); Kirmeyer (2002); and AWWA (2010). Information on the collection and
handling of drinking water samples is provided in Practices for the Collection and Handling
of Drinking Water Samples (MOE, 2009).
4.2.2 Controlling Plant Flow Rate
Plant flow rate is a primary means for process control at many small plants that are operated
for less than 24 hours each day. At these plants, an excessive hydraulic loading rate on the
treatment processes can be avoided by operating at a lower flow rate for a longer period of
time. Eliminating or reducing the frequency of starts and stops of the treatment processes,
and high hydraulic loading rates on start-up, can also improve performance. This provides an
option to meet more rigorous performance requirements with existing units without major
capital improvements.
The capability to reduce plant flow rate to improve performance is offset by the need to staff
the plant for longer periods of time, or the provision of additional automated controls, which
adds to operating costs. Therefore, plant administrators, in conjunction with the CTA
facilitator, should evaluate both options. The ability to modify plant flow rate also depends
on the availability of storage at the plant or in the distribution system.
4.2.3 Control of Chemical Dosages
Dosages of key treatment chemicals, such as primary coagulants, should be verified. Feed
rates from dry feeders can be checked by collecting a sample for a specified time and
weighing the accumulated chemical. Similarly, liquid feeders can be checked by collecting a
sample in a graduated cylinder for a specified time. In both cases, the feed rate in mL/min or
mg/min of chemical should be converted to mg/L based on flow measurements made at the
point of chemical addition at the same time as the chemical addition rate is measured. The
calculated dosage should be compared with the reported dosage. Dosage checks for liquid
chemical feed systems should ideally be conducted by replicating actual pump suction and
discharge head conditions.
During this evaluation, the operating staff should be asked how they conduct chemical feed
calculations, prepare polymer dilutions and set chemical feeders. Additionally, staff should
be asked how they arrived at the reported dosage.
If jar testing is used, the evaluation team should discuss this procedure, including preparation
of stock solutions. Often, this discussion can be used to assess the operators’ understanding
of jar testing as a coagulation control technique.
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4.2.4 Filter Investigations
Field evaluations should be conducted to assess the integrity of the filter media, support
gravel and underdrain system for a selected filter. This requires that the filter be drained and
that the evaluation team inspect the media.
The filter should be investigated for surface cracking, proper media depth, mounding,
mudballs and segregation of media in dual media filters. The media can be excavated to
determine the depth of the different media layers in multi or dual media filters. The media
should be placed back in the excavated filter in the reverse sequence that it was removed. The
filter should also be probed with a steel rod to check for displacement of the support gravel
and to verify the media depth within the filter, where appropriate. Variations of over 5 cm in
depth of media or support gravel from the design would signify a potential problem.
Deviations in media depth, uniformity coefficient and effective size relative to the design
specifications should be noted. Media loss should be quantified and assessed.
If possible, components downstream of the filters and the clearwell should be observed for
the presence of filter media. Often, operations staff can provide feedback on media in the
clearwell if access is limited. If support gravel or media loss is apparent, a more detailed
study of the filter should be undertaken.
Filter backwash capability often can be determined from the flow measurement device on the
backwash supply line. If this measurement is in question or if the meter is not available, the
backwash rate should be field-verified by assessing either the backwash rise rate or bed
expansion. Rise rate is determined by timing the rise of water for a specific period within the
filter box. For example, a filter having a surface area of 14 m2 would have a backwash rate of
approximately 49 m/h if the rise rate was 27 cm in 20 seconds (Backwash rate = (0.27 m ÷ 20
s) x 3600 s/h = 48.6 m/h). This technique is not suitable for filters where the peak backwash
rate is not reached until the washwater is passing over the troughs.
Bed expansion is determined by measuring the distance from the top of the unexpanded
media to a reference point (e.g. top of filter wall) and from the top of the expanded media to
the same reference point. The difference between these two measurements is the bed
expansion. A variety of techniques can be used to determine the top of the expanded bed. A
light-coloured can lid attached to the end of a pole is effective. The percent bed expansion is
determined by the bed expansion measurement divided by the total depth of expandable
media (i.e. media depth less gravel) multiplied by 100. A proper wash rate should expand the
filter a minimum of 25 percent (ASCE & AWWA, 2004). The backwash rate should be
variable, with the maximum rate designed to provide for 50 percent expansion of the filter
media bed at the highest water temperature (MOE, 2008).
4.2.5 Tracer Testing
Tracer test techniques evaluate the hydraulic characteristics of process tanks. Test results can
indicate short-circuiting, determine existing mixing regimes, locate dead zones within the
fluid volume, evaluate baffling arrangements and identify predominant flow patterns within
the process tank (MOE et. al., 1999). Tracer tests may be applied to coagulant mixing,
flocculation, sedimentation basins, chlorine contact tanks, distribution system storage
facilities or other unit processes for which it is necessary to evaluate or control residence time
characteristics. Information on the conduct of tracer studies is provided in USEPA (1990) and
Teefy (1996).
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A tracer test is started by adding a conservative (i.e. non-reactive) chemical into a basin and
observing the change in concentration of this chemical over time in the basin effluent until a
steady state is reached. The shape of the resulting concentration versus time curve provides
insight as to the degree of short-circuiting within the basin and the actual residence time of
the water in the basin.
Commonly used tracer chemicals include fluoride, rhodamine WT, lithium, sodium, chloride
and calcium (Teefy, 1996). In selecting a tracer chemical, consideration must be given to
whether the tracer will react with other chemicals used in the water treatment process. In
addition, all chemicals used in the conduct of tracer tests should meet all applicable quality
standards for chemicals and other water contacting materials set by AWWA and the
consumer safety standards NSF/ANSI Standard 60: Drinking Water Treatment Chemicals -
Health Effects and NSF/ANSI Standard 61: Drinking Water System Components - Health
Effects.
Tracer tests most commonly used in water treatment plants are pulse (slug dose) and step
(continuous-feed) inputs.
A pulse input test involves adding the entire amount of tracer to be used at the beginning of the
test as a slug. The addition of the slug tracer must be as instantaneous as possible, and the
chemical must be completely mixed with the influent flow stream. One of the disadvantages of
the pulse input test is the risk of not adequately measuring the peak tracer concentration exiting
the unit process being evaluated. This means that when a pulse input test is conducted through a
basin that may have a significant amount of short-circuiting, care should be taken to collect
enough samples early in the test to define the output tracer curve properly.
A step input test involves continuously feeding the tracer into the process basin to be
tested at a constant rate. Step inputs can be conducted in either an increasing or
receding mode. For the increasing mode, the start of the test is triggered by the
beginning of the addition of the tracer at a constant feed rate to the basin influent. The
increase in tracer concentration over time is measured in the basin effluent. For the
receding mode, the test begins when the tracer feed is discontinued, and the decrease in
tracer concentration is measured over time in the basin effluent.
Example tracer response curves for both pulse and step input tests are presented in Figure 4-1.
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Figure 4-1 – Example Tracer Response Curve
Adapted from USEPA (1990)
Table 4-1 summarizes the advantages and disadvantages of the pulse input and step input
tests.
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Table 4-1 – Summary of Advantages and Disadvantages of Pulse and Step Input Tests
Adapted from Tracer Studies in Water Treatment Facilities: A Protocol and Case Studies
(Teefy, 1996)
Testing Mode Advantages Disadvantages
Pulse Input Less chemical is needed
Mean residence time can be
determined more readily
Chemical addition can be simple (e.g.
use existing chemical feed systems or
manually add a slug of chemical) in
most situations
Danger of missing the peak if
sampling frequency is not
sufficient
More mathematical manipulation
of results is needed to determine
effective contact time
Cannot repeat the test easily (no
receding curve available)
Difficult to determine the amount
of tracer that should be added for
the test
Step Input Sometimes can be done with existing
plant chemical feed equipment
Effective contact time can be
determined graphically from curve
Results can be verified by monitoring
the receding curve if an increasing
and receding curve is available
More tracer chemical is required
Cannot reliably calculate mean
residence time
May have to install chemical feed
equipment if not already present
4.2.6 Stress Testing
Stress testing involves increasing the hydraulic loading to the existing process in order to
identify the “failure point”. Stress testing is generally applied to clarification and/or filtration
processes, therefore the failure point can be defined either as an exceedance of the settled
water turbidity goal, or excessive head loss or turbidity breakthrough in the subsequent
filtration process.
Both continuous monitoring and grab sampling are required to evaluate process performance
during a stress test. For example, frequent grab sampling for testing the settled water turbidity
or continuous monitoring of filter effluent turbidity are needed to identify the “failure point”.
In addition, the sludge blanket depth should be measured regularly during a stress test of a
clarifier.
Criteria for evaluating performance of clarification and/or filtration processes are provided in
Chapters 7 and 8, respectively.
Consideration should be given to the potential impact on treated water quality if testing
involves stressing a unit process to the “failure point”. Contingency plans should be
developed in consultation with the local MOE District Office and the Drinking Water
Inspector for the drinking water system, to ensure that the water directed to consumers during
the test meets all applicable regulations.
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4.2.7 Pilot Plants
Pilot plants are used to provide a physical simulation of a drinking water system. Pilot-scale
testing combines chemical responses with physical processes so that results are reasonably
reflective of full-scale plant conditions (Douglas et. al., 2008). Pilot-scale testing also
provides the advantage of being able to study non-optimal conditions without jeopardizing
the quality of the finished water. In general, pilot plants are designed with the same treatment
processes that are used in the full-scale system; however, they can also be designed to allow
for insertion (e.g. chemical addition) or removal (e.g. sedimentation to simulate direct
filtration) of unit processes to simulate various operating conditions.
Pilot plants are commonly used for the evaluation of:
Filter media changes;
Eliminating pre-chlorination;
Enhanced coagulation and flocculation;
Optimizing aluminum residuals; and
Taste and odour control.
The use of pilot-scale facilities can be advantageous, as the costs, time and resources needed
for pilot scale experiments are generally lower than those that would be required for full scale
testing. In addition, they can serve as a valuable training tool for operations staff.
While the design and construction of a pilot plant may not be practical or economically
feasible for smaller systems, the construction of pilot filters is relatively simple. Pilot filters
can be used to supplement jar testing results for the optimization of direct and conventional
filtration processes.
Information on the design of pilot plants and pilot-scale experiments is provided in Lang et.
al. (1993); Ndiongue et. al. (2006); Ford et. al. (2001); and Huck et. al. (2002).
4.3 MODELLING AND SIMULATION
A model is a set of mathematical relationships that are used to describe physical, chemical
and biochemical interactions. In some cases, the mathematical relationships that form a
model can be quite simplistic, as is the case when describing the concentration of a treatment
chemical in a completely mixed reactor. In other cases, the model can be quite complex and
involve multiple interacting relationships, such as models that describe nitrification reactions
in a distribution system. The model complexity required often depends on the modelling
objectives.
Models require calibration and validation to ensure that they provide meaningful results.
Calibration involves modifying model parameters so that the model output matches actual
field measurements. Validation involves running a series of model calculations using field
data independent from those used for calibration, and comparing the model output to actual
field results. If the output during validation matches the actual field results, the model can be
assumed to be properly calibrated.
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Simulators are computer programs which use a model, or set of models, as a basis for
calculations. The user can configure the simulator to describe the physical layout of a
treatment plant or specific unit processes within the plant. The simulator can be used to
perform simulation runs at various operating conditions to identify impacts on process
performance. Some simulators allow both steady-state (static) and dynamic (time varying)
simulations.
4.3.1 Applications of Modelling and Simulation
4.3.1.1 Hydraulic Modelling
A hydraulic model is used to determine the hydraulic capacity of an existing drinking water
system by describing the characteristics of flow through pipes, channels, process tanks,
pumps, and flow control devices, such as weirs, gates and baffles. Hydraulic modelling can
be used to:
Determine a facility’s hydraulic capacity;
Identify hydraulic bottlenecks;
Identify locations of flow imbalances; and
Identify optimal locations for chemical addition to promote mixing.
The first step in developing a hydraulic model is to identify the hydraulic elements within the
facility. On-site measurements and surveying may be required to confirm the dimensions and
elevations of hydraulic elements, channels, piping and other structures shown on plant record
drawings.
Under ideal conditions, flow through a WTP changes very gradually. As a result, steady-state
hydraulic calculations can be used, greatly simplifying the complexity of the required
calculations.
There are very few commercially available hydraulic modelling software packages. In most
cases, a spreadsheet program or computer programming languages are used to develop
hydraulic models on a case-by-case basis.
Details regarding the calibration and validation of hydraulic profiles can be found in Nicklow
& Boulos (2005).
4.3.2 Clarifier Modelling
Clarifier hydrodynamic models describe the characteristics of flow and solids settling that
take place within a clarifier. Development of clarifier models is based on fluid dynamics,
solids flux theory, and the physical configuration of the clarifier(s). Clarifier hydrodynamic
modelling can be used to:
Determine a clarifier’s hydraulic capacity;
Predict the impact of operational changes on clarifier performance; and
Determine optimal baffling, inlet structure, and weir configurations to improve
clarifier performance.
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Clarifier hydrodynamic models can be divided into three types, namely one-dimensional (1-
D), two-dimensional (2-D), and three-dimensional (3-D).
Generally, 1-D models are based on flux theory. Only the settling processes that occur in the
vertical direction are modelled, as it is assumed that the horizontal velocity and concentration
profiles are uniform. These models can be calibrated with actual plant data, and can provide a
good representation of the solids inventory within the system. However, the 1-D model cannot
take into account influences from tank geometry, sludge removal processes, density currents or
short circuiting. Due to its simplistic nature, a 1-D model may only be capable of identifying a
settling problem within a clarifier. More detailed 2-D or 3-D modelling may be required to
identify the nature and cause(s) of other operational problems.
2-D models take into account flux theory, entrance and exit effects, and sludge removal
processes. Only the settling and flow processes that occur in the vertical and horizontal (from
clarifier entrance to exit) directions are modelled, as it is assumed that the flow characteristics
within the clarifier are consistent across all cross sections perpendicular to the bulk flow. 2-D
models are reported to give reasonably good predictions of the behaviour of circular clarifiers
and some rectangular clarifiers, and can therefore be used to estimate the impact of baffle
installation or modification on clarifier performance. A 3-D model may be required for
circular clarifiers that are subject to asymmetric flow due to the configuration of the inlet port
or effluent weirs, or rectangular clarifiers with non-uniform lateral feed. Square clarifiers
often exhibit strong 3-D flow impacts and, as such, a 2-D model may not be capable of
providing sufficient information regarding the flow characteristics within these clarifiers.
3-D models take into account flux theory, entrance and exit effects, sludge removal
processes, and variations in flow patterns in all three dimensions. Although these models
provide detailed information regarding the characteristics of flow within the clarifier, they
require a great deal of input data and computing power.
4.3.3 Modelling Reactor Flow Characteristics
The two simplest models that can be used to describe flow through a reactor are the
“complete mix model” and the “plug flow model”. In a complete mix reactor, it is assumed
that the composition of the reactor contents is homogeneous throughout the reactor volume,
and that mixing of the influent occurs instantaneously. In a plug flow reactor, it is assumed
that all influent to the reactor has the same residence time, and that the flow moves as a
“plug” down the length of the reactor. Therefore, in a plug flow reactor, the composition of
the reactor contents varies in the direction of flow.
In practice, full scale reactors only approximate the behaviour of complete mix or plug flow
reactors due to non-ideal flow conditions, such as dead zones, short circuiting, and
longitudinal dispersion in plug flow reactors. Tracer testing can be used to identify and
quantify the effects of these non-ideal flow conditions. Information regarding tracer testing
methods and data analysis is presented in Section 4.2.5. Depending on the objectives of the
reactor modelling and/or the severity of non-ideal flow conditions, complete mix and plug
flow models can provide a good approximation of reactor flow characteristics.
Typical examples of reactors in drinking water systems that approximate complete mix
characteristics can include flocculators and storage facilities that are designed to be
completely mixed. Examples of reactors that approximate plug flow characteristics can
include ultraviolet (UV) reactors and chlorine contact tanks.
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If more detailed information is required for complete mix reactors, mixing modelling can be
used to describe the reactor hydrodynamics. This is explained in more detail in Section 4.3.4.
The behaviour of plug flow reactors can be approximated by modelling several complete mix
reactors operating in series. The number of complete mix reactors to be used in the model
depends on the geometry of the plug flow reactor, the flow rate through the reactor, and any
known non-ideal flow conditions.
A 2-D or 3-D model would be required to identify the causes of non-ideal flow conditions,
and to evaluate alternative options to optimize the plug flow behaviour of the reactor, such as
baffle installation or modification of inlet and/or outlet structures.
4.3.4 Mixing Modelling
Hydrodynamic mixing models describe the characteristics of flow and suspended solids
mixing that take place within a mixed reactor, such as flocculation tank. The development of
mixing models is based on fluid dynamics, including the rheology of the reactor contents (i.e.
the manner in which the fluid flows), and the physical configuration of the subject reactor.
Hydrodynamic mixing modelling can be used to:
Identify potential dead-zones within a mixed reactor;
Identify potential short-circuiting within a mixed reactor;
Predict the impact of operational changes on mixing performance; and
Determine optimal baffling and mixer configurations to improve performance.
Mixing modelling is generally accomplished through the use of 3-D models. In general, a
simulator computer program utilizes computational fluid dynamics (CFD) theory to solve the
model’s system of equations, and to allow for the user to modify reactor configuration to
model the impact on mixing performance.
The presence of dead-zones and/or short-circuiting within a complete mix reactor reduces the
effective reactor volume available, thus reducing the effective treatment capacity. In such
cases, the mixing efficiency can be optimized by making adjustments, such as installation of
baffles, addition or modification of mechanical mixers, and/or inlet and outlet structure
modifications. Mixing modelling can be used to evaluate the impact of these changes on
process performance and to select the optimal upgrade approach.
4.3.5 Distribution System Modelling
A variety of mathematical models of water distribution systems have been developed and
used by water utilities to assess the movement of water and water quality parameters within
the distribution system. Such models may be divided into three general categories:
Hydraulic models, which simulate the flow quantity, flow direction and pressure in
the system;
Steady state water quality models and flow-tracing models, which determine the
movement of substances, including their flow paths and travel times, through the
network under steady state operational and demand conditions; and
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Dynamic water quality models, which simulate the movement and transformation of
substances in the water under conditions that vary over time.
Optimization models incorporating water quality, that examine a wide range of operational
and/or design variables and select the best solution based on a stated objective function and
specified constraints, are also available. Each type of model serves a particular purpose in
assessing distribution system water quality and is essential in investigating water quality
issues in a distribution system.
Additional information on hydraulic and water quality models for distribution system
optimization can be found in Clark & Grayman (1998) and AWWA (2005).
4.3.6 Limitations of Modelling and Simulation
4.3.6.1 Safety Factors
Due to the nature of the mathematical relationships used, models may have a less inherent
safety margin than typical design guidelines. Dynamic modelling may give a more
representative prediction of system performance than steady-state modelling; however,
dynamic modelling may not always be feasible, due to a lack of suitable data available for
calibration, limitations of the model, and/or the type of system being modelled. As a result, a
separate safety factor should be applied to designs based on modelling results and/or field
testing should be completed to confirm the modelling results (Section 4.2).
4.3.6.2 Quality of Data
The accuracy of a model depends on the quality of the data used in its development,
calibration and validation. For this reason, all data should be screened to identify any outliers
or other inconsistencies, and to identify any data gaps that would require additional data
collection.
4.3.6.3 Improper Calibration
Improper calibration occurs when key model parameters are incorrectly adjusted to match
actual field data.
During model calibration, it is possible to adjust model parameters to make the simulator
output match actual field data; however, this alone does not ensure that the model is
accurately describing the actual behaviour within the system. If improperly calibrated, the
model would not be able to predict system behaviour for any conditions other than those used
for calibration.
4.4 CASE HISTORIES
4.4.1 Peterborough Utilities Commission – Distribution System Tracer Study
The following case study is based on information presented in Light (2003).
System Description
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The expansive nature of the Peterborough distribution system, which includes approximately
380 km of buried pipe, 1,872 hydrants and 24,141 water services connections, had
historically led to issues with increasing water age. Water age is the amount of time it takes a
certain volume of water to travel from the water treatment plant to a point in the distribution
system. Excessive water age can contribute to water quality problems, including disinfection
by-product (DBP) formation, tastes and odours, microbial growth and sediment deposition
within distribution piping.
An assessment of water age in a distribution system can be used to indicate hydraulic
deficiencies in the system, such as long retention times in storage facilities, short-circuiting,
areas that may require redesign or operational changes, and other system problems (closed
valves, pipe roughness, oversized watermains, dead ends, etc).
Optimization Strategies
The Peterborough Utilities Commission (PUC) undertook a tracer study in the distribution
system to identify areas with excessive water age. For this study, fluoride was chosen as the
tracer chemical because it persists in the distribution system, was already being added as part
of the treatment process, could be analyzed easily by operations staff and was approved for
use in drinking water systems.
The concentration of fluoride in the source water, the Otanabee River, is approximately 0.12
mg/L. The dose applied at the WTP for fluoridation is usually between 0.50 and 0.60 mg/L,
for a total fluoride concentration of approximately 0.60 to 0.70 mg/L. Fluoridation at the
WTP was ceased for a period of two to three weeks prior to the study to eliminate fluoridated
water within the distribution system.
When fluoridation was resumed for the purposes of the study, the total fluoride concentration
leaving the WTP was maintained at 0.60 mg/L. Samples were collected from 19 locations
throughout the distribution system over a period of five days, starting the day the fluoride
feed was restarted.
Results of the distribution system sampling indicated that it took from 10 to more than 105
hours to attain a target fluoride concentration of 0.50 mg/L at the various locations
throughout the city. The tracer travel time for each location was plotted and then graded in
increments of 15 hours, with an “A” grade representing the shortest time to reach the target
concentration of 0.50 mg/L (0 to 15 hours) and an “F” grade representing the longest time
(more than 105 hours). Figure 4-2 shows a distribution system map of Peterborough with the
colour-coded grades (A to F) assigned for each of the 19 sample locations.
The longest tracer response times were noted in reservoirs and elevated tanks, even though
the storage facilities, in some cases, were located relatively close to the WTP. The graph
shown in Figure 4-2 indicates that in some cases, the fluoride concentrations never reached
the target concentration of 0.50 mg/L during the study (e.g. at the end of 105 hours). These
sample locations were under the direct influence of storage facilities that had a lower fluoride
concentration than the water in the distribution mains.
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Figure 4-2 – Tracer Travel Time for Distribution System Sample Locations
From Light (2003)
Summary
In large volume reservoirs (22.7 ML total storage capacity), the study duration was not
sufficient to draw down the entire volume of water within the reservoir and the target fluoride
concentration of 0.50 mg/L was not achieved. It should also be noted that it is difficult to
turnover these reservoirs completely while still maintaining adequate volumes for fire
protection and consumer demand.
The results of the testing identified areas of the distribution system where increased sampling
and monitoring would be beneficial for improving control of chlorine residuals and DBPs.
The PUC also modified their operating strategies for reservoirs and elevated tanks to increase
the frequency of water turnover and reduce water age. The study also identified areas in need
of more frequent flushing to reduce water age, and in some cases, led to the installation of
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“bleeder” lines to allow a controlled flow of water-to-waste, particularly in areas where
watermains are oversized.
4.4.2 City of Toronto – CFD Modelling of Flocculation Mixing Performance
The following case study is based on information presented in Zhang et. al. (2006).
System Description
The City of Toronto’s (the City) R.L. Clark WTP is a conventional treatment plant that treats
water from Lake Ontario and has a rated capacity of 615 ML/d. The treatment process
consists of coagulation, flocculation, sedimentation, filtration, fluoridation and chlorine
disinfection. This plant has three parallel coagulation/flocculation trains. After adding alum
prior to rapid mixers, water flows through over-and-under hydraulic mixing chambers in
series for coagulation, followed by flocculators. Each flocculation tank consists of a primary
cell and a secondary cell. At the time of this study, the primary flocculation tanks had been
retrofitted with impeller-type mixers and the old walking beam mixing equipment in the
secondary cells were also being replaced with impeller-type mixers.
The purpose of this study was to develop a three-dimensional CFD model and apply it to
provide indications of the mixing performance of a complex full-scale flocculator with a
vertical shaft impeller mixer to assist the upgrading of the secondary flocculation process at
the R.L. Clark WTP.
Optimization Strategies
A three-dimensional model of the secondary flocculator was generated by inputting the
geometry of the flocculation tank and impellers using commercial software applications. The
flows in the flocculator were assumed to be isothermal. The influent flow rate used for the
modelling was 2.55 m3/s.
Simulations were conducted to evaluate the effects of impeller speed and the location of
baffle walls on the residence time distribution (RTD) and velocity gradient, G, within the
flocculator.
It was observed that the velocity of the incoming water could significantly influence the flow
field and lead to short-circuiting and dead zone problems, particularly at low impeller speeds
(5 rpm). At higher impeller speeds (20 and 30 rpm) the effects of the influent flow rate were
reduced; however, the mixing efficiency of the impellers may be reduced at higher speeds
because of the presence of local swirls. Longer residence times were also predicted at lower
impeller speeds.
G value distributions were predicted inside the flocculator for the different impeller speeds.
At 5 rpm, local G values at locations around the impellers were in the range of 100 to 1000 s-1
and significantly lower (less than 30 s-1
) at locations close to the walls. With impellers speeds
of 20 or 30 rpm, the local G values in most areas in the tank were higher than 100 s-1
, which
is higher than the desired range for this process (see Chapter 6).
To obtain a better G value distribution and reduce swirling in the flocculator, simulations
were conducted to evaluate the benefits of installing baffle walls in the tank where, (1) the
baffle was installed in the middle of the tank, and (2) the baffle was installed near the tank
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inlet. For the first simulation, the velocity profiles indicated that the flow mixing regime in
the region downstream of the baffle had been improved; however, the region upstream of the
baffle was still poorly mixed. With the baffle installed 1.5 m downstream of the inlet, the G
value distribution was improved throughout the tank, with an average G value for the total
tank being approximately 44 s-1
.
Summary
This study demonstrated the potential of CFD as an efficient tool for understanding impeller
mixing performance and provided useful information for the design and operation of the
flocculation process. The initial CFD simulation results suggested that dead zones and short-
circuiting may exist in the secondary flocculation tank as a result of the installation of vertical
shaft turbine flocculation impellers at the R.L. Clark WTP, which may have an impact on
flocculation efficiency. CFD simulation showed that installing a single baffle at the inlet
would be a better choice than positioning a baffle in the middle of the tank. It was also
suggested that experimental studies, such as tracer testing to evaluate the actual detention
time in the tank, be conducted to validate the CFD modelling results.
4.5 REFERENCES
American Society of Civil Engineers and American Water Works Association (2004). Water
Treatment Plant Design, 4th Ed. McGraw-Hill. ISBN 0-07-141872-5.
AWWA (1999). Water Quality and Treatment: A Handbook of Community Water Supplies,
5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
AWWA (2005). Water Quality in the Distribution System. First Edition. American Water
Works Association. Denver, CO. ISBN 1-58321-323-6.
AWWA (2010). Water Quality: Principles and Practices of Water Supply Operations. 4th
Ed. AWWA. Denver, CO. ISBN 1-58321-780-1.
AwwaRF (2002). Online Monitoring for Drinking Water Utilities. AWWA Research
Foundation and AWWA. Denver, CO. ISBN 1-58321-183-7.
Clark, R.M. & W.M Grayman (1998). Modeling Water Quality in Drinking Water
Distribution Systems. American Water Works Association. Denver, CO. ISBN 0-89867-972-
9.
Ford, R., M. Carlson and W.D. Bellamy (2001). Pilot Testing with the End in Mind. Journal
AWWA, Vol. 93, Issue 5, May 2001, p. 67-77.
Huck, P.M., B.M. Coffey, M.B. Emelko, D.D. Maurizio, R.M. Slawson, W.B. Anderson, J.
Van den Oever, I.P. Douglas and C.R. O'Melia (2002). Effects of Filter Operation on
Cryptosporidium Removal. Journal AWWA, Vol. 94, Issue 6, June 2002, p. 97-111.
Hudson, H.E., Jr. (1975). Residence Times in Pretreatment. Journal AWWA, Vol. 67, No. 1.
January 1975.
Kirmeyer, G.J. (1999). Maintaining Water Quality in Finished Water Storage Facilities.
AwwaRF and AWWA. Denver, CO. ISBN 0-89867-983-4.
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Optimization Guidance Manual for Drinking Water Systems 2014
Kirmeyer, G.J. (2002). Guidance Manual for Monitoring Distribution System Water Quality.
AwwaRF and AWWA. Denver, CO. ISBN 1-58321-186-1.
Lang, J.S., J.J. Giron, A.T. Hansen, R.R. Trussell, W.E. Hodges, (1993) Investigating Filter
Performance as a Function of the Ratio of Filter Size to Media Size. Journal AWWA, Vol.
85, Issue 10, October 1993, p. 122-130.
Light, Kevan M. (2003). Follow the Fluoride to Decrease Water Age. Opflow, Vol. 29, Issue
1. AWWA. January 2003.
MOE (2008). Design Guidelines for Drinking Water Systems, 2008. ISBN 978-1-4249-8517-
3.
MOE (2009). Practices for the Collection and Handling of Drinking Water Samples. Version
2.0. Queen's Printer for Ontario. PIBS 4464e01.
MOE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process Audits.
Ndiongue, S., W.B. Anderson, A. Tadwalkar, J. Rudnickas, M. Lin and P.M. Huck (2006).
Using Pilot-Scale Investigations to Estimate the Remaining Geosmin and MIB Removal
Capacity of Full-Scale GAC-Capped Drinking Water Filters. Water Quality Research Journal
of Canada. Volume 41, No. 3, p. 296–306.
Nicklow, J.W., Boulos, P.F. (2005). Comprehensive Water and Wastewater Treatment Plant
Hydraulics Handbook for Engineers and Operators, MWH Soft: Pasadena, California. ISBN
0-9745689-4-5.
Teefy, S.M. (1996). Tracer Studies in Water Treatment Facilities: A Protocol and Case
Studies. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-857-9.
USEPA (1990). Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources. Office of Drinking
Water, USEPA. Washington, DC.
Zhang, J., W.B. Anderson, P.M. Huck, G.D. Stubley and A. Tadwalkar (2006). Evaluation of
a Computational Fluid Dynamics Modelling Approach for Prediction of Flocculation Mixing
Performance at the City of Toronto’s R.L. Clark Water Treatment Plant, presented at the
2006 OWWA/OMWA Joint Annual Conference. Toronto, ON.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 5 INTAKE STRUCTURES AND SCREENING
WATER SOURCES, INTAKE STRUCTURES AND SCREENING
5.1 Introduction ............................................................................................................ 5-1
5.2 Sources of Supply ................................................................................................... 5-1
5.2.1 Source Water Quality and Treatment ...................................................... 5-1
5.2.2 Evaluating Performance ........................................................................... 5-2
5.2.3 Common Problems and Potential Impacts ............................................... 5-3
5.2.4 Optimization Techniques ......................................................................... 5-5
5.3 Intake Structures ..................................................................................................... 5-6
5.3.1 Purpose and Types of Surface Water Intake Structures .......................... 5-6
5.3.2 Purpose and Types of Well Components ................................................. 5-7
5.3.3 Evaluating Performance ........................................................................... 5-7
5.3.4 Common Problems and Potential Impacts ............................................... 5-7
5.3.5 Optimization Techniques ......................................................................... 5-8
5.4 Screens .................................................................................................................... 5-9
5.4.1 Purpose and Types of Screens ................................................................. 5-9
5.4.2 Evaluating Performance ......................................................................... 5-10
5.4.3 Common Problems and Potential Impacts ............................................. 5-10
5.4.4 Optimization Techniques ....................................................................... 5-11
5.5 Low-Lift (Raw Water) Pumping .......................................................................... 5-11
5.5.1 Purpose of Low-Lift Pumping and Types of Stations ........................... 5-11
5.5.2 Evaluating Performance ......................................................................... 5-11
5.5.3 Optimization Techniques ....................................................................... 5-12
5.6 Pre-Chlorination/Oxidation and Zebra Mussel Control ....................................... 5-15
5.6.1 Purpose and Types of Pre-Oxidation Processes for Zebra Mussel
Control ................................................................................................... 5-15
5.6.2 Evaluating Performance ......................................................................... 5-15
5.6.3 Optimization Techniques ....................................................................... 5-16
5.7 Case Histories ....................................................................................................... 5-16
5.7.1 County of Oxford – Source Water Protection Program ......................... 5-16
5.7.2 City of Brandon – Source Water Blending Study .................................. 5-17
5.8 References ............................................................................................................ 5-19
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CHAPTER 5
WATER SOURCES, INTAKE STRUCTURES AND SCREENING
5.1 INTRODUCTION
In the design of new DWSs, the selection of a water supply source, whether surface water,
groundwater or GUDI, involves a review of the alternative sources available and their
respective characteristics. Raw water quality affects the treatment processes selected as well
as the cost of water treatment.
When optimizing an existing facility, in general it will not be possible or cost effective to
select a new source of water for a DWS; however, measures can be taken to ensure the best
possible raw water quality from the existing source by a) implementing a source water
protection plan and b) optimizing the means by which raw water is conveyed to the treatment
process. Consideration should also be given to potential changes in water quality and quantity
as a result of climate change.
5.2 SOURCES OF SUPPLY
5.2.1 Source Water Quality and Treatment
The general categories of water supply sources are surface water, groundwater and GUDI.
Although water quality is variable from source to source, surface waters have many qualities
in common; likewise, groundwater supplies have many similar characteristics. However,
treatment requirements for surface water and groundwater supplies are different. Reference
should be made to applicable regulations under the SDWA, 2002, and the Procedure for
Disinfection of Drinking Water in Ontario (MOE, 2006b), for specific minimum treatment
requirements for drinking water systems.
Surface water and GUDI supplies are susceptible to seasonal (e.g. stratification, algal growth)
and sometimes event-driven (e.g. heavy rains, snow melt) changes. Consequently, treatment
processes should be designed and operated with consideration given to the occurrence of such
events. Water quality problems most often associated with surface water sources include high
particulate content (i.e. turbidity), colour, taste and odour, and microbiological content
(AWWA, 1999).
Groundwater is relatively constant in quality from season to season; however, groundwater
supplies may be highly variable in quality from one well location to another. Changes in
hydrogeological conditions can produce different water quality over a relatively short
distance. The most common water quality problems associated with groundwater supplies are
high concentrations of hardness, iron and manganese (AWWA, 1999).
The available capacity of the water source (as defined by the Permit to Take Water) should
be evaluated relative to the projected water demand for the design period.
Source water protection can be implemented to prevent, minimize or control potential sources
of pollution or enhance raw water quality. In addition to reducing public health risks,
effective watershed management minimizes operating costs by reducing the degree of
drinking water treatment required, the quantity of chemicals used during treatment and the
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creation of treatment by-products (CCME, 2002). Additional information regarding source
water protection programs is provided in Section 5.2.4.1.
5.2.2 Evaluating Performance
5.2.2.1 Source Water Quality Evaluation
In a multiple barrier system for providing safe drinking water, the selection and protection of
a reliable, high quality drinking water source is the first barrier. The previous raw water
characterization used in the water treatment system design, as well as any subsequent
changes in source water quality and/or quantity, should be reviewed to determine if the
impact of those changes on the water treatment system are addressed adequately during the
optimization of a drinking water system.
5.2.2.2 Aquifer Performance
Aquifer performance can be evaluated using the following three methods:
Drawdown method;
Recovery method; and
Specific-capacity method.
In the drawdown method, the production well is pumped and water levels are periodically
observed in two or more observation wells. The data are plotted and analyzed by various
methods to relate drawdown in meters (or feet) to time measured in hours or days at a
specific pump rate.
The recovery method involves measuring the change in water level in an observation well
after pumping has stopped.
The specific-capacity method is the well yield per unit of drawdown. It does not indicate
aquifer performance as completely as the other methods, however, it is useful for evaluating
well production after a period of time and in making comparisons with data collected when
the well was new. A sudden drop in specific capacity indicates problems, such as screen
plugging or other operating issues.
The presence of other wells in the same aquifer can influence the well yield. Two wells
located close to each other and drawing from the same aquifer may experience interference,
which increases the drawdown in both wells. Well interference is possible in confined and
unconfined aquifers. For some wells, this additional drawdown may not affect well yield, but
will lead to higher pumping costs because the water must be lifted a greater distance. For
other wells, the additional drawdown may lower the water level in the well below the pump
intake causing the well to go “dry”. In this case, it may be necessary to lower the level of the
pump in the affected well.
New wells or increased pumping from existing wells can also lead to potential changes in
groundwater quality. The potential effects from nearby sources of contamination should be
considered, including naturally occurring poor water quality such as induced recharge from
adjacent formations.
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5.2.3 Common Problems and Potential Impacts
5.2.3.1 Source Water Quality Changes
The quality of a water source can be impacted by both natural and human factors. The degree
of the impact of these factors will vary depending on the type and characteristics of the
source. The major factors that may influence source water quality are outlined in Table 5-1.
Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts
Adapted from Water Quality and Treatment, AWWA (1999)
Factor Potential Impact
Natural Factors:
Climate Too much or too little precipitation can affect water quality as
well as quantity (high or low flow rates, run off, temperature
changes, etc).
Watershed characteristics The natural characteristics of a watershed (i.e. flora and fauna)
can have a significant impact on water quality (e.g. organics,
microorganisms).
Geology Geology directly impacts the source water quality (e.g.
hardness, recharge rates).
Microbial growth (nutrients) Algal and cyanobacterial growth can affect treatment
processes, causing filter clogging and taste and odour
problems.
Fire The destruction of brush and forest increases the likelihood of
erosion and increased runoff rates.
May lead to higher sediment and organic loading in the water
supply.
Density (Thermal stratification) Changes in water quality can occur either due to higher water
temperatures in summer, or in winter if an ice cover develops.
Lake or reservoir turnover can result in increased nutrient and
solids concentrations.
Human Factors (Point-source):
Wastewater discharges Sewage treatment plant by-passes or sewer failures can lead to
increased bacterial loadings and higher levels of organic and
inorganic contaminants.
Septic tanks and leach fields Improperly sited and/or maintained septic systems can release
organic and inorganic compounds, as well as microbiological
contaminants.
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Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts (cont’d)
Adapted from Water Quality and Treatment, AWWA (1999)
Factor Potential Impact
Industrial discharges Industrial activities can affect water quality through the release
of contaminants by air, water or soil.
Hazardous waste facilities The operation of a hazardous waste facility within a water
supply watershed or aquifer requires extensive precautions to
prevent accidental or intentional release of hazardous
contamination to the potable water supply.
Mine drainage Mining operations can disturb subsurface topography leading
to erosion and re-suspension of sediments, turbidity, colour,
etc.
Drainage from mining activities may also cause a change in
acidity of the receiving water.
Spills and releases Spills and accidental or intentional releases can have a major
impact on water quality depending on the nature of the
contaminant.
Improperly abandoned wells and
exploration holes Abandoned wells provide a direct pathway for surface runoff
and/or other sources of contamination.
Human factors (non-point source):
Agricultural runoff Application and storage of manure, pesticides, herbicides and
fertilizers can affect both groundwater and surface water
quality.
Erosion cause by improper tilling techniques can lead to
increased sediment load, colour and turbidity.
Livestock The presence of livestock in watersheds and over aquifers has a
direct effect on bacterial and protozoan concentrations.
Urban runoff Runoff from highways, city streets and commercial areas can
direct a number of contaminants, such as petroleum products,
metals (e.g. cadmium, lead), salt and other de-icing
compounds, and sediment into water sources.
Land development Development may increase erosion and therefore sediment
loading.
Land development may also decrease percolation, which
reduces groundwater quantities.
Landfills Landfill leachate can lead to groundwater contamination.
Erosion Erosion of soil may cause increased turbidity, colour and
eutrophication.
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Table 5-1 – Factors Influencing Source Water Quality and Potential Impacts (cont’d)
Adapted from Water Quality and Treatment, AWWA (1999)
Factor Potential Impact
Atmospheric deposition Airborne contamination, such as “acid rain” can adversely
affect surface water quality.
Recreational activities Swimming, boating and camping in water supply reservoirs
and watersheds can impact surface water quality.
Water quality in streams and rivers can be impacted by upstream users within the watershed.
Spills from barges, leaks from tank facilities, broken pipelines, accidental industrial spills and
other incidents can impact water quality. Some watercourses also have occasional periods
when water quality is especially poor as a result of natural causes, such as heavy spring
runoff.
Lakes and reservoirs are also vulnerable to natural and human contamination. Runoff from
agricultural areas may increase pathogen concentrations, nitrates and other nutrient
concentrations in the source water. Excessive growth of algae, cyanobacteria and aquatic
weeds in reservoirs is also quite common and can lead to taste and odour problems as well as
the development of toxic by-products; this is usually caused by high levels of nutrients in the
water.
5.2.4 Optimization Techniques
5.2.4.1 Source Water Protection
Under the CWA, 2006, communities are required to develop plans to protect both the quality
and quantity of their municipal drinking water sources. The CWA requires the identification
of vulnerable areas related to drinking water sources and the activities in those areas that are,
or could be, significant drinking water threats. The committees are also required to develop
source protection plans containing policies intended to eliminate or prevent significant
drinking water threats.
For surface water supplies, a Surface Water Vulnerability Analysis is conducted to identify
surface water areas that may be vulnerable to contamination. An intake protection zone (IPZ)
is designated around the drinking water intake. A vulnerability score is assigned for the IPZ,
which refers to the comparative likelihood of a contaminant of concern reaching an intake.
The scores depend on various factors, such as the depth of the intake from the water’s
surface, the length of the intake from the shoreline, the size of the water body where the
intake is located, and how water interacts within the zone (MOE, 2006a).
A Groundwater Vulnerability Analysis is conducted by first identifying the vulnerable areas
within the Source Protection Area, and second, by mapping the relative vulnerability of the
aquifers within each vulnerable area. The vulnerable areas considered in the assessment
include:
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Wellhead Protection Areas around municipal drinking water supply wells;
Highly Vulnerable Aquifers;
Significant Groundwater Recharge Areas; and
Future Municipal Supply Areas.
The relative vulnerability within each of these areas will be characterized as high, medium or
low (MOE, 2006a).
5.2.4.2 Blending Source Waters
Source water blending can be used to increase the available quantity of raw water or to
improve raw water quality. For example, various blending ratios can be used to obtain a
target concentration for a specific parameter (e.g. blending surface water with a groundwater
supply to decrease total organic carbon concentrations) (XCG, 2009).
5.3 INTAKE STRUCTURES
5.3.1 Purpose and Types of Surface Water Intake Structures
Intake structures are used to draw water from lakes, reservoirs or rivers. In Ontario,
submerged single- or fixed-level intake systems are the most common type of intake
structure. The single-level intake is generally placed in the deepest location or area of the
river or reservoir to ensure that service can be provided if water levels are reduced in the
supply body (i.e. drought conditions) and to avoid water quality changes that may occur at or
near the water surface. Figure 5-1 shows a typical single level intake.
Figure 5-1 – Surface Water Intake Schematic From AWWA (1995)
The advantage of single-inlet intake structures is that they are usually much less complicated
and therefore much less costly to construct and operate than multi-level structures.
Major disadvantages of single-level intake facilities become apparent when they are used in
deeper, more complex lake environments. In some cases, water entering the inlet during
spring, summer and fall months may be of poorer quality due to lake stratification.
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Multi-level intake structures have inlets to the system at depths ranging from near the surface
to the deeper zones. Variable depth intakes can allow different levels to be accessed as raw
water conditions change during the year. To obtain good water quality, it may be necessary to
draw water from different levels during different seasons.
The advantage of this type of intake structure is that water can be provided from the depth
where the best quality of water is located at a given time. The disadvantages are that they are
generally more complex and expensive to construct and operate than single-level intakes.
Although submerged intakes are generally more common in Ontario, there are some systems
using surface intakes or open channel intakes, which consist of a natural or artificial
waterway or conduit that is used to convey water from the source to the treatment plant.
These intakes can be simpler to construct and maintain; however, common problems
associated with these structures include the accumulation of silt and debris, ice formation, as
well as algae and bacterial growth.
5.3.2 Purpose and Types of Well Components
In general, the sub-surface components of a well include the well casing, seal, intake screen
and gravel packing. All of these components must be properly designed and installed to
prevent contamination of the well and to maximize the well yield.
5.3.3 Evaluating Performance
The intake size and well yield should be sufficient for the projected water demand over an
extended design period.
Raw water sampling and testing programs should be in place to monitor water quality, for
both process control and for trending water quality changes over time.
5.3.4 Common Problems and Potential Impacts
5.3.4.1 Zebra Mussels
Zebra mussels have the potential to obstruct public water supply intakes and cause loss of
intake capacity, as well as contribute to taste and odour problems. A discussion of zebra
mussel control systems is provided in Section 5.6.
5.3.4.2 Icing
In cold weather conditions, frazil ice or anchor ice can occur. When water is almost at the
freezing point and is rapidly being cooled, small, disk-shaped frazil ice crystals will form and
be distributed throughout the water mass. When the frazil crystals are carried to the depth of a
water intake, they can adhere to the intake screen and quickly build up to a solid plug across
the opening. Anchor ice is slightly different in that it is composed of sheet-like crystals that
adhere to and grow on submerged objects.
Icing of an intake will cause loss or reduction of intake capacity, plug screens and/or may
cause damage to pumps. It is generally best to stop using the intake immediately when icing
is noticed, if possible, because the blockage will only get worse with continued pumping.
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5.3.4.3 Siltation
Siltation occurs when sediment carried by a stream or river is deposited when water loses
velocity upstream from a dam or other impediment to flow. The rate of siltation is generally a
function of both the type of soil in the area and how well the land is protected from erosion
(AWWA, 1995).
5.3.4.4 Well Deterioration
Well deterioration can be caused by chemical, biological and physical problems. Chemical
and biological causes are mainly associated with corrosion and incrustation of the well
components. The physical causes of well deterioration include changes in hydrogeologic
conditions, subsidence due to a decline in water level, effects of variations in verticality and
alignment, mechanical blockage, sand pumping and erosion-corrosion (AwwaRF, 1993).
5.3.5 Optimization Techniques
5.3.5.1 Maintenance of Surface Water Intake Structures
Proper design, maintenance and operation of intake structures are essential to prevent partial
or complete shut-down of the drinking water system. It is recommended that lake or river
intake piping and screens be inspected by divers to ensure no damage has occurred over the
winter. If necessary, cleaning of the intake should also be performed.
For small intakes, consideration should be given to backflushing the intake, if practical.
5.3.5.2 Minimizing Frazil Ice Formation
Potential solutions for water systems that frequently experience icing may include: providing
the intake with piping to backflush the line, or blowing the line with compressed air or steam.
If more than one intake is available, the use of each intake can be alternated to allow any
accumulated ice to melt and float away from the intake opening. Throttling the intake pumps
to decrease the flows into the plant is another possible remedy if immediate shut-down is not
possible.
Design considerations for new or modified intake structures to minimize ice formation are
provided in the Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008).
5.3.5.3 Well Maintenance and Restoration
Wells are subject to a natural aging process, which can be slowed or minimized with proper
prevention and remediation techniques. The design of groundwater wells must conform to the
requirements of the Wells Regulation (O. Reg. 903), made under the Ontario Water
Resources Act, 1990, and AWWA Standard A100: Water Wells.
Prevention and maintenance strategies for wells should focus on:
Preventing occurrence and limiting recurrence of corrosion;
Preventing occurrence and limiting recurrence of incrustation;
Preventing biofouling;
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Preventing structural failure and sanding; and
Pump maintenance.
Well restoration, remediation or rehabilitation are the processes that may be necessary once
prevention and maintenance have failed to forestall a problem or when prevention and
maintenance are neglected. Well rehabilitation should be conducted by an experienced,
licensed well contractor with the technical assistance of a consultant. Additional information
regarding well maintenance activities is provided in AwwaRF (2003).
5.4 SCREENS
5.4.1 Purpose and Types of Screens
In surface water treatment plants screens are used to remove large debris from raw water,
such as logs or fish, or other unwanted material (e.g. algae). Screens can be designed to
remove coarse or fine matter. A discussion of various types of screens is provided below.
Bar Screens
Bar screens are used to screen out large debris (e.g. logs and fish). They vary in size from
fine (1.5 to 13 mm) to coarse (32 to 100 mm). Bar screens are cleaned either mechanically
(which is necessary if there are large amounts of debris) or manually. They are generally
installed at 60 to 80 degrees to horizontal.
Wire Mesh Screens
Wire-mesh screens are usually made of corrosion resistant material, such as stainless steel.
The size of the openings in the screens typically varies between 0.4 mm and 10 mm. One
type of wire-mesh screen is a “travelling screen” which consists of an endless belt made of
fine wire mesh mounted on a chain that moves the screen through the water. These screens
can be cleaned manually or automatically. When the screen rises above the water level, the
debris is collected and discharged into a trough, usually with the help of a water jet.
Travelling screens are usually located in the inflow channel to the pumps for easy access for
inspection and maintenance.
Microstrainers
Microstrainers are very fine screens used primarily to remove algae and other aquatic
organisms. They usually consist of a rotating drum with finely woven material
(approximately 250 openings per square millimetre). Water passes through the screen, into
the drum, while the unwanted material does not. High pressure water jets remove
accumulated material from the exterior of the drum. Due to the small size of the openings,
problems such as siltation, zebra mussel growth and frazil ice formation must be carefully
controlled.
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5.4.2 Evaluating Performance
Table 5-2 presents recommended monitoring, in terms of sampling locations and analyses, in
order to evaluate the performance of screens and strainers. Typically, screen performance is
evaluated based on the achieved removal of screenings.
Table 5-2 – Screening – Recommended Monitoring to Evaluate Performance
Location Types of Sample /
Measurement
Parameters /
Analyses Comments
Upstream and
Downstream of
Screens
Level Measurement Head loss across
screens
The maximum operating
head loss across a screen unit
is usually provided by the
supplier.
Upstream and
Downstream of
Screens
Flow Measurement Velocity across
screens
The maximum velocity of
water through the screen
should be 0.6 m/s regardless
of water level in the screen
well (MOE, 2008).
Screenings Bin Quantity Measurement Mass of screenings
Volume of
screenings
The quantity of screenings
depends on the water source,
screen type, and type of
washing system.
Figure 5-2 presents a process schematic of a typical screening process, along with the
identification of various sampling locations.
Screen
To Pumping or TreatmentRaw Water
ScreeningsScreenings Quantity
Measurement
Water Level
Measurement
Water Level
Measurement
Figure 5-2 – Screening – Process Schematic and Sampling Locations
5.4.3 Common Problems and Potential Impacts
Clogging and corrosion are the most common problems associated with screening.
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5.4.4 Optimization Techniques
5.4.4.1 Maintenance of Screening Equipment
As a screen traps coarse material and debris, the screen develops more resistance to the flow
of water through the openings. This increases water levels upstream of the screen and the
overall head loss experienced across the screen.
Screens are generally designed so that they can be removed for inspection, maintenance and
cleaning. Methods of cleaning screens at the treatment plant include the use of rakes, brooms,
bristle brushes, and water sprays.
Some screens have devices that measure the head loss between the water surface upstream
and downstream from the screen. When a specified head loss is exceeded, a cleaning cycle is
started. The cleaning cycle might consist of high-pressure water sprays which clean the
screen in place, or the screen might need to be lifted out of the water for cleaning.
5.5 LOW-LIFT (RAW WATER) PUMPING
5.5.1 Purpose of Low-Lift Pumping and Types of Stations
Low-lift pumps are used to lift surface water and convey it to a treatment plant. These pumps
move large volumes of water at relatively low discharge pressures.
Well pumps are used to draw water from shallow or deep wells and discharge it to a
treatment plant or into the distribution system. They can either be submerged or located at the
ground surface.
In either case (low-lift or well pumping), the pumping station can either be located within the
treatment plant facility or be remote from the facility (e.g. when the treatment plant is not
located near the raw water source).
5.5.2 Evaluating Performance
Symptoms and causes of common problems encountered with low-lift and well pumping
stations are presented in Table 5-3.
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Table 5-3 – Raw Water Pumping – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Impacts Common Causes
Lack of hydraulic
capacity at pump
station
Operating above rated capacity for
extended periods
Undersized pumps
Clogged pumps
Frequent cycling of
pump operation Inconsistent flows resulting in
alternating periods of flow and no-
flow (and loading) to treatment
processes
Settling of solids and debris in
channels, pipes or wet wells during
no-flow or low flow conditions
Oversized pumps
Pumps not equipped with variable
frequency drives (VFDs)
Insufficient storage and/or
mismatched supply and demand
5.5.3 Optimization Techniques
5.5.3.1 Pump Selection and Sizing
The selection and sizing of pumps should be based on firm capacity, meaning that the raw
water pumping station should be able to supply the water treatment plant design capacity with
the largest unit out of service. Multiple pumps should be provided, and pumping stations should
be designed to handle the 20-year design flow, or for the ultimate service area requirement, if
practicable (MOE, 2008).
To optimize pump efficiency in pumping stations with a wide range of operating flows,
consideration should be given to the installation of multiple pumps of different sizes or
variable capacities to cover the expected range of flows (MOE, 2008). In small pumping
stations, a minimum of two units, each sized to meet the design flow, should be provided.
Oversized pumps can operate in an on-off mode during low flow conditions, causing uneven
flows or periods of no-flow to downstream unit processes. This can cause settling of
suspended solids in downstream processes and conduits, bumping of particles in filters and
other operational problems.
Problems with pump over-sizing are commonly encountered in new or newly expanded
facilities where the pumps were sized to be capable of handling the expected design flows at
build-out, without consideration of the demand at current conditions. The installation of
multiple, smaller capacity pumps, which operate according to a filtration rate set point or
treated water storage level can minimize the frequency of on-off cycling and provide
consistent flows to the WTP throughout the day. Pump efficiency and operational energy
savings should be considered during pump selection.
5.5.3.2 Variable Frequency Drives
Where the existing pumping station configuration does not allow for the installation of
multiple, lower capacity pumps in place of a single larger capacity pump, a variable
frequency drive (VFD) can be installed on the existing pump(s).
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The purpose of a VFD is to allow a degree of control over the output of the pump by varying
the frequency of the power to the motor. By varying the power to the motor, the speed of the
motor and pump can be controlled. As opposed to throttling the output of the pump with
control valves, adjusting the operating speed of the motor and pump reduces the output of the
pump from the source and saves energy by optimizing the pump operation.
Installation of a VFD allows the pump to operate at different pump outputs to match varying
flow conditions and by providing flexibility to operate over a range of flows. This effectively
maintains the desired flow to downstream processes, minimizing process upsets and
optimizing pump operation.
VFDs can also allow for soft starts and stops of the pump motor, minimizing hydraulic and
mechanical stresses on system piping, channels and unit processes and equipment. Hydraulic
stresses, often referred to as water-hammer, are the result of sudden increases in pressure, sending
out shock waves and potentially damaging system components. Mechanical stresses refer to the
mechanical wear that motors and pumps undergo as a result of frequent starts and stops.
Installation of VFDs can optimize energy usage by reducing the power going to the motor at
lower flows, and reducing the frequency of energy intensive pump start cycles.
Most pumps with VFDs are operated between 50 and 100 percent of the rated capacity. This
is limited by the motor and equipment. Motors are typically cooled by a fan on the same
drive as the motor, and the fan operates at the same speed as the motor. At low speeds, the
fan does not rotate rapidly enough to provide sufficient airflow to cool the motor, resulting in
increased mechanical stress and rapid wear. Equipment manuals or suppliers should be
referred to in order to determine the optimum operating range for the existing pump and
motor assembly. It is also important to consider the larger switchgear footprint needed for
VFDs being incorporated into an existing facility.
Sequence control (i.e. controlling the number of operating pumps) is applicable to pump
groups consisting of constant-speed pumps and variable-speed pumps. Sequence control of
constant- and variable-speed pumps in combination results in more economical and precise
operational control at larger pumping stations.
When controlling a number of pumps with different capacities, an operating sequence and
combination that gives optimum control efficiency should be determined. This leads to
operation in the higher region of the pump efficiency curve, contributing to energy savings
(AwwaRF and Japan Water Works Association, 1993).
Control Strategies
Several control strategies can be employed at pumping stations:
Level setpoint control;
Level band control; and
Discharge flow rate control.
In level setpoint control, pump station operation is dictated by the water level in the treated
water storage reservoir (i.e. clearwell). Specific setpoints are established based on different
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water levels within the reservoir, and pump start sequence and operation are based on the
setpoints. Maintaining control too tightly can reduce the effectiveness of treated water storage
levels in moderating flows to the plant. The drive speed of the pumps may also vary wildly in
an attempt to maintain the reservoir level with varying flows.
Level band control is a variation on level setpoint control where pump operation steps are
based on clearwell level ranges rather than setpoints based on distinct clearwell levels. By
setting the steps to operate across overlapping ranges, the discharge flow rate is smoothed.
This has the benefit of dampening peak flows to the treatment process.
For larger systems, level control may not be as important; in such cases, discharge flow
control (e.g. based on a set filtration rate) can be used. This control strategy can optimize the
flows to downstream processes, ensuring even, consistent flows to the WTP.
5.5.3.3 Impeller Modification
Where a pump is undersized or oversized, or where downstream hydraulic conditions have changed,
impeller replacement or modification can potentially eliminate the need for pump replacement.
Modifying or replacing the impeller in a centrifugal pump shifts the pump’s operating curve,
effectively changing the efficiency operating point of the pump. In addition to potentially
avoiding costs associated with pump replacement, impeller modification or replacement can
allow for more efficient operation of the pump, reducing operating costs.
Depending on the size of the pump volute and existing impeller, it may not always be
possible to replace the impeller with one of a larger or smaller size. In such cases, if a smaller
impeller is required for an oversized pump, the impeller can be trimmed to reduce its size.
Conversely, if a larger impeller is needed, total pump replacement may be required.
The selection or modification of a pump impeller is based on the size of the pump, the system
head curve, pump configuration, pump power and required capacity. Pump suppliers should
be consulted when considering modification or replacement of an impeller, to ensure that the
new or modified impeller will not negatively impact pump performance.
5.5.3.4 Clogged Pumps
One of the most common groundwater pumping problems is plugging of the well pump
screen. The causes can be mechanical, chemical or bacteriological in nature. Repairs to well
components should always be performed by a licensed pump installer.
Bacteriological samples should be collected periodically from each well. These samples should
be analyzed for total coliforms, heterotrophic plate count bacteria, iron bacteria and sulphate
reducing bacteria. If there are indications of contamination, regular disinfection of the well may
be necessary to prevent growth of nuisance bacteria that can lead to production problems.
As noted in Section 5.4, screens are commonly used in surface water systems for the removal
of coarse material and debris from raw water prior to pumping, minimizing pump downtime
for cleaning of clogged pumps. For details regarding the design and selection of screening
devices, reference should be made to the Design Guidelines for Drinking Water Systems,
2008 (MOE, 2008).
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5.6 PRE-CHLORINATION/OXIDATION AND ZEBRA MUSSEL CONTROL
5.6.1 Purpose and Types of Pre-Oxidation Processes for Zebra Mussel Control
Chemical oxidants are often added before water enters the treatment plant, mainly to control
algae and other forms of biological growth (e.g. zebra mussels) that may occur at the intake or
in wet wells. Oxidants are also added in the first step of treatment either as first-stage
disinfectants or for other purposes such as control of biological growth in basins, colour
removal, control of taste and odours, reduction of specific organic pollutants, precipitation of
metals, and as coagulant aids (AWWA, 1999). These applications are discussed in Chapters 9
and 10.
The most accepted and currently recommended form of chemical treatment for zebra mussel
control in public water supplies is the use of oxidants such as chlorine, chlorine dioxide,
potassium permanganate and ozone (MOE, 2008). Chemical dosages are typically applied at
the intake through solution piping and a diffuser to prevent the formation of zebra mussel
colonies within the intake and piping. In addition, intake screens manufactured with special
alloys that prevent the growth of zebra mussels on the intake itself are available.
5.6.2 Evaluating Performance
Table 5-4 presents a list of parameters that should be monitored to either measure the
effectiveness of zebra mussel control strategies or monitor for environmental conditions that
may favour zebra mussel reproduction.
Table 5-4 – Monitoring Parameters for Zebra Mussel Control Processes
Adapted from Mackie (2008)
Parameter Comment
Chlorine (or other oxidant) residual Assess effectiveness of applied dose relative to chlorine
demand
Calcium Dissolved calcium in water is an essential constituent of
shells for zebra mussels growth (Chang, 1996)
Alkalinity May be an indication of availability of calcium
pH May be an indication of availability of calcium
Hardness May be an indication of availability of calcium
Dissolved oxygen May indicate an area that is suitable for zebra mussel
infestation (Chang, 1996)
Nutrients (phosphorus, nitrogen) Indication of when reproduction and larval development will
occur
Temperature Indication of when reproduction and larval development will
occur (temperatures above 12 to 15°C)
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5.6.3 Optimization Techniques
Pre-chlorination has been the most common treatment for control of zebra mussels; however,
the main concern with the application of chlorine to raw water is the potential formation of
THMs and other disinfection by-products. In addition, concerns have been raised regarding
the release of oxidant chemicals, such as chlorine, into the natural environment. Several other
chemical and non-chemical alternatives have been evaluated with varying levels of success,
including: potassium permanganate, oxygen deprivation, thermal treatment, exposure and
desiccation, UV light irradiation, manual scraping, high-pressure jetting, mechanical
filtration, removable substrates, molluscicides, ozone, antifouling coatings, electric currents
and sonic vibration.
Experience has shown that low levels of chlorine can be applied to control settlement of
zebra mussel veligers (larval stage); higher dosages and contact times may be required to
control adult colonies once established (Van Benschoten, 2008).
Other studies have shown that it may be possible to optimize chemical addition for zebra
mussel control by monitoring environmental parameters that indicate seasonal sensitivity of
larvae and adults and the seasonal toxicity of molluscicides (Mackie, 2008).
5.7 CASE HISTORIES
5.7.1 County of Oxford – Source Water Protection Program
The following case study is based on information presented in Goudreau (2007).
System Description
The County of Oxford (the County) owns and operates the City of Woodstock (the City)
Water Supply System, which consists of 10 municipal groundwater wells. Approximately 80
percent of the City’s permitted water capacity is from the Thornton and Tabor well fields
located southwest of the City in a predominately agricultural area. Several of the wells within
the Thornton well field have elevated levels of nitrates. Nitrate levels in the aquifer began
increasing in the 1970s and have been attributed to historical farming practices on the
surrounding lands.
Groundwater Characterization and Protection Studies
Work to protect the Thornton Supply wells started in the mid-1990s from two different
perspectives. The former Woodstock Public Utilities Commission (PUC), which operated the
water system at the time, began looking at the well field to determine the source of the rising
nitrate levels. Around the same time, the County began to assess the vulnerability of its
municipal well supplies. In conjunction with the University of Waterloo, the County and the
PUC undertook a number of studies to characterize the extent and source of the nitrate plume,
as well as numerous County-wide groundwater protection studies addressing potential threats
to drinking water.
Mitigation Strategies
Based on the results of these studies, the County has begun implementing proactive measures
to reduce the nitrate loading to the Thornton aquifer. Specific measures include:
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Groundwater Protection: Several groundwater studies were undertaken starting in the
mid-1990s, leading to the development of Wellhead Protection Areas (WHPAs) for
each municipal well. The WHPAs consisted of the 2, 5, 10 and 25 year time of travel
(TOT) zones for the well or well field.
Nutrient Management Strategies: A Nutrient Management Committee was formed,
which led the development of a County-wide Nutrient Management Strategy and
ultimately resulted in the implementation of bylaws that require farm operations over
a certain size to follow best practices for nutrient application, manure storage and
separation distances. These by-laws are being superseded by the provincial Nutrient
Management Act (NMA), 2002.
Nitrate Investigations: In conjunction with the University of Waterloo, the
Woodstock PUC undertook a number of studies to estimate the spatial distribution
and concentration of nitrates in the area. The studies showed that agricultural
activities were likely the main contributor to nitrate levels, and significant quantities
of nitrates were stored in unsaturated zones beneath the study area’s agricultural
lands. Research indicates that it may take several (e.g. 15 to 30) years to “flush”
excess nitrates from the aquifer system.
Land Use Management: Since 2003, the County has purchased approximately 300
acres of farmland within the 2-year TOT of the Thornton well field. Plots of land are
leased back to farmers for agricultural production. The farmers leasing the plots are
required to maintain “enhanced” Nutrient Management Plans that are more stringent
than provincial requirements under the NMA.
Well Pumping and Treatment: In order to reduce nitrate concentrations to well below
the Ontario Drinking Water Quality Standard of 10 mg/L, the County has
implemented a pumpage strategy that includes minimizing the use of high nitrate
wells and blending the water with water from low-nitrate wells.
Additional Servicing: The Village of Sweaburg (the Village) is located entirely
within the 2-year TOT of the Thornton WHPA. In 2003, residents were serviced by a
combination of municipal and private well systems. In order to remove the threat of
contamination from the preferential pathway to the aquifer, both the private and
municipal wells were recommended for abandonment. The Village was connected to
the new Thornton water treatment plant and the distribution system was extended to
service the properties that had used private wells. A sanitary servicing study is also
planned for Sweaburg to determine the best way to mitigate the approximately 300
septic systems that are located in the 2-year TOT of the Thornton well field.
Summary
Early results of the management strategies discussed above are positive and suggest that they
would be useful for protection of sensitive sources outside the Thornton well field. The
County is supporting continued research on the effects of the management strategies and new
research into in-situ remediation to reduce current nitrate levels.
5.7.2 City of Brandon – Source Water Blending Study
The following case study is based on information presented in XCG (2009).
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System Description
The City of Brandon (the City) Water Treatment Plant (WTP) is a conventional lime-soda
ash softening plant, with filtration and disinfection using chlorine. The raw water source is
the Assiniboine River. The Assiniboine River flows from its headwaters in eastern
Saskatchewan into and across the western portion of Manitoba to its confluence with the Red
River within the City of Winnipeg. Raw water data collected by the City indicate that
concentrations of turbidity, total organic carbon (TOC), colour, alkalinity and hardness are
elevated and highly variable based on seasonal conditions.
Disinfection Study Methodology
A study was initiated to minimize the formation of DBPs in the City’s drinking water system.
The first phase of the study consisted of an evaluation of the existing treatment and
disinfection practices at the Brandon WTP and their effect on the DBP concentrations.
The recommended alternative for the reduction of DBPs in the drinking water system was
the implementation of chloramination for secondary disinfection. The second phase of the
Disinfection Study included bench-scale testing and additional sampling to evaluate the
benefits of chloramination for minimizing the formation of THM and HAA in the treated
water. The monthly chloramination jar testing program was carried out over a period of
one year; at that time, it was decided to investigate source water blending.
The City was interested in investigating blending of the Assiniboine River source with
the Curran Park (Turtle Crossing) and Canada Games (Westbran Park) wells as a
potential option for the reduction of TOC in the raw water. Bench-scale jar testing was
completed and a full-scale trial was conducted to confirm the results of the bench-scale
analysis.
Samples of the raw water from each well were analyzed for parameters contained in the
Guidelines for Canadian Drinking Water Quality (GCDWQ). The results of the well raw
water quality analyses indicated that the average TOC levels in the groundwater sources
approximately 2.2 mg/L, while those in samples collected from the Assiniboine River were
approximately 9.8 mg/L.
The rated capacities of the Brandon WTP and the two wells were evaluated and a ratio of 55
percent groundwater to 45 percent Assiniboine River water was selected for the bench-scale
study. The average TOC concentration in the raw water at this blending ratio was
approximately 7.5 mg/L (note: the average concentrations were based on a number of
monthly samples, which resulted in a variation in the average blended TOC).
Summary
The results of the jar testing indicated that THM concentrations measured after a 24-hour
chlorine contact time were found to be 91 µg/L and 80 µg/L, during the spring and summer
trials, respectively. Concurrently with the summer trial, during which the Brandon WTP was
supplied solely from the Assiniboine River, samples were collected at the furthest point in the
Brandon distribution system and the THM concentration was 149 µg/L. These results
indicated the potential for a 46 percent reduction in the total THM concentration by blending
the surface and groundwater sources at the above mentioned ratio.
CHAPTER 5. Water Sources, Intake Structures and Screening 5-19
Optimization Guidance Manual for Drinking Water Systems 2014
Further reductions in the total THM concentration were achieved in jar testing runs using
chloramination for secondary disinfection.
Full-scale plant trials confirmed the results of the jar testing. In addition, the results of the
plant trial indicated that the higher the ratio of groundwater to surface water, the greater the
reduction in THMs.
5.8 REFERENCES
American Water Works Association (1995). Water Sources, 2nd
Ed. AWWA. ISBN 0-89867-
778-5.
American Water Works Association (1999). Water Quality and Treatment: A Handbook of
Community Water Supplies, 5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
American Water Works Association Research Foundation (1993). Evaluation and
Restoration of Water Supply Wells. AwwaRF and AWWA. ISBN 0-89867-659-2
American Water Works Association Research Foundation and Japan Water Works
Association (1993). Instrumentation & Computer Integration of Water Utility Operations.
ISBN 0-89867-630-4.
Chang, T.J., M.A. Hoover, and T.A. Bartrand (1996). Optimization of a Vacuum Device for
Zebra Mussel Control.
CCME (2002). From Source To Tap: The Multi-Barrier Approach to Safe Drinking Water,
prepared by the Federal-Provincial-Territorial Committee on Drinking Water and the Water
Quality Task Group of the Canadian Council of Ministers of the Environment.
Goudreau, D. (2007). “Addressing and Mitigating Known Water Quality Issues: A Source
Protection Case Study”, presented at the 2007 OWWA-OMWA Joint Annual Conference,
Town of the Blue Mountains, ON.
Mackie, G. (2008). “Control and Disinfection II. Optimizing Chemical Disinfections”,
presented at the American Water Works Association Research Foundation (AwwaRF)
Workshop on Quagga/Zebra Mussel Control Strategies for Water Users in the Western
United States. AwwaRF Project #4200.
MOE (2006a). Assessment Report: Draft Guidance Modules. PIBS 5600e.
http://www.ene.gov.on.ca/envision/water/cwa-guidance.htm
MOE (2006b). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.
MOE (2008). Design Guidelines for Drinking Water Systems. ISBN 978-1-4249-8517-3.
Van Benschoten, J. (2008). “Control of Dreissenid Mussels by Chemical Oxidants”,
presented at the American Water Works Association Research Foundation (AwwaRF)
Workshop on Quagga/Zebra Mussel Control Strategies for Water Users in the Western
United States. AwwaRF Project #4200.
CHAPTER 5. Water Sources, Intake Structures and Screening 5-20
Optimization Guidance Manual for Drinking Water Systems 2014
XCG Consultants Ltd. (2009). “Evaluation of Disinfection Formation with Source Water
Blending”, report for the City of Brandon.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 6COAGULATION AND FLOCCULATION
COAGULATION AND FLOCCULATION
6.1 Introduction ............................................................................................................ 6-1
6.2 Coagulation and Flocculation ................................................................................. 6-1
6.2.1 Purpose of Coagulation and Types of Coagulation Chemicals ............... 6-1
6.2.2 Purpose of and Types of Flocculation ..................................................... 6-2
6.2.3 Evaluating Performance ........................................................................... 6-3
6.2.4 Common Problems and Potential Impacts ............................................... 6-6
6.3 Optimization Techniques ....................................................................................... 6-7
6.3.1 Jar Testing ................................................................................................ 6-7
6.3.2 Zeta Potential ......................................................................................... 6-10
6.3.3 Streaming Current Detectors ................................................................. 6-10
6.3.4 Particle Counters .................................................................................... 6-10
6.3.5 Residual Aluminum Control .................................................................. 6-10
6.3.6 Optimizing Residence Time in Flocculators ......................................... 6-11
6.4 Case Histories ....................................................................................................... 6-12
6.4.1 Regional Municipality of Waterloo – Mannheim WTP ........................ 6-12
6.4.2 City of Owen Sound – R.H. Neath WTP ............................................... 6-16
6.5 References ............................................................................................................ 6-19
CHAPTER 6. Coagulation and Flocculation 6-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 6
COAGULATION AND FLOCCULATION
6.1 INTRODUCTION
Surface water sources are likely to contain particulate impurities, such as bacteria and algae,
as well as suspended and dissolved organic and inorganic material. The objective of
coagulation and flocculation is to increase the size of the particulate matter present in the raw
water, especially the nonsettleable solids (e.g., colloidal particles, algae and colour) to
improve the removal of these impurities through the clarification and/or filtration processes.
The focus of this chapter is on coagulation and flocculation as a treatment strategy to remove
particulate matter. Optimization techniques related to coagulation for the removal of other
parameters, such as enhanced coagulation and flocculation for removal of natural organic
matter (NOM) to reduce DBP formation, are addressed in Chapters 9 and 10. The impact of
changes in coagulants and coagulant dosage on corrosion control in the distribution system
and premise plumbing are discussed in Chapter 11.
6.2 COAGULATION AND FLOCCULATION
6.2.1 Purpose of Coagulation and Types of Coagulation Chemicals
Coagulation involves the rapid dispersion of a chemical coagulant into water to destabilize
particles so they can agglomerate or come together and form larger particles or “floc”.
Coagulation of turbidity in water treatment occurs predominantly by two mechanisms
(AWWA, 1999):
1. Charge neutralization
– Most particles in water are negatively charged and repel each other. The
coagulant is positively charged and neutralizes particle charge to allow the
particles to agglomerate during the subsequent flocculation process.
2. Sweep-floc coagulation
– Sufficient coagulant is added to form a precipitate that settles and sweeps, or
enmeshes, suspended particles.
– Higher coagulant dosages are used for sweep coagulation than for charge
neutralization.
There are advantages and disadvantages to the use of either method. For example, with
charge neutralization, if too much coagulant has been added the particles will attain a positive
charge and re-stabilize, resulting in higher residual turbidity. For sweep-floc coagulation,
higher coagulant dosages are needed than for charge neutralization, resulting in higher
chemical costs, greater sludge production and potentially leading to higher iron or aluminum
residuals in the treated water. However, the use of sweep-floc coagulation may be
advantageous for systems where raw water turbidity and organic carbon concentrations are
elevated and/or variable. Additional information on the application of these coagulation
CHAPTER 6. Coagulation and Flocculation 6-2
Optimization Guidance Manual for Drinking Water Systems 2014
mechanisms, and guidance on process selection and design, is provided in AWWA (1999),
MWH (2005) and AWWA (2007).
The mixing of the coagulant chemical into the raw water is commonly referred to as flash
mixing. The purpose of the flash mix is to rapidly and thoroughly mix the coagulant chemical
throughout the water. The entire process occurs in a very short time (i.e. seconds) and results
in the formation of very small floc particles.
Mixing can be achieved with a number of different types of devices. Mechanical mixers
(paddles, turbines, propellers and jet mixers) are frequently used in coagulation facilities.
Hydraulic mixing with in-line static mixers, baffles or throttling valves works well in systems
that have sufficient water velocity to cause significant turbulence in the water being treated.
The chemicals most frequently used as primary coagulants include:
Aluminum sulphate or “alum” (Al2(SO4)314H2O)
Polyaluminum chloride (PACl)
Iron-based coagulants:
– Ferric chloride (FeCl36H2O)
– Ferric sulphate (Fe2(SO4)39H2O)
– Ferrous sulphate (FeSO47H2O)
Polymers (polyelectrolytes)
Poor control of the coagulation process (e.g. coagulation pH, dosage, mixing, etc.) may result
in elevated iron or aluminum residuals in the treated water. As such, monitoring of these
parameters in the treated water is needed to verify that their concentration is below the
aesthetic objective or operational guideline, as applicable.
Coagulant aids can be used in conjunction with a primary coagulant, such as alum or other
metallic salts, to provide bridging between floc particles and to create larger, heavier and/or
stronger floc. The three general types of coagulant aids are:
Activated silica (Na2SiO3)
Weighting agents (e.g. bentonite clay)
Polymers (polyelectrolytes)
6.2.2 Purpose of and Types of Flocculation
Flocculation is a process that involves the gentle agitation of water to promote contact
between particles to form particle clusters called “floc”. As particles collide, they become
larger through chemical joining and bridging. Larger particles are more easily settled and/or
filtered.
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Optimization Guidance Manual for Drinking Water Systems 2014
The purpose of flocculation is to create a floc of an optimum size, density and strength for
later removal in the clarification and filtration processes. Flocculation normally follows
coagulation, which is the first step necessary to destabilize particles with surface charges and
allow flocculation to occur.
Sufficient detention time, proper mixing intensity and a properly shaped basin for uniform
mixing are needed to allow efficient flocculation. While coagulant mixing is designed to
allow rapid and complete dispersion of the coagulant chemicals under very turbulent
conditions, flocculation is a much more gentle stirring process. Insufficient mixing may cause
poor floc formation, while excessive mixing may shear flocculated particles. Sheared
particles cannot re-agglomerate, which can result in higher settled and filtered water
turbidity.
Two common types of mechanical flocculators are horizontal paddle wheel types and vertical
flocculators (paddle, turbine or propeller). Hydraulic flocculators of various configurations
are also common in Ontario.
6.2.3 Evaluating Performance
The selection of chemical coagulants and coagulant aids is a continuing process of trial and
evaluation. Table 6-1 presents monitoring recommended, in terms of sampling locations and
analyses, in order to evaluate the performance of the coagulation and flocculation processes.
The following can be indicators of inadequate coagulant mixing, inadequate flocculation
mixing, or incorrect chemical dosage:
Very small floc (called pinpoint floc), unless specifically desired for direct filtration.
High turbidity in settled or filtered water;
Too-frequent filter backwashing; and
Elevated aluminum or iron concentration in treated water (depending on the
coagulant used).
Table 6-1 – Coagulation/Flocculation – Recommended Monitoring to Evaluate
Performance
Location Types of Sample / Measurement Parameters / Analyses
Raw water Continuous monitoring Temperature
Continuous monitoring pH
Grab sample Alkalinity
Continuous monitoring Turbidity
Grab sample Colour
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Optimization Guidance Manual for Drinking Water Systems 2014
Table 6-1 – Coagulation/Flocculation – Recommended Monitoring to Evaluate
Performance (cont’d.)
Location Types of Sample / Measurement Parameters / Analyses
Flocculation
chambers/basins Visual observation Size and distribution of floc
Filtered or treated
water
Grab sample or continuous
monitoring
pH
Grab sample Alkalinity
Continuous monitoring Turbidity
Particle counts
Grab sample Colour
Grab sample Aluminum or Iron residual (depending
on the coagulant used)
Figure 6-1 presents a process schematic of a typical coagulation and flocculation process,
along with the identification of various sampling locations.
Raw Water
Sample Location
Raw Water
To Clarification or
Filtration
Coagulant
Addition with
Rapid Mixing
Coagulant Aid Addition
(if applicable)
with Rapid Mixing
Flocculation Basins
with Mechanical Mixing
Figure 6-1 – Coagulation/Flocculation – Process Schematic and Sampling Locations
The rapid mix/coagulation step can be achieved either in a separate process tank or by the use
of an in-line mixer. The detention period in the mixing zone should be minimized and limited
to no more than 30 seconds. Typically, a rapid mixing with a mixing intensity velocity
gradient, G value, in the order of 1000 s-1
is effective (MOE, 2008). G values can be
calculated using the formula presented in Appendix G.
The projection of flocculation basin capacity is based primarily on available hydraulic
detention time (HDT). The detention time required for adequate flocculation is highly
variable depending water temperature and downstream processes. When sedimentation is
CHAPTER 6. Coagulation and Flocculation 6-5
Optimization Guidance Manual for Drinking Water Systems 2014
included in the treatment process, HDTs of 25-30 minutes are usually sufficient in summer.
However, when water temperatures are less than 5°C, floc formation can be delayed. In these
instances, longer (30-40 minute) detention times may be required.
In assessing the adequacy of flocculation HDT, seasonal variations in flow should be
considered. Plant flows are generally lower in winter, but not always. In northern Ontario,
flows are often highest during winter when consumers allow their taps to run continuously to
avoid frozen service lines.
For direct filtration plants, detention times as low as 15 minutes may be adequate. Even
shorter times may be adequate for coagulation/flocculation for membrane filtration processes
or for in-line flocculation processes with high quality raw water sources. Because of these
variables, judgement should be used when assessing the required HDT of flocculation basins.
Jar testing can be used to obtain additional information on the HDT needed for adequate
flocculation.
In general, G values of 10 to 70 s-1
are needed for successful flocculation. Tapered
flocculation (reducing G in each stage) is desirable and is typically designed as three or four
sequential process tanks. Lower velocity gradients are required for the more fragile organic
floc than for flocculated suspended material (turbidity). Higher G values are needed for direct
filtration to produce denser pinpoint floc (MOE, 2008).
To permit flexibility of operation and for maintenance purposes, two separate parallel
flocculation tanks should be provided as a minimum. It is desirable to have at least two stages
per tank to prevent short-circuiting.
Since variable mixing energy and staging can often be added as “minor” modifications, these
items are not considered as significant in the capacity rating. If adequate basin volume is
available as determined during a CPE (e.g. typically a Type 1 DWS Component), a one-stage
flocculation basin may result in a Type 2 capability rating, and follow-up CTA activities
would be required to establish if added baffling or flocculator drives could improve
performance.
Criteria used to evaluate flocculation processes as part of the major DWS component
evaluation are presented in Table 6-2.
Table 6-2 – Flocculation – Criteria for Major DWS Component Evaluation Using the
Performance Potential Graph Rating System
Characteristic Typical Assessment Criteria
Hydraulic Detention Time (minutes) 15 – 40
Velocity Gradient (G), sec-1
10 – 70
Stages 2 – 3
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Optimization Guidance Manual for Drinking Water Systems 2014
6.2.4 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with coagulation and flocculation
are shown in Table 6-3.
Table 6-3 – Coagulation/Flocculation – Symptoms and Causes of Common Problems
Adapted from Water Treatment Plant Operation: Volume I (1999), California State University
Problem Description
Mitigation
Source water quality
changes
(Turbidity, colour,
temperature, pH,
alkalinity)
Poor floc formation
Over- or under-dosing of
coagulant chemicals
Increase in settled water
turbidity
Early turbidity
breakthrough and/or
significant change in
particle counts in
individual filter effluent
Elevated aluminum or iron
residual in treated water
Increase frequency of raw water and process
monitoring
Perform jar tests, if needed
Adjust coagulant dosage, alkalinity or pH
Add coagulant or filter aid
Adjust flash mixing/flocculator mixing
intensity1
Low raw water
temperature Lower rate of floc settling
Decrease in floc strength
(higher turbidity
breakthrough in filters)
Optimize coagulation pH
Adjust coagulant dosage
Consider addition of weighting agent to
increase floc density and/or other coagulant
aid to increase floc strength
Consider use of an alternative coagulant
Insufficient raw
water alkalinity Slow floc formation Increase raw water alkalinity by adding
lime, soda ash or other alkali
Low raw water
turbidity Slow floc formation Artificially increase raw water turbidity by
recycling sludge from sedimentation basins
or by adding weighting agent (e.g. bentonite
clay)
CHAPTER 6. Coagulation and Flocculation 6-7
Optimization Guidance Manual for Drinking Water Systems 2014
Table 6-3 – Coagulation/Flocculation – Symptoms and Causes of Common Problems
(cont’d.)
Adapted from Water Treatment Plant Operation: Volume I (1999), California State University
Problem Description
Mitigation
Poor floc formation
(size, dispersion,
strength)
Floc carryover from
sedimentation basins to
filters
Cloudy or foggy
appearance of water in
flocculation basins
Excessive sludge
production
Elevated aluminum or iron
residual in treated water
Increase frequency of raw water and process
monitoring
Perform jar tests and adjust chemical
dosages, if needed
Verify process performance: (a) check
chemical feed rates and pumps and (b) flash
mixer operation
Adjust flocculation mixing, if possible
Assess flocculation time based on operating
flow rate
Notes:
1. Very few treatment plants have provisions for adjusting the flash mixer. However, many
plants have variable-speed drives on flocculators to allow for adjustment of mixing intensity.
6.3 OPTIMIZATION TECHNIQUES
6.3.1 Jar Testing
Jar testing is the most common coagulant control and optimization technique. Jar tests may
be used for the following (AWWA, 1999):
Coagulant selection;
Coagulant dosage selection;
Coagulant aid selection;
Coagulant aid dosage selection;
Determination of need for alkalinity adjustment;
Determination of optimum pH;
Determination of point of addition of pH adjustment chemicals and coagulant aids;
Optimization of mixing energy and time for rapid mixing and slow mixing; and
Determination of optimum dilution of coagulant.
Jar tests can be set up to represent plant operating conditions by determining actual plant
theoretical mixing, flocculation and sedimentation detention times, and by setting jar test
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Optimization Guidance Manual for Drinking Water Systems 2014
mixing energy inputs, mixing times and settling times to values similar to those in the plant.
The jar test procedure should then be adjusted as necessary to obtain results similar to actual
plant operation. For example, if the apparent optimal dose in the plant is much greater than
indicated by jar tests, then mixing and flocculation conditions should be checked and
adjusted. The use of square jars rather than round graduated cylinders is recommended
because experience has shown that square jars are more representative of the geometry of
the flocculation tanks than round beakers or graduated cylinders. A jar testing apparatus is
shown in Figure 6-2.
Chemicals should be added to duplicate plant conditions. For example, if alum is added to the
flash mix and polymer is added to a pipeline 30 seconds later downstream from the flash mix,
the same sequence should be used in the jar test. The use of syringes without needles to
measure and deliver the appropriate chemical dose to each jar simplifies chemical addition.
Another essential part in the successful use of a jar test for coagulant control is the
interpretation of the test results. For direct filtration plants, a small volume (about 50 mL)
should be removed from the jars and passed through filter paper. Typically, a 5 or 8 µm filter
paper can be used to approximate filter performance (MWH, 2005). The filtered samples
should be tested for turbidity, colour, aluminum residual and other parameters of concern.
The sample that provides the optimum results for the combination of these parameters
represents the optimum dose.
Figure 6-2 – Jar Testing Apparatus
For conventional plants, the jar contents should be allowed to settle for a period of time
relative to the surface overflow rate of the basins. The sampling time, which is based on
particle settling velocity, can be determined using the formula presented in Appendix G
(USEPA, 1998).
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Optimization Guidance Manual for Drinking Water Systems 2014
After the correct sampling time is determined, samples should be drawn from a sample tap
located 10 cm from the top of the jar, and the turbidity, colour and aluminum or iron residual
of the sample should be determined. If sample taps are not available on the jars, pipettes can
be used to draw-off samples from the jars. Supernatant can be filtered using 5 or 8 micron
filter paper to approximate filtration.
Excellent references are available to guide the facilitator in implementing jar testing to
determine optimum coagulant doses (AWWA, 2007; Hudson, 1981).
Once the correct chemical dose is determined, the staff should be able to adjust the chemical
feeders to deliver the desired dosage. This requires the ability to conduct chemical
calculations and to develop and utilize calibration curves for chemical feeders. For example,
a concentration dose in mg/L has to be converted to a feed rate (e.g. kg/day or mL/min) in
order to correctly adjust chemical feed equipment. Calibration curves, which indicate feed
rate setting versus feeder output, should be developed for all chemical feeders to ensure the
correct feeder setting for a desired chemical dosage.
Some chemicals, such as polymers, must often be prepared in dilute solutions prior to
introduction into the plant flow stream. Therefore, the capability to prepare chemical
dilutions should be transferred to the operators during a CTA.
The chemical dose should not only be carefully controlled, but the correct type of coagulants,
flocculants and filter aids should also be applied.
Typically, a metal salt (alum or iron based coagulants) and polymer should be added
in the coagulation zone prior to flocculation. The metal salt should always be added
to the rapid mix; however, the addition point of the polymer, which may be before,
after, or into the rapid mix, should be determined on a site-specific basis by
conducting a special study.
If alum is being utilized with a raw water pH exceeding 8.0 to 8.5, consideration
should be given to switching to iron salts or polyaluminum chloride, the use of pH
depressing chemicals, or acidified alum.
The use of a polymer to enhance floc formation and settling can also be investigated.
Investigation of filter aid polymers should be conducted since these aids may be
required if filtered water turbidities less than 0.1 NTU are to be achieved on a
continuous basis. These products should be introduced into the plant flow stream at a
point of gentle mixing since excessive turbulence will shear the polymer chains and
make the product ineffective.
For low alkalinity water (e.g. less than 20 mg/L), consideration should be given to
adding alkalinity (e.g. soda ash, lime).
Competing chemicals should not be added at the same location. For example, the addition of
lime and alum at the same point is counterproductive if the lime is raising the pH to the
extent that the optimum range for alum coagulation is exceeded.
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Optimization Guidance Manual for Drinking Water Systems 2014
6.3.2 Zeta Potential
Zeta potential (zp) is a measure of the excess number of electrons found on the surface of
particulate matter (AWWA, 2005). It can be measured by a zeta meter, and its value
determines the extent of the electrostatic forces of repulsion between charged particles. The
zp of particles in natural water are typically -20 to -40 mV (AWWA, 1999). Suspensions that
are well destabilized (likely to flocculate) by the charge neutralization mechanism following
coagulant addition have a zp close to zero. The zp is not a reliable predictor of optimum
sweep coagulation.
For plant optimization, the zp of coagulated particles after the rapid mixing or slow mixing
operation in jar tests are measured. For conventional treatment, the zp after the rapid mixing
is preferred. The optimum coagulant dosage is determined when the zp of the charge-
neutralized particles is close to zero.
6.3.3 Streaming Current Detectors
A streaming current monitor is an instrument that passes a continuous sample of coagulated
water past a streaming current detector (SCD). The detector produces a continuous readout of
the measurement of the net ionic and colloidal surface charge in the sample. Comparison
between zeta potential and SCD data indicate that a strong correlation exists between these
measurements and that either one is suitable for determination of charge neutralization
(AWWA, 1999).
The optimal SCD reading varies with source water pH; changes in pH therefore require
different SCD goal readings. The potential advantage of the SCD compared to zp is that it
provides continuous monitoring for coagulation control and may be used for automatic
control of coagulant dosage if the pH remains constant (AWWA, 1995).
6.3.4 Particle Counters
There is increasing interest in optimizing the coagulation/flocculation/filtration process to
ensure removal of Cryptosporidium and Giardia lamblia cysts. The only practical real-time
or on-line method to determine the presence of cysts in water at this time is to monitor the
size and concentration of minute particles in the finished water (AWWA, 1995). Turbidity
measurement is inadequate for this task because the concentration of cysts considered
undesirable is well below the normal range that can be indicated in turbidity tests; in addition,
turbidity tests give no indication of particle size.
In addition, for drinking water systems that are able to achieve filtered water turbidities of
less than 0.1 NTU, turbidity measurements may not be responsive to small changes in
coagulant dosage. In this instance, the number of particles larger than 2 µm per mL in filtered
water has proved sensitive to minor variations in coagulant dosage to optimize filter
operating conditions. As such, total cumulative particle counts (NP ≥ 2.0 µm/mL) portrayed
as percentile or probability plots can be used in optimization studies as an indicator of plant
performance (Hargesheimer et. al., 1998).
6.3.5 Residual Aluminum Control
One of the reasons for using zeta potential or SCD measurements is to avoid overdosing
alum-based coagulants and therefore minimize the residual aluminum in the finished water.
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Optimization Guidance Manual for Drinking Water Systems 2014
The most common strategy to reduce residual aluminum levels in treated water is the
adjustment of pH to 6.0, close to the minimum solubility of aluminum (AWWA, 1999).
Other effective strategies for reduction of total aluminum residuals are:
Use of alternative coagulants (such as polyaluminum chloride or iron-based
coagulants);
Reduction of alum dosage by alum-polymer combinations, keeping in mind that
either too high or too low an alum dosage can increase residual aluminum levels; and
Optimized removal of floc during filtration.
6.3.6 Optimizing Residence Time in Flocculators
As discussed in Section 6.2.3, residence time in flocculators has a direct impact on plant
performance. Too little and too much mixing can have a detrimental effect on sedimentation
performance (Hudson, 1975). Key residence time characteristics of flocculation basins
include plug flow, mixed flow and dead space. Other factors that contribute to performance
problems include back-mixing and process recirculation.
Means for evaluating and optimizing detention time and mixing, such as tracer testing, stress
testing and hydraulic modelling, are discussed in Chapter 4. Other strategies, such as
reducing plant flow rate, improving mixing and providing baffles, are discussed below.
6.3.6.1 Controlling Plant Flow Rate
Plant flow rate is a primary means for process control at many small plants that are operated
for less than 24 hours each day. At these plants, an excessive hydraulic loading rate on the
flocculation process can be avoided by operating at a lower flow rate for a longer period of
time. This provides an option to meet more rigorous performance requirements with existing
units without major capital improvements. The capability to improve plant performance by
reducing the plant flow rate is offset by the need to staff the plant for longer periods of time,
which adds to operating costs. Therefore, plant administrators, in conjunction with the CTA
facilitator, should evaluate both options.
Adequate time for chemical reaction is typically more important in water with temperatures
below 5°C, and this time can often be extended operationally by reducing plant flow.
6.3.6.2 Mixing Intensity, Patterns and Time
In general, experience has shown that improvements in flocculation performance can be
obtained by using compartmentalization (e.g. three or four cells in a flocculator) and tapering
the velocity gradients from a G value of 40 to 60 s-1
in the first cell down to 15 to 25 s-1
in the
last cell (AWWA, 1999). The higher G values are needed to produce high-density floc
quickly, while the lower G values are needed to prevent settling of floc in the flocculator.
In addition, the dimensionless parameter Gt (mixing intensity multiplied by retention time in
the floc tank) can be used to represent the degree of flocculation. In general, Gt values
ranging from 104 to 10
5 are recommended (AWWA, 1999).
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Optimization Guidance Manual for Drinking Water Systems 2014
Optimum G and Gt values are best determined by pilot studies and/or full scale trials. Jar
testing does not always involve back-mixing, which is typical for flocculation processes, and
is therefore a limited guide for optimization of flocculation mixing (MOE, 2008).
Flocculation energy input is often fixed at small plants, either by hydraulic flocculation
systems or by constant speed flocculation drives. However, flocculation energy, if low
enough to allow formation of settleable floc, is not considered an essential variable to achieve
desired performance of a small plant. More important are the plug flow characteristics of the
flocculation system. Plug flow characteristics, similar to those found in most hydraulic
flocculation systems, result in the formation of floc particles of uniform size, which greatly
aids settleability. As such, greater priority may be placed on installing baffling in flocculation
systems rather than trying to optimize mixing energies.
6.3.6.3 Baffling
For horizontal flow flocculators, mixing by hydraulic means can be possible by installing
vertical baffles arranged for over-and-under or around-the-end flow patterns. The baffles
cause hydraulic head loss or energy dissipation, which are associated with velocity gradients
in the liquid stream, and minimize the amount of mechanical equipment used for flocculation.
Typical designs use 0.25 to 0.40 m/s for the horizontal velocity of flow (AWWA, 1999).
6.4 CASE HISTORIES
6.4.1 Regional Municipality of Waterloo – Mannheim WTP
The following case study is based on information presented in DeWolfe et. al. (2003).
System Description
The Mannheim Water Treatment Plant (WTP), located in Kitchener, Ontario, treats
approximately 72 ML/d (19 mgd). There are two identical treatment trains, each able to treat
approximately 36 ML/d (9.5 mgd). Raw water is drawn from the Grand River into a pre-
sedimentation reservoir.
Treatment begins with flash mix in-line blenders, where the coagulation chemicals are added.
Coagulation is followed by two-stage flocculation, where the coagulant aid (polymer) is
added in the second stage, stirred by mechanical paddle wheels. Sedimentation takes place by
discrete settling in lamella plate settlers to achieve a settled water turbidity goal of less than 1
NTU. Ozonation then takes place for primary disinfection, taste and odour control, and
colour removal. There are four gravity filters, two granular activated carbon (GAC) and two
dual media (anthracite/sand), operated at a fixed flow rate to maintain the plant flow rate
during backwashing of a filter. Chlorination takes place to maintain chlorine residual in two
30 ML (8 Mgal) clearwells. A higher chlorine dose is required in the winter when high raw
water ammonia concentrations are experienced. Treated water is then pumped into a 5-cell
580 ML (153 Mgal) reservoir where the water is blended with groundwater, chloraminated at
the reservoir inlet, and finally pumped through the distribution system.
Coagulant Testing Facilities and Strategies
The Mannheim WTP was using alum for coagulation, but was having difficulties achieving
low settled water turbidity during cold water conditions, decreasing filter run times and
CHAPTER 6. Coagulation and Flocculation 6-13
Optimization Guidance Manual for Drinking Water Systems 2014
increasing the frequency of backwashing. The Region identified the chemical coagulant
vendors in their area and invited each of them to jar test their products at the plant. They
initially compared each candidate coagulant’s performance to the performance of alum in
terms of turbidity removal. Any coagulant that did not perform as well as alum was not
considered further. Additional jar testing was conducted to determine the optimum dose of
each product, then all products at their optimum doses were compared simultaneously
through jar testing. After one product was selected as the best alternative, a full scale plant
trial confirmed that this product would perform as desired.
Six candidate coagulants, in addition to alum, were evaluated through extensive jar testing at
the Mannheim WTP. Characteristics of these products are shown in Table 6-4.
Table 6-4 – Initial Coagulant Comparison – Mannheim WTP
Coagulant Strength
(%)
Estimated
Cost
($/dry ton)
Freezing
Point
(°C)
Dosage
(dry mg/L)
Water Treatment
Residual (WTR)
(kg/kg coagulant)
Alum 48.5 211 -15 40-45 0.44
PACl-11
33 1,242 -12 15-20 0.80
PACl-21 33 1,373 -12 15-20 0.83
PACl-31 43 2,212 -11 15-20 1.20
PASS2
34 868 < 0 18-21 0.66
Ferric chloride 27 458 -35 40-45 0.083
Ferric sulphate 44 513 -35 NA NA
Notes:
1. Polyaluminum chloride (PACl). Trade names are not identified. PACl from different vendors
are identified as 1, 2 and 3.
2. Polyaluminum silicate sulphate (PASS).
3. This data point appears to be inconsistent with the other values; however, it was reproduced
as per the original case study (DeWolfe et. al., 2003).
NA - not available.
The jar testing protocol that was used was as follows:
1. Measure raw water temperature, turbidity, true and apparent colour, dissolved
organic carbon (DOC) and pH.
2. Add raw water to 2-litre jars in water bath maintained at ambient temperature.
3. Add full strength coagulant at desired dosage to 2-litre jars.
4. Rapid mix at 300 revolutions per minute (rpm) for 1 minute.
CHAPTER 6. Coagulation and Flocculation 6-14
Optimization Guidance Manual for Drinking Water Systems 2014
5. Add 0.01% polymer at desired dose to 2-litre jars.
6. Mix for 1 minute at 100 rpm.
7. Continue mixing at 15 rpm for 15 minutes.
8. Record speed of floc formation, size, colour and density of floc.
9. Stop mixing, settle floc for 7 minutes, and record observations.
10. Take water samples at mid-point of beakers using a pipette.
11. Measure final turbidity, apparent colour, true colour and pH, in that order.
12. Filter samples for DOC measurement.
13. Record results.
It is noteworthy that flocculation and settling times used in jar testing were one half the full-
scale values at the WTP’s maximum flow rate.
From the initial screening, ferric sulphate did not perform better than alum, but it was
included in subsequent jar testing. The optimum doses of each of the coagulants and alum are
shown in Table 6-5. The typical alum dose used was 35 to 45 mg/L (dry weight as alum), and
all three PACl products were effective at dosages less than half (18 mg/L dry weight as alum)
that needed with alum. The performance of all three PACl products was comparable. There
was slightly better colour and DOC removal using PACl-3. Ferric chloride did not perform
well at the dose recommended by the vendor, but it did perform well at twice the originally
recommended dosage. PASS did not perform as well as any of the three PACl coagulants. A
higher PASS dose of 21 mg/L (dry weight) was necessary to achieve the desired settled
turbidity of less than 1 NTU.
CHAPTER 6. Coagulation and Flocculation 6-15
Optimization Guidance Manual for Drinking Water Systems 2014
Table 6-5 – Summary of Optimum Coagulant Doses and Jar Test Results –
Mannheim WTP
Parameter Alum PACl-1
PACl-2 PACl-3 PASS Ferric
chloride
Coagulant dose
(mg/L) 35-45 18 18 18 21 45
Polymer dose
(mg/L) 0.075 0.075 0.075 0.075 0.075 0.075
Final turbidity
(NTU) > 2 0.53 0.47 0.57 0.84 0.92
Final pH NA 7.96 7.93 7.97 8.05 7.42
Final true
colour NA 9 10 5 11 8
Final apparent
colour NA 16 14 11 17 24
Final DOC
(mg/L) NA 4.7 4.9 4.2 NA 3.4
Notes:
1. NA - not available.
Table 6-6 summarizes the coagulant comparison for the Mannheim WTP, including the
water treatment residual (WTR) generation rates (in kg per million litres of treated
water). The approximate amount of solids generated by each coagulant was an
important evaluation criterion.
PACl-1 and PACl-2 both generated about 20 percent less WTR than alum. PACl-3
generated 8 percent more WTR than alum. PASS generated the least amount of WTR.
Ferric chloride produced the greatest amount of WTR, due to the high dose required (45
mg/L). WTR generation was estimated from the dry weight of total solids, raw water
solids and polymer solids left in the jar, using the equation shown below:
TS – RWS – PS = CS
where:
TS = total solids in jar in mg (dry weight)
RWS = raw water solids in jar in mg (dry weight)
PS = polymer solids in jar in mg (dry weight)
CS = coagulant solids in jar in mg (dry weight)
CHAPTER 6. Coagulation and Flocculation 6-16
Optimization Guidance Manual for Drinking Water Systems 2014
For example, using an 18 mg/L dose of PACl-1 in a 2-litre jar test volume, TS was 17.5 mg,
RWS was 3.55 mg and PS was 0.075 mg. This produced an estimated quantity of CS of 13.88
mg (17.5 – 3.55 – 0.075 = 13.88).
Table 6-6 – Summary of Coagulant Comparison – Mannheim WTP
Coagulant Performance
Optimum
Dose
(mg/L)
Cost
($/ML)
Residuals
(kg/ML)
Alum High settled water
turbidity 42 0.62 1.29
PACl-1
Low settled water turbidity 18 1.56 1.00
PACl-2 Low settled water turbidity 18 1.72 1.04
PACl-3 Low settled water
turbidity; slightly better
DOC and colour removal
18 2.76 1.51
PASS Low settled water turbidity 21 1.27 0.97
Ferric chloride Low settled water
turbidity; slightly better
DOC and colour removal
45 1.44 2.51
Summary
From extensive jar testing, the Region was able to identify one coagulant from a number of
candidates as the one most suited to their unique water treatment characteristics. PACl-1
performed better than alum in cold water and provided treatment equal to or better than other
candidate coagulants. At an optimal dosage of 18 mg/L, PACl-1 produced less WTR than
alum and equal to or less than other candidates. Ferric chloride also yielded low turbidity
values, but the high doses required produced considerably more residuals than PACl-1. All
candidate coagulants did cost more than alum, but with the exception of the ferric sulphate,
their performance was far superior to alum in the cold water.
While the cost of the selected coagulant was greater than alum, the improved treatment
performance documented in the jar testing and plant scale trial, which leads to a more robust
treatment and therefore barrier, justify its use as the primary coagulant during cold water
conditions.
6.4.2 City of Owen Sound – R.H. Neath WTP
The following case study is based on information presented in XCG (1999).
CHAPTER 6. Coagulation and Flocculation 6-17
Optimization Guidance Manual for Drinking Water Systems 2014
System Description
The R.H. Neath WTP is a direct filtration plant with the following unit process components:
pre-chlorination for seasonal zebra mussel control, coagulant addition (polyaluminum
chloride) and flash mixing, flocculation, filtration, post-chlorination for disinfection and
fluoridation. The R.H. Neath WTP contains two water treatment trains. Each treatment train
is equipped with similar unit process components, but convey separate flow streams
according to equipment on line, demand and their individual rated capacities.
Coagulant Testing Facilities and Strategies
PACl is used year round at the R.H. Neath WTP for coagulation. The average PACl dosage
for period from 1993 to 1995 was 1.02 mg/L as Al (or 6.30 mg/L as PACl). Typically,
coagulant dosages range from 0.2 to 1.0 mg/L as Al for direct filtration facilities using alum.
Therefore, the average PACl dosage at the facility over the historic period was at the high end
of the typical range for direct filtration facilities.
The PACl is added to the raw water at the rapid mix tanks where turbine mixers evenly
distribute the coagulant throughout the flow. Theoretically determined mixing intensities, G
values, have indicated that the rapid mixer is providing between 335 to 387 s-1
in Plant 1 and
between 386 to 446 s-1
in Plant 2 over the temperature range from 5 to 15C. The typical
design value at the time (MOE, 1982) recommended a G value at around 1,000 s-1
.
To identify the optimum conditions for coagulation for the R.H. Neath WTP, a bench scale
investigation consisting of jar testing was developed. The objective was to identify the
optimum coagulant, coagulant aid, pH, and dosages to minimize the filtered water turbidity,
soluble aluminum residual and solids production.
Jar testing was conducted using alum, PACl and ferric chloride, with and without pH
adjustment. The optimum coagulant and dosage with pH adjustment was then tested to
determine if a coagulant aid polymer would provide any additional benefit. Jar testing should
normally be performed to mimic the mixing velocity gradients and retention times in the
rapid mix and flocculation mix tanks. However, the jar testing equipment at the plant could
not attain the impeller speeds required and therefore, 2 minutes of rapid mix at 100 rpm and
30 minutes of flocculation mix at 25 rpm were used.
The results of the jar testing indicated that:
Alum and PACl performed well on their own, with slightly higher than target
aluminum residuals;
pH adjustment to lower levels (7.0 and 6.5) resulted in a decrease in the aluminum
residuals for both alum and PACl;
Ferric chloride performed well with respect to filtered water turbidity at dosages
greater than 1 mg/L as Fe, but produced more solids than alum or PACl for
comparable turbidity results; and
No additional benefit was observed with addition of coagulant aid polymer.
CHAPTER 6. Coagulation and Flocculation 6-18
Optimization Guidance Manual for Drinking Water Systems 2014
Two full scale trials using acidified alum were conducted at the plant. The primary purpose
of these trials was to compare the performance of acidified alum and PACl on the finished
water aluminum residual concentration. The results of the trials indicated that the use of
acidified alum resulted in a lower average aluminum residual, but that the water treated with
PACl had an average filtered water turbidity lower than the water treated with acidified alum.
Bench Scale Evaluation of Rapid Mixing Intensity
The rapid mixing intensity applied at the facility was less than half that recommended by the
MOE Design Guidelines. Bench scale testing, while showing some small differences in
treated water turbidity, was inconclusive. It was recommended that, if the issue of uniform
coagulant dispersion arises in the future, pilot scale testing be conducted to evaluate the
impacts of increasing the rapid mixing intensity on the finished water quality.
Streaming Current Monitors for Process Control
Two streaming current monitors (SCM), installed in one flocculation tank of each plant train,
were not being used for operational control. To determine how the SCM could be applied to
operating practices, a desktop evaluation of the accumulated historical data was performed.
The data review indicated that the SCM output signal correlated to the raw water turbidity.
No other significant correlation to either raw water parameters or operating variables was
observed. It was recommended that a program be developed to familiarize facility staff with
adjusting the coagulant dose using the SCM and to incorporate the use of the SCM into
everyday operations; ultimately, the SCM could be used to automatically control coagulant
dosing.
Bench Scale Evaluation of Flocculation Mixing Intensity
The first phase of the study had looked at the mixing intensities, G values, being provided by
the mixing equipment in the flocculation tanks in each of the plant trains. The calculated G-
values ranged from 84 to 101 s-1
, which is typical of mixing intensities recommended for
direct filtration plants. The Gt values (mixing intensity multiplied by retention time in the
floc tank) were also determined for both the current average day flow of 10,260 m3/d and the
plant design flow of 60,480 m3/d. At the current average day flow, the Gt values were
extremely high, ranging from 884,394 to 1,020,875 in Plant 1 and from 510,104 to 588,823 in
Plant 2 depending on the water temperature. The recommended design value at the time for
Gt for flocculation was between 50,000 and 125,000 (MOE, 1982).
To determine if the flocculation mixing intensity was affecting the finished water quality, a
bench scale investigation consisting of a jar test was performed. The jar test performed
involved adding equal amounts of coagulant to two jars, providing equal rapid mix intensity
and time, followed by providing 20 minutes or 2 hours of flocculation time. The treated water
was then filtered and tested for turbidity and aluminum residual.
The results obtained showed a large increase in filtered soluble aluminum residual with the
increase in flocculation time. These retention times were sometimes experienced in the plant.
The long retention time may be breaking up the floc causing it to resolubilize.
CHAPTER 6. Coagulation and Flocculation 6-19
Optimization Guidance Manual for Drinking Water Systems 2014
Summary
In this case study, jar testing was successful for evaluating coagulant chemicals and dosages;
however, bench-scale testing of the rapid mix was inconclusive and experiments with
flocculation mixing could not be repeated at full-scale conditions. To further improve facility
performance, the construction of a pilot plant was recommended for optimizing coagulant
dosages on an on-going basis. A pilot plant could also be used to investigate the effects of
flocculation mixing intensity and duration on finished water quality, as well as investigate
treatment options for other operational problems identified during the study.
6.5 REFERENCES
American Water Works Association (1995). Water Treatment, 2nd
Ed. AWWA. ISBN 0-
89867-789-0.
AWWA (1999). Water Quality and Treatment: A Handbook of Community Water Supplies,
5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
AWWA (2007). M37: Operational Control of Coagulation and Filtration Processes. 2nd
Ed.
AWWA. ISBN 978-1-58321-055-0.
California State University (1999). Water Treatment Plant Operation: Volume I. 4th Ed.
DeWolfe, J., B. Dempsey, M. Taylor and J.W. Potter (2003). Guidance Manual for
Coagulant Changeover. AwwaRF & AWWA. Denver, CO. ISBN 1-58321-289-2.
Hargesheimer, E.E., N.E. McTigue, J.L. Mielke, P. Yee, and T. Elford (1998). Tracking
Filter Performance with Particle Counting. Journal AWWA, Vol. 90 No. 12. December
1998.
Hudson, H.E., Jr. (1975). Residence Times in Pretreatment. Journal AWWA, Vol. 67, No. 1.
January 1975.
Hudson, H.E. Jr. (1981). Water Clarification Processes: Practical Design and Evaluation.
Van Nostrand Reinhold Co. ISBN 9780442244903.
MOE (1982). Guidelines for the Design of Water Treatment Works. Publications Ontario.
ISBN 0-7778-4878-3.
MOE (2008). Design Guidelines for Drinking Water Systems, 2008. ISBN 978-1-4249-8517-
3.
MOEE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process
Audits.
MWH (2005). Water Treatment Principles and Design. 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
Teefy, S.M. (1996). Tracer Studies in Water Treatment Facilities: A Protocol and Case
Studies. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-857-9.
CHAPTER 6. Coagulation and Flocculation 6-20
Optimization Guidance Manual for Drinking Water Systems 2014
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program, EPA/625/6-91-027.
XCG Consultants Ltd. (1999). Report for R. H. Neath WPP Optimization Practices
Study, prepared for Owen Sound Public Utilities Commission.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 7CLARIFICATION
CLARIFICATION
7.1 Introduction ............................................................................................................ 7-1
7.2 Clarification ............................................................................................................ 7-1
7.2.1 Purpose and Types of Clarification ......................................................... 7-1
7.2.2 Evaluating Performance ........................................................................... 7-2
7.2.3 Common Problems and Potential Impacts ............................................... 7-5
7.3 Optimization Techniques ....................................................................................... 7-6
7.3.1 Optimizing Flow Arrangements .............................................................. 7-6
7.3.2 Controlling Plant Flow Rate .................................................................... 7-7
7.3.3 Optimizing Sludge Removal .................................................................... 7-7
7.3.4 Tracer Testing .......................................................................................... 7-7
7.3.5 Stress Testing ........................................................................................... 7-8
7.4 Case Histories ......................................................................................................... 7-8
7.4.1 Town of Slave Lake, Alberta – Optimization and Upgrading Study ....... 7-8
7.4.2 Newport News, Virginia – Sludge Control Study ................................... 7-9
7.5 References ............................................................................................................ 7-11
CHAPTER 7. Clarification 7-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 7
CLARIFICATION
7.1 INTRODUCTION
Clarification is the process used to remove suspended solids following coagulation and
flocculation and reduce solids loading on subsequent filtration processes. This can be
achieved by gravity sedimentation or flotation. Clarification is also used to remove the
chemical precipitates formed during the lime-soda softening process.
This chapter describes different types of sedimentation basins or clarifiers. It also provides
information about methods that can be used to evaluate and improve process performance.
Optimization of the sedimentation process can involve modifying flow control structures
(such as effluent weirs or baffles within the clarifiers) and operational practices (such as
sludge removal frequency or coagulant chemical dosage) to improve performance with
respect to solids removal.
7.2 CLARIFICATION
7.2.1 Purpose and Types of Clarification
As noted above, the purpose of the clarification process is to reduce the solids loading onto
the filtration processes which follow. Clarification processes can be categorized into the
following general types.
Horizontal flow sedimentation basins are generally classified as either rectangular or
circular centre-feed types. They are typically large concrete or steel basins, designed to keep
the velocity and flow distribution as uniform as possible. A diagram of a typical
sedimentation tank is shown in Figure 7-1.
Figure 7-1 – Typical Horizontal Flow Sedimentation Basin
CHAPTER 7. Clarification 7-2
Optimization Guidance Manual for Drinking Water Systems 2014
Upflow reactor and sludge blanket clarifiers include several types of solids contact units,
such as simple upflow sludge blanket clarifiers, pulsed upflow sludge blanket clarifiers, and
reactor clarifiers. These units combine coagulation, flocculation and clarification in a single
unit. They generally allow the controlled removal of solids and are usually proprietary
designs. The advantages of the solids-contact clarifier include a good turbidity removal in a
compact and economical design. The disadvantages are that they are sensitive to changes in
flow and temperature, and time is required to build up the necessary sludge blanket. They
also have relatively high maintenance costs and require greater operator skill than for simple
sedimentation basins.
Adsorption clarifiers combine coagulation, flocculation and clarification processes in a
single upflow clarifier. Coagulant is added to the raw water, which enters at the bottom of the
unit and passes through a bed of plastic media that floats on the surface of the water. The
solids adhere to the media, which results in relatively high removal rates (AWWA, 1995).
The media must be cleaned when the solids accumulation results in excessive head loss, or
when effluent quality becomes unacceptable.
Dissolved air flotation (DAF) is a process in which dissolved gases under pressure are
released as micro-bubbles and attach to solid particles causing them to rise to the surface
rather than settle. The sludge that accumulates on the surface is called “float”, and must be
removed either by flooding the basin to overflow the float or by mechanical scraping.
Sand-ballasted flocculation-sedimentation or high-rate microsand sedimentation involves
the addition of ballast (usually microsand) that attaches to the floc and increases the settling
velocity of the floc by increasing its density. These are proprietary systems that have surface
loading rates that are several times greater than those used for conventional sedimentation
basins.
Inclined plates or tube settlers can be used with rectangular and circular sedimentation
basins and are designed to increase settling efficiency. These types of equipment provide a
high ratio of effective settling surface area per unit volume of water and reduce the distance
that floc have to fall. Settled particles collect on the inside surfaces of the tubes or plates, and
slide down the surface to settle at the bottom of the tank.
Additional information regarding the design of clarification processes is provided elsewhere
(MOE, 2008; MWH, 2005; AWWA, 1995).
7.2.2 Evaluating Performance
In conventional surface water treatment plants, clarification is one of the multiple barriers
normally provided to reduce the potential of turbidity and microorganisms to pass through the
treatment process and into the distribution system. The performance of the clarification
process is assessed based on achieving a settled water turbidity of less than 1 NTU 95 percent
of the time when the average raw water turbidity is less than or equal to 10 NTU, and less
than 2 NTU 95 percent of the time when the average raw water turbidity exceeds 10 NTU
(USEPA, 1998).
Criteria to be used to evaluate clarification processes as part of the major DWS component
evaluation are shown in Table 7-1. The projection of sedimentation basin capacity is
primarily based on surface overflow rate (SOR), with consideration given for depth and
sludge removal characteristics. Greater depths generally result in more quiescent conditions
CHAPTER 7. Clarification 7-3
Optimization Guidance Manual for Drinking Water Systems 2014
and allow higher SORs to be used. Sludge removal mechanisms should also be considered
when establishing an SOR for projecting sedimentation capability. If sludge is manually
removed from the sedimentation basin(s), additional depth is required to allow volume for
sludge storage and the selected SOR should therefore be lowered.
In cases where flocculated colour (i.e. a lightweight floc) and/or low water temperatures are
encountered, the projected capacity should be based on the lower SORs in Table 7-1. Criteria
are shown for rectangular and upflow solids contact units with or without tube settlers.
Table 7-1 – Clarification – Criteria for Major DWS Component Evaluation Using the
Performance Potential Graph Rating System
Conventional (circular and rectangular) and Solids Contact Units (Cold Water < 5°C)
Conventional
Depth (m)
Solids
Contact
Depth (m)
Operating Mode
Turbidity Removal
SOR (m/h)
Softening
SOR (m/h)
Colour Removal
SOR (m/h)
3.0 3.7 – 4.3 1.2 1.2 0.7
3.7 – 4.3 4.3 – 4.9 1.5 1.8 1.0
> 4.3 > 4.9 1.7 2.4 1.2
Conventional (circular and rectangular) and Solids Contact Units with Vertical (> 45°)
Tube Settlers
Depth (m)
Operating Mode
Turbidity Removal
SOR (m/h)
Softening
SOR (m/h)
Colour Removal
SOR (m/h)
3.0 2.4 3.7 1.2
3.7 – 4.3 3.7 4.9 1.8
Higher SORs than those shown in Table 7-1 can be used to project capacity in cases where
plant data demonstrate that a sedimentation basin achieves the desired settled water turbidity
performance goals at the higher loading rates.
Loading rates for projecting performance potential of other settling processes are discussed
briefly below (MOE, 2008).
Dissolved Air Flotation – The retention time and loading rates for DAF units largely
depends on the water being treated, the nature of the contaminant being removed, the
coagulants used and the design of the DAF process. Traditional loading rates have been in the
10 to 12 m/h range; however, higher loading rates, up to 29 m/h, can be used if confirmed
through appropriate pilot testing.
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Optimization Guidance Manual for Drinking Water Systems 2014
Ballasted Flocculation and Clarification – Typical surface loading rates are 35 to 73 m/h.
A specific combination of chemicals may be needed for effective treatment depending on raw
water characteristics.
Adsorption Clarifiers – These systems are proprietary; SORs are in the range of 19.5 to 25.5
m/h.
Table 7-2 presents monitoring recommended, in terms of sampling locations and analyses, in
order to evaluate the performance of the clarification process.
Table 7-2 – Clarification – Recommended Monitoring to Evaluate Performance
Location Types of Sample / Measurement Parameters / Analyses
Raw water Continuous monitoring Temperature
Turbidity
Influent to
Clarification
Continuous monitoring Flow rate
Grab sample Turbidity
Alkalinity
Effluent from
Clarification
Continuous monitoring or Grab sample Turbidity
Process waste
stream (settled
sludge)
Continuous monitoring or Grab sample Flow or volume
Total suspended solids
Chlorine residual (if applicable)
Additional monitoring may be required for proprietary systems; the evaluator should review
manufacturer’s literature for recommended process monitoring parameters.
Figure 7-2 presents a process schematic of a typical clarification process, along with the
identification of various sampling locations.
From Coagulation /
FlocculationClarifier Effluent
Clarifier Blowdown
(settled sludge)
Clarifier Influent
Sample Location
Clarification Effluent
Sample Location
Sludge Sample Location
Clarifier
Figure 7-2 – Clarification – Process Schematic and Sampling Locations
CHAPTER 7. Clarification 7-5
Optimization Guidance Manual for Drinking Water Systems 2014
In addition to the recommended sample locations and analyses presented in Table 7-2,
consideration should also be given to the performance of coagulation and flocculation (see
Chapter 6) when evaluating the performance of clarification processes.
7.2.3 Common Problems and Potential Impacts
A summary of symptoms and causes of common problems encountered with clarification
processes is presented in Table 7-3.
Table 7-3 – Clarification – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Impacts
Common Causes
Uneven flow
distribution between
clarifiers
Some clarifiers are overloaded,
potentially resulting in poor
effluent quality due to limited
settling.
Other clarifiers are underloaded,
potentially resulting in stagnant,
septic conditions, reducing effluent
quality due to resuspension of
sludge and/or causing tastes and
odours.
Uneven rate of effluent flow
between clarifiers visible in
effluent launders.
Uneven clarifier weir levels.
Different clarifier weir lengths.
Poor hydraulics of upstream flow
control devices.
Hydraulic short-
circuiting within
clarifiers
Increased clarifier effluent
turbidity.
Regions of high flow and poor
settling within clarifier.
Erratic clarifier performance.
Poor design of inlet structures and
in-clarifier baffling (Section 7.3.1).
Density currents due to temperature
gradients, and/or wind-driven
circulation cells (Section 7.3.1).
Long sludge
retention time Deep sludge blanket, resulting in
increased effluent turbidity due to
floc carryover, especially during
periods of increased demand (high
flow).
Development of septic sludge,
reducing effluent quality and
potentially causing taste and odour
problems.
Poor control of sludge pumping
(Section 7.3.3).
CHAPTER 7. Clarification 7-6
Optimization Guidance Manual for Drinking Water Systems 2014
Table 7-3 – Clarification – Symptoms and Causes of Common Problems (cont’d.)
Problem Common Symptoms and
Potential Impacts
Common Causes
Short sludge
retention time Low sludge solids concentration,
resulting in increased hydraulic
loading on residuals handling
processes.
Little to no sludge blanket.
Poor solids removal performance.
Poor control of sludge pumping
(Section 7.3.3).
Poor clarification
performance not
attributable to
problems identified
above
Removal efficiencies below typical
removal rates, resulting in poor
effluent quality.
Changes to raw water quality (e.g.
cold water temperatures leading to
reduced settling rates).
Floc carryover due to poor
coagulation/flocculation
performance (Chapter 6).
Clarification process hydraulically
overloaded as a result of operating
at flows exceeding design values.
7.3 OPTIMIZATION TECHNIQUES
7.3.1 Optimizing Flow Arrangements
Short-circuiting occurs when water bypasses the normal flow path through the basin and
reaches the outlet in less than the design detention time.
Inlets and outlets should be designed to ensure that water is distributed evenly across the
clarifier/settling tank at uniform velocities to minimize short-circuiting.
In horizontal-flow basins where problems with flow distribution have been identified, baffles
may be installed at the inlet and outlet to improve flow conditions. In evaluating different
inlet baffling methods, consideration should be given to:
The number of ports provided;
The distribution of the ports (e.g. uniform distribution of flow across the baffle wall)
Head loss through the ports; and
The potential for floc breakage across the baffle wall.
Density currents caused by changes in water temperature, wind effects, and solids
concentrations should also be minimized to prevent short-circuiting. The provision of a cover
or structure over the sedimentation basin can reduce the impact of the sun and wind on
settling efficiency. Installation of baffles or diffuser walls can promote mixing of the density
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Optimization Guidance Manual for Drinking Water Systems 2014
current with the ambient water, improving the flow distribution in the tank and the efficiency
of hydraulic performance (MWH, 2005).
Hydraulic modelling packages (e.g. computational fluid dynamics) can be used to evaluate
existing in-tank hydraulics (see Chapter 4). Calibrated models can then be used to project the
impact of inlet and outlet structure upgrades or modifications on sedimentation performance.
Tracer testing can be used to support hydraulic modelling to evaluate hydraulic conditions.
After modifications are implemented, tracer testing can also be used to verify the impact of
these changes on hydraulic performance (see Chapter 4).
7.3.2 Controlling Plant Flow Rate
In many small plants that are operated less than 24 hours each day, plant flow rate is the
primary means for process control. At these plants, an excessive hydraulic loading rate on the
sedimentation process can be avoided by operating at a lower flow rate for a longer period of
time. Continuous flow through the sedimentation units is generally a preferable operating
mode, especially for upflow units where start-up can disrupt the sludge blanket as well as
take time to stabilize operation.
Controlling plant flow rates provides an option to meet more rigorous performance
requirements with existing units without major capital improvements. The capability to
reduce plant flow rate to improve performance is offset by the need to staff the plant for
longer periods of time, which adds to operating costs. Therefore, both options should be
considered.
7.3.3 Optimizing Sludge Removal
Sludge needs to be removed from conventional sedimentation basins frequently enough to
prevent solids carryover to the filters. To optimize sludge removal, the amount of sludge
accumulated in a basin can be determined by using a sludge depth measuring device such as a
sludge judge.
For basins with mechanical and/or automatic sludge removal systems, the duration of sludge
pumping can be determined by collecting samples during draw-off (e.g. every 30 seconds)
and determining when the sludge begins to thin. A centrifuge, graduated cylinder or Imhoff
cone can be used to observe the density changes (USEPA, 1998).
Sludge control is very important in the operation of reactor type upflow sedimentation basins
that operate using a sludge blanket. The reactor section of the basin must be monitored daily
and the appropriate amount of sludge removed from the basin to maintain the optimum
reactor concentration and sludge blanket depth. Inadequate monitoring of the basin can lead
to a loss of the sludge blanket over the weirs, which significantly impacts basin and,
ultimately, filter performance.
7.3.4 Tracer Testing
As discussed in Chapter 4, tracer test techniques are used to evaluate the hydraulic
characteristics of unit process tanks. For sedimentation basins, tracer testing can be used to
identify hydraulic short-circuiting and locate dead-zones, identify density currents and sludge
blanket carryover problems, and evaluate baffling arrangements (MOE et. al., 1999).
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Optimization Guidance Manual for Drinking Water Systems 2014
Additional information regarding the conduct of tracer tests is provided in Chapter 4.
7.3.5 Stress Testing
Stress testing involves increasing the hydraulic loading to the existing process in order to
identify the “failure point”. For clarification processes, the failure point can be defined either
as an exceedance of the settled water turbidity goal, or excessive head loss or turbidity
breakthrough in the subsequent filtration process.
Both continuous monitoring and grab sampling are required to evaluate sedimentation
process performance during a stress test. For example, frequent grab sampling for testing the
settled water turbidity or continuous monitoring of filter effluent turbidity are needed to
identify the “failure point”. In addition, the sludge blanket depth should be measured
regularly during the stress test.
Criteria for evaluating performance of clarification processes in terms of settled water
turbidity are provided in Section 7.2.2. More detailed information regarding typical stress
testing protocols can be found in Chapter 4.
7.4 CASE HISTORIES
7.4.1 Town of Slave Lake, Alberta – Optimization and Upgrading Study
The following case study is based on information presented in Drachenberg et. al. (2007).
System Description
The Town of Slave Lake (the Town) is located in the north-central area of the province of
Alberta and receives its water supply from Lesser Slave Lake. The existing conventional
WTP has a rated capacity of 7 ML/d and consists of coagulation, flocculation, clarification
and dual media filtration, followed by pH adjustment, fluoridation and disinfection.
The source water posed many treatment challenges. Periodic high winds caused turbidity
increases from 6 NTU to 100 NTU within a period of hours. Heavy rains also caused
significant increases in colour and turbidity. During periods of elevated raw water colour and
turbidity, reducing plant production was the only means for ensuring adequate settling and
filter performance.
Several operating problems associated with the original design of the WTP had been
identified and a conversion to membrane filtration was being considered to meet anticipated
changes to provincial regulations and guidelines. As such, a series of studies and reports were
commissioned to evaluate the plant’s ability to meet new treated water requirements and to
identify improvements needed to enhance treatment effectiveness.
Optimization Strategies
The objective of the WTP study was to improve plant performance to meet a filtered water
turbidity objective of less than 0.05 NTU and particle counts of less than 20 particles larger
than 2µm/mL with a minimum of upgrades.
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An assessment of available plant operating data, water quality data and hydraulic data was
undertaken. The results of the data review led to the development of bench-scale and full-
scale studies to define the most appropriate upgrade path for the Town.
As part of the bench-scale studies, jar testing was conducted to determine optimum coagulant
chemical dosages and verify the effectiveness of the existing mixing equipment. The results
of the jar testing in conjunction with various pilot-scale studies led to the adoption of an
enhanced coagulation approach consistent with the strategy presented in the Enhanced
Coagulation and Enhanced Precipitative Softening Guidance Manual (USEPA, 1999).
A tracer study was conducted for the flocculation and sedimentation tanks to establish the
effective residence times. Short-circuiting of water in the sedimentation tank was confirmed.
The existing sedimentation tanks were not equipped with mechanical sludge removal systems
and had to be cleaned manually twice per year.
As part of the upgrading plan, modifications to the existing sedimentation tanks were
proposed, including upgrades to improve inlet flow distribution, re-alignment of the
collection troughs, installation of tube settlers and automatic sludge collection equipment.
Summary
As a result of the improvements completed as part of the upgrade plan as well as the
implementation of enhanced coagulation, the WTP achieved all of its treatment goals. The
upgrades also allowed the Town to extend the service life of the treatment facility beyond its
original design period, which could postpone future upgrades, including the installation of
membrane filtration, by several years.
7.4.2 Newport News, Virginia – Sludge Control Study
The following case study is based on information presented in Hoehn et. al. (1987).
System Description
The City of Newport News (the City) owns and operates two WTPs. Both the Lee Hall WTP
and the Harwood’s Mill WTP are conventional plants that draw raw water from the
Chickahominy River. The raw water source is generally high in organic content, moderately
coloured, and has low alkalinity.
In 1982, the City discontinued pre-chlorination at the WTPs to reduce THM formation. Since
then, problems associated with the deterioration of alum sludge in sedimentation basins had
been observed, as well as occasional declines in settled water quality. Laboratory and field
studies showed that anaerobic conditions had developed in manually cleaned sedimentation
basins (but not in those that were mechanically cleaned), allowing manganese to be released
from the sludge into the overlying water.
As such, a study was designed with the following three objectives:
To contrast rates of development of anaerobic conditions in manually cleaned and
mechanically cleaned sedimentation basins;
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To determine the extent to which anaerobic conditions in the sedimentation basins
altered settled water quality, filter performance and sludge dewatering characteristics;
and
To evaluate the benefits of pre-oxidation of the raw water with an oxidant that would
not contribute to THM formation (chlorine dioxide).
Optimization Strategies
Laboratory studies were conducted to evaluate changes in sludge dewatering characteristics
and in the quality of the supernatant. Field studies were conducted which measured dissolved
oxygen (DO) concentration profiles across the depth of the sedimentation basins, as well as
iron, manganese and TOC in the clarifier effluent. Sludge dewatering characteristics were
also evaluated during the field studies by the specific resistance test.
The laboratory study indicated that seasonal changes in raw water quality had a significant
effect on sludge and supernatant quality. Concentrations of TOC, iron and manganese in the
supernatant were much higher in samples collected in summer (June) compared to those
collected in spring (March). It was concluded that the strongly reducing environment that
developed in June were likely created by biological activity that was stimulated either by a
greater concentration of organic matter within the sludge or by an increase in the
biodegradability of the organic matter.
The results of the field studies indicated that the frequency of basin cleaning had a significant
impact on sludge conditions and supernatant quality. Testing was conducted at the Lee Hall
WTP, where one of the basins was manually cleaned approximately every six weeks, whereas
the other was mechanically cleaned for four hours each morning. The manually cleaned basin
had been drained and cleaned only four days before the first DO measurements were made,
yet significant reductions in DO concentrations were observed at depths below 3 m. In
contrast, DO persisted to the bottom of the mechanically cleaned basin (up to 5 m). The data
indicated that the accumulation of sludge, even for a period as brief as a few days, could
create anaerobic conditions in the sludge blanket.
In the third phase of the study, pre-oxidation using chlorine dioxide was initiated at the
Harwood’s Mill WTP. Improvements in performance were noted, including better manganese
removal, faster sludge dewatering rates and longer filter runs.
Summary
The results of the study confirmed the effectiveness of chlorine dioxide pre-oxidation as an
alternative to no pre-oxidation. Although the study notes that the results are likely site-
specific, the benefits to WTP performance were noted through the following improvements:
Manganese release from settled sludge to the overlying water was suppressed;
Alum sludge dewatering was improved, due to increased particle size in the settled
sludge when chlorine dioxide was applied; and
The length of the filter runs was doubled, from approximately 30 hours to more than
60 hours.
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7.5 REFERENCES
American Water Works Association (1995). Water Treatment – Principles and Practices of
Water Supply Operations. 2nd
Ed. AWWA. Denver, CO. ISBN 0-89867-789-0.
Drachenberg, G.E., S. Suthaker and H.C. Suan (2007). “Getting membrane Performance Out
of a Conventional Filtration Plant in a Small Community”, presented at the 2007 American
Water Works Association Annual Conference and Exposition, Toronto, ON.
Hoehn, R.C., J.T. Novak and W.E Cumbie (1987). Effects of Storage and Preoxidation on
Sludge and Water Quality. Journal AWWA, Vol. 79, No. 6. June 1987.
Hudson, H.E., Jr. (1975). Residence Times in Pretreatment. Journal AWWA, Vol. 67, No. 1.
January 1975.
MOE (2008). Design Guidelines for Drinking Water Systems. ISBN 978-1-4249-8517-3.
MOEE, EC, & WEAO (1999). Guidance Manual for Sewage Treatment Plant Process
Audits.
MWH (2005). Water Treatment: Principles and Design, 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program. EPA/625/6-91-027.
USEPA (1999). Enhanced Coagulation and Enhanced Precipitative Softening Guidance
Manual. U.S. EPA, Office of Water. EPA 815-R-99-012.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 8 FILTRATION
FILTRATION
8.1 Introduction ............................................................................................................ 8-1
8.2 Granular Media Depth Filters ................................................................................. 8-1
8.2.1 Purpose and Types of Granular Media Depth Filters .............................. 8-1
8.2.2 Evaluating Performance ........................................................................... 8-2
8.2.3 Common Problems and Potential Impacts ............................................... 8-5
8.2.4 Optimization Techniques ......................................................................... 8-8
8.3 Slow Sand Filters .................................................................................................. 8-13
8.3.1 Purpose of Slow Sand Filters ................................................................. 8-13
8.3.2 Evaluating Performance ......................................................................... 8-13
8.3.3 Common Problems and Potential Impacts ............................................. 8-16
8.3.4 Optimization Techniques ....................................................................... 8-16
8.4 Membrane Filters ................................................................................................. 8-17
8.4.1 Purpose and Types of Membrane Filters ............................................... 8-17
8.4.2 Evaluating Performance ......................................................................... 8-19
8.4.3 Common Problems and Potential Impacts ............................................. 8-21
8.4.4 Optimization Techniques ....................................................................... 8-23
8.5 Case Histories ....................................................................................................... 8-24
8.5.1 Racine, Wisconsin – Optimizing Membrane Maintenance ................... 8-24
8.5.2 Fort McMurray, Alberta – Filter Media Optimization and Upgrading
Study ...................................................................................................... 8-26
8.6 References ............................................................................................................ 8-27
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CHAPTER 8
FILTRATION
8.1 INTRODUCTION
The purpose of filtration is to remove suspended particulate matter from water. Filtration is a
key component of the multi-barrier approach. All regulated drinking water systems that
obtain water from a surface water source or GUDI source must provide a minimum level of
treatment consisting of chemically-assisted filtration and disinfection or other treatment
capable of producing water of equal or better quality (MOE, 2006).
Filtration processes discussed in this chapter include granular media filtration, slow sand
filtration and membrane filtration. Filtration processes designed for other purposes (e.g.
greensand, granular activated carbon, biologically active filters) are discussed in Chapter 10.
8.2 GRANULAR MEDIA DEPTH FILTERS
8.2.1 Purpose and Types of Granular Media Depth Filters
Granular media filtration is the most widely used filtration process in drinking water
treatment (LeChevallier, 2004). In granular filtration, water passes through a filter consisting
of a packed bed of granular materials. The removal of particles occurs throughout the
granular medium (depth filtration) rather than on the top layer only (cake filtration).
Granular filters can be constructed as monomedium (e.g. silica sand), dual media (e.g.
anthracite coal and sand) and trimedia (e.g. coal, sand and garnet). Granular activated carbon
(GAC) is often used when both the removal of particles and adsorption of organic
compounds, such as taste and odour producing compounds, are desired. The use of GAC for
this purpose is discussed in Chapter 10.
Depending on raw water quality, granular filters can be operated within three different
treatment processes:
Conventional treatment, which includes addition of coagulants, flocculation,
sedimentation and filtration;
Direct filtration, in which the sedimentation step is omitted; or
In-line filtration, in which coagulation and flocculation occur within the influent
piping to a filter.
Conventional treatment is appropriate for most surface water sources, whereas direct and in-
line filtration may be used for raw waters with consistently low levels of turbidity and colour.
Guidance on selecting an appropriate treatment strategy is provided in the Design Guidelines
for Drinking Water Systems, 2008 (MOE, 2008) and Ten State Standards (Recommended
Standards for Water Works, Great Lakes-Upper Mississippi River Board of State Public
Health and Environmental Managers, 2007).
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There are two basic modes of filtration control:
Constant rate filtration; and
Declining rate filtration.
In constant rate filtration, the flow to each filter is maintained at as constant a rate as possible,
with clearwell storage absorbing fluctuations in demand and in total filter output (i.e. when a
filter is taken out of service for backwashing). This is typically accomplished by a flow meter
and a flow modulation valve on each filter effluent pipe, or by constant level filtration with
equal flow splitting inlet weirs, a water level sensor, and a flow modulating valve.
In declining rate filtration, the filtration rate is not kept constant. Rather, the rate for a
particular filter gradually decreases as the filter captures particles and the head loss increases.
Using this method, all filters receive water from a common influent channel without any
devices to measure or control the flow to individual filters. Each filter accepts the proportion
of total flow based on its bed condition (e.g. accumulated solids and head loss). As a filter
gets “dirty”, the flow through it decreases. Flow is then redistributed to cleaner filters and
total plant capacity does not decrease. To prevent excessive flow rates from occurring in
clean filters, a flow restricting orifice plate may be placed in the effluent line of each filter.
Regardless of the control strategy used, the system should control the flow to each individual
filter, divide the total flow among the individual filters equally, and accommodate rising head
loss through each individual filter run. Flows to individual filters should remain constant.
Backwashing and changes in demand and should be met as much as possible with clearwell
storage at the plant.
Filters must be backwashed periodically to remove accumulated solids. The need for
backwashing is generally determined based on one of the following criteria: terminal head
loss, a fixed time interval, or a breakthrough of solids (measured as turbidity or particle
counts).
8.2.2 Evaluating Performance
8.2.2.1 Major DWS Component Evaluation
Filter performance should be assessed based on the capability to achieve effluent turbidity of
less than 0.1 NTU continuously to ensure the integrity of filtration as a viable barrier in the
treatment scheme. Operation of filters to produce filtered water quality of less than 0.1 NTU
is attainable by many plants, and provides greater confidence that pathogens, such as
Cryptosporidium oocysts and Giardia cysts, are being removed prior to disinfection, the final
treatment barrier. If particle counters are available, the maximum filtered water measurement
should be less than 10 particles (in the 3 to 18 µm range) per mL (USEPA, 1998).
Projection of filtration capacity is based primarily on hydraulic loading rates, with
consideration given to media type. For example, a monomedium sand filter would be
assessed at a maximum rate of 7 m3/m
2·h (or m/h) because of the susceptibility of this filter
to surface blinding by removing particles at the top of the filter media; whereas a dual or
mixed media filter would be assessed at a higher rate because of the ability to utilize the
solids storage capacity within the anthracite layer.
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Limitations caused by air binding can also impact the selected loading rate for projecting a
filter’s performance potential and could bias the selected loading rate toward more
conservative values within each range.
Inadequate backwash or surface wash facilities, rate control systems, media depth and
underdrain integrity are areas that can often be addressed through minor modifications. These
would be assessed during a CPE as performance limiting factors, but are typically not
considered in evaluating the filter loading rate.
Criteria to be used to evaluate filtration processes as part of the major DWS component
evaluation are shown in Table 8-1. Direct and in-line filtration processes should be assessed
based on the same criteria as conventional filtration processes.
Table 8-1 – Granular Media Depth Filtration – Criteria for Major DWS Component
Evaluation Using the Performance Potential Graph Rating System
Characteristic Typical Assessment Criteria
Filtration Rate (m/h)
Monomedium
Dual/mixed media
2 – 7
7 – 18
Backwash Rate (m/h) 37 – 50
Bed Expansion During Backwash (%) 25 – 50
Backwash Duration (minutes) 10 – 15
The rate of filtration should be determined through consideration of such factors as raw water
quality, degree of pre-treatment provided, filter media type(s) and depth, and the competency
of operating personnel. For traditional conventional dual media filter designs with a
maximum filtration rate of 12 m/h, this rate may not be achievable with floc formed from
highly coloured water (MOE, 2008). Higher filtration rates, up to 20 m/h or higher, may be
achievable while still maintaining filtered water quality. The maximum filtration rate to be
used as part of the DWS component evaluation should be assessed based on stress testing.
Continuous effluent turbidity measuring and recording devices should be provided for each
filter (MOE, 2008). Particle counters should be used if it is necessary to analyze the number
and size of particles in the filter effluent at levels below the detectable range of a turbidimeter
(AWWA, 1995). Table 8-2 presents monitoring recommended, in terms of sampling
locations and analyses, in order to evaluate the performance of the filtration process.
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Table 8-2 – Granular Media Depth Filtration – Recommended Monitoring to
Evaluate Performance
Location Types of Sample/
Measurement
Parameters/ Analyses
Filter influent Continuous monitoring or
Grab sample Turbidity
Individual filter Continuous monitoring Loss of head
Flow rate
Filter run time
Individual filter effluent Continuous monitoring Turbidity
Particle counts
Filtered water Grab sample Colour
pH
Alkalinity
Aluminum or iron residual
Microbiological parameters, zooplankton,
etc.
Backwash Continuous monitoring Backwash duration
Washwater flow
Duration and rate of air application (air
scour systems)
Process waste stream
(backwash water)
Continuous monitoring or
Grab sample Flow or volume
Turbidity or total suspended solids
Chlorine residual (if applicable)
Figure 8-1 presents a process schematic of a typical granular media filtration process, along
with the identification of various sampling locations.
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Filter Influent (from clarification or
coagulation/flocculation)
Filter Effluent
Filter Effluent
Sample Location
Filter Influent
Sample Location
Anthracite
Sand
Support Gravel
Underdrain
Figure 8-1 – Granular Media Depth Filtration – Process Schematic and Sampling Locations
8.2.2.2 Field Evaluations
Field evaluations should be conducted to assess the integrity of the filter media, support
gravels and underdrain system for a selected filter. This requires that the filter be drained and
that the evaluation team inspect the media. Additional information on conducting filter
investigations is provided in Section 4.2.4.
8.2.3 Common Problems and Potential Impacts
Most filtration problems occur in the following major areas:
Chemical treatment before the filter;
Control of filter flow rate; and
Backwashing the filter.
If these three procedures are not performed effectively, the quality of the filtered water, filter
run times, and production will suffer, and additional maintenance problems may occur.
The following are common indicators that proper filter control is not practiced.
Individual filter performance is not monitored;
Rapid increases in overall plant flow rate (poor ramping of filter flow changes) are
made without consideration of filtered water quality;
Filter performance after backwash is not monitored;
Filters are removed from service without reducing plant flow rate, resulting in the
total plant flow being directed to the remaining filters;
Operators backwash filters without regard for filter effluent turbidity; or
Operators backwash at a low rate for a longer period of time, or stop the backwash
when the filter is still dirty to "conserve" water;
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Filters have significantly less media than specified, there is damage to underdrains or
support gravel, and/or there is a significant accumulation of mudballs and these
conditions are unknown to the operating staff because there is no routine examination
of the filters;
The purpose and function of the rate control device cannot be described.
Design issues that may contribute to poor performance and that can be addressed through
minor modifications include:
Insufficient freeboard above the filter (particularly in cold water conditions); and
Improper media selection, including media type, depth, effective size, uniformity co-
efficient, or a combination of these factors.
Symptoms and causes of other common problems encountered with granular media filtration
are shown in Table 8-3.
Table 8-3 – Granular Media Depth Filtration – Symptoms and Causes of Common
Problems
Problem Description
Mitigation
Rapid head loss Large floc accumulating on
surface Optimize coagulation/flocculation
(Chapter 6)
Monitor head loss across various
points within the media depth
Mudball formation Floc/media sticking together Improve backwashing (Section
8.2.4.3)
Optimize coagulation/flocculation
(Chapter 6)
Excessive head loss
remaining after filter
backwash
Filter media not clean Check if underdrain system clogged
Check for mudballs
Improve backwashing (Section
8.2.4.3)
Faulty head loss measurement
equipment
Decreased turbidity
removal efficiency with
no increase in influent
water turbidity
Filter cannot hold solids Perform backwash
Optimize coagulation/flocculation
(Chapter 6)
Filter bed sand boil Backwash rate(s) too high Control backwash rate, surface wash
rate or duration, and time sequence or
duration of backwash (Section 8.2.4.3)
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Table 8-3 – Granular Media Depth Filtration – Symptoms and Causes of Common
Problems (cont’d.)
Problem Description
Mitigation
Media loss Media is being lost during
backwash Control backwash rate, surface wash
rate or duration, and time sequence or
duration of backwash (Section 8.2.4.3)
Decreased turbidity
removal efficiency with
increase in influent water
turbidity
Filter cannot hold solids Optimize coagulation/flocculation to
reduce solids loading (Chapter 6)
Shortened filter runs Decrease in the pre-
treatment performance
resulting in floc carryover
Filtration rates too high
Excessive mudball
formation
Clogging of the filter
underdrain system
Air binding
Optimize coagulation/flocculation
(Chapter 6)
Reduce filter rates, if possible
Check for clogged or broken
underdrains
See air binding (below)
Air binding (Gas bubbles
accumulate in the filter
between backwashes)
Dissolved air in the water
Increased head loss
Shortened filter runs
Violent agitation during
backwashing, causing loss
of media
Terminate the filter run before the total
head loss is greater than the depth of
the water above the unexpanded media
Allow time for the air to dissipate
before beginning a backwash
Filter bed cracking Filter has reached terminal
head loss resulting in
negative pressures
Terminate the filter run before the total
head loss is greater than the depth of
the water above the unexpanded media
Control backwash rate, surface wash
rate or duration, and time sequence or
duration of backwash (Section 8.2.4.3)
Check underdrains, or for foreign
objects in the filter which may be
blocking the underdrains
Gravel mounding Backwash rate too high
Underdrain broken
Optimize filter backwash rate
Check underdrains
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8.2.4 Optimization Techniques
As noted in the previous section, most operational problems associated with filtration
processes are related to pre-treatment, filter flow control and backwashing. Optimization
techniques to address each of these issues are discussed below.
Extensive information regarding the optimization of filtration processes is available in other
references (AWWA, 2007; Nix and Taylor, 2003; Beverly, 2005; Cleasby et. al., 1992;
Amirtharajah et. al., 1991; Hess et. al., 2002; Patania et. al., 1995).
8.2.4.1 Optimizing Chemical Pre-Treatment
Proper chemical pre-treatment of the water prior to filtration, as previously discussed, is the
key to acceptable filter performance. For waters that are properly chemically conditioned,
acceptable performance can be achieved even at higher filtration rates.
Floc should be strong enough not to shear apart when subjected to the hydraulic forces occurring
within the filter bed, and the settled water turbidity applied to the filter should be low enough to
provide reasonable filter runs between backwashes. If weak floc is a problem, even after
seemingly good pre-treatment, it may be beneficial to use a filter aid polymer to strengthen the
floc. Testing of a filter aid polymer can be accomplished either through jar testing, pilot studies or
full scale trials.
A number of chemical pre-treatment optimization strategies were presented in Chapter 6,
including the use of jar testing, zeta potential, particle counters, streaming current monitors,
etc. In addition to these tests, the filterability of water to which coagulant has been added can
be measured to determine how efficiently the coagulated water can be filtered.
The filterability test measures the amount of water filtered in a given time when flocculated plant
flow (i.e. before sedimentation) is passed through a small diameter tube known as a “pilot filter”.
The pilot filter usually contains the same type of filter media used in the plant filters and is
equipped with a recording turbidimeter to continuously monitor the filtered water effluent. The
amount of water passing through the filter before turbidity breakthrough occurs can be correlated
to how well the plant filters will operate under the same coagulant dosage.
The water used in the pilot filter is usually the actual coagulated/flocculated water from the plant;
however, the test can also be applied to settled water supernatant from jar testing trials. Because
the test takes much less time than it would for the coagulated and flocculated water to pass
through the full-scale plant (e.g. several hours retention time in sedimentation basins and filters),
changes in coagulant dosages can be applied as raw water quality changes, preventing
deterioration of plant effluent quality. This test is particularly useful for direct filtration plants,
where it is essential to properly control the chemical dosage in the short time span between
application of the chemicals and the point where the water reaches the filters.
8.2.4.2 Improving Filter Control
The most important aspect of flow rate control related to filter performance is minimizing the
magnitude of a change in flow rate and the speed at which the change occurs (Renner et. al.,
1990; Cleasby et. al., 1963). Rapid, high magnitude flow rate increases cause a large number
of particles to be pushed through the filter as evidenced by significant increases in turbidity.
This breakdown in filter performance, which allows previously contained/removed particles
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to pass into the distribution system, disrupts the continuous performance that is required in
water treatment. Since filtration is the most effective barrier within the treatment system to
cysts such as Cryptosporidium, even short-term performance problems can potentially expose
consumers to significant concentrations of cysts. These performance failures can occur even
when the finished water turbidity objectives are being met.
Filtration rate changes most often occur when:
A filter is removed from service for backwashing;
High volume constant speed raw water pumps are cycled on and off;
A filter is started when it is dirty; or
A filter rate controller is malfunctioning.
Removing a filter from service for washing and directing the entire plant flow to the
remaining filter(s) causes an instantaneous flow increase on the remaining filters, causing
attached particles to be swept out of the filter. This can be prevented by lowering the plant
flow rate prior to removing the filter from service, thereby controlling the hydraulic loading
on the filters remaining in service.
Starting dirty filters results in a rapid increase in flow rate and subsequent poor filtered water
quality. Backwashing of filters prior to returning them to service is essential to maintaining
the integrity of the filtration process.
Rapid changes in plant influent flow by starting and stopping constant speed raw water
pumps also hydraulically pushes particles through filters. This may be prevented by using a
control valve (automatic or manual) to slowly adjust plant influent flow rate or by
installing/modifying pumps with variable frequency drives.
Filter control valves should not leak. Malfunctioning filter rate control valves can result in
rapid changes in filter flow rate. Proper installation and an on-going preventive maintenance
program are necessary to keep the valves in good working order and avoid this source of poor
filter performance. If the hydraulic loading rate that the filters are expected to handle is too
high, reduction of flow rate to the plant should be considered.
The use of a low dose of filter aid polymer can improve filtered water quality in dual or
mixed media filters; however, these products, while effective, are very “sticky” and can
quickly cause surface blinding of a filter when used inappropriately. They should therefore be
used at optimum doses (generally less than 0.1 mg/L) to avoid excessively short filter runs.
Polymer-based coagulants, such as polyaluminum chloride, can be used as a filter aid
provided the dose does not exceed 5 percent of the initial coagulant dose. The optimum
dosages can be determined using jar testing (see Chapter 4). These products are subject to
shearing because of their long polymer chains and should be fed at points of low turbulence,
such as flocculation basins or sedimentation basin effluent pipes or channels. Filter
backwashing also needs to be operated optimally to ensure removal of these products.
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8.2.4.3 Optimizing Backwash Processes
Filters must be backwashed periodically to prevent accumulated particles from washing
through the filter, to prevent the filter from reaching terminal head loss, to prevent
compaction of the media or to prevent excessive biological growth in the media. Filters
should be backwashed based on effluent turbidity if breakthrough occurs before terminal
head loss to prevent poor filtered water quality. For example, particles that are initially
removed by the filter are often "shed" when velocities and shear forces increase within the
filter as head loss accumulates (e.g. filter becomes "dirty").
Operators should reduce or limit the duration of the filtration cycle prior to bed exhaustion or
maximum head loss. One approach that can be used as a starting point when assessing the
proper duration for a filter run is to determine the unit filter run volume (UFRV). UFRV
varies according to site-specific conditions, but a UFRV of approximately 200 m3 per m
2 of
filter area per cycle can be used as an initial assessment. This corresponds to filter runs of 20
to 40 hours at filtration rates of 10 m/h and 5 m/h, respectively. Net water production (UFRV
less the amount used for backwashing) should also be considered. Very long filter runs (e.g.
in excess of 90 hours) should be avoided because they can make filters difficult to clean
during backwash due to compaction of the media and can also allow an increase in biological
growth on the filter (Logsdon et. al., 2002).
Inadequate washing, both in terms of rate and duration, can also result in a residual
accumulation of particles in the filter, resulting in poor filtered water quality when filtering is
resumed.
The filter backwash duration and intensity should be great enough to clean the filter, but not
so great as to damage the support gravels/underdrain system or to blow media out of the
filter. The length of wash should be long enough to produce clean spent backwash water,
because inadequate washing can result in a degradation of filter performance and the possible
formation of mudballs. The accumulation of mudballs takes up effective filter surface area
and raises the filtration rate through those areas of the filter where water can still pass. The
filter can also reach a point where minimal additional particles can be removed because
available storage sites within the media already have an accumulation of filtered particles. It
should be noted that excessively long backwashes may lead to increased residuals
management volumes and handling costs.
In some cases, changing the rate at which backwash water is throttled back can optimize
mixing at the interface between different layers of filter media and improve filter
performance.
Figure 8-2 shows a profile of turbidity in spent backwash water as a function of time. This
type of graph can be developed as part of a special study or field investigation and may assist
in the determination of optimum backwash duration. As shown in the graph, turbidity in
spent backwash water may peak at levels greater than 300 NTU depending on the pre-
treatment processes used and raw water conditions, but generally decrease to below 10 NTU
within 6 to 8 minutes of backwashing (Wolfe, 2003).
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0
50
100
150
200
250
300
350
400
450
0 1 2 3 4 5 6 7 8 9 10Time (min.)
Tu
rbid
ity
(N
TU
)
Figure 8-2 – Filter Backwash Turbidity Versus Time
Adapted from Filtration Fundamentals (Wolfe, 2003)
Other special studies that could also be conducted to evaluate the effectiveness of
backwashing include a time versus turbidity profile conducted on filters before and after
backwashing. Acceptable performance is judged to be an increase in filtered water turbidity
of less than 0.2 to 0.3 NTU for less than 10 minutes following a backwash. An example of
unacceptable filter performance is depicted in the turbidity versus time graph presented in
Figure 8-3.
As shown, a significant breakthrough of turbidity occurred after the backwash (e.g., turbidity
increased to 24 NTU). Samples taken from the clearwell at the same time showed turbidity
values of 6.3 NTU, far in excess of regulatory criteria for finished water turbidity.
At some plants where high quality filtered water cannot be achieved (after the filter is placed
into service), modifications allowing filter to waste capability, or an equivalent procedure,
during filter ripening should be implemented. This allows directing the initial filtered water
to a drain until quality improves to the extent that the water can be redirected to the clearwell.
Another parameter that should be monitored after backwashing is the initial filtering head
loss which can give an indication of the “cleanliness” of the filter.
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Figure 8-3 – Filter Effluent Turbidity Versus Time
The investigation should determine whether inadequate washing is caused by a design or an
operational limitation. The filter should be probed periodically (semi-annually or annually) to
inspect for support gravel problems and to check media depths. Other field evaluations, such
as bed expansion and rise rate, that can be conducted to determine the capability of backwash
facilities were discussed in Section 8.2.2.2.
Operating procedures should be developed to describe consistent methods of backwashing
filters. The procedure should include measures to prevent rapid flow rate increases to the
remaining filter(s), to ensure the filter is properly cleaned, and to prevent damage to the filter
by operating valves too quickly. The method of returning a filter to service should also be
described because this is another time when degraded filter performance can occur. This can
be minimized by optimizing coagulation chemicals and filter aid dosages and by increasing
the filtration rate gradually when returning a recently washed filter to service. Additional
information is provided in Logsdon et. al. (2002).
8.2.4.4 Optimizing Filter Configuration
The type and size of media affects filter throughput, performance and head loss.
Characteristics such as media size, shape, composition, density, hardness and depth can be
considered during optimization, although some of these parameters are difficult to change as
part of an optimization program. If an issue is identified, it can be considered as part of
longer term planning for filter upgrades.
The most common types of media in granular filters are anthracite and sand. Problems may
arise with the filter due to improper media selection. If the media grain size is too small, head
loss during the filter run will increase. If the media grain size is too large, smaller particulate
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Optimization Guidance Manual for Drinking Water Systems 2014
matter in the filter influent may not be removed effectively. Additional information regarding
the selection and design of media in granular filters is provided in MOE Design Guidelines
(MOE, 2008).
8.2.4.5 Stress Testing
As discussed in Chapter 4, stress testing can be used to quantify the capacity and
performance of the filter under high flow or solids loading conditions. Temporary changes to
operation for experimental purposes should be discussed with the Ministry of the
Environment (local MOE District Office) before testing is undertaken. During the test, the
flow rate to each filter should be incrementally increased. Effluent quality parameters (e.g.
turbidity and/or particle counts) are monitored and compared to the required effluent quality.
The capacity of the filter is assessed based on the ability of the filter to meet effluent limits
for turbidity at increasing flow rates.
Incremental solids loading impacts can be used to assess the filter response to higher solids
loading rates due to challenging conditions (i.e. increased sedimentation effluent turbidity
levels due to upsets).
8.3 SLOW SAND FILTERS
8.3.1 Purpose of Slow Sand Filters
Slow sand filtration involves passing water through a sand filter by gravity at a very low filtration
rate (e.g. less than 0.4 m/h), generally without the use of coagulation pre-treatment. The filter
typically consists of a layer of sand supported on a layer of graded gravel. The use of a slow sand
filtration process is limited by the quality of raw water sources (or influent water after pre-
treatment) having turbidity of less than 10 NTU and colour less than 15 TCU (MOE, 2006).
Design criteria for slow sand filters are provided in the Design Guidelines for Drinking Water
Systems, 2008 (MOE, 2008). Slow sand filtration systems can be difficult to optimize after they
are designed. Proprietary enhanced slow sand filtration technologies are available that can be used
for a wider range of applications than conventional slow sand filter designs.
Removal of particles by slow sand filtration occurs predominantly in a thin layer on top of
the sand bed. This biologically active layer is termed schmutzdecke. As operation progresses,
deposited materials and biological growth on the sand medium increase the head loss across
the filter. When the head loss reaches the operational limit (normally 1 to 2 m), the filter is
removed from service. It is then usually cleaned by scraping away some of the accumulated
material and sand from the top layer of the sand bed, before being returned to service. A
typical filter run could be from one to six months, depending on raw water quality and
filtration rate (LeChevallier, 2004).
8.3.2 Evaluating Performance
As noted in Section 8.2.2, the projection of filtration capacity is based mainly on hydraulic
loading rates and the ability to meet filter effluent turbidity objectives. The operational
guidelines for slow sand filters specified in the Disinfection Procedure (MOE, 2006) include
the following criteria:
Maintain an active biological layer;
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Regularly carry out effective filter cleaning procedures;
Use filter-to-waste or an equivalent procedure during filter ripening periods;
Continuously monitor filtrate turbidity from each filter or take a daily grab sample;
and
Meet the performance criterion for filtered water turbidity of less than or equal to 1.0
NTU in 95 percent of the measurements each month.
Criteria to be used to evaluate slow sand filtration processes as part of the major DWS
component evaluation are shown in Table 8-4.
Table 8-4 – Slow Sand Filtration – Criteria for Major DWS Component Evaluation
Using the Performance Potential Graph Rating System
Characteristic Typical Assessment Criteria (MOE, 2008)
Filtration Rate (m/h) 0.04 – 0.4
Sand Media
Depth (m)
Effective Size (mm)
Uniformity coefficient
0.75 – 1.5
0.15 – 0.30
< 2.5
Higher filtration rates than those shown in Table 8-4 may be used in installations where pre-
treatment processes are provided and/or as demonstrated through pilot studies.
Because of the selective mechanisms of slow sand filtration processes, filter effluent turbidity
levels exceeding 1.0 NTU can occur as a result of passage of inorganic particles through the
filter without influencing the effective removal of harmful organisms. Therefore, turbidity
may not be a suitable surrogate for evaluating removal of pathogens by slow sand filtration.
Table 8-5 presents monitoring recommended, in terms of sampling locations and analyses, in
order to evaluate the performance of the slow sand filtration process.
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Table 8-5 – Slow Sand Filtration – Recommended Monitoring to Evaluate Performance
Location Types of Sample/
Measurement
Parameters/ Analyses
Raw water Continuous monitoring Turbidity
pH
Temperature
Continuous monitoring or
Grab sample Colour
Total and/or dissolved organic carbon
Dissolved oxygen
Pre-treatment effluent (if
applicable)
Continuous monitoring or
Grab sample Turbidity
Total and/or dissolved organic carbon
Dissolved oxygen (for systems using ozone
as pre-treatment)
Individual filter Continuous monitoring Loss of head
Flow rate
Water level above filter media
Individual filter effluent Continuous monitoring Turbidity
Filtered water Grab sample Colour
pH
Total and/or dissolved organic carbon
Dissolved oxygen (to monitor biological
conditions in filter, i.e. aerobic vs.
anaerobic)
Figure 8-4 presents a process schematic of a typical slow sand filtration process, along with
the identification of various sampling locations.
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Sand
Raw Water
Inlet SchmutzdeckeVent
Filter Effluent
Sand
Raw Water
Inlet SchmutzdeckeVent
Filter Effluent
Figure 8-4 – Slow Sand Filtration – Process Schematic and Sampling Locations
8.3.3 Common Problems and Potential Impacts
A properly designed and constructed slow sand filter should operate reliably with very little
operator intervention.
The primary maintenance activity associated with slow sand filters is cleaning, or scraping,
which is discussed in the following subsection.
8.3.4 Optimization Techniques
8.3.4.1 Scraping and Resanding
Similar to rapid rate granular media filters, slow sand filters operate over a cycle of two
stages, consisting of a filtration cycle and a cleaning cycle. Slow sand filters, however, are
not backwashed. Head loss builds slowly during a filter run that may last up to weeks or
months. Filter runs are generally terminated when the head loss reaches between 1 to 2 m.
After the overlying water is drained below the surface of the sand media, the filter is cleaned
by removing the schmutzdecke along with a small amount of sand (1 to 2 cm). Scraping can
be accomplished either mechanically or manually.
The sand that is removed is usually cleaned hydraulically and stockpiled for later replacement
in the filter. The operation and scraping cycle can be repeated several times until the bed
depth has decreased to approximately 0.4 to 0.5 m, at which time the stockpiled sand or new
sand is added to the filter.
A filter with new media typically has a ripening period that can last several days, during
which the schmutzdecke forms and the effluent quality improves. The schmutzdecke is said
to be ‘mature’ when the microbial population becomes well established and the filter
produces acceptable filtered water quality. Frequent monitoring of the filter effluent is needed
to ensure that acceptable removal of microorganisms and turbidity is occurring. Additional
information is also provided in Logsdon (2008) and Eighmy et. al. (1993).
Filter-to-waste piping should be provided to allow for disposal of filtered water during the
ripening period. After several filter runs and scrapings, however, the microbial community
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can become established deeper in the bed and the ripening period is reduced or eliminated.
The duration of filter-to-waste needed during the ripening period should be determined
through pilot- or full-scale testing.
The longer a filter is drained for the scraping operation, the longer the ripening period will be
during the subsequent run (Cullen and Letterman, 1985). Therefore, cleaning should be done
quickly, and the filter returned to service as soon as possible.
It may be possible to extend the time between scraping by raking the surface of the filter
between scrapings. In general, the run time gained with each raking diminishes, and when the
scraping is required, it may be necessary to remove up to 15 cm of sand (Cleasby et. al.,
1984).
8.3.4.2 Pre-treatment for Enhancement of Slow Sand Filtration
The operation of slow sand filters can be enhanced by the use of additional pre-treatment
processes prior to the slow sand filter to allow treatment of more challenging source waters.
Most of these processes are proprietary systems; optimization of these systems is beyond the
scope of this manual, and the manufacturer should therefore be consulted.
Where organic material in the raw water is not easily biodegradable, the application of ozone
(up to 1 mg/L) upstream of the slow sand filter can promote biological activity by making the
NOM in the water more amenable to biological removal. Ozone addition also increases
dissolved oxygen, which is beneficial to microbial activity. However, residual ozone needs to
be removed before water enters the slow sand filter.
8.4 MEMBRANE FILTERS
8.4.1 Purpose and Types of Membrane Filters
In the simplest membrane processes, water is forced through a porous membrane under
positive or negative pressure, while suspended solids, larger molecules or ions are held back
or rejected. The four general membrane processes used in drinking water systems include
microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).
Table 8-6 provides a summary of operating pressure, pore sizes, primary application and the
type of microorganism that can be removed with the various membrane types.
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Table 8-6 – Overview of Membrane Filtration Processes Used in Drinking Water
Treatment
Adapted from AWWA (1996) and AWWA (1999)
Membrane
Type
Operating
Pressure
(kPa)
Pore Size
(µm) Primary Applications Microbes Removed
MF 30 – 50 0.1-0.2 Removal of particles and
turbidity
Algae, protozoa and
most bacteria
UF 30 – 50 0.01-0.05 Removal of dissolved non-
ionic solutes
Algae, protozoa, most
bacteria and viruses
NF 500 – 1000 0.001-0.0051
Removal of divalent ions
(softening) and dissolved
organic matter
Algae, protozoa, most
bacteria and viruses
RO 1000 – 5000 Non-porous1
Removal of monovalent
ions (desalination)
Algae, protozoa, most
bacteria and viruses
Notes:
1. For NF and RO membranes, the concept of discernable "pores" is inappropriate and the
ability of the membrane to remove a particular contaminant is described by the molecular
weight cutoff (MWCO) rather than pore size. The MWCO for NF membranes ranges from
200 to 1,000 Daltons, while for RO membranes, the typical range of MWCO levels is less
than 100 Daltons (USEPA, 2005).
MF and UF are the membrane systems most commonly used in Ontario. There are a few NF
systems in Ontario, and there are some installations across Canada used primarily for
organics removal. Reverse osmosis membrane systems are mainly used as point-of-entry or
point-of-use treatment systems in Ontario. Given the limited application of these systems in
the province to date, optimization measures for these processes are not presented in this
Manual.
Chemical coagulation is not usually needed before membrane treatment for the removal of
suspended solids and microorganisms. However, pre-treatment is sometimes employed to
reduce membrane fouling (caused by accumulation of chemicals, particles and biological
growth on membrane surfaces) and to avoid membrane degradation from chemical attack
(LeChevallier, 2004). Pre-treatment systems may include microstraining, pH adjustment and
addition of pre-oxidants. If the source water is of poor quality, advanced pre-treatment
systems (e.g. conventional coagulation, flocculation and sedimentation, or other membrane
processes) may be necessary.
The water passing through the membrane is called permeate, and water remaining on the feed
side is called retentate or reject water. As solids accumulate against the filter, the
transmembrane pressure (TMP) across the filter that is required to maintain constant
permeate production increases. To minimize fouling, TMP should be kept below 100 kPa
(MWH, 2005).
Membrane filters operate over a repeating filtration and backwashing cycle, similar to
granular filters. Although the backwash removes accumulated solids, a gradual but
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Optimization Guidance Manual for Drinking Water Systems 2014
continuous loss of performance occurs due to fouling of the membranes. Fouling is removed
with periodic chemical cleaning, which typically involves soaking the membranes for several
hours in one or more warm solutions containing surfactants, acids or bases. The cleaning
frequency may range from a few days to several months, depending on the membrane
material, operating conditions and raw water quality.
Membrane degradation is inevitable, although membrane manufacture as well as performance
have shown continual improvement since membranes came into more general use in the
drinking water industry. There are measures that can be taken to prolong membrane life;
however, experience with full scale applications in Ontario have generally shown that
membrane replacement is generally required every 7 to 10 years.
8.4.2 Evaluating Performance
MF and UF membranes have chemically formed and uniformly sized pores that are 1 micron
(1 µm) or less in diameter (MOE, 2006). Membrane filtration removes pathogens, such as
Cryptosporidium and Giardia, mainly by size exclusion (i.e. microbes larger than the
membrane pores are removed). Virus removal capability will vary with the type and
manufacturer of a particular membrane.
As noted in Section 8.2.2, the projection of the capacity of a filtration process is based mainly
on hydraulic loading rates and the ability to meet filter effluent turbidity objectives. For
membrane systems, the filtration rate, or flux, is defined by the volume or mass of permeate
(water) passing through the membrane per unit area per unit time (MOE, 2008). The flux is
commonly expressed as m3/m
2/s or m/s.
The operational requirements for membrane filtration systems specified in the Disinfection
Procedure (MOE, 2006) include the following compliance criteria (or as required by the most
recent version of the Disinfection Procedure):
Maintain effective backwash procedures, including filter-to-waste or an equivalent
procedure, to ensure that the effluent turbidity requirements are met at all times;
Monitor integrity of the membrane by continuous particle counting or equivalently
effective means (e.g., intermittent pressure decay measurements);
Continuously monitor filtrate turbidity; and
Meet the performance criterion for filtered water turbidity of less than or equal to 0.1
NTU in 99 percent of the measurements each month.
Membrane filtration systems are proprietary and the manufacturer should be consulted for
specific design criteria. Consideration should also be given to water demand during the cold
season, as cold water will significantly reduce the flux in a membrane system.
Table 8-7 presents monitoring recommended, in terms of sampling locations and analyses, in
order to evaluate the performance of membrane filtration processes.
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Table 8-7 – Membrane Filtration – Recommended Monitoring to Evaluate Performance
Location Types of Sample/
Measurement Parameters/ Analyses
Raw water Continuous monitoring Turbidity
pH
Temperature
Flow rate into membrane system or
individual membrane trains
Continuous monitoring or
Grab sample Colour
Total and/or dissolved organic carbon
Iron and manganese (if applicable)
Pre-treatment effluent
(if applicable)
Continuous monitoring or
Grab sample Turbidity
Total and/or dissolved organic carbon
Individual permeate line
(each membrane train)
Continuous monitoring Filtration rate and volume of permeate
Turbidity
Particle counts
Individual membrane
train
Continuous monitoring Transmembrane pressure (to measure
degree of fouling and initiate cleaning)
Backpulse pressure (prevent damage to
membranes)
Individual reject or
concentrate lines (each
membrane train)
Continuous monitoring Flow and volume of waste stream (to
calculate overall recovery rate)
Individual backwash
lines
Continuous monitoring Backwash flow rate and volume
Combined filter effluent Continuous monitoring or
Grab sample Flow rate
Colour
pH
Total and/or dissolved organic carbon
Iron and manganese (if applicable)
Aluminum or iron residual (if applicable)
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Table 8-7 – Membrane Filtration – Recommended Monitoring to Evaluate Performance
(cont’d.)
Location Types of Sample/
Measurement Parameters/ Analyses
Process waste stream
(membrane backwash
water)
Continuous monitoring or
Grab sample Flow or volume
Turbidity or total suspended solids
Chlorine residual (if applicable)
Individual membrane
Clean-in-place tank
Continuous monitoring or
Grab sample pH
Residual measurement (cleaning solution
concentration)
Other cleaning solution strength
measurement (as recommended by the
manufacturer)
Additional monitoring may be required for proprietary systems; the evaluator should review
manufacturer’s literature for recommended process monitoring parameters.
Figure 8-5 presents a process schematic of a typical membrane filtration process, along with
the identification of various sampling locations.
Filter Influent
Combined
Filter Effluent
Sample Location
Individual Train
Permeate Line
Sample Location
MF/UF Membrane
System
Filter Influent
Sample Location
Figure 8-5 – Membrane Filtration – Process Schematic and Sampling Locations
8.4.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with the membrane filtration
process are shown in Table 8-8.
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Table 8-8 – Membrane Filters – Symptoms and Causes of Common Problems
Problem Description
Mitigation
Fouling Adsorption or clogging of material
on the membrane surface which
cannot be removed during the
backwash cycle.
Fouling reduces the recovery rate
achieved by the system.
Caused by raw water or feedwater
with iron or other metal oxides,
organics, colloids, bacteria and other
microorganisms.
The rate of membrane fouling can
be reduced but it cannot be
prevented from occurring over time.
Pre-treatment prior to membrane
filtration (such as upstream
clarification and/or fine screening).
Membrane backwashing with water
and/or membrane scouring with air.
Chemical cleaning of membranes.
Increase membrane surface scouring
or crossflow velocity.
Increase amount of membrane
surface area to reduce applied flux.
Optimization of upstream chemical
addition (coagulant and/or polymer).
Scaling Formation of scales or precipitates
on the membrane surface.
Scaling occurs in raw water or
feedwater with calcium sulphate,
calcium carbonate, metal oxides and
silica (AWWA, 1995).
Preventative cleaning (backwashing
or chemical cleaning).
Adjustment of operational variables,
recovery rate, pH, temperature.
Optimization of upstream chemical
(coagulant and/or polymer) addition.
Membrane
degradation Gradually with time, membrane
degradation is inevitable (MWH,
2005).
Over time, the flux gradually
decreases and less permeate is
produced by the membrane (MWH,
2005).
To prolong membrane life the
following substances should be
limited in the feedwater: acids, bases,
pH extremes, chlorine and other
oxidants, bacteria (AWWA, 1995).
Eventual replacement of membranes
required, generally after a period of 5
to 10 years (MWH, 2005).
Poor effluent
quality Increase in turbidity or particle
count may indicate damage to
membrane, process piping or
process seals.
Optimization of upstream processes.
Integrity testing should be performed
to identify possible damage to
membranes, process piping or
process seals.
Increase or
decrease in
transmembrane
pressure
Either a gradual increase or a sudden
drop in membrane pressure is
observed.
Membrane performance is strongly
affected by changes in temperature.
At low temperatures, water viscosity
increases and membrane
permeability decreases.
Gradual increase indicates that a
membrane cleaning sequence needs
to be initiated.
Sudden decrease is a sign of
membrane damage.
Temperature of the feed water should
be monitored.
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8.4.4 Optimization Techniques
8.4.4.1 Optimizing Pre-Treatment
Optimization of pre-treatment, such as upstream coagulation/flocculation and clarification,
and/or micro-screening, will increase the efficiency and life of the membranes. Pre-treatment
requirements will depend on the quality of the raw water, the type of membrane used and
filter effluent turbidity goals. Membrane fouling, backwashing and chemical cleaning
frequency can also be minimized through the optimization of pre-treatment processes. Jar
testing and/or pilot testing is recommended (see Chapter 4).
Additional information regarding optimization of screening, coagulation/flocculation and
clarification processes is presented in Chapters 5, 6 and 7 of this Manual, respectively.
8.4.4.2 Optimizing Membrane Cleaning
Operating membranes at elevated flux levels can increase fouling potential. Routine
monitoring of membrane flux is recommended to ensure that the membrane is operating
within the design value at which deterioration of system performance begins to occur. The
optimum membrane design flux is normally established during pilot testing and is based on
the fouling characteristics of the raw water or feedwater, the membrane material and the
membrane system configuration. Conversely, operating at a reduced flux can result in
inefficient use of installed membrane capacity. Membrane modules can be taken off-line or
put back on-line to allow operation at an optimum flux for performance and membrane life.
Optimization of backwash frequency will aid in maintaining low TMP during operation of a
membrane system. Consideration should be given during optimization to ensure that the
increased backwashing does not decrease the overall recovery of water. As with granular
filters, the production per filter run (e.g. m3 of filtrate per m
2 of filter area per cycle) should
be monitored.
Backwashing of membranes generally involves forcing permeate water through the fibre wall
in the reverse direction at a pressure higher than the normal filtration pressure (MWH, 2005).
Backwash can include air scour to loosen material on the membrane surface. The frequency
and duration of backwash can vary depending on the type of membrane used. The
manufacturer/supplier of the membranes should be consulted for appropriate cleaning
procedures. An enhanced chemical backwash, which involves using chlorinated backwash
water, can be used to control biological growth on the membranes in some systems.
Despite frequent backwashing, membrane filters gradually lose filtration capacity due to
fouling or adsorption of materials that cannot be effectively removed during the backwash
cycle. A chemical clean-in-place is a method of cleaning in which the membranes are
submerged in proprietary cleaning solutions that are often heated to 30 or 40°C (MWH,
2005).
Frequency of chemical cleaning is site specific and should be determined based on pilot study
data or as directed by the manufacturer (MOE, 2008). The frequency of cleaning will depend
on the fouling characteristics of the raw water, the applied flux, and use of chlorine upstream
of the membrane.
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8.4.4.3 Integrity Testing
Integrity testing is used to routinely evaluate membrane and housing integrity and overall
filtration performance. There are two basic types of integrity testing: continuous indirect
integrity testing and periodic direct integrity testing.
Indirect integrity testing includes on-line particle counting or turbidity used as a continuous
indication of the membrane integrity. In general, sustained particle counts in the filtrate
should remain below 20 counts/mL. If filtrate particle counts exceed 20 counts/mL for an
extended period of time, this may be an indication that a membrane fibre has been breached
and the membrane module should be isolated and checked for integrity.
Direct integrity testing includes such measures as pressure decay, vacuum hold, bubble point
or sonic testing. The frequency of direct integrity testing will depend on the quality of the raw
water and the robustness of the membranes. The manufacturer should be consulted for
additional information.
Integrity testing, as noted above, is a requirement if the membrane process is to be used for
disinfection removal credits (refer to the Disinfection Procedure; MOE, 2006). The integrity
monitoring technique used should be able to confirm numerically that the required log
disinfection credit is being achieved and process train leaks are repaired to consistently
achieve this performance.
8.5 CASE HISTORIES
8.5.1 Racine, Wisconsin – Optimizing Membrane Maintenance
The following case study is based on information presented in Kosterman (2010).
System Description
The Racine Water Utility (RWU) owns and operates a conventional water treatment plant.
Following the Cryptosporidium outbreak in Milwaukee in 1993 and two boil-water notices in
the spring of 1994, the RWU began investigating advanced treatment technologies to
improve the protection of public health. In 2005, the RWU began operating a 190 ML/d
immersed membrane system that was installed downstream of the conventional plant to
provide an additional barrier against potential pathogens.
RWU’s UF membrane plant consists of 4,032 modules in 7 trains (each train with 6 cassettes
of 96 modules). Each module’s filtration surface area is approximately 46 m2 with between
20,000 and 30,000 individual fibres. Integrity testing of the membranes is conducted three
times per day, in accordance with federal and state regulations. The membranes are air
pressurized and the pressure decay is measured for 5 minutes and a log removal value is
calculated from the pressure decay.
With more than 120 million fibres in the membrane plant, even a small percentage of breaks
can lead to significant membrane repair. RWU’s membrane repair constitutes the single
largest investment of labour dedicated to the membrane plant.
Backwashing of the membrane includes air scour and is conducted once every 30 minutes.
Chemical clean-in-place is also conducted periodically to remove fouling.
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Optimization Guidance Manual for Drinking Water Systems 2014
Optimization Strategies
Because of the consistently high level of performance of the membrane filtration process, the
installation of membrane filters at the plant has allowed a shift in operating strategy at the
RWU from optimizing water quality to optimizing water production. Optimization goals
therefore focus on reducing membrane fouling and train downtime.
Maintenance Clean: Original SOPs required a daily maintenance clean on each train. After a
lengthy full-scale trial study, permission was granted by the manufacturer to decrease
maintenance cleans to once per week. This change decreased maintenance cleans from 49 to
7 per week, increased available production time by 24.5 hours per week and significantly
lowered chemical use.
Minor Equipment Modifications: Additional membrane modules were installed to provide
additional filtration surface area, resulting in lower operating TMPs and extending the time
between chemical cleans. In addition, the membrane integrity testing air system regulator was
replaced with a higher capacity unit, allowing faster pressurization. Other modifications were
also completed resulting in more efficient priming of the membranes and piping after integrity
test completion. With these equipment changes, the duration of the integrity test was reduced
from approximately 45 minutes to 25 minutes. For RWU, this increased production time by 7
hours per day. By decreasing membrane downtime and increasing filtration surface area, it was
possible to operate the trains at a lower flux and TMP.
Membrane Fouling Reduction: RWU had traditionally used an iron-based coagulant as part
of the conventional treatment process. Over time, however, operations staff noticed
discolouration of the membrane fibres during membrane repairs. Staff members believed that
iron carryover from the conventional treatment process was causing a build-up on the
membrane surface and increased fouling. A series of total and dissolved iron tests were
conducted on the membrane feed and permeate waters, confirming that iron was depositing
on the fibres. After consulting with the manufacturer, the RWU switched to a PACl coagulant
and a plant trial was initiated. Almost immediately, a noticeable increase in permeability
occurred. The chemical pre-treatment change in the conventional plant decreased membrane
fouling, decreased citric acid cleans, and reduced TMPs (and permeate pump speeds), making
operations more efficient and reducing costs.
Cold-Water Operations Improvements: RWU had experienced increased transmembrane
pressures and fouling rates when water temperature fell below 10°C, requiring more frequent
chemical cleans. RWU, in consultation with the manufacturer, modified the control system to
allow more trains to be switched on to produce the same amount of water, resulting in lower
TMP and fouling rates and returning the system to normal chemical clean intervals.
Summary
The RWU has found that membrane filtration is a considerable capital and operational
investment. Optimizing membrane operations decreases costs as well as chemical and
mechanical stresses on membrane fibres. Even minor modifications can result in more
efficient operation and reduce costs.
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Optimization Guidance Manual for Drinking Water Systems 2014
8.5.2 Fort McMurray, Alberta – Filter Media Optimization and Upgrading Study
The following case study is based on information presented in Suthaker et. al. (2007).
System Description
The Fort McMurray WTP is owned and operated by the Regional Municipality of Wood
Buffalo (RMWB). The WTP draws raw water from the Athabasca River and the rated
hydraulic capacity of the plant is 40 ML/d. The treatment process consists of pre-disinfection,
coagulation, flocculation, clarification and filtration.
As a result of a robust economy and massive expansions to the oil sands operations in the
region, rapid population growth within the RMWB area occurred. Between 2000 and 2002,
the RMWB undertook a number of studies to define potential options and costs for upgrading
the Fort McMurray WTP. The two plant upgrading concepts consisted of expansion using
either conventional treatment or membrane filtration. In view of the population growth
uncertainty, the RMWB opted for a flexible, staged expansion strategy. Costs for upgrading
to a membrane filtration process to provide 60 ML/d of capacity were estimated at $11
million (2002 CDN dollars). During a Value Engineering session conducted in 2003, the
RMWB elected to proceed with a combination of optimization measures and minor capital
improvements to expand the plant capacity to 50 ML/d and to defer the membrane upgrades.
Optimization Strategies
One of the key optimization goals was to improve the filtration process to meet new
regulatory requirements at the target expanded capacity. The filters had originally been
designed to treat 44 ML/d by operating at a filtration rate of 11.2 m/h; however, the process
could not meet filter effluent turbidity goals at these elevated filtration rates. The current
maximum filtration rate of 8 m/h (needed to maintain regulatory compliance) limited the
plant capacity to 30 ML/d. Given the challenges of turbidity and particle count compliance,
the existing filters needed to be upgraded to meet the expanded capacity of 50 ML/d. It was
decided to modify the existing filters to allow for deep bed filtration operating at much higher
filtration rates (up to 20 m/h). As such, pilot studies were initiated to evaluate media depth,
size and backwash considerations, as well as pre-treatment requirements.
Filtration objectives used to evaluate filter performance during the pilot studies were
established as follows:
Turbidity of less than 0.3 NTU;
Particle counts (> 2 µm) of less than 50/mL (according to Alberta Environment
Standards); and
Differential head loss increase of 1.5 m.
Filter runs would be terminated if any of the above criteria were exceeded.
Pilot testing indicated that an optimum combination of filtered water quality and filter run
length could be achieved using a dual media configuration (0.5 mm size crushed quartz and 1
mm anthracite) and total media depth between 1.6 and 1.9 m.
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Optimization Guidance Manual for Drinking Water Systems 2014
The pilot testing also confirmed that the existing backwash facilities were sufficient to
provide for adequate air scour, backwash rate and bed expansion for the upgraded filters.
At full scale, additional process optimization was conducted to minimize the solids loading
on the filters, including upgrading the clarifiers with tube settlers and increasing the
coagulant dosage (based on the results of the pilot testing). The physical improvements to the
sedimentation process resulted in longer filter runs and slightly improved particle counts in
the full-scale filters. Increasing the coagulant dose also had a dramatic effect on particle
counts and filter run length. Lower colour and turbidity levels were also recorded in the filter
effluent following the coagulation change.
Summary
Modifying existing filtration facilities for deep bed high-rate filtration offers an alternative to
expansion of conventional treatment plants and can improve finished water quality to meet
more stringent regulatory requirements. Filtration rates of over 18 m/h were achieved as a
result of the upgrades. Pilot studies are recommended to establish appropriate design
parameters specific to site conditions (raw water quality, pre-treatment requirements, etc.).
8.6 REFERENCES
American Society of Civil Engineers and American Water Works Association (2004). Water
Treatment Plant Design, 4th Ed. McGraw-Hill. ISBN 0-07-141872-5.
Amirtharajah, A., N. McNelly, G. Page and J. McLeod (1991). Optimum Backwash of Dual
Media Filters and GAC Filter-Adsorbers with Air Scour. AwwaRF and AWWA. Denver,
CO. ISBN 0-89867-576-6.
AWWA (1995). Water Treatment, 2nd
Ed. AWWA. Denver, CO. ISBN 0-89867-789-0.
AWWA, Lyonnaise des Eaux and Water Research Commission of South Africa (1996).
Water Treatment Membrane Processes. McGraw-Hill Inc. New York.
AWWA (1999). Water Quality and Treatment: A Handbook of Community Water Supplies,
5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
AWWA (2007). M37: Operational Control of Coagulation and Filtration Processes. 2nd
Ed.
AWWA. ISBN 978-1-58321-055-0.
Beverly, R.P. (2005). Filter Troubleshooting and Design Handbook. AWWA. Denver, CO.
ISBN 978-1-58321-349-0.
Cleasby, J.L, M.M. Williamson and E.R. Baumann (1963). Effect of Filtration Rate on
Changes in on Quality. Journal AWWA, 55:869-878.
Cleasby, J.L., D.J. Hilmoe, C.J. Dimitracopoulos and L.M. Diaz-Bossio (1984). Effective
Filtration Methods for Small Water Supplies. Project Summary U.S. EPA Cooperative
Agreement CR808837-01-0. EPA 600/S2-84-088.
CHAPTER 8. Filtration 8-28
Optimization Guidance Manual for Drinking Water Systems 2014
Cleasby, J.L.. G.L. Sindt, D.A. Watson and E.R. Baumann (1992). Design and Operation
Guidelines for Optimization of the High-Rate Filtration Process: Plant Demonstration
Studies. AwwaRF and AWWA. Denver, CO. ISBN 0-89867-604-5.
Cullen, T.R. and R.D. Letterman (1985). The Effect of Slow Sand Filter Maintenance on
Water Quality. Journal AWWA, Vol. 77, No. 12. December 1985.
Eighmy, T.T., J.P. Malley Jr. and M.R. Collins (1993). Biologically Enhanced Slow Sand
Filtration for Removal of Natural Organic Matter. AWWA. Denver, CO. ISBN 0-89867-
644-4.
Great Lakes-Upper Mississippi River Board of State Public Health and Environmental
Managers (2007). Recommended Standards for Water Works, (known as the “Ten State
Standards”).
Hess, A., M. Chipps and A. Rachwa (2002). Filter Maintenance and Operations Guidance
Manual. AwwaRF and AWWA. Denver, CO. ISBN 978-1-58321-234-9.
Kosterman, M. (2010). Decrease Operational Costs with Membrane Maintenance. AWWA
Opflow, Vol. 36, No. 4. April 2010.
LeChevallier, M.W. and K.-K. Au (2004). Water Treatment and Pathogen Control: Process
Efficiency in Achieving Safe Drinking Water. World Health Organization. ISBN 92-4-
156255-2.
Logsdon, G.S., A. Hess, M. Chipps and A. Rachwa (2002). Filter Maintenance and
Operations Guidance Manual. AwwaRF & AWWA. Denver, CO. ISBN 1-58321-234-5
Logsdon, G.S. (2008). Water Filtration Practices: Including Slow Sand Filters and Precoat
Filtration. AWWA, Denver, CO. ISBN 978-1-58321-595-1.
MOE (2006). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.
MOE (2008). Design Guidelines for Drinking Water Systems, 2008. ISBN 978-1-4249-8517-
3.
MWH (2005). Water Treatment: Principles and Design, 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
Nix, D.K and J.S. Taylor (2003). Filter Evaluation Procedures for Granular Media. AWWA.
Denver, CO. ISBN 978-1-58321-026-0.
Patania, N.L., J.G. Jacangelo, L. Cummings, A. Wilczak, K. Riley and J. Oppenheimer
(1995). Optimization of Filtration for Cyst Removal. AwwaRF and AWWA. Denver, CO.
ISBN 0-89867-825-0.
Renner, R.C., B.A. Hegg and J.H. Bender (1990). EPA Summary Report: Optimizing Water
Treatment Plant Performance with the Composite Correction Program. U.S. EPA Centre for
Environmental Research Information. Cincinnati, OH. EPA 625/8-90/017.
CHAPTER 8. Filtration 8-29
Optimization Guidance Manual for Drinking Water Systems 2014
Suthaker, S.S., G.E. Drachenberg and M.H. Mack (2007). Modified Deep Bed Filtration:
Low-cost Option for Increasing Capacity and Improving Quality Within Existing Filter Cells,
presented at the 2007 American Water Works Association Annual Conference and
Exposition, Toronto, ON.
USEPA (2005). Membrane Filtration Guidance Manual. Office of Drinking Water.
Cincinnati, OH. EPA 815-R-06-009.
Wolfe, T. (2003). Filtration – Part I: Filtration Fundamentals, presented at the 2003 Annual
Kentucky Water and Wastewater Operators’ Conference, Fort Mitchell, Kentucky, March
2003.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 9DISINFECTION
DISINFECTION
9.1 Introduction ............................................................................................................ 9-1
9.2 Chemical Inactivation ............................................................................................. 9-1
9.2.1 Purpose and Chemicals Commonly Used ................................................ 9-1
9.2.2 Evaluating Performance ........................................................................... 9-3
9.2.3 Common Problems and Potential Impacts ............................................... 9-8
9.2.4 Optimization Techniques ......................................................................... 9-9
9.3 Ultraviolet (UV) Irradiation ................................................................................. 9-15
9.3.1 Purpose and Mode of Disinfection ........................................................ 9-15
9.3.2 Evaluating Performance ......................................................................... 9-16
9.3.3 Common Problems and Potential Impacts ............................................. 9-17
9.3.4 Optimization Techniques ....................................................................... 9-19
9.4 Case Histories ....................................................................................................... 9-21
9.4.1 Port Rowan WTP – pH Control for Optimizing Disinfection ............... 9-21
9.4.2 Ameliasburgh WTP – Optimization Study to Control the Formation of
DBPs ...................................................................................................... 9-22
9.5 References ............................................................................................................ 9-25
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Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 9
DISINFECTION
9.1 INTRODUCTION
The disinfection process is the most important barrier in the treatment process and is
responsible for inactivating pathogens that have not been removed by upstream unit
processes. For the purposes of this Manual, the assessment of disinfection capability is based
on the requirements of the Procedure for Disinfection of Drinking Water in Ontario
(Disinfection Procedure, MOE, 2006) adopted by reference by O. Reg. 170/03 under the
SDWA, 2002.
A clear distinction is made between primary disinfection and secondary disinfection, which
are often completely separate treatment processes and are designed with different objectives.
Primary disinfection is a process or a series of processes intended to inactivate human
pathogens, such as viruses, bacteria and protozoa, potentially present in raw water before the
water is delivered to the first consumer. The entire process of primary disinfection must be
completed within the water treatment component of the drinking water system, which may
include a dedicated part of the distribution system before reaching the first consumer.
Secondary disinfection is the maintenance of a disinfectant residual throughout the
distribution system to protect the drinking water from microbiological re-contamination,
reduce microbial re-growth, control biofilm formation and serve as an indicator of
distribution system integrity.
Five disinfection agents are commonly used in drinking water treatment: free chlorine,
combined chlorine, ozone, chlorine dioxide and UV light. The first four agents are chemical
oxidants, whereas UV light involves the use of electromagnetic radiation (MWH, 2005). A
discussion of advantages and disadvantages of various primary disinfectants, as well as
process selection and design guidance for these processes, can be found elsewhere (USEPA,
1999; White, 1999; USEPA, 2006).
This chapter covers the various disinfection processes used in primary disinfection of
drinking water to inactivate pathogenic microorganisms. Secondary disinfection is addressed
in Chapter 11.
9.2 CHEMICAL INACTIVATION
9.2.1 Purpose and Chemicals Commonly Used
The selection of an appropriate disinfection process depends upon site specific conditions and
raw water characteristics that are unique to each drinking water system. The choice of
disinfectant should consider and balance the need to inactivate pathogens with the need to
minimize the formation of DBPs. Chemical disinfectants accepted for use in primary
disinfection in Ontario include chlorine, chlorine dioxide and ozone.
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Optimization Guidance Manual for Drinking Water Systems 2014
9.2.1.1 Chlorine
Chlorine is the most commonly used disinfectant in water treatment in Ontario and
throughout the world. Chlorine is a strong oxidant that is highly effective for inactivating
bacteria and viruses. It has been found to affect reproduction and metabolism, cause
mutations, and ultimately cause death of microorganisms. Protozoan cysts are highly resistant
to chlorine and may require prolonged contact times at a high chlorine residual to achieve
adequate inactivation (LeChevallier, 2004).
The most common chlorine chemicals used for drinking water disinfection are chlorine gas
(Cl2), sodium hypochlorite (NaOCl) and calcium hypochlorite (Ca(ClO)2).
Free chlorine, in the form of hypochlorous acid (HOCl) and hypochlorite ion (OCl-), is
formed by the reaction between chlorination chemicals and water.
If ammonia is present in the water, HOCl will react readily with ammonia to form three
species of chloramines, which are generally referred to as “combined chlorine”.
Monochloramine, usually the predominant form of combined chlorine, is a weak disinfectant
and rarely suitable for use as a primary disinfectant, because it requires very long contact
times at typical concentrations to achieve adequate disinfection. Because of its persistence in
the distribution system, monochloramine is more commonly used as a secondary disinfectant
(see Chapter 11).
In situations where breakpoint chlorination is being practiced (to oxidize natural raw water
ammonia), the reaction should be effectively complete before the water leaves the
disinfection process; otherwise, the chlorine residual may be prematurely and rapidly lost
through continuing chemical reactions. Where ammonia and other nitrogenous substances are
present in the influent water, the application of chlorine should be such that the resulting free
chlorine residual comprises more than 80 percent of the total chlorine residual at the end of
the primary disinfection process.
9.2.1.2 Chlorine Dioxide
When chlorine dioxide (ClO2) is used as a disinfecting agent, it must be generated on-site
through the reaction of sodium chlorite with chlorine gas, hypochlorous acid or hydrochloric
acid (HCl), or through the use of an electrochemical process.
Chlorine dioxide is a more powerful disinfectant than chlorine, but less than ozone. Chlorine
dioxide is also more effective over a greater pH range (pH 5 to 10) than free chlorine
(LeChevallier, 2004). Chlorine dioxide is an effective disinfectant for control of cysts and
oocysts. Chlorine dioxide also has the capability of providing a lasting residual and has been
used as a secondary disinfectant.
Chlorine dioxide is capable of oxidizing iron and manganese, removing colour, and oxidation
of natural organic compounds without THM formation. It also oxidizes many organic and
sulphurous compounds that cause tastes and odours. The application of chlorine dioxide for
these purposes is discussed in Chapter 10.
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Optimization Guidance Manual for Drinking Water Systems 2014
9.2.1.3 Ozone
Ozone (O3) must be generated on-site by means of an electrical discharge in oxygen or dry
air. Although ozone is a highly effective disinfectant, it does not produce a lasting residual,
and is therefore not suitable for secondary disinfection.
Once dissolved in water, ozone begins a process of decay that results in the formation of
radicals, such as hydroxyl radicals (HO·). Ozone reacts with microorganisms and other
contaminants in two ways: (1) by direct oxidation and (2) through the action of hydroxyl
radicals generated during its decomposition.
The disinfection efficiency of ozone is not affected by pH, although ozone decomposition
occurs faster in solutions with higher pH; therefore, more ozone should be applied at high
pHs to maintain required ozone concentrations (USEPA, 1999).
In addition to its use as a primary disinfectant, ozone can be used for oxidation of iron
and manganese, taste and odour causing compounds and natural organic matter, as a
potential flocculant aid and for the destruction of algal toxins. The application of ozone
for purposes other than disinfection is discussed in Chapter 10.
9.2.2 Evaluating Performance
9.2.2.1 CT Approach
In Ontario, the minimum level of treatment required for municipal and regulated non-
municipal residential drinking water systems is specified in the Disinfection Procedure
(MOE, 2006). The treatment requirements for these drinking water systems are as follows:
For groundwater systems, the treatment process must consist of disinfection and must
be credited with achieving an overall performance that provides, at a minimum, 2-log
(99%) removal or inactivation of viruses.
For surface water or groundwater under the direct influence of surface water (GUDI)
systems, the treatment process must consist of chemically assisted filtration and
disinfection (or other treatment capable of producing water of equal or better
quality), and achieve an overall performance that provides, at a minimum, 2-log
(99%) removal or inactivation of Cryptosporidium oocysts, 3-log (99.9%) removal or
inactivation of Giardia cysts, and 4-log (99.99%) removal or inactivation of viruses.
It should be noted that these are the minimum levels of removal or inactivation required for
human pathogens, and the disinfection requirements for a specific system may need to be
increased if the raw water source is subject to excessive contamination from cysts and/or
viruses. Cyst and virus removal credits for the different types of treatment processes (e.g.
conventional filtration, membrane filtration, etc.) are provided in the Disinfection Procedure
(MOE, 2006).
The Disinfection Procedure (MOE, 2006) ensures that the required levels of chemical
disinfection are achieved by using the CT concept. CT values are calculated using the
disinfectant residual concentration (C) multiplied by the actual time (T) that the finished
water is in contact with the disinfectant. In the Disinfection Procedure, CT values are
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Optimization Guidance Manual for Drinking Water Systems 2014
provided that can be used to determine the log inactivation for various disinfectants at
specific operating conditions (e.g. temperature, pH and disinfectant residual).
The calculated CT value should, at all times during plant operation, be equal to or greater
than the required CT value. Where pH and disinfectant residual levels change significantly in
different sections of the process, a more accurate estimate of the overall treatment is
obtainable by adding log inactivation values for each type of microbial threat in each section.
The Integrated Disinfection Design Framework (IDDF) (Bellamy, et. al., 1998) method for
accounting for disinfection decay and true process hydraulics can be used for determining the
CT values and associated logs of microbial inactivation as a means of optimizing pathogen
control while minimizing DBP formation.
The approach described below can be used to determine the capability of a plant to meet
the disinfection requirements based on the CT values presented in the Disinfection
Procedure. Procedures are presented for both pre- and post-disinfection, with pre-
disinfection defined as adding the disinfectant ahead of the filtration process and post -
disinfection defined as adding the disinfectant following filtration. Whether or not a
utility can use pre-disinfection depends on raw water quality. Concerns associated with
pre-disinfection include the potential formation of DBPs and the possible ineffectiveness
of disinfectants in untreated water.
Any volume required for providing storage for fire or equalization is not available for
contact time and should not be included in CT calculations.
Post-Disinfection
The following procedure is used to assess the plant’s disinfection capability when using only
post-disinfection:
Project the total log Giardia reduction and inactivation required by the water
treatment process based on the raw water quality or watershed characteristics.
Typically, Giardia inactivation requirements are more difficult to achieve than the
virus requirements; consequently, Giardia inactivation is the basis for this
assessment.
Project the log removal capability of the existing treatment plant. Expected removals
of Cryptosporidium, Giardia and viruses by various types of filtration processes are
presented in the Disinfection Procedure. A 2.5 log Giardia reduction may be
assigned for a conventional plant with adequate unit treatment process capability
(e.g. Type 1 units preceding disinfection as determined during the CPE). If the
existing plant does not meet the performance goals to be rated as a Type 1 facility, a
lower log removal capability may need to be assigned to the facility. For the purposes
of the projection of major DWS component capability, it should be assumed that the
plant will be operated to achieve optimum performance from existing units.
Select the required CT value from the tables in the Disinfection Procedure based on
the required log removal/inactivation, the log removal capability projected for the
plant, the maximum pH and minimum temperature of the water being treated, and the
projected maximum disinfectant residual. The maximum pH and minimum
temperature of the water being treated are selected to evaluate capability under worst
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Optimization Guidance Manual for Drinking Water Systems 2014
case conditions. When chlorine is used as the disinfectant, the maximum residual
utilized in the evaluation should not exceed 2.5 mg/L free residual, based on research
that indicates that contact time is more important than disinfectant concentration at
free chlorine residuals above 2.5 mg/L (Regli, 1990).
Using these parameters, calculate the required detention time, Treq, to meet the
required CT (equations are provided in Appendix G; sample calculations are included
in the example CPE provided in Appendix C).
Determine an effective volume of the existing clearwell and/or distribution piping to
the first user. Effective volume refers to the volume of a basin or piping that is
available to provide adequate contact time for the disinfectant. Effective volumes are
estimated by multiplying the nominal basin and/or piping volumes by a baffle factor.
The nominal basin and/or piping volumes are calculated based on worst case
operating conditions using the minimum operating depths, in the case of basins. This
is especially critical in plants where high lift pumps significantly change the
operating levels of the clearwell and for plants in which the backwash water is
supplied from the clearwell. Depending on the information available, there are two
ways to determine the effective volume.
Tracer studies or mathematical modelling (see Chapter 4) can be conducted to
determine the actual contact time of basins. Effective contact time is defined as T10,
which is the length of time during which not more than 10 percent of the influent
water would pass through that process. The use of T10 ensures that 90 percent of the
water will have a longer contact time. For plants where T10 has been determined
through tracer studies, the effective volume is the peak instantaneous operating flow
rate (m3/minute) multiplied by the T10 value (minute). It is important to note that the
tracer study results must also consider peak instantaneous operating flows as well as
minimum operating depths in order to determine an accurate CT.
For those plants where tracer studies have not been conducted, the effective volume
upon which contact time will be determined can be estimated by multiplying the
nominal clearwell and/or piping volumes by a baffle factor. The baffle factor is
defined as the ratio of T10/T, where T is the theoretical mean residence time and is
equal to the basin and/or piping volume divided by the bulk flow rate. A summary of
baffle conditions and baffle factors to be used in determining effective volume is
presented in the Disinfection Procedure.
Calculate a flow rate (Q) where the plant will achieve the required CT values for
post-disinfection based on the above determined effective volume. Equations are
provided in Appendix G. Use this flow rate to project the post-disinfection system
capability on the performance potential graph.
Pre-Disinfection
The following procedure is used to assess the plant’s disinfection capability when using pre-
disinfection along with post-disinfection. For purposes of the calculations, the approach
assumes that the disinfection requirements can be met independently by both pre- and post-
disinfection; therefore, these capabilities are additive when projecting plant disinfection unit
process capability. The procedure is used to determine the additional disinfection capability
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Optimization Guidance Manual for Drinking Water Systems 2014
provided by using pre-disinfection. If pre-disinfection is practised and the utility is concerned
about DBP formation, the performance potential graph should be developed with two bars for
disinfection: one including pre- and post-disinfection, and one including only post-
disinfection capability. This allows the evaluators and the utility to assess process capability
if pre-disinfection is excluded.
Project the total log Giardia reduction and inactivation required by water treatment
processes based on the raw water quality or watershed characteristics.
Project the log removal capability of the existing treatment plant and determine the
log inactivation required.
Select the required CT value for pre-disinfection from the tables in the Disinfection
Procedure. This value should be based on the required log reduction, the log removal
capability of the plant, the maximum pH and minimum temperature of the water
being treated and the projected maximum disinfectant residual. The required pre-
disinfection CT value may be different than the post-disinfection conditions if
different temperature, pH and residual conditions exist for the two processes (e.g.
addition of lime or soda ash to increase the pH of finished water would change the
required post-disinfection CT value relative to the pre-disinfection value).
Calculate Treq (i.e.. CT value required divided by the projected operating disinfectant
residual as presented in the post-disinfection procedure).
Select an effective volume available to provide adequate contact time for pre-
disinfection. Assess which basins, pipes and conduits will provide contact time.
These typically include the flocculation and sedimentation basins, but could
include raw water transmission lines if facilities exist to inject disinfectant at the
intake structure. Filters typically are not included because of the short detention
times typically provided by filtration and the reduction in chlorine residual that
often occurs through filters. The actual basin volumes should be converted to
effective volumes by applying baffle factors as described in the Disinfection
Procedure and discussed previously in the post-disinfection procedure. Add the
individual effective volumes together to obtain the total effective pre-disinfection
volume.
Calculate a flow rate where the plant will achieve the required CT values for both
pre- and post-disinfection using the formula shown in Appendix G. Use this flow rate
to project the pre- and post-disinfection system capability on the performance
potential graph.
9.2.2.2 Monitoring of Primary Disinfection
Routine monitoring of the relevant parameters associated with the performance of the
disinfection process must be carried out to ensure that the finished water has been properly
disinfected. Primary disinfection facilities, for all regulated drinking water systems, must
be equipped with continuous disinfection process monitoring and recording devices with
alarms unless otherwise specified in O. Reg. 170/03.
Where appropriate instrumentation is available, consideration should be given to using
continuous monitoring data to provide a real-time and recorded display of the relevant
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CT data and microbial log removal/inactivation actually being achieved by the overall
treatment process for all targeted microbial threats.
Table 9-1 presents recommended monitoring, in terms of sampling locations and
analyses, in order to evaluate the performance of the disinfection process using free
chlorine, chlorine dioxide and ozone.
Table 9-1 – Primary Disinfection (Chemical Inactivation) – Recommended Monitoring
to Evaluate Performance
Location Types of Sample /
Measurement1 Parameters / Analyses Comments
Upstream of
the primary
disinfection
process
Continuous
monitoring Turbidity
pH
Temperature
Flow rate
Factors that may affect the
effectiveness of
disinfection and/or
influent disinfectant
demand
Individual
filter effluent
Continuous
monitoring Turbidity
Particle counts
To monitor the
effectiveness of the
filtration process for
particulate removal and
assess log removal
Chlorination
feed system
Continuous
monitoring Chlorine gas flow rate
(evaporators)
Chlorinator feed rate
(chlorinator)
Chlorine feed rate (liquid
chlorine systems)
To monitor disinfectant
dosage (note: can be
augmented with scale
weight loss over time)
Chlorine
dioxide2
generation
system
Continuous
monitoring Sodium chlorite flow rate
Chlorine gas (or HCl, or
HOCl) flow rate
Water flow rate
Chlorine dioxide
concentration
To monitor disinfectant
dosage
Ozone3
generation
process
Continuous
monitoring Gas flow rate
Water flow rate
Applied ozone dose and off-
gas concentration
To monitor disinfectant
dosage
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Table 9-1 – Primary Disinfection (Chemical Inactivation) – Recommended Monitoring
to Evaluate Performance (cont’d.)
Location Types of Sample /
Measurement Parameters / Analyses Comments
Downstream of
primary
disinfection
process
Continuous
monitoring Disinfectant residual
concentration (either free
chlorine residual, chlorine
dioxide residual or ozone
concentration, as applicable)
Where primary disinfection
is accomplished through a
series of distinct
disinfection
processes/steps, a
continuous sample must be
taken at the downstream
end of each distinct
process/step
Grab sample THM
HAA
Chlorite and/or chlorate (if
applicable)
Bromate (if applicable)
Total coliform, E. coli and
heterotrophic plate count
Notes:
1. Although continuous monitoring is recommended for several parameters, for small systems or
groundwater systems where water quality is relatively consistent, grab sampling may be more
appropriate, except where continuous monitoring is required by regulation.
2. Chlorine dioxide generation systems are proprietary and the associated monitoring equipment
may vary by supplier.
3. Ozone generation systems are proprietary and the associated monitoring equipment may vary
by supplier. Many systems include residual monitoring at various points in the contactor to
maintain desired ozone residual and prevent energy-wasting overdosing. Some advanced
control strategies allow the ozone treatment process to continue using power and liquid
oxygen feed information in lieu of a temporarily malfunctioning ozone residual analyzer in
order to maintain disinfection continuity and water quality.
9.2.3 Common Problems and Potential Impacts
Table 9-2 presents the symptoms and causes of common problems encountered with primary
disinfection processes.
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Table 9-2 – Chemical Disinfection – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Impacts Common Causes
Loss of or Low
Disinfectant Residual
Concentration
Higher than typical disinfectant
dosages required to maintain
target disinfectant residual.
Potential for detection of
microbiological indicator
organisms in treated water.
Upstream process upsets.
Underdosing of disinfectant
chemical.
Poor performance of upstream
treatment processes (Section
9.2.4.1).
Changes in raw water quality
leading to increase disinfectant
demand.
Insufficient Initial
Mixing of
Chlorination
Chemical
Higher than typical disinfectant
dosages required to maintain
target disinfectant residual.
Potential for detection of
microbiological indicator
organisms in treated water.
Inadequate mixing energy
available at chemical addition
point (Section 9.2.4.2).
Insufficient Contact
Time
Higher than typical disinfectant
dosages required to maintain
target CT.
Potential for detection of
microbiological indicator
organisms in treated water.
Short-circuiting or dead zones in
contact chamber (Section 9.2.4.3).
Adequate plug flow conditions not
achieved in contact chamber
(Section 9.2.4.3).
Disinfection By-
Product Formation
Detection of elevated
concentrations of DBPs in
treated water.
Excessive disinfectant dose or
contact time (Section 9.2.4.5).
Insufficient removal of DBP
precursors (Section 9.2.4.5).
Tastes and Odours Customer complaints.
“Swimming pool” odour (for
systems using chlorine).
Over or underdosing of
disinfection chemical (9.2.4.4)
relative to the breakpoint curve.
9.2.4 Optimization Techniques
9.2.4.1 Optimizing Pre-Treatment Processes
Treated water quality (or filter effluent quality) has a strong impact on disinfectant demand
and disinfection efficiency. Generally, the characteristics of the filter effluent affect the
efficiency of chemical disinfection in two ways:
1. Exerting an additional oxidant demand thereby requiring a higher disinfectant
dosage to achieve the same level of pathogen reduction; and
2. Interference with the disinfection process.
Water characteristics that have a significant impact on the efficiency of disinfection may
include:
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NOM;
Turbidity;
Ammonia, nitrite and organic nitrogen;
Iron and manganese;
pH;
Low water temperature;
UVT; and
Higher than normal loading of microbial pathogens.
Generally, optimizing upstream processes will improve the efficiency of disinfection by
reducing the disinfectant demand and preventing the shielding of pathogens by suspended
solids.
In many cases, it may not be possible to change the characteristics of the raw water (i.e.
presence of cysts and viruses, water temperature, etc.); however, the following approaches
can be used to optimize disinfection:
Practice enhanced coagulation to reduce NOM concentrations in filtered water
(Section 9.2.4.5) resulting in lower DBP formation and reduced disinfectant demand.
Optimize filtration processes to reduce turbidity (Chapter 8).
Address causes of process upsets (e.g. floc carryover and/or poor coagulant chemical
dosage control) which may result in poor filter effluent quality and reduce the
effectiveness of disinfection.
Consider a change to ozonation with or without biofiltration, or consider eliminating
pre-chlorination to promote biological activity in filters (Chapter 10).
Seasonal variations in water quality (e.g. spring run-off, anaerobic conditions under
prolonged ice-cover) can affect the oxidant demand for disinfection. Variability in
water quality can cause difficulty in predicting the required chlorine dosages.
Incorporate measures such as increased monitoring of raw water and implementing
source water protection programs, if required.
9.2.4.2 Optimizing Initial Mixing
The disinfection effectiveness of chlorine is greatly enhanced by effective mixing of the
water and chlorine solution. Proper mixing optimizes the disinfection process in the
following ways:
Optimizes the amount of contact between the chlorine and the pathogens in the
water; and
Avoids the formation of chlorine concentration gradients resulting in inefficient
disinfection.
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In general, the use of a diffuser is sufficient to provide adequate mixing of chlorine in the
water stream. However, when ammonia is present, it is important that the chlorine be rapidly
blended with the bulk flow. If this is not accomplished, disinfection is compromised and both
chlorine and ammonia are lost in localized breakpoint reactions (MWH, 2005). In this case,
rapid mixing is required.
Disinfection can be optimized by the installation of, or improvements to, chemical diffusers,
mixing baffles or mechanical mixers, or other mechanisms to create a highly turbulent
regime. In some instances, moving the chemical addition point to a more turbulent location
can result in improved initial mixing.
Tracer tests and/or mathematical modelling (i.e. CFD) can be used to assess the degree of
mixing available for chlorination (Chapter 4).
9.2.4.3 Optimizing Contact Time
To optimize the inactivation of pathogens, it is necessary to maintain contact between the
target microorganisms and a minimum disinfectant residual concentration for a specified
period of time. As noted previously, this is assessed on the basis of the CT concept. The CT
achieved should exceed the CT required at all times. It should be noted, however, that
excessive contact times can lead to increased formation of DBPs (see Section 9.2.4.5).
Chemical inactivation of pathogens normally occurs in a contact chamber, which is typically
designed as a serpentine chamber to create plug flow conditions. In some drinking water
systems, the discharge piping or a portion of the distribution system prior to the first
consumer is used to provide some or all of the contact time.
Tracer tests should be conducted to verify that the required contact time is provided and to
ensure that there is no short-circuiting in the contact chamber (Chapter 4).
The following modifications can be incorporated to optimize contact time and prevent short-
circuiting:
Modify contact chambers to create plug flow conditions. Baffles or walls can be
incorporated to create a serpentine flow configuration. Length to width ratios of at
least 40:1 should be provided;
Provide rounded corners to reduce dead zone areas and eddy currents; and
Outlet structures of contact chambers should be provided with either a diffuser baffle
or a launder-type weir (White, 1999).
Chlorine contact chambers should also be cleaned regularly to ensure efficient performance.
9.2.4.4 Optimizing Disinfectant Dose
As discussed previously, current disinfection requirements for drinking water systems subject
to O. Reg. 170/03 are based on the CT approach presented in the Disinfection Procedure. In
general, the calculations used to achieve a desired CT for a target log inactivation tend to be
conservative, as they factor in worst case conditions for pH, temperature, flow, etc. and may
not reflect actual operating conditions. For example, temperatures are typically lowest in
winter, while peak flows are typically experienced in summer. The two challenging
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conditions may not coincide, and the actual CT achieved may be much higher than the CT
required.
Several optimization strategies, techniques and software tools are available that allow
operators to evaluate CT based on actual operating conditions. Examples include the IDDF
(Bellamy, et. al., 1998) and Disinfection Profiling and Benchmarking (USEPA, 2003). A
disinfection profile is a graphical representation of a system’s level of Giardia or virus
inactivation measured during the course of a year. A benchmark is the lowest monthly
average microbial inactivation achieved during the disinfection profile time period.
Proprietary spreadsheet or modelling tools can be used to support the implementation of
IDDF or disinfection profiling.
Monitoring of the actual CT achieved with regards to the CT required may allow a reduction
in the disinfectant dosage, resulting in reduced chemical usage and potentially reducing the
formation of DBPs.
9.2.4.5 Minimizing DBP Formation
The application of disinfectants and other oxidants to water may result in the formation of
disinfection by-products, some of which may be a public health concern.
Table 9-3 presents a summary of the most common DBPs formed as a result of the use of
chlorine, chloramines, chlorine dioxide and ozone during drinking water treatment.
Table 9-3 – Common Disinfection By-Products
Class By-Product
Chemical Agent
Trihalomethanes1 Chloroform Chlorine
Bromodichloromethane Chlorine
Dibromochloromethane Chlorine
Bromoform Chlorine, Ozone
Haloacetic acids2 Monochloroacetic acid Chlorine
Dichloroacetic acid Chlorine
Trichloroacetic acid Chlorine
Monobromoacetic acid Chlorine
Dibromoacetic acid Chlorine
Oxyhalides Chlorite Chlorine Dioxide
Chlorate Chlorine Dioxide
Bromate Ozone
Table 9-4 – Common Disinfection By-Products (cont’d.)
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Optimization Guidance Manual for Drinking Water Systems 2014
Class By-Product
Chemical Agent
Nitrosamines N-Nitrosodimethylamine Chlorine, Chloramines
Notes:
1. Several other THM compounds are known; however, only these four are included in the O.
Reg. 169/03 maximum acceptable concentration (MAC) for total THMs.
2. Four other HAA compounds are known; however, regulatory standards for HAAs are
generally based on the total of these five compounds (HAA5).
Chlorine By-Products
Optimization strategies to reduce the formation of THMs and HAAs include:
Elimination of pre-chlorination;
Improving precursor removal (enhanced coagulation, membrane filtration, GAC
filtration, ion exchange);
Optimizing pH during disinfection;
Optimizing chlorine dosage through disinfection profiling and benchmarking; and
Using alternative disinfectants.
Additional information is presented in Strategies for Minimizing the Disinfection By-
Products Trihalomethanes and Haloacetic Acids (MOE, 2009).
Technologies are also available for the removal of THMs and HAAs, such as GAC filtration
and aeration or air stripping; however, the application of these technologies at water
treatment plants is seldom practical compared to the other DBP reduction strategies discussed
above (MWH, 2005).
Other by-products, such as perchlorate, bromate, chlorate and chlorite, have also been found
as impurities in hypochlorite solutions. These contaminants may form during manufacturing,
or transport and storage. Dilution, temperature control, and less storage time are considered
to be the most practical approach for reducing by-products being added to finished water
from hypochlorite solutions (Stanford et. al., 2010).
Chlorine Dioxide By-Products
Chlorine dioxide does not form halogenated by-products like chlorine; however, it does
produce two inorganic by-products, chlorite and chlorate.
Chlorate may be naturally present in raw waters as a result of agricultural or industrial
activity and is also a degradation product of chlorine in liquid hypochlorite solutions (MWH,
2005).
Chlorite may be injected into the water stream as a result of inefficient chlorine dioxide
generation (sodium chlorite is one of the chemicals used to generate ClO2). The decay of
chlorine dioxide after it is applied to the water may also result in the formation of chlorite and
chlorate through one of two ways:
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The oxidation of various water constituents, such as reduced iron, manganese or
NOM; or
Under high temperature and/or high pH conditions, chlorine dioxide disproportionate
to form chlorite and chlorate.
The formation of chlorite limits the chlorine dioxide dose that can be applied during drinking
water disinfection, unless chlorite removal technologies are implemented downstream.
Currently, the only available measure to reduce chlorite formation is to reduce the chlorine
dioxide dose, which is accomplished by reducing the chlorine dioxide demand (i.e. improving
NOM removal and/or improving iron and manganese precipitation using other oxidants, prior
to application of chlorine dioxide).
The most common chlorite destruction or removal technologies for full scale WTPs are:
Reduction of chlorite to chloride with ferrous iron;
Reduction or removal with activated carbon; and
Oxidation with ozone.
Ozone By-Products
When added to water, ozone reacts with NOM and bromide (if present) to form various by-
products, including bromate. Strategies that can be implemented to reduce ozone by-products
include reducing NOM and/or bromide concentrations before the application of ozone, or
using less ozone.
Reducing ozone dosage is generally not practical, because the ozone dose is determined by
other factors, such as disinfection requirements or taste and odour control. Options for the
removal of NOM are the same as those discussed for minimizing the formation of
chlorination by-products (enhanced coagulation, GAC filtration, etc).
The following two measures have also been used to reduce the formation of bromate:
pH depression: Lowering the pH of water during ozonation hinders the formation of
intermediate compounds that react with ozone to form bromate.
Ammonia addition: Ammonia further reduces the concentration of intermediate
compounds that react with ozone to form bromate. Combining pH depression and
ammonia addition to some waters can be used to reduce bromate formation by more than
90 percent (MWH, 2005).
Several technologies exist for the removal of bromate and organic by-products formed as a
result of ozonation, including ion exchange, membrane filtration and biological filtration.
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9.2.4.6 Improving Process Control
Most municipal drinking water systems have some form of automated process control
system, particularly when alternative disinfectants (such as ozone, which require a greater
degree of operator attention) are employed. However, a chlorination system with manual
control can be optimized by employing an automated feed control strategy to regulate the
chlorination dosage. This approach will minimize chemical consumption and ensure that a
minimum chlorine residual is maintained at all times.
Control systems for chlorination dosage typically consist of:
1. Manual control: The operator adjusts dosages manually based on process conditions
and measured chlorine residual.
2. Flow proportional (or open-loop) control: The chlorine feed rate is paced to the flow
rate as measured by the filtered water meter (where post-disinfection is practiced).
Flow proportional control is sometimes referred to as “feed-forward” control.
3. Automatic residual (or closed-loop) control: The chlorine dosage is controlled by the
automatic measurement of the chlorine residual with an on-line chlorine analyzer.
Residual control is sometimes referred to as “feed-back” control.
4. Automatic compound-loop control: The chlorine dosage is controlled by both the
water flow rate and an automatic chlorine analyzer. The output from the water flow
meter and the residual analyzer is used by a programmable logic controller (PLC) to
control chlorine dosage and residual.
The chlorine residual analyzer is a key piece of instrumentation available to optimize the
chlorination disinfection process. Accurate measurement of chlorine residual is important to
ensure proper disinfection, while avoiding excessive chemical dosages and the potential
formation of DBPs.
The analytical method adopted to monitor chlorine residual at a water treatment plant must be
able to measure a range of concentrations with an appropriate level of accuracy and
reproducibility. In addition, proper maintenance and calibration, in accordance with
manufacturer’s instructions, must be conducted to ensure continued analyzer accuracy.
9.3 ULTRAVIOLET (UV) IRRADIATION
9.3.1 Purpose and Mode of Disinfection
The application of UV light is an acceptable primary disinfection process; however, since it
does not produce a residual, it is not suitable for secondary disinfection.
Specific requirements for the design and operation of UV systems are provided elsewhere
(MOE, 2006; MOE, 2008; USEPA, 2006).
UV systems are proprietary. Different UV technologies are available, including low pressure,
medium pressure (MP) and low pressure high output (LPHO) lamps.
The mechanism of disinfection by UV light differs considerably from the mechanisms
associated with chemical disinfectants such as chlorine and ozone. Chemical disinfectants
inactivate microorganisms by destroying or damaging cellular structures, interfering with
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metabolism and growth. UV light inactivates microorganisms by damaging their nucleic acid,
thereby preventing them from replicating. A microorganism that cannot replicate cannot
infect a host.
It has been determined that the germicidal effect of UV light is most effective at wavelengths
between 250 and 265 nm (White, 1999). Low-pressure lamps emit light at a specific
wavelength, 254 nm (MWH, 2005). Newer lamp technologies exist, as mentioned above,
which provide UV radiation at wavelengths different than 254 nm; therefore, the dosage
provided by a specific UV reactor should always be expressed as a 254 nm-equivalent UV
dose.
9.3.2 Evaluating Performance
Similar to the CT concept, the degree to which the destruction or inactivation of
microorganisms occurs by UV radiation is directly related to the UV dose. UV dose is
defined as the product of the UV light intensity (W/m2 or mW/cm
2) and the exposure time
(s). Units commonly used to express UV dose are mJ/cm2 or J/m
2.
The UV dosage, at a target design 254 nm-equivalent UV dose, required for water
disinfection for groundwater systems is set by the Disinfection Procedure as a pass-through
UV dose of 40 mJ/cm2. For surface water and GUDI systems, where other treatment barriers
ensure pathogens such as viruses and bacteria are removed, or inactivated by chemical
disinfection, or where UV is used only for a part of primary disinfection, lower UV doses
may be acceptable.
UV manufacturers commonly design their reactors to operate using either:
The UV Intensity Setpoint Approach; or
The Calculated Dose Approach.
The monitoring approach used for a particular system depends on the type of unit used. As
specified in the Disinfection Procedure, all UV disinfection facilities must continuously
monitor those parameters that allow the operator to determine that the target design 254 nm-
equivalent UV pass-through dose or higher is being delivered. All systems must annunciate
failure alarms when this design dose is not being delivered.
Table 9-4 presents monitoring recommendations, in terms of sampling locations and
analyses, in order to evaluate the performance of the UV disinfection process.
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Table 9-5 – UV Disinfection – Recommended Monitoring to Evaluate Performance
Location Types of Sample /
Measurement1
Parameters /
Analyses Comments
Raw water Continuous monitoring Turbidity
pH
Temperature
Flow rate
Filter effluent or
other location
upstream of UV
disinfection
process (for
systems not using
filtration)
Continuous monitoring Turbidity
UV transmittance
(UVT)
Turbidity may shield
pathogens from UV light.
UVT has a direct impact on
UV dose delivery.
Grab sample pH
Alkalinity, Hardness
Calcium
Iron and manganese
Water quality parameters
that can affect the type and
amount of sleeve fouling
that occurs in UV reactors.
UV System Continuous monitoring UV dose To evaluate performance of
UV disinfection process
Downstream of
UV disinfection
process
Continuous monitoring Disinfectant residual
(if chemical
disinfectant is applied
downstream of the UV
process)
UV disinfection used in
combination with another
disinfectant may be more
effective than either
disinfectant acting alone.
Grab sample Total coliform, E. coli
and heterotrophic plate
count
Notes:
1. Although continuous monitoring is recommended for several parameters, for small systems or
groundwater systems where water quality is relatively consistent, grab sampling may be more
appropriate, except where continuous monitoring is required by regulation.
9.3.3 Common Problems and Potential Impacts
Table 9-5 presents the symptoms and causes of common problems encountered with UV
disinfection.
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Table 9-6 – UV Disinfection – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Impacts Common Causes
High Levels of
Turbidity in UV
Influent
Higher than typical
disinfectant dosages
required to maintain target
disinfectant residual.
Potential for detection of
microbiological indicator
organisms in treated water.
Upstream process upsets.
Poor performance of upstream treatment
processes.
Low UVT in UV
Influent
Reduced ability of water to
transmit UV light.
Potential for detection of
microbiological indicator
organisms in treated water.
Due to raw water characteristics, such as
organic compounds (e.g. natural organic
matter) and inorganic compounds (iron,
manganese).
Use of iron-based coagulants, as iron has
a high absorbency of UV light.
Fouling Reduces the intensity of the
UV light that reaches the
microorganisms.
Higher UV dosage required.
Potential for detection of
microbiological indicator
organisms in treated water.
Lamp fouling occurs due to the
accumulation of inorganic, organic, and
biological solids on the quartz sleeves
that surround the lamp.
Biofilms and algae growth can be a
problem if these are not removed in
upstream processes.
Inadequate cleaning and maintenance of
UV lamps.
Poor System
Hydraulics
Reduces the average contact
time resulting in ineffective
disinfection.
Density currents causing flow to move
along the bottom or top of the lamps.
Entry and exit conditions that lead to the
formation of eddy currents, thereby
inducing uneven velocity profiles.
Dead spaces or zones within the reactor
reduce the effective reactor volume and
shorten the average hydraulic retention
time.
System is hydraulically overloaded.
Poor Disinfection
Performance not
Attributable to
Problems
Identified Above
Detection of
microbiological indicator
organisms in treated water
or increased demand in
subsequent chemical
disinfection processes.
Burned out UV lamps.
Operating at flows in excess of design
flow capacity.
Excessive turbidity, such that micro-
organisms are being shielded from the
UV rays. Particle size distribution testing
can be used to diagnose this problem.
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9.3.4 Optimization Techniques
9.3.4.1 Optimizing Pre-Treatment Processes
Poor raw water quality or poor filter effluent quality can reduce the effectiveness of UV
disinfection. Generally, the characteristics of the water to be treated affect the efficiency of
UV disinfection in three ways:
1. Absorbing and/or scattering UV light, thereby reducing the UV light that reaches the
microorganisms;
2. Shielding of microorganisms from exposure to UV light by suspended solids; and
3. Contributing to fouling of quartz sleeves that surround the lamp, reducing the
intensity of the UV light that reaches the microorganisms.
The UVT of the raw water or filter effluent can be variable. This can be attributed to diurnal
or seasonal variations in raw water quality as a result of climatic conditions (e.g. heavy rain
and runoff, prolonged ice cover leading to anaerobic conditions).
In many cases, it may not be possible to change the characteristics of the water to improve
the efficiency of UV disinfection. However, the following approaches to optimize UV
disinfection are available:
Implement on-line monitoring of UVT to measure and document any diurnal or
seasonal variations in UVT and apply UV dosage corrections;
Increase raw water monitoring and implementing source water protection programs,
if required;
Optimize upstream pre-treatment processes to reduce turbidity and improve UV
transmittance (Chapter 8); and
Address causes of process upsets (e.g. floc carryover or poor coagulant chemical
control) which may result in poor filter effluent quality, reducing the effectiveness of
UV disinfection.
9.3.4.2 Minimizing Fouling
Fouling of quartz sleeves that surround the UV lamp will reduce the intensity of the UV light
that reaches the microorganisms, thereby reducing the efficiency of UV disinfection. The
total hardness, manganese and iron concentrations of the water are indicators of the potential
for fouling of the UV lamps.
Lamp fouling can be caused by:
Accumulation of inorganic, organic, and biological materials on the quartz sleeves
that surround the lamp;
High iron concentrations due to the addition of iron-based coagulants;
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Optimization Guidance Manual for Drinking Water Systems 2014
High levels of calcium and magnesium due to elevated hardness;
Organic fouling; and
pH (which can affect the solubility of the scaling material).
To optimize performance, fouling can be controlled by mechanical, sonic or chemical
cleaning units. Lamps should be regularly cleaned and maintained according to the
manufacturer’s recommendations to sustain performance.
Pumping-to-waste on well start-up can be used to reduce sleeve fouling.
The presence of algae and/or biofilms in the water can also reduce the effectiveness of UV
disinfection by shielding bacteria and other microorganisms, or by growing on the lamps and
reducing the amount of light transmitted. It may be necessary to provide pre-treatment, such
as microscreening (see Chapter 5) and/or chlorination (see Section 9.2) to reduce algae or
control biofilm formation, upstream of the UV reactors.
Optimization techniques for coagulation processes to reduce iron residuals in the treated
water are presented in Chapter 6.
9.3.4.3 Optimizing Reactor Hydraulics
Reactor hydraulics are a key factor in the performance of UV disinfection. Plug-flow
conditions with radial mixing are required for efficient disinfection. Good radial mixing is
required to prevent microorganisms from passing through the UV reactor between lamps and
receiving a smaller UV dose than the average value. Radial turbulence is important because it
ensures adequate mixing, minimizing the effects of short-circuiting and particle shading.
These conditions are typically controlled by the reactor geometry, the lamp array geometry,
and the flow rate of water to the UV disinfection system.
Poor system hydraulics will reduce the efficiency of the UV disinfection process. Common
hydraulic problems that result in short-circuiting include:
Density currents causing influent flow to move along the bottom or top of the lamps;
Entry and exit conditions that lead to the formation of eddy currents inducing uneven
velocity profiles; and
Dead spaces or zones within the reactor, reducing the effective reactor volume and
shortening the average hydraulic retention time.
Although it may not be possible to change the reactor hydraulics of an existing system,
techniques such as offsetting the inlet and outlet and using perforated stilling plates, have
been used to accommodate the contradicting characteristics of plug flow and turbulence
(USEPA, 1996).
Additional information is presented in MOE (2008) and Bolton & Cotton (2008).
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9.3.4.4 Collimated Beam Testing
Collimated beam tests can be used with raw water or filter effluent samples collected over a
representative range of operating conditions to produce a dose-response relationship. The
dose-response relationship established can be used to establish the required UV dose to meet
inactivation requirements.
Plant operators or owners should contact a UV system supplier to discuss collimated beam
testing.
9.3.4.5 Improving Process Control
Process control strategies, such as flow pacing and dose pacing, can be used to optimize the
performance of UV disinfection systems.
Flow pacing controls the lamp intensity and/or the number of lamps in operation based on the
flow rate through the UV disinfection system. This can reduce energy use during low flow
periods. On-line flow monitoring equipment is required to implement flow pacing.
Dose pacing involves adjusting the lamp intensity and/or the number of lamps in operation
based on not only the flow rate through the UV disinfection system, but also the UVT of the
stream being treated. This ensures that a constant UV dose is being applied. Online UVT
sensors and flow monitoring, or UV intensity sensors, are required to implement dose pacing.
Additional information regarding instrumentation and control strategies and requirements can
be found in USEPA (2006).
9.4 CASE HISTORIES
9.4.1 Port Rowan WTP – pH Control for Optimizing Disinfection
The following case study is based on information presented in Poisson and Wilson (2006).
System Description
The Port Rowan WTP draws raw water from Long Point Bay on Lake Erie and serves the
Town of Port Rowan and outlying areas. The rated capacity of the WTP is 3,040 m3/d. The
treatment process consist of coagulation, flocculation, sedimentation and filtration in two
Ecodyne Monoplants, disinfection by chlorine contact time in a clearwell and GAC
adsorption for taste and odour control.
Due to several regulatory changes in 2000 and 2001, a number of upgrades were required for
the disinfection system. The C of A issued to the Port Rowan WTP in 2001 required 3.0 log
removal/inactivation of Giardia and 4.0 log removal/inactivation of viruses. Given that the
existing chemically-assisted filtration process was operating well, the plant was credited with
2.5 log removal of Giardia and 2.0 log removal of viruses, meaning the remaining
disinfection credits of 0.5 log reduction of Giardia and 2.0 log removal of viruses were
required to be achieved through inactivation.
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Optimization Guidance Manual for Drinking Water Systems 2014
Based on an analysis of alternative disinfection methods, it was decided to install a UV
disinfection system to provide for Giardia inactivation and achieve the remaining 2.0 log
virus inactivation using free chlorine.
Due to increased algal growth in the summer months, the raw water pH at the Port Rowan
WTP usually exceeds 9.5. This relatively high pH increases the CT required to achieve a
target log inactivation. Using the existing chlorine contact facilities, an increase in CT
required an increase in chlorine dose, which likely contributed to higher treated water and
distribution system THM concentrations. Also, higher chlorine dosages were reducing the
useful life of downstream GAC filters. To address both the CT and THM issues, it was
decided to install a pH control system as part of the plant upgrades.
Optimization Strategies
A number of studies were undertaken prior to the plant upgrades to evaluate the capability of
the existing system and to establish design criteria for the upgraded works.
A review of existing conditions was undertaken to establish historical data for raw water
temperature, pH, peak flow and chlorine residual. It was determined that the limitations on
the CT achieved at the existing plant were influenced by two factors:
Cold winter water temperatures (0.5°C); and
Requirement to maintain a low chlorine residual concentration (0.2 mg/L) leaving the
clearwell and entering the GAC filters.
This evaluation also showed that the 2 log inactivation of viruses could only be achieved
within the existing plant and dedicated section of watermain by maintaining higher chlorine
residuals, possibly affecting the GAC contactors and increasing the formation of THMs.
The study also showed that by decreasing the pH of the influent water to 8.0, the pre-
chlorination residual could be maintained at the operational objective of 0.2 mg/L and the
plant could meet the required 2 log inactivation of viruses for most water temperatures. It was
also determined that the GAC filters could be by-passed during the period of December to
April (when taste and odour causing compounds are generally not present) and water
temperatures are at their lowest, allowing higher chlorine dosages to achieve the required CT.
Summary
A carbon dioxide injection system was installed at the plant, resulting in a consistent pre-
treatment water pH of approximately 8 throughout the year. This improved the plant’s ability
to meet CT requirements for virus inactivation while maintaining chlorine residuals within
established operational guidelines. THM concentrations in the distribution system also
decreased significantly, particularly for samples collected in August and November, as a
result of the decrease in pH.
9.4.2 Ameliasburgh WTP – Optimization Study to Control the Formation of
DBPs
The following case study is based on information presented in Andrews, Hofmann &
Associates and R.V. Anderson Associates (2009).
CHAPTER 9. Disinfection 9-23
Optimization Guidance Manual for Drinking Water Systems 2014
System Description
The Ameliasburgh WTP draws water from Roblin Lake and has a rated capacity of 360 m3/d.
Raw water is screened and then pumped into a 7.3 m3 high lift well. Sodium hypochlorite is
added at the discharge pipe of the high lift well to target a free chlorine residual of
approximately 0.2 mg/L measured at the inlet to the downstream pressurized clarifier.
The high lift pumps supply water to two parallel 180 m3 Culligan Multi-Tech filtering trains,
each consisting of a clarifier and pressure filter. Coagulant is added just upstream of a static
mixer and the clarifiers/filters. Post-chlorination (following filtration) is performed through
injection of sodium hypochlorite into the discharge header, with a target free chlorine
residual of 2.4 mg/L at the inlet of the contact pipe (400 mm diameter, 112 m long).
Historical plant water quality data indicated that treated water THM concentrations ranged
between 18 and 137 µg/L, while distribution system THM concentrations ranged from 17 to
273 µg/L. Historical HAA data were not available for the Ameliasburgh WTP.
Bench scale treatability and full scale testing was undertaken to determine if changes in
coagulant dosage could be used to achieve a reduction in THM and HAA formation to below
80 µg/L.
Optimization Strategies
Jar tests were performed with various coagulants and doses and were designed to simulate
plant conditions where possible. A number of raw water quality parameters were evaluated in
filtered samples, and testing was conducted for chlorine decay and Simulated Distribution
System (SDS) THM formation.
For the Ameliasburgh WTP, the optimum coagulant dose was selected based on the highest
TOC removal. Optimized samples resulted in 5 to 20 percent lower TOC levels than the
control sample (existing plant dosage). THM concentrations were approximately 30 to 50
percent lower in optimized samples than in the control samples, while HAA levels were
approximately 25 to 40 percent lower than the control sample.
Subsequent to the bench scale studies, full scale testing was conducted to evaluate the effect
of optimized coagulation (application of the optimal coagulant dose determined during jar
testing) on potential DBP reduction. The results of the full scale testing at Ameliasburgh
indicated that:
Implementation of enhanced coagulation resulted in minor improvements in TOC
removal;
Enhanced coagulation, when compared to historical (lower) coagulant doses, resulted
in reductions in THM and HAA formation; and
SDS tests appeared to provide a reasonable estimate of DBP formation levels in the
treated water and distribution system. This relationship may be useful when
considering future disinfection optimization, by allowing testing to be performed at
bench scale.
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Optimization Guidance Manual for Drinking Water Systems 2014
A modified disinfection benchmarking evaluation was also undertaken to determine if
reductions in chlorine dosage could further reduce DBP formation, while still maintaining
adequate CT. The Amerliasburgh CT values were recalculated to consider varying flow rates,
temperature and pH, and the corresponding Giardia and virus inactivation levels were
determined.
A spreadsheet was used to calculate the CT (mg·min/L) that was achieved at the WTP for
each day in 2005 and 2006. The results of the disinfection benchmarking are presented in
Figure 9-1. The required CT was not met 18 times in the 2005-2006 period. Most of these
occurrences were between January and March. Conversely, in the summer and fall of 2005-
2006, the CT values provided were much higher (approximately 20 to 200 mg·min/L higher)
than the required CT. This indicated that lower doses of chlorine could potentially have been
applied while still meeting CT requirements, providing that an adequate residual was
maintained throughout the distribution system. As a result, chlorine usage may have been
reduced and a reduction in THM and HAA formation could potentially have been achieved.
0
20
40
60
80
100
120
140
160
180
200
01/0
1/20
05
01/0
3/20
05
01/0
5/20
05
01/0
7/20
05
01/0
9/20
05
01/1
1/20
05
01/0
1/20
06
01/0
3/20
06
01/0
5/20
06
01/0
7/20
06
01/0
9/20
06
01/1
1/20
06
Date
CT
(m
g-m
in/L
)
CT Provided
CT Required
Figure 9-1 – CT Provided and Required for 1.0-log Giardia Inactivation (2005-2006) –
Ameliasburgh WTP
Summary
Based on the results of the bench and full scale testing, enhanced coagulation appeared to
provide a reduction in THM and HAA formation in both the treated water and in the
distribution system. As such, enhanced coagulation is an easily implemented strategy for
reducing TOC, and therefore DBP formation, without major capital investment.
CHAPTER 9. Disinfection 9-25
Optimization Guidance Manual for Drinking Water Systems 2014
9.5 REFERENCES
Andrews, Hofmann & Associates Inc. and R.V. Anderson Associates Ltd. (2009).
Optimization Study to Control the Formation of THMs and HAAs – Optimization Report,
prepared for the Ontario Ministry of the Environment.
Bellamy, W.D., G.R. Finch, C.N. Hass (1998). Integrated Disinfection Design Framework.
AWWA Research Foundation and AWWA. Denver, CO. ISBN0-89867-933-8.
Bolton, J.R. and C.A. Cotton (2008). The Ultraviolet Disinfection Handbook. AWWA.
Denver, CO. ISBN 978-1-58321-584-5.
MOE (2006). Procedure for Disinfection of Drinking Water in Ontario. PIBS 4448e001.
MOE (2009). Strategies for Minimizing the Disinfection By-Products Trihalomethanes and
Haloacetic Acids. PIBS 7152e.
MWH (2005). Water Treatment Principles and Design. 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
Poisson, R. E. and D. Wilson (2006). “Using pH Control by Carbon Dioxide Injection to
Reduce Required CT and Distribution System THM Concentrations”, presented at the 2006
OWWA/OMWA Joint Annual Conference and Trade Show. Toronto, ON.
Regli, S. (1990). “How’s and Why’s of CTs”, presented at AWWA Annual Conference,
Cincinnati, OH.
Stanford, B.D., A.N. Pisarenko, S.A. Snyder and G. Gordon (2009). Minimize Perchlorate
Formation in Hypochlorite Solution. AWWA Opflow, Vol. 35, Iss. 10, October 2009.
USEPA (1996). Ultraviolet Light Disinfection Technology in Drinking Water Application -
An Overview. Office of Ground Water and Drinking Water. EPA 811-R-96-002.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program. EPA/625/6-91-027.
USEPA (1999). Alternative Disinfectants and Oxidants Guidance Manual. Office of Water.
EPA 815-R-99-014.
USEPA (2003). LT1ESTWR Disinfection Profiling and Benchmarking Technical Guidance
Manual. Office of Water. EPA 816-R-03-004.
USEPA (2006). Ultraviolet Disinfection Guidance Manual For the Final Long Term 2
Surface Water Treatment Rule. Office of Water. EPA 815-R-06-007.
White, Geo. Clifford (1999). Handbook of Chlorination and Alternative Disinfectants. Fourth
Edition. John Wiley & Sons Inc. New York, NY. ISBN 0-471-29207-9.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 10 OTHER TREATMENT PROCESSES
OTHER TREATMENT PROCESSES
10.1 Introduction .......................................................................................................... 10-1
10.2 Aeration and Air Stripping ................................................................................... 10-1
10.2.1 Purpose and Types of Aeration and Air Stripping Systems .................. 10-1
10.2.2 Evaluating Performance ......................................................................... 10-1
10.2.3 Common Problems and Potential Impacts ............................................. 10-3
10.2.4 Optimization Techniques ....................................................................... 10-4
10.3 Ion Exchange ........................................................................................................ 10-4
10.4 Biologically Active Filtration ............................................................................... 10-5
10.5 Iron and Manganese Control ................................................................................ 10-6
10.5.1 Purpose and Types of Iron and Manganese Control Processes ............. 10-6
10.5.2 Evaluating Performance ......................................................................... 10-7
10.5.3 Common Problems and Potential Impacts ............................................. 10-9
10.5.4 Optimization Techniques ..................................................................... 10-10
10.6 Taste and Odour Control .................................................................................... 10-11
10.6.1 Purpose and Types of Taste and Odour Control Processes ................. 10-11
10.6.2 Evaluating Performance ....................................................................... 10-12
10.6.3 Common Problems and Potential Impacts ........................................... 10-13
10.6.4 Optimization Techniques ..................................................................... 10-15
10.7 Natural Organic Matter Removal ....................................................................... 10-16
10.7.1 Purpose and Types of NOM Removal Processes ................................ 10-16
10.7.2 Evaluating Performance ....................................................................... 10-17
10.7.3 Common Problems and Potential Impacts ........................................... 10-18
10.7.4 Optimization Techniques ..................................................................... 10-19
10.8 Internal Corrosion Control ................................................................................. 10-20
10.8.1 Purpose and Types of Internal Corrosion Control Processes .............. 10-20
10.8.2 Evaluating Performance ....................................................................... 10-21
10.8.3 Common Problems and Potential Impacts ........................................... 10-24
10.8.4 Optimization Techniques ..................................................................... 10-24
10.9 Case Histories ..................................................................................................... 10-25
10.9.1 Washington, D.C. – Optimization of Orthophosphate Addition ......... 10-25
10.9.2 Chicago, IL – Optimization of Taste and Odour Control with Pilot
Plant Testing ........................................................................................ 10-26
10.10 References .......................................................................................................... 10-27
CHAPTER 10. Other Treatment Processes 10-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 10
OTHER TREATMENT PROCESSES
10.1 INTRODUCTION
The previous unit process chapters presented in this Optimization Manual focused primarily
on improving the performance of conventional unit treatment processes using the approach of
the USEPA Handbook entitled Optimizing Water Treatment Plant Performance Using the
Composite Correction Program (USEPA, 1998). The USEPA CCP approach is designed to
improve particulate removal and disinfection to meet regulatory requirements through the
optimization of coagulation, flocculation, sedimentation, filtration and disinfection.
In this chapter, the optimization of other unit processes that may or may not be included in a
conventional water treatment train are presented. Processes described include aeration and air
stripping, and processes used for control of iron and manganese, taste and odour, NOM and
corrosion.
10.2 AERATION AND AIR STRIPPING
10.2.1 Purpose and Types of Aeration and Air Stripping Systems
Aeration and air stripping are gas-liquid contact processes. The primary use of aeration in the
water treatment industry is for the removal of:
Carbon dioxide (CO2);
Hydrogen sulphide (H2S);
Methane;
Volatile organic chemicals (VOCs);
Radon;
Iron and manganese, which are oxidized and then removed by settling and/or
filtration; and
Tastes and odours.
Aeration can also be used to add dissolved oxygen (DO) to water.
Air stripping is the aeration process most commonly used in Ontario for the removal of
methane and/or H2S from groundwater.
Aeration and air stripping can be achieved by the use of multiple tray spray aerators or
towers, pressure aerators and packed towers, diffused air, cascades and mechanical aeration.
10.2.2 Evaluating Performance
The performance of aeration and air stripping processes is assessed on the basis of removal of
the targeted compound.
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Optimization Guidance Manual for Drinking Water Systems 2014
Table 10-1 presents monitoring recommended, in terms of sampling locations and analyses,
in order to evaluate the performance of aeration processes.
Table 10-1 – Aeration – Recommended Process Monitoring to Evaluate Performance
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Influent to
aeration process
Continuous monitoring
or grab sample1
Temperature
pH
Water temperature
affects the solubility of
oxygen in water
Grab sample Iron
Manganese
CO2
Tastes and odours
VOCs
To measure the
effectiveness of aeration
for the removal of the
parameter(s) of concern
Treatment process Continuous monitoring Air flow rate
Water flow rate
For process control
Aeration effluent Continuous monitoring
or grab sample1
pH
pH is an indicator of
CO2 removal
Controlling pH can help
to optimize removal of
other targeted
parameters (iron,
manganese, H2S)
Dissolved oxygen Monitoring DO
concentration can help
to optimize air addition
and minimize energy
costs
Grab sample Iron
Manganese
CO2
Tastes and odours
VOCs
To measure the
effectiveness of aeration
for the removal of the
parameter(s) of concern
Notes:
1. Test frequency depends on both the variability of raw water quality and the parameter
measured. For example, groundwater temperature tends to be relatively constant and less
frequent monitoring may be warranted.
CHAPTER 10. Other Treatment Processes 10-3
Optimization Guidance Manual for Drinking Water Systems 2014
In addition to the recommended sample locations and analyses presented in Table 10-1, it is
recommended that frequent visual inspections of the aeration equipment and downstream
processes be conducted to monitor for common problems associated with aeration equipment,
as described in the following subsection.
10.2.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with aeration processes are shown
in Table 10-2.
Table 10-2 – Aeration – Symptoms and Causes of Common Problems
Problem Description
Mitigation
Corrosion Excessive DO concentration can
accelerate the corrosion of metal
surfaces in downstream unit
processes or in the distribution
system.
Operate the aeration process to
provide an adequate but not
excessive level of DO (see Section
10.2.4).
Provide protective coatings on
exposed metal surfaces.
Floating Floc in
Clarifiers Excessive aeration can cause air
bubbles to come out of solution and
attached to floc particles in
clarification processes, causing the
particles to float rather than settle.
Increased solids loading on filters.
Optimize DO concentration.
Air Binding of
Filters Dissolved air in the water causes
gas bubbles to accumulate in the
filter between backwashes.
Increased head loss.
Shortened filter runs.
Violent agitation during
backwashing, causing loss of
media.
Optimize DO concentration.
Terminate the filter run before the
total head loss is greater than the
depth of the water above the
unexpanded media (see Chapter 8).
Allow time for the air to dissipate
before initiating a backwash.
If aeration process is included in
treatment train, relocate to
downstream of filters.
Slime Growth on
Aerator Surfaces Bacteria growing on surfaces of
trays, cascades and spray
equipment may result in tastes and
odours in the treated water, as well
as sloughing of bacteria.
Routinely inspect equipment
surfaces and maintain a chlorine
residual, if needed.
CHAPTER 10. Other Treatment Processes 10-4
Optimization Guidance Manual for Drinking Water Systems 2014
Table 10-2 – Aeration – Symptoms and Causes of Common Problems (cont’d.)
Problem Description
Mitigation
Increased Turbidity
During H2S Removal Undesirable reaction of oxygen and
ionized H2S to release elemental
sulphur, which results in fine
colloidal particles and gives water a
milky appearance.
Optimize pH of the water prior to
aeration to improve removal
efficiency (see Section 10.2.4).
Clogged Diffusers Clogging of diffusers as a result of
dust, oil, debris or chemical
deposits around diffuser opening.
Maintain clean air filters.
Avoid over-lubricating blowers.
Prevent backflow of water into
diffusers.
10.2.4 Optimization Techniques
Optimization of aeration processes is achieved through proper control of the DO
concentration, pH and temperature of the water.
Knowing the DO concentration needed for a particular treatment objective and monitoring
the amount of DO present in the water will prevent over- or under-aeration. For example, on
a stoichiometric basis, 1 mg of oxygen can oxidize 7 mg of soluble iron and 3.4 mg of
soluble manganese (MWH, 2005). The actual amount of oxygen required will be site specific
and can vary seasonally as water quality changes. Monitoring of DO concentrations is
required to determine the correct amount. As a general rule, DO concentrations of 2 to 4
mg/L are sufficient (AWWA, 1995).
The pH of the water can be used to monitor CO2 removal, as pH decreases CO2 is removed.
pH will also affect the effectiveness of H2S, iron and manganese removal. The best pH range
for H2S scrubbing is 6 or less, while iron and manganese are best treated in a pH range of 8 to
9 (AWWA, 1995).
The saturation concentration of oxygen in water varies based on water temperature, with the
amount of dissolved oxygen decreasing as water temperature increases. Therefore, operators
should adjust the aeration process to maintain the correct level of DO as water temperature
changes.
10.3 ION EXCHANGE
Ion exchange is a process in which ions of like charge are exchanged between the water
phase and the solid resin phase. The ion exchange resin is regenerated periodically using a
suitable regenerant. Brine solutions are used to regenerate exhausted water softeners.
Water softening is one of the more common applications of ion exchange, and is achieved by
cation exchange. Water is passed through a bed of cationic resin, and the calcium ions and
magnesium ions in the water are absorbed on the cationic resin in replacement of the sodium
ions.
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Optimization Guidance Manual for Drinking Water Systems 2014
Anion exchange can be used to remove contaminants such as nitrate, which is exchanged for
chloride. Nitrate-specific resins are available for this purpose. Other contaminants that can be
removed through the use of ion exchange and inorganic adsorbents in full-scale operations
include barium, radium, fluoride, arsenate, perchlorate and uranium. In addition, the MIEX®
process, which operates in a completely mixed reactor, has been developed to remove
dissolved organic carbon (MWH, 2005).
An ion exchange plant normally consists of two or more resin beds contained in pressure
shells with appropriate pumps, pipework and ancillary equipment for regeneration. The
pressure shells are typically up to 4 m in diameter, containing 0.6 to 1.5 m depth of resin
(WHO, 2008). Ion exchange units may be of pressure or gravity type, with either an upflow
or downflow design (MOE, 2008).
The design of ion exchange processes will vary depending on the size of the installation and
the application (i.e. type of contaminant to be removed). As such, assessment criteria and
monitoring programs to be used for the evaluation of ion exchange processes should be
developed in consultation with the design engineer and/or the manufacturer.
Ion exchange processes have to date not been widely used in large-scale water treatment
plants in Ontario; therefore, limited optimization guidance is available. There are a number of
operational parameters that should be considered in the development of an optimization
program for ion exchange processes:
Characteristics and type of the ion exchange resin;
Raw water or feed water characteristics;
Rate of flow applied to the ion exchange unit(s);
Brine concentration; and
Brine contact time.
Additional information on the optimization of ion exchange processes is provided in Clifford
& Zhang (1994); Liu & Clifford (1998); Ghurye, Clifford & Tripp (1999); and Clifford,
Ghurye & Tripp (2003).
10.4 BIOLOGICALLY ACTIVE FILTRATION
In a biologically active filter, microbial growth developed in the filter medium can have
several beneficial aspects. Some specific compounds can be removed by biological oxidation
rather than by adsorption, such as dissolved organic carbon, DBP precursors, geosmin and
MIB, and many more (AWWA, 1999).
Intentional biologically active filtration often includes the use of ozone as a pre-oxidant to
break down natural organic materials into more easily biodegradable organic matter.
Granular activated carbon filter media is often used to support denser biofilms because it has
more surface area than other traditionally employed media. Design guidelines for
conventional and biological granular media filters are provided in the MOE Design
Guidelines for Drinking Water Systems, 2008 (MOE, 2008).
CHAPTER 10. Other Treatment Processes 10-6
Optimization Guidance Manual for Drinking Water Systems 2014
In general, the evaluation of a biologically active process will be based on the degree of
removal achieved for the target parameter(s). Assessment criteria and recommendations for
monitoring for conventional granular filters were presented in Chapter 8. Table 10-3 presents
a summary of typical process parameters for biologically active filters based on DOC
removal.
Table 10-3 – Biologically Active Filtration – Typical Assessment Criteria
Parameter Typical Assessment Criteria
Ozone dosage (if applicable) 0.5 to 1.0 g O3/g DOC
Biological degradation ~ 100 g DOC/(m3)(day)
O2 demand (for DOC oxidation) ~ 200 g O2/(m3)(day)
Empty bed contact time (EBCT) 15 to 30 min
Process control considerations that are needed to prevent undesirable effects in biologically
active filters include:
Aerobic conditions should be maintained at all times within the filters to support the
biomass; anaerobic conditions may develop (and cause odour problems) if oxygen
concentrations are depleted. This may occur if large concentrations of ammonia enter
the filter, if insufficient dissolved oxygen is in the water, or if the bed is allowed to
stand idle for a period of time (AWWA, 1999).
Biological activity may be limited during periods of the year when low water
temperatures (e.g. less than 5°C) occur.
EBCT, media type and depth will have an impact on the distribution of
microorganisms, with deeper beds generally having a lower number of organisms in
the filtrate.
Additional information on the optimization of biologically active filters is provided in Liu,
Huck & Slawson (2001); Smith & Emelko (1998); Elhadi, Huck & Slawson (2006); and
Huck et. al. (2000).
10.5 IRON AND MANGANESE CONTROL
10.5.1 Purpose and Types of Iron and Manganese Control Processes
Iron and manganese are frequently encountered nuisance parameters that can affect aesthetic
water quality. They can cause visible colour and turbidity in water, and cause brown and
black staining of plumbing fixtures and laundry. These effects can occur at specific locations
in a distribution system even when the concentration of either metal in the treated water
entering the distribution system is below the aesthetic objective stated in the Technical
Support Document for Ontario Drinking Water Standards, Objectives and Guidelines (MOE,
2006). This occurs as a result of precipitation and resolubilization processes, which can
produce local pockets of elevated iron and manganese concentrations.
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Optimization Guidance Manual for Drinking Water Systems 2014
Elevated iron and manganese concentrations occur most frequently with groundwater
sources. Surface water sources may also have elevated concentrations of these metals at
anoxic depths in lakes or seasonally under long-duration ice cover. Five control technologies
are commonly used in Ontario.
Removal of iron by oxidation (air or chlorine) and sedimentation is used in groundwater
treatment systems where iron levels are near the aesthetic objective. On exposure to active
chlorine or oxygen, dissolved iron is rapidly oxidized to an insoluble state and precipitates as
a brown solid. Oxygen and chlorine oxidize manganese at too slow a rate for effective
removal unless the manganese is present at very low levels relative to the iron concentration.
Sequestering with silicates or polyphosphates is an inexpensive and commonly adopted
palliative measure for iron control that slows, but does not stop, the formation of the typical
yellow/brown colour of iron precipitates. Sequestering temporarily traps the iron in a
complexed or colloidal form; at most, the effects last for only a few days. Oxidized iron will
then be slowly released into the water.
Ion exchange water softeners are often used by consumers in small groundwater systems to
reduce hardness. An added feature of ion exchange softening is that dissolved iron and
manganese are also removed in the same way as calcium and magnesium on the exchanger
resin beads. The resin must be regenerated periodically by treating it with a brine solution.
Oxidation and removal by greensand processes has historically depended on using
greensand, a manganese ore, as the filter medium downstream of the addition of a chemical
oxidizing agent. Proprietary media has replaced manganese ore particles in current
“greensand” processes. The media used are surface treated to physically adsorb and retain an
oxidized iron and/or manganese surface layer. The filters require periodic backwashing to
remove the deposited materials.
Pre-oxidation and chemically-assisted granular or membrane filtration may be used when iron
and manganese control is required in addition to pathogen removal. Oxidants commonly used in this
treatment process include potassium permanganate (KMnO4) or ozone (O3).
Biological processes can also be used for iron and manganese removal (see Section 10.4).
10.5.2 Evaluating Performance
The performance of iron and manganese control processes is generally assessed based on the
degree of removal of either or both parameters and by monitoring iron and manganese
concentrations in the distribution system.
Sequestering does not remove iron and manganese from the water; therefore, the performance
of the process should be measured based on other parameters, such as turbidity and colour,
particularly at remote points in the distribution system.
Table 10-4 presents monitoring recommended, in terms of sampling locations and analyses,
in order to evaluate the performance of iron and manganese control processes.
CHAPTER 10. Other Treatment Processes 10-8
Optimization Guidance Manual for Drinking Water Systems 2014
Table 10-4 – Iron and Manganese Control – Recommended Process Monitoring to
Evaluate Performance
Location Types of
Sample /
Measurement
Parameters / Analyses Comments
Raw water Grab sample Temperature
pH
Total and dissolved iron
Total and dissolved
manganese
pH and temperature can affect the
rate of oxidation of iron and
manganese
Treatment
Process1
Continuous
monitoring Oxidant or sequestrant
dosage
Head loss and filtration rate
(if filtration is used)
Dissolved oxygen (if
aeration is used)
For process control
Treated
water
Continuous
monitoring Turbidity
Oxidant residual (oxygen,
chlorine, KMnO4 or ozone
concentration), if
applicable
pH
Iron and manganese should be
measured in the treated water to
evaluate effectiveness of removal
process
Increases in turbidity and/or
colour may indicate poor removal
and are caused by oxidation and
precipitation of iron and
manganese
pH can influence degree of
removal, particularly for
greensand processes
Grab sample Total iron
Total manganese
Colour
Sequestrant concentration
Distribution
system
Grab sample Total iron
Total manganese
Turbidity
Colour
Free chlorine residual
Deposition of iron and manganese
precipitates in the distribution
system may require more frequent
flushing
Maintenance of a minimum free
chlorine residual is required to
prevent growth of iron bacteria,
particularly when sequestering is
used as the control technique
Notes:
1. Reference should be made to Chapter 7 (Clarification) and Chapter 8 (Filtration) for
additional information on recommended process control monitoring for these types of
processes. See Section 10.2 for information on process control monitoring for aeration
systems.
CHAPTER 10. Other Treatment Processes 10-9
Optimization Guidance Manual for Drinking Water Systems 2014
10.5.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with iron and manganese control
processes are shown in Table 10-5.
Table 10-5 – Iron and Manganese Control – Symptoms and Causes of Common
Problems and Potential Optimization Strategies
Process Problem
Mitigation
Sequestering Stabilization reaction duration
shorter than expected; deposition of
iron and/or manganese in
distribution system, or increase in
colour or turbidity
Evaluate sequestrant chemical,
dosage and expected duration (i.e.
delay time to perceptible colour
development) through bench-scale
testing (see MOE Design
Guidelines, 2008)
Excessive growth of iron bacteria
in the distribution system
Increase free chlorine residual in
treated water to achieve at least 0.2
mg/L at all points in the
distribution system
Ion Exchange Decrease in iron and manganese
removal efficiency
Resin should be regenerated using
appropriate brine solution
Increased fouling and more
frequent regeneration of resin
needed to maintain process
efficiency
Examine raw water quality for
presence of oxidized iron or
manganese or dissolved oxygen
Ensure no oxidants are added
upstream of ion exchange process
Prolonged exposure may require
replacement of resin
Oxidation and
Sedimentation Lack of or poor formation of
precipitates, resulting in ineffective
removal
Evaluate optimum oxidant dose and
process pH through jar testing (see
Chapter 4)
Evaluate other oxidant chemicals
Slow oxidation reaction or poor
settling of precipitates leading to
deposition of iron and/or
manganese in distribution system
Optimize detention time by
conducting bench-scale settleability
tests
Optimize settling/contact basin
hydraulics to promote settling (see
Chapter 7)
Oxidation with
Potassium
Permanganate
Underdosing resulting in poor
removal of manganese
Overdosing resulting in a pink
colour in the water
Determine optimum dose through
bench-scale testing (see Chapter 4)
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Table 10-5 – Iron and Manganese Control – Symptoms and Causes of Common
Problems and Potential Optimization Strategies (cont’d.)
Process Problem
Mitigation
Oxidation with
Conventional or
Membrane Filtration
Lack of or poor formation of
precipitates, resulting in ineffective
removal
Evaluate optimum oxidant dose and
process pH through jar testing (see
Chapter 4)
Evaluate other oxidant chemicals
Slow oxidation reaction resulting in
dissolved iron and/or manganese
passing through filters, leading to
deposition of iron and/or
manganese in distribution system
Optimize detention time by
conducting bench-scale settleability
tests (see Chapter 4)
Optimize settling/contact basin
hydraulics to promote settling (see
Chapter 7)
Excessive head loss across filter Verify condition of filter media and
filter hydraulic loading rate (see
Chapter 8)
Improve backwashing procedures
(see Chapter 8)
Greensand Filtration Low iron concentration and high
manganese concentration in treated
water
Increase frequency of bed
regeneration
Verify oxidant chemical dosages
Elevated iron and manganese
concentrations in treated water
Determine optimum process pH
through jar testing (see Chapter 4)
Verify condition of filter media and
filter hydraulic loading rate (see
Chapter 8)
Consider coagulant addition prior
to filtration to improve solids
removal
Excessive head loss across filter Verify condition of filter media and
filter hydraulic loading rate (see
Chapter 8)
Improve backwashing procedures
(see Chapter 8)
10.5.4 Optimization Techniques
The information presented in Table 10-5 above provides an overview of general optimization
techniques that may be used to optimize iron and manganese removal and control processes.
Additional information is provided in Sommerfeld (1999).
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Depending on the type of iron and manganese control method used, reference should also be
made to other chapters of this Manual for optimization strategies for clarification (see
Chapter 7) and filtration (see Chapter 8) processes.
10.6 TASTE AND ODOUR CONTROL
10.6.1 Purpose and Types of Taste and Odour Control Processes
There are a number of possible causes of tastes and odours in drinking water. The presence of
specific metals or salts, H2S, synthetic organics or water treatment chemicals may cause
objectionable tastes and odours. Decaying vegetation and metabolites of microorganisms,
such as cyanobacteria and actinomycetes, can produce compounds such as geosmin and
methylisoborneol (MIB), which are probably the most common sources of taste and odour
problems in surface water supplies (AWWA, 1999). Specific information regarding the
identification and control of odorous algal metabolites is provided in Rashash et. al. (1996).
As discussed in Chapter 5, source water management to prevent the occurrence of taste and
odour problems is an important aspect of any taste and odour control strategy. Treatment
plant and distribution system maintenance activities, including removal of screening debris
and sludge, regular flushing and disinfection of equipment and piping, can also assist in
reducing taste and odour problems.
Where treatment is required to control taste and odour in a drinking water system, the type of
process used will depend on the specific taste and odour causing compound(s) present in the
source water. Two general approaches are used for control of taste and odour causing
compounds: removal and destruction. Removal may be accomplished by microscreening,
conventional treatment (i.e. coagulation, flocculation, clarification and filtration), activated
carbon adsorption or aeration. Destruction is typically accomplished through conventional or
advanced oxidation processes.
Microscreens or microstrainers are mechanical screens with very small openings capable
of removing suspended matter from the water by straining. They are used during periods
when raw water contains nuisance organisms, such as algae.
Improving coagulation, flocculation and sedimentation can be an effective means for
removing the taste and odour of water, depending on the type of taste and odour causing
compounds present in the raw water. This strategy may be particularly effective if taste and
odour quality has deteriorated during a period when sudden changes in raw water turbidity,
colour or pH have occurred (e.g. spring or fall turnover of lakes or reservoirs, high flows,
storm runoff, algal blooms, etc).
Activated carbon can be used to remove a wide range of water contaminants that cause
offensive tastes and odours. Activated carbon may be in powdered (PAC) or granular (GAC)
form.
Aeration is effective for taste and odour control only for the removal of gases and organic
compounds that are relatively volatile. Aeration may also change some compounds by
oxidation, such as producing insoluble inorganic compounds (e.g. iron or manganese).
Aeration typically does not provide a sufficiently strong oxidant to destroy organic taste and
odour causing compounds.
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Optimization Guidance Manual for Drinking Water Systems 2014
Oxidation can be used to control many taste and odour causing substances through chemical
oxidation to less odorous substances. Chemical oxidants used for taste and odour control
include chlorine, monochloramine, chlorine dioxide, potassium permanganate, hydrogen
peroxide and ozone.
Advanced oxidation processes (AOPs) are processes that provide powerful oxidizing
conditions to break down organic water contaminants. AOPs involve the use of any one of
several possible combinations of UV, hydrogen peroxide, ozone and titanium dioxide to
create hydroxyl radicals (HO·). Although AOPs have been demonstrated to be effective in
destroying geosmin and MIB, it is unlikely that AOPs would be used in a water treatment
plant only for taste and odour removal, because ozone alone is generally effective in
eliminating geosmin and MIB (MWH, 2005). The use of AOPs for this application is
therefore not discussed further in this chapter.
10.6.2 Evaluating Performance
The performance of taste and odour control processes is assessed on the basis of removal of
the targeted compound, and the monitoring program will therefore differ depending on the
contaminant of concern and the control method used.
The threshold odour number (TON) is a subjective test that can be used to evaluate the odour
of a drinking water sample. The TON test involves diluting a sample with odour-free water
until the least definitely perceptible odour is achieved (American Public Health
Association/American Water Works Association/Water Environment Federation, 2005).
Similar subjective tests, such as flavour profiling (APHA/AWWA/WEF, 2005), can also be
used for the measurement of taste or flavour in water.
Table 10-6 presents potential monitoring, in terms of sampling locations and analyses, in
order to evaluate the performance of taste and odour control processes.
Table 10-6 – Taste and Odour Control – Recommended Process Monitoring to Evaluate
Performance
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Raw water Continuous monitoring
or grab sample Parameter of concern,
may include:
Geosmin
MIB
H2S
VOCs
Metals
Salts
The frequency of
sampling will be site
specific and will
depend on the nature of
the contaminant,
whether it is present
year-round, ability to
perform testing on-site,
etc.
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Table 10-6 – Taste and Odour Control – Recommended Process Monitoring to Evaluate
Performance (cont’d.)
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Continuous monitoring
or grab sample Temperature
pH
Dissolved oxygen
Nutrients
These parameters may
be indicators that raw
water quality is
changing, and can
potentially be used to
predict the occurrence
or onset of a taste and
odour event (e.g. lake
turnover, anoxic
conditions, algal
growth, etc.).
Treatment
Process1
Continuous monitoring Oxidant dosage and
residual concentration.
Head loss (if screening
or filtration is used).
Will vary depending on
the type of treatment
process used. See
Section 10.6.4 and
Chapter 8 for
additional information.
Treated water Continuous monitoring
or grab sample Parameter of concern,
may include:
Geosmin
MIB
H2S
VOCs
Metals
Salts
To evaluate degree of
removal of parameter
of concern.
Notes:
1. Reference should be made to Chapter 5 (Screening), Chapter 7 (Clarification) and Chapter 8
(Filtration) for additional information on recommended process control monitoring for these
types of processes. See Section 10.2 for information on process control monitoring for
aeration systems.
10.6.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with taste and odour control
processes are shown in Table 10-7.
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Table 10-7 – Taste and Odour Control – Symptoms and Causes of Common Problems
and Potential Optimization Strategies
Process Problem
Mitigation
Microscreens or
Microstrainers See Chapter 5 See Chapter 5
Coagulation,
Flocculation and
Sedimentation
See Chapter 6 and 7 See Chapter 6 and 7
Activated Carbon
Adsorption Poor removal of taste and odour
using PAC
Evaluate optimum PAC dose and
type, mixing intensity and contact
time through jar testing (Section
10.6.4.1)
Excessively high dosages of PAC
(greater than 50 mg/L) are required
for effective removal
Consider change to GAC contactor,
as high PAC dosages can make
process cost prohibitive
Caking of PAC on filter surfaces,
shortening filter runs and
increasing backwash frequency
Optimize upstream treatment to
improve removal of PAC in settling
processes (see Chapter 7)
Penetration of PAC through filters,
resulting in “dirty water”
complaints from consumers
Reduce carbon dose or filtration
rate, if possible
Consider addition of filter aid
Poor removal of tastes and odours
through GAC contactors
Frequent need for GAC media
regeneration or replacement
See Section 10.6.4.2
Aeration See Section 10.2.3 See Section 10.2.4
Chemical Oxidation Odours are not being removed
through oxidation, and in some
cases increase (particularly when
using chlorine as oxidant and/or if
phenols are present in raw water)
Evaluate optimum oxidant dose
through jar testing (see Chapter 4)
Increase contact time or optimize
hydraulics to improve effective
contact time
Evaluate other oxidant chemicals
Very high doses of chlorine are
required to achieve sufficient
reduction in taste and/or odour
Consider implementation of
superchlorination followed by
dechlorination, if disinfection by-
products are not a concern
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Table 10-7 – Taste and Odour Control – Symptoms and Causes of Common Problems
and Potential Optimization Strategies (cont’d.)
Process Problem
Mitigation
When using KMnO4, pink coloured
water is carrying over into
clearwells
Conduct jar testing to determine
maximum KMnO4 dosage that can
be applied and determine required
contact time (see Chapter 4);
additional information specific to
jar testing for KMnO4 addition is
available elsewhere (California
State University, 1999)
10.6.4 Optimization Techniques
10.6.4.1 Optimizing PAC Addition for Taste and Odour Control
The appropriate dose of PAC for a particular drinking water issue will vary depending upon
the nature of the target contaminant, the concentration of the substance to be removed, the
mixing available, the contact time and the location of the application points. Jar tests should
be used to determine the necessary PAC doses required to treat the specific taste and odour
problem. If the concentration of the taste and odour compound varies significantly during a
taste and odour event, jar testing should be conducted frequently during the event to ensure
that the optimal dose is being applied.
Adsorption isotherms can be developed to evaluate the dosage and type of PAC used for a
specific application. The test is performed by exposing a known quantity of adsorbate (the
target compounds to be removed, for example, geosmin) in a fixed volume of liquid to
various dosages of adsorbent (PAC). Additional information on performing adsorption
isotherms is provided in MWH (2005), Najm et. al. (1991) and McGuire et. al. (1989).
Jar testing can be used to determine the most effective range of carbon dosage by simulating
actual mixing intensity and detention times achieved within the plant for a variety of
application points.
Analytical testing identified in Table 10-6 can be used to evaluate the effectiveness of
different carbon dosages used during jar testing. The TON method can also be used if only a
few tests are required. Accurate determination of the TON is difficult when several jar tests
are conducted concurrently because a person’s sense of smell becomes rapidly fatigued
following just two or three individual TON tests (California State University, 1999).
10.6.4.2 Optimizing GAC Filtration for Taste and Odour Control
The operation of GAC filters is similar to the procedures used for the operation of
conventional granular media filters (see Chapter 8).
Two specific considerations for GAC filters are the empty bed contact time (EBCT) and the
frequency of regeneration or replacement of the carbon. The EBCT required for taste and
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odour control depends on the nature of the taste and odour compounds and typically varies
from 10 to 30 minutes (MOE, 2008).
Periodic regeneration or replacement of GAC is necessary as the capacity of the filter to
adsorb and retain organic compounds decreases with time. The time between regenerations or
replacement will vary with the type of compound being removed and the volume of water
treated.
Spent GAC can be regenerated on-site for larger installations; for smaller systems, it may be
more cost effective to have the GAC processed off-site.
Pilot testing (Chapter 4) should be conducted to evaluate the required EBCT and regeneration
or replacement frequency for a particular application.
10.7 NATURAL ORGANIC MATTER REMOVAL
10.7.1 Purpose and Types of NOM Removal Processes
NOM has traditionally been partly removed from drinking water for aesthetic reasons, as it
often imparts colour to the water. The low molecular weight fractions of NOM are mostly
responsible for chlorination by-product formation (see Chapter 9) and therefore, a reduction
of the NOM concentration is desirable. The presence of NOM may also affect other water
treatment processes, including:
Coagulation – change of coagulant dosage and optimum pH;
Membrane filtration – potential for increased fouling;
Disinfection – increase in disinfectant demand or decrease in UVT;
Activated carbon adsorption – Increased activated carbon usage rates; and
Distribution system water quality – potential for bacteriological regrowth and DBP
formation.
Enhanced coagulation can be used in some systems to achieve improved removal of DBP
precursors by optimizing conventional treatment processes and coagulant dosages
specifically for TOC removal. The effectiveness of enhanced coagulation is measured by
achieving a targeted percentage removal of TOC, a surrogate for NOM. Additional
information is provided in the USEPA’s Enhanced Coagulation and Enhanced Precipitative
Softening Guidance Manual (USEPA, 1999).
PAC addition and GAC filtration can be used for reducing NOM concentration, and may also
be operated in a biologically active mode for NOM reduction. The use of GAC to adsorb
NOM is generally not very effective or economically attractive as the GAC rapidly loses
adsorption capacity.
Nanofiltration can be used to remove a large fraction of the NOM. This process can be costly
as relatively high pressures are used and pre-treatment is needed to protect the membranes
from particulate accumulation. Nanofiltration has not yet found wide application in Ontario,
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and specific optimization techniques for this process are therefore not presented in this
Manual.
10.7.2 Evaluating Performance
The sampling locations and parameters to be analyzed for monitoring NOM removal
processes will depend on the type of treatment provided and on whether the NOM removal
processes occur as part of a conventional treatment process (e.g. enhanced coagulation) or as
a stand-alone unit process (e.g. GAC contactors).
Table 10-8 presents monitoring recommended, in terms of sampling locations and analyses,
in order to evaluate the performance of NOM removal processes.
Table 10-8 – NOM Removal – Recommended Process Monitoring to Evaluate
Performance
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Raw water Continuous monitoring pH
Grab sample TOC or DOC
Colour
UVT
UV254
Alkalinity
THM formation
potential and/or THM
simulated distribution
system
TOC, DOC, colour and
UVT can be used as
surrogates for NOM.
Higher alkalinity
waters are more
challenging to treat, as
it is more difficult to
achieve the optimum
pH for TOC removal
during coagulation.
Treatment
Process (for
conventional
treatment with
enhanced
coagulation)
Continuous monitoring Coagulation pH
Coagulant dosage
Mixing intensity
Flocculation detention
time
Filtration rate
Optimal pH and
coagulant dosage for
NOM removal
typically is different
than for turbidity
removal.
Typically, lower
mixing intensity,
longer flocculation
detention times and
lower filtration rates
are needed for NOM
removal (see Chapter 6
and Chapter 8).
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Table 10-8 – NOM Removal – Recommended Process Monitoring to Evaluate
Performance (cont’d.)
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Treatment
Process (GAC
contactors with or
without
conventional
treatment)
Continuous monitoring EBCT as function of
flow rate
To ensure optimum
EBCT is provided.
Grab sample Bacterial populations To evaluate bacterial
activity within the
filter.
Treated water Grab sample UVT
UV254
DBP formation potential
TOC or DOC
Colour
Surrogate parameters
used to measure the
effectiveness of NOM
removal.
10.7.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with NOM removal processes are
shown in Table 10-9.
Table 10-9 – NOM Removal – Symptoms and Causes of Common Problems and
Potential Optimization Strategies
Process Problem
Mitigation
Coagulation,
Flocculation and
Sedimentation
See Chapter 6 and 7 See Chapter 6 and 7, as well as
Section 10.7.4
Activated Carbon
Adsorption Poor removal of NOM using PAC Evaluate optimum PAC dose and
type, mixing intensity and contact
time through jar testing (Section
10.7.4)
Develop adsorption isotherm (see
references in Section 10.7.4 for
procedures)
Excessively high dosages of PAC
(greater than 50 mg/L) are required
for effective removal
Consider change to GAC contactor,
as high PAC dosages can make
process cost prohibitive
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Table 10-9 – NOM Removal – Symptoms and Causes of Common Problems and
Potential Optimization Strategies (cont’d.)
Process Problem
Mitigation
Caking of PAC on filter surfaces,
shortening filter runs and
increasing backwash frequency
Optimize upstream treatment to
improve removal of PAC in settling
processes (see Chapter 7)
Penetration of PAC through filters,
resulting in “dirty water”
complaints from consumers
Reduce carbon dose or filtration
rate, if possible
Consider addition of filter aid
Poor removal of NOM through
GAC contactors
Frequent need for GAC media
regeneration or replacement
Develop adsorption isotherm (see
references in Section 10.7.4 for
procedures)
See Section 10.7.4
10.7.4 Optimization Techniques
The removal of NOM in water treatment is often problematic and extensive research has been
conducted on the optimization of treatment processes for NOM removal.
For conventional treatment plants, the process can be optimized by enhanced coagulation,
which may include adjusting the pH and coagulant dose to improve NOM removal or by
using a different coagulant chemical. Jar testing can be used to evaluate the optimum
conditions for coagulation pH, chemical and dose. Information on enhanced coagulation
gained from studies conducted in Ontario is provided in Anderson et. al. (1995).
Optimization of flocculation and clarification processes, such as improving mixing and
providing adequate hydraulic detention times as discussed in Chapters 6 and 7, can also
improve NOM removal.
Jar testing can also be used to evaluate different types and dosages of PAC to improve NOM
removal. Adsorption isotherms can be performed to quantify the affinity of the target organic
compounds for a specific type of activated carbon.
Comprehensive information on the optimization of conventional and activated carbon
treatment for NOM removal is available, including:
Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual
(USEPA, 1999);
Characterization of Natural Organic Matter and Its Relationship to Treatability
(Owen et. al., 1993);
Control of Organic Compounds with Powdered Activated Carbon (Najm et. al.,
1991); and
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Optimization Guidance Manual for Drinking Water Systems 2014
Optimization and Economic Evaluation of Granular Activated Carbon for Organic
Removal (McGuire et. al., 1989).
10.8 INTERNAL CORROSION CONTROL
10.8.1 Purpose and Types of Internal Corrosion Control Processes
Corrosion of water distribution system materials can cause failure of the distribution
infrastructure resulting from leakage or reduced hydraulic capacity and/or the release of
corrosion by-products, such as lead, copper, iron and antimony. In Ontario, lead is used as an
indicator of corrosion and for the potential requirement for corrosion control under the
Drinking Water Systems Regulation (O. Reg. 170/03).
Many different types of corrosion exist, depending on the materials used and construction of
the system, the formation of scale and hydraulic conditions. In some cases, corrosion may be
relatively uniform, while in others pits or tubercules may form.
Corrosion can occur for a variety of reasons. For example, differences in potential may exist
due to differences or imperfections in the structure of the metal, or due to the concentrations
of oxidants and reductants in the water (AWWA, 1999). Galvanic corrosion occurs when two
different types of metals or alloys contact each other; one metal serves as the anode (and
deteriorates) while the other serves as the cathode. Additional information on the different
types of corrosion is presented in AwwaRF & TZW (1996).
The primary approaches to internal corrosion control in drinking water systems are to modify
the water chemistry to make it less corrosive and to encourage formation of less soluble
compounds (passivation). This is typically accomplished through pH and/or alkalinity
adjustment or through the addition of a corrosion inhibitor.
Although a corrosion control strategy may be developed specifically to reduce lead
concentrations in a distribution system, most treatment techniques will also be beneficial for
reducing corrosion of copper, iron, steel and galvanized pipe.
pH and/or alkalinity adjustment can be accomplished via chemical or non-chemical means.
Chemical methods include addition of:
Sodium hydroxide, NaOH (caustic soda);
Potassium hydroxide, KOH (caustic potash);
Calcium hydroxide, Ca(OH)2 (lime);
Sodium carbonate, Na2CO3 (soda ash);
Sodium bicarbonate, NaHCO3; or
Carbon dioxide (CO2).
Limestone contactors and aeration are two other commonly used pH and/or alkalinity
adjustment strategies.
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Phosphate corrosion inhibitors are available in a variety of compositions: phosphoric acid,
orthophosphate, zinc orthophosphate, polyphosphates and blends of orthophosphate and
polyphosphate. They are generally proprietary compounds with varying percentages of
orthophosphate, the active agent in the formation of passivating films for lead control.
Guidance for corrosion control planning is provided in the Guidance Document for
Preparing Corrosion Control Plans for Drinking Water Systems (MOE, 2009) and the
Revised Guidance Manual for Selecting Lead and Copper Control Strategies (USEPA,
2003).
10.8.2 Evaluating Performance
Assessing the effectiveness of corrosion control involves monitoring of:
Operating conditions for the corrosion control process;
Lead levels and other corrosion related parameters in the distribution system and
premise plumbing; and
Secondary water quality impacts that may occur.
Typically, a corrosion control monitoring program will include testing for regulated and
aesthetic parameters, as well as tracking of customer complaints (e.g. dirty water). Many
physical and chemical factors can affect corrosion or corrosion control; the inclusion of
specific parameters in a testing program will be site specific. Parameters to be considered
include: temperature, pH, alkalinity, dissolved inorganic carbonate (DIC), hardness,
dissolved oxygen, total dissolved solids, chlorine residual, chloride and sulphate, hydrogen
sulphide, ammonia, natural organic matter and metals (e.g. iron, zinc, manganese, copper,
etc.).
Table 10-10 presents monitoring recommended, in terms of sampling locations and analyses,
in order to evaluate the performance of corrosion control processes.
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Table 10-10 – Corrosion Control – Recommended Process Monitoring to Evaluate
Performance
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Raw water Continuous monitoring pH
Grab sample Alkalinity
Treatment process
(post-adjustment)
Continuous monitoring pH
Inhibitor dosage (if
applicable)
Air/water flow rates (if
aeration is used)
For process control
Grab sample Alkalinity
Inhibitor concentration
(if applicable)
DO concentration (if
applicable)
Treated water Continuous monitoring
or Grab sample Lead
Alkalinity
pH
Temperature
Total dissolved solids
Specific conductance
Chloride:sulphate mass
ratio (CSMR)
To monitor the
consistency of treated
water quality and for
comparison with
distribution system water
quality
Note that this table is in addition to the required regulatory monitoring under the Drinking
Water Systems Regulation (O. Reg. 170/03).
MOE recommendations for distribution system sampling to evaluate the effectiveness of a
corrosion control plan are provided in Table 10-11.
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Table 10-11 – Corrosion Control – Recommended Distribution System Monitoring to
Evaluate Performance
Adapted From Guidance Document for Preparing Corrosion Control Plans for Drinking
Water Systems (MOE, 2009)
Parameters Distribution System
Residential and
Non-Residential
Taps
Distribution System
Dead Ends and Areas
of Low Chlorine
Residual
Lead X X X
Alkalinity, pH X X X
Orthophosphate
and/or silicate X X X
Temperature,
TDS, specific
conductance
X X X
Dissolved oxygen X
Iron, manganese X X
Chloride, sulphate X X
Turbidity, colour X X
Calcium, zinc,
aluminum X X
Microbiological
parameters
(coliform, HPC)
X X
Nitrate, nitrite,
free ammonia1
X X
Notes:
1. For systems that operate with chloramination for residual maintenance in the distribution
system.
Additional information on the frequency and number of samples to be collected is provided
in O. Reg. 170/03 and the Guidance Document for Preparing Corrosion Control Plans for
Drinking Water Systems (MOE, 2009).
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10.8.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with corrosion control processes are
shown in Table 10-12.
Table 10-12 – Corrosion Control – Symptoms and Causes of Common Problems and
Potential Optimization Strategies
Process Problem
Mitigation
Calcium hydroxide
(slaked lime or
quicklime) addition
Oversaturation may cause calcium
deposits
pH control is difficult when applied
to poorly buffered water
Slurry feed can cause excess
turbidity
Careful monitoring of the finished
water is required to prevent
oversaturation
To prevent increase in turbidity,
lime can be dissolved in water and
clarified prior to being added to the
treated water
Sodium hydroxide
(caustic soda)
addition
pH control can be difficult when
applied to poorly buffered water
Solution tends to freeze in colder
temperatures
Consider process that also increases
alkalinity
Consider lower strength solution or
dilution to prevent freezing
Sodium bicarbonate
or sodium carbonate
(soda ash) addition
Dry solid must be mixed to form
solution feed; solid tends to form
cake in presence of moisture
Ensure large dissolving chambers
are provided to ensure adequate
detention time and mixing
Inhibitor addition May cause leaching of lead in
stagnant waters
May encourage growth of
microorganisms (by increasing
availability of nutrients)
May not be compatible with some
industrial processes or downstream
wastewater treatment processes
Conduct jar testing to determine
optimum treated water pH and
inhibitor concentration to prevent
destabilization of existing scales
Ensure adequate chlorine residuals
persist in all areas of distribution
system
Aeration See Section 10.2.3 See Section 10.2.4
10.8.4 Optimization Techniques
Several techniques are available for the optimization of corrosion control processes. As
mentioned in previous subsections, comprehensive information is provided in the Guidance
Document for Preparing Corrosion Control Plans for Drinking Water Systems (MOE, 2009)
and USEPA’s Revised Guidance Manual for Selecting Lead and Copper Control Strategies
(USEPA, 2003).
Optimization studies for corrosion control processes should be conducted over a minimum of
6 to 9 months, as corrosion rates are commonly observed to take from 6 months to 1 year to
stabilize after changes have been made to water quality (MOE, 2008). A reliable testing
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Optimization Guidance Manual for Drinking Water Systems 2014
technique is to make changes to water composition in one area of a distribution system while
leaving the water composition unchanged in the remainder of the system. Test results from
the two areas should then be compared after a period of 6 months to a year.
10.9 CASE HISTORIES
10.9.1 Washington, D.C. – Optimization of Orthophosphate Addition
The following case study is based on information presented in Standard (2006).
System Description
The Washington (D.C.) Aqueduct operates and maintains the raw water supply facilities and
two treatment plants that supply water to the Washington, D.C., Water and Sewer Authority
(WASA) and parts of Northern Virginia (Arlington County and the City of Falls Church).
Combined, the two treatment facilities treat an average of 680 ML/d (180 mgd).
In November 2000, Washington Aqueduct switched its secondary disinfectant from chlorine
to chloramines in an effort to meet the new total THM maximum contaminant level (MCL)
requirement of the Stage 2 Disinfectants and Disinfection Byproducts Rule (USEPA, 2006).
WASA reported a significant increase in lead levels in its distribution system for the Lead
and Copper Rule monitoring period following the conversion to chloramines. Continued
sampling at homes served by lead service lines showed that lead levels exceeded the federal
action level for lead in drinking water.
Optimization Strategies
Computer modelling by the Washington Aqueduct determined that raising the pH by
increasing the dosage of calcium hydroxide to improve corrosion control would result in
excessive levels of calcium carbonate precipitation in the distribution system. In a series of
separate experiments, it was determined that orthophosphate addition could decrease lead
leaching from service lines.
Orthophosphate was first added to water in a small, isolated section of the distribution
system. The purpose of this trial was to determine if any negative effects would occur as a
result of the orthophosphate addition. The trial was successful and full-scale orthophosphate
addition was implemented.
Automated orthophosphate feed systems were installed with continuous on-line phosphate
residual monitoring. The chemical feed system is designed to be controlled either manually
or automatically, with flow pacing being the preferred control method. The feed system is
controlled by the plants’ supervisory control and data acquisition (SCADA) system based on
an operator-entered dosage set point, the actual flow rate and actual orthophosphate feed rate.
Continuous on-line orthophosphate monitoring at both plants is supplemented by daily grab
samples that operators use to assess and verify the accuracy of the on-line analyzers.
The current orthophosphate dose at both plants is approximately 2.5 mg/L as PO4 entering the
distribution system. Pipe-loop studies are on-going to determine whether dosage levels can
ultimately be reduced. The calcium hydroxide system is also carefully controlled so that the
optimum pH for inhibitor addition (between 7.4 and 7.8) for lead control is maintained.
CHAPTER 10. Other Treatment Processes 10-26
Optimization Guidance Manual for Drinking Water Systems 2014
Summary
For the WASA reporting periods of January-June 2005 and July-December 2005, the 90th
percentile lead level had been significantly reduced, but was still at levels near the federal
action level of 15 µg/L. For the period of January-June 2006, the 90th percentile lead level
was found to be 10 µg/L.
The results of the study to date indicate that lead levels in Washington’s distribution system
will continue to decrease, provided that orthophosphate residuals in the distribution system
are maintained consistently and within the optimal pH range.
10.9.2 Chicago, IL – Optimization of Taste and Odour Control with Pilot Plant
Testing
The following case study is based on information presented in Putz et. al. (2007).
System Description
The City of Chicago Department of Water Management (DWM) owns and operates two large
water treatment plants, the Jardine Water Purification Plant (WPP) and the South WPP. Both
plants consist of a conventional treatment train, with chlorine, polymer and fluoride addition
followed by coagulation with alum, flocculation, sedimentation and rapid sand filtration.
Blended phosphate is applied to the treated water for distribution system corrosion control.
The source water, Lake Michigan, has raw water quality typical of the Great Lakes, with
turbidity being the parameter with the most variability. Raw water temperature also has a
large seasonal range that typically peaks in August. An increase in temperature often
correlates with an increase in the microbial production of taste and odour causing
compounds, such as MIB and geosmin. This taste and odour season lasts from June through
October.
Optimization Strategies
The DWM had been unsuccessful in attempts to control these taste and odour events using
PAC. A pilot study was undertaken to evaluate the effectiveness of ozone for the oxidation of
taste and odour causing compounds.
Several trials were undertaken to determine the required ozone dosage, ozone demand and
ozone decay rates. MIB and geosmin were added to the raw water to simulate an extreme
taste and odour event. The raw water was treated at ozone dosages of 1.5 and 3.0 mg/L for
contact times ranging from less than 10 seconds up to 30 minutes.
The results indicated that geosmin and MIB removal occurred more rapidly at the higher
ozone dosage of 3.0 mg/L. Following 10 minutes of contact time, MIB and geosmin were
reduced by approximately 96 and 74 percent, respectively, to below 5 ng/L. It should be
noted, however, that at this ozone dosage, bromate concentrations were found to exceed the
MCL of 10 µg/L set under the Stage 2 Disinfectants and Disinfection Byproducts Rule
(USEPA, 2006) due to the oxidation of naturally-occurring bromide in the raw water.
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Optimization Guidance Manual for Drinking Water Systems 2014
Additional pilot plant trials were conducted to evaluate ozonation strategies that would
control taste and odour while minimizing the formation of bromate, including a reduction of
the ozone dosage, lowering the pH and ammonia addition.
The results of the testing indicated that bromate formation increased significantly with ozone
doses higher than 2.5 mg/L at a pH of 8.3; at this dosage, bromate levels were above the
MCL for all tested contact times. By decreasing the ozone dosage to 1.5 mg/L for a contact
time of less than 13 minutes, bromate concentrations were maintained below the MCL of 10
µg/L. Reducing the pH to 7.3 or lower (with an ozone dosage of 1.5 mg/L and a contact time
of 13 minutes) was also effective in reducing bromate formation to below the MCL.
Ammonia addition (doses ranging from 0.065 to 0.13 mg/L) was also effective in reducing
bromate formation.
Summary
The findings of the pilot study indicated that ozonation is a viable option for full-scale taste
and odour control. Additional full-scale trials are needed to evaluate the optimum treatment
conditions for effective taste and odour control while maintaining bromate levels below the
MCL of 10 µg/L.
10.10 REFERENCES
American Public Health Association/American Water Works Association/Water
Environment Federation (2005). Standard Methods for the Examination of Water &
Wastewater. 21st Edition. APHA/AWWA/WEF. ISBN 0-87553-047-8.
Anderson, W.B., I.P. Douglas, J. Van Den Oever, R.B. Hunsinger and P.M. Huck (1995).
Enhanced Coagulation With and Without Pre-Ozonation for Turbidity, NOPC and Colour
Control. Proceedings, AWWA Annual Conference, Water Quality Section, Anaheim, CA.
AWWA (1995). Water Treatment – Principles and Practices of Water Supply Operations. 2nd
Ed. AWWA. Denver, CO. ISBN 0-89867-789-0.
AWWA (1999). Water Quality and Treatment: A Handbook of Community Water Supplies,
5th Ed. AWWA and McGraw Hill. ISBN 0-07-001659-3.
AwwaRF & DVGW-Technologiezentrum Wasser (1996). Internal Corrosion of Water
Distribution Systems. 2nd Ed. AwwaRF and AWWA. Denver, CO. ISBN 0-89867-759-9.
California State University (2008). Water Treatment Plant Operation – Volume 1. 6th Ed.
California State University, Office of Water Programs. Sacramento, CA. ISBN 978-
1593710033.
Clifford, D.A., Z. Zhang (1994). Modifying Ion Exchange for Combined Removal of Uranium
and Radium. Journal AWWA, Vol. 86, Iss. 4, April 1994, p. 214-227.
Clifford, D.A., G.L. Ghurye, A.R. Tripp (2003). Arsenic Removal Using Ion Exchange with
Spent Brine Recycling. Journal AWWA, Vol. 95, Iss. 6, June 2003, p. 119-130.
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Optimization Guidance Manual for Drinking Water Systems 2014
Elhadi, S., P.M. Huck, R.M. Slawson (2006). Factors Affecting the Removal of Geosmin and
MIB in Drinking Water Biofilters. Journal AWWA, Vol. 98, Issue 8, August 2006, p. 108-
119.
Ghurye, G.L., D.A. Clifford, A.R. Tripp (1999). Combined Arsenic and Nitrate Removal by
Ion Exchange. Journal AWWA, Vol. 91, Iss. 10, October 1999, p. 85-96.
Huck, P.M., B.M. Coffey, A. Amirtharajah and E.J. Bouwer (2000). Optimizing Filtration in
Biological Filters. Submitted to American Water Works Association Research Foundation
and American Water Works Association, Report No. 90793. Denver, CO. ISBN 1-58321-
065-2.
Liu, X., D.A. Clifford (1998). Ion Exchange With Denitrified Brine Reuse. Journal AWWA,
Vol. 88, Iss. 11, November 1996, p. 88-99.
Liu, X., P.M. Huck, R.M. Slawson (2001). Factors Affecting Drinking Water Biofiltration.
Journal AWWA, Vol. 93, Issue 12, December 2001, p. 90-101.
McGuire, M.J., M.K. Davis, L. Liang, C.H. Tate, E.M. Aieta, I.E. Wallace, D.R. Wilkes, J.C.
Crittenden and K. Vaith (1989). Optimization and Economic Evaluation of Granular
Activated Carbon for Organic Removal. AwwaRF and AWWA. Denver, CO. ISBN0-89867-
469-7.
MOE (2006). Technical Support Document for Ontario Drinking Water Standards,
Objectives and Guidelines. PIBS 4449e01.
MOE (2008). Design Guidelines for Drinking Water Systems, 2008. ISBN 978-1-4249-8517-
3.
MWH (2005). Water Treatment Principles and Design. 2nd
Ed. John Wiley & Sons, Inc.
ISBN 0-471-11018-3.
Najm, I.N., V.L. Snoeyink, T.L. Galvin and Y.R. Degrémont (1991). Control of Organic
Compounds with Powdered Activated Carbon. AwwaRF and AWWA. Denver, CO. ISBN 0-
89867-528-6.
Owen, D.M., G.L. Amy and Z.K. Chowdhury (1993). Characterization of Natural Organic
Matter and Its Relationship to Treatability. AwwaRF and AWWA. Denver, CO. ISBN 0-
89867-698-3.
Putz, A.R.H., A. Atassi, C. Feizoulof and J.F. Spatz Jr. (2007). “Optimizing Full-Scale
Operations Using Pilot Plant Studies”, presented at the 2007 AWWA Annual Conference &
Exposition. Toronto, ON.
Rashash, D.M.C., R.C. Hoehn, A.M. Dietrich, T.J. Grizzard and B.C. Parker (1996).
Identification and Control of Odorous Algal Metabolites. AwwaRF and AWWA. Denver,
CO. ISBN 0-89867-855-2.
Smith, E.F., M.B. Emelko (1998). Benefiting From Biological Growth in Filters. Opflow,
Vol. 24, Issue 11, November 1998, p. 1, 4-5.
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Optimization Guidance Manual for Drinking Water Systems 2014
Sommerfeld, E.O. (1999). Iron and Manganese Removal Handbook. AWWA. Denver, CO.
ISBN 1-58321-012-1.
Standard, D.S. (2006). On-line Orthophosphate Monitoring, Automated Dosing Optimize
Washington, D.C.’s Lead Reduction Program. Journal AWWA, Vol. 98, Issue 10, October
2006, p.p. 38-40.
USEPA (1998). Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program, EPA-625-6-91-027.
USEPA (1999). Enhanced Coagulation and Enhanced Precipitative Softening Guidance
Manual. Office of Water. EPA-815-R-99-012.
USEPA (2003). Revised Guidance Manual for Selecting Lead and Copper Control
Strategies. Office of Water. Washington, DC. EPA-816-R-03-001.
USEPA (2006). National Primary Drinking Water Regulations: Stage 2 Disinfectants and
Disinfection Byproducts Rule; Final Rule. Federal Register, Vol. 71, No. 2. January 4, 2006.
World Health Organization (2008). Guidelines for Drinking Water Quality - Volume 1:
Recommendations. Third Edition. World Health Organization. Geneva. ISBN 978-92-4-
154761-1.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 11 DISTRIBUTION SYSTEMS
DISTRIBUTION SYSTEMS
11.1 Introduction .......................................................................................................... 11-1
11.2 Treated Water Pumping Stations .......................................................................... 11-1
11.2.1 Purpose and Types of Treated Water Pumping Stations ....................... 11-1
11.2.2 Evaluating Performance ......................................................................... 11-1
11.2.3 Common Problems and Potential Impacts ............................................. 11-2
11.2.4 Optimization Techniques ....................................................................... 11-2
11.3 Treated Water Storage .......................................................................................... 11-4
11.3.1 Purpose and Types of Treated Water Storage Facilities ........................ 11-4
11.3.2 Evaluating Performance ......................................................................... 11-4
11.3.3 Common Problems and Potential Impacts ............................................. 11-5
11.3.4 Optimization Techniques ....................................................................... 11-6
11.4 Distribution System Piping and Appurtenances ................................................... 11-8
11.4.1 Purpose and Types of Distribution System Facilities ............................ 11-8
11.4.2 Evaluating Performance ......................................................................... 11-9
11.4.3 Common Problems and Potential Impacts ........................................... 11-11
11.4.4 Optimization Techniques ..................................................................... 11-13
11.5 Case Histories ..................................................................................................... 11-20
11.5.1 Region of Durham – Water Loss Control Strategy .............................. 11-20
11.5.2 Region of Niagara – Treated Water Pumping & Storage Optimization11-21
11.6 References .......................................................................................................... 11-22
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CHAPTER 11
DISTRIBUTION SYSTEMS
11.1 INTRODUCTION
Water distribution systems are designed and operated to provide a balance between hydraulic
water supply needs and water quality. The characteristics of a “high quality distribution
system” are defined in the report of the Walkerton Commission as “reliable, providing a
continuous supply of potable water at adequate pressure. Reservoirs within the system
balance pressure and cope with peak demands, fire protection and other emergencies without
causing undue water retention, while looped watermains prevent stagnation and minimize
customer inconvenience during repairs. Since water quality can decline with the length of
time the water remains in the system, and the rate of decline depends partly on the attributes
of the distribution system, a high-quality system has as few dead ends as possible and
maintains adequate flow and turnover” (O’Connor, 2002).
This chapter provides guidance on measures to optimize distribution system operation and
maintain water quality, system pressure and supply needs, while minimizing energy use and
water losses.
11.2 TREATED WATER PUMPING STATIONS
11.2.1 Purpose and Types of Treated Water Pumping Stations
High-lift pumps are used to discharge water from the treatment plant under pressure to the
distribution system. Booster pumps are used to increase pressure in the distribution system
and/or to supply elevated storage tanks.
High-lift pumping facilities are typically located at or near the water treatment plant. Booster
pumping stations are located throughout the distribution system and/or near storage facilities.
11.2.2 Evaluating Performance
The performance of treated water pumping facilities is typically assessed based on the ability
to provide design flows at design pressures to the distribution system.
The minimum capacity of high-lift pumping facilities should be equal to the maximum day
demand for the system, with consideration given to the distribution system configuration and
storage capacity.
Booster pumping stations, either alone or in conjunction with storage, should be capable of
meeting the various demand requirements of the area being serviced, based on peak hourly
flows, night flows with refilling of remote storage facilities, fire flows, etc.
The discharge pressure from the pumping station should be adequate to ensure that the
pressure in the area to be served is within the range of 275 kPa to 700 kPa during peak and
minimum demand periods. In the case of fire flows, it may be acceptable to allow the
pressure in the system to drop to a level less than 275 kPa but maintain a minimum pressure
of 140 kPa.
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Additional information that can be used to evaluate the performance of treated water
pumping facilities is provided in the Design Guidelines for Drinking Water Systems, 2008
(MOE, 2008).
11.2.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with high-lift and booster pumping
stations are presented in Table 11-1.
Table 11-1 – Treated Water Pumping – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Process Impacts Common Causes
Lack of hydraulic
capacity at the pump
station/pumps
Operating above firm capacity for
extended periods
Undersized pumps
Inadequate distribution system
storage
Frequent cycling of
pump operation Inconsistent flows and pressures
resulting in alternating periods of
flow and no-flow (and potential
flow reversals) in distribution
piping
Settling of solids in pipes during
no-flow or low flow conditions
Oversized pumps
Pumps not sized to meet the range of
demands
Pumps not equipped with variable
frequency drives (VFDs)
11.2.4 Optimization Techniques
11.2.4.1 Pump Selection and Sizing
For high-lift pumping stations, the minimum number of pumps to be provided should be two,
to ensure redundancy, in addition to any pumps needed to provide fire flows. The minimum
capacity should be equal to the maximum day demand and the actual capacity will be dictated
by the distribution system and storage capacity (MOE, 2008).
Each booster pumping station should contain not less than two pumps with capacities such
that the firm station capacity can be satisfied with the largest pump out of service (MOE,
2008).
Oversized pumps will often operate in an on-off mode during low flow conditions, causing
uneven flows or periods of no-flow to downstream DWS components. This can cause settling
of suspended solids in downstream piping, flow reversals and other operational problems.
Improper design or the installation of oversized pumps (often to meet the ultimate design
capacity) can result in the requirement to throttle the pump discharge valve in order to reduce
cavitation. This can result in a significant waste of energy for pumping.
Problems with pump over-sizing are commonly encountered in new or newly expanded
facilities where the pumps were sized to be capable of handling the expected design flows at
build-out, without consideration of the demand at current conditions. The installation of
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multiple, smaller capacity pumps, which operate according to a pressure or flow set point can
minimize the frequency of on-off cycling and provide consistent flows to the distribution
system throughout the day. Pump efficiency and operational energy savings should be
considered during pump selection.
11.2.4.2 Variable Frequency Drives
Where pumping station configuration does not allow for the installation of multiple, lower
capacity pumps in place of a single larger capacity pump, a VFD can be installed on the
existing pump(s). The installation of a VFD can optimize pump operation by providing
flexibility to operate over a range of flows. Additional information regarding VFDs is
provided in Section 5.5.3.2.
11.2.4.3 Control Strategies
The type of control for pump operation is an important consideration for pump specification
and selection, and depends on whether the pumps are part of an open or closed pumping
system.
In closed systems (e.g. a system that has no elevated storage and uses continuously running
pumps to provide pressure and meet water usage demands), a control valve is typically
provided to ensure proper operation of the pump. For very small systems, hydropneumatic
tanks (pressure tanks) may also be provided to maintain acceptable system pressures without
the need for frequent cycling of pumps.
Pressure control is commonly used for pump operation in both open systems and closed
systems. A combination of flow control and pressure control may be used in smaller systems.
Whatever control system is implemented, operation of the pumps near their maximum
efficiency points should be maintained.
11.2.4.4 Impeller Modification
Where a pump is undersized or oversized, or where downstream hydraulic conditions have changed,
impeller replacement or modification can potentially eliminate the need for pump replacement.
Modifying or replacing the impeller in a pump shifts the pump’s operating curve, effectively
changing the efficiency operating point of the pump. In addition to potentially avoiding costs
associated with pump replacement, impeller modification or replacement can allow for more
efficient operation of the pump, reducing operating costs.
Depending on the size of the pump volute and existing impeller, it may not always be
possible to replace the impeller with one of a larger or smaller size. In such cases, if a smaller
impeller is required for an oversized pump, the impeller can be trimmed to reduce its size.
Conversely, if a larger impeller is needed, total pump replacement may be required.
The selection or modification of a pump impeller is based on the size of the pump, the system
head curve, pump configuration, pump power and required capacity. The pump manufacturer
should be consulted when considering modification or replacement of an impeller to ensure
that the new or modified impeller will not negatively impact pump performance.
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11.3 TREATED WATER STORAGE
11.3.1 Purpose and Types of Treated Water Storage Facilities
Treated water storage facilities are provided in a distribution system to maintain adequate
flows and pressure during periods of peak water demand, to meet critical water demands
during fire flow and emergency conditions, and to reduce the capacity required for the water
treatment plant.
There are several types of treated water storage facilities, which can be located either at the
water treatment plant or in the distribution system. Some of the most common types of
storage facilities in Ontario are listed below.
At the water treatment plant:
Clearwells;
Reservoirs;
Pumping wet wells; and
Pressure tanks.
In the distribution system:
Elevated tanks;
Standpipes; and
Reservoirs.
The type of water storage facility used in a drinking water system will depend on many
factors, such as function, the size of the service area, topography, costs, the balance between
water treatment capacity and demand, and the amount of storage required at the water plant
and in the distribution system.
11.3.2 Evaluating Performance
The performance of treated water storage facilities is assessed based on the ability to meet
water demands that exceed the daily water supply capacity of the treatment plant, and where
fire protection is provided, fire flow demands.
The capacity of treated water storage facilities can be evaluated using the method described
in the Design Guidelines for Drinking Water Systems, 2008 (MOE, 2008). This method
considers the need for fire storage, equalization storage and emergency storage in the system.
It should be noted that any volume required to provide storage for fire or equalization is not
available for contact time and should not be included in CT calculations. Additional
information on primary disinfection and contact time is provided in Chapter 9.
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Storage facilities should also be designed to maintain water quality and prevent
contamination. Stagnation and detention times should therefore be minimized. Table 11-2
provides recommendations in terms of sampling locations and analyses, to monitor and
evaluate the performance of storage facilities with respect to maintaining treated water
quality.
Table 11-2 – Treated Water Storage – Recommended Monitoring to Evaluate
Performance
Location Types of Sample / Measurement Parameters / Analyses
Treated water
(at a location where
water enters the
distribution system)
Continuous monitoring Turbidity
Disinfectant residual
Grab sample Microbial parameters
Influent to storage
facility
Continuous monitoring Flow rate or water level in tank
Grab sample Temperature
pH
Disinfectant residual
Microbial parameters
Effluent from
storage facility
Continuous monitoring Flow rate or water level in tank
Disinfectant residual
Grab sample Temperature
pH
Microbial parameters
Nitrate/nitrite1
Notes:
1. For systems using chloramination
11.3.3 Common Problems and Potential Impacts
Symptoms and causes of common problems encountered with treated water storage facilities
are presented in Table 11-3.
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Table 11-3 – Storage Facilities – Symptoms and Causes of Common Problems
Problem Common Symptoms and
Potential Impacts Common Causes
Deterioration in
water quality Loss of disinfectant residual
concentration
Increased microbiological growth
Increase in consumer complaints
related to colour, taste and/or odour
DBP formation (see Section
11.3.4.3)
Improper or poor control of
disinfectant dosage
Excessive detention time in storage
facility
Nitrification (see Section 11.4.4.4)
Elevated turbidity
in storage facility
effluent
Increase in customer complaints
related to turbid or coloured water
Frequent cleaning of storage
facilities required
Deposition of silt, calcium carbonate,
aluminum, iron or manganese
precipitates
Precipitation of solids caused by
changes in pH
Corrosion of metal surfaces
Floc carryover into clearwells
Freezing and ice
formation Loss of or inadequate flow Poor turnover of water and/or
inadequate mixing in storage facility
Excessive detention time in storage
facility
11.3.4 Optimization Techniques
11.3.4.1 Storage Facility Cleaning and Maintenance
All storage structures should be inspected, and routine maintenance performed, every three to
five years. Regular maintenance of storage facilities includes draining, cleaning, painting and
repair, if necessary. The person inspecting the structure should look for deposition patterns on
the floors and walls to determine flow patterns and assess dead zones. Checks should also
include calibration and cleaning of critical instrumentation, and inspection of internal
structures and appurtenances (such as stairs, ladders, valve handles, sample lines, etc).
Internal inspection of reservoirs using submersible robots equipped with cameras is becoming
more common, as they do not require the reservoir to be taken out of service. The results of
the inspection can be used to determine the required frequency for regular maintenance on a
site-specific basis.
Periodic inspection of water storage facilities is needed to find any structural problems and
correct them before they become serious. Tanks should be inspected for corrosion and cracks
on both the inside and outside surfaces. Overflows and vents should be examined to ensure
they are not obstructed and that screens are clean and in place. The inspection should also
include checks of control valves and any instrumentation used in the operation of the facility.
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Additional information is provided in AWWA Standard D101, Inspecting and Repairing
Steel Water Tanks, Standpipes, Reservoirs and Elevated Tanks for Water Storage.
After cleaning and/or painting are complete, water storage tanks must be disinfected before
being placed in service. Reference should be made to the most recent version of AWWA
Standard C652: Disinfection of Water Storage Facilities for more information.
11.3.4.2 Preventing Freezing in Storage Facilities
When freezing temperature conditions exist for several days, ice formation can occur in both
underground and elevated distribution storage reservoirs. In underground reservoirs, ice
formation is usually limited to surface ice. In elevated tanks, icing can be more severe and ice
can accumulate in thick layers on the sidewalls. Ice accumulation or falling ice can damage
walls and structures. As water freezes, expansion pressure can separate steel plates or panels
and the tank diameter can be altered resulting in damage to the interior coating. Interior
ladders, water level indicators, floats or electronic sensors can be damaged by ice.
Ice formation can be minimized by continuously fluctuating reservoir water levels. The
pumping and flow into and out of the reservoir should be adjusted to allow continuous water
circulation and to prevent ice from becoming attached to walls and columns. Storage tanks
can also be equipped with a small compressor and tank bubbler in order to circulate water in
the tank.
In most cases, the normal inflow and drawdown results in sufficient circulation to keep ice
formation to a minimum. In elevated tanks, the water level should be varied by 50 percent
every 24 hours. In underground reservoirs, 25 percent fluctuations in water levels every 24
hours are generally sufficient to minimize icing (California State University & USEPA,
1996). In arctic and sub-arctic areas, circulating water systems that continuously pump and
reheat the water in the system may be required to prevent severe icing.
If an excessive ice build-up inside an elevated distribution reservoir has occurred or the tank
malfunctions due to icing, a number of steps can be taken to restore operation. The affected
tank should be isolated and the distribution system pressurized using alternate means, such as
other storage tanks. The ice can be most effectively thawed by inserting a steam generator
equipped with a hose through one of the access hatches. Water storage tanks must be
disinfected before being placed back in service.
11.3.4.3 Maintaining Water Quality
Stagnation and excessive retention time in the distribution system and storage facilities may
result in a deterioration of water quality, which may be indicated by a loss of disinfectant
residual, formation of DBPs and bacterial regrowth.
It may be possible to improve hydraulic conditions within a storage facility by providing:
separate inlet and outlet piping; baffle walls; diffusers; and/or by locating the inlet and outlet
piping to promote water circulation.
In standpipes where only the upper portion of the storage provides useful system pressure, the
water should be circulated through the storage facility to maintain water quality and minimize
ice formation.
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For smaller systems, high water temperatures can be alleviated by providing a circulation
system to prevent deterioration of water quality.
Where design limitations prevent sufficient turnover of water in a storage facility to maintain
water quality, a pumped recirculation system can be provided, with or without a booster
disinfection system.
Water quality deterioration in storage may be particularly rapid where sequestering agents are
used with hard water or where natural organic matter reacts rapidly with a free chlorine
residual. In such cases, the use of monochloramine as the secondary disinfectant should be
considered (see Section 11.4.4.3).
For systems using chloramination for secondary disinfection, nitrification can lead to the
formation of nitrate and nitrite in the distribution system, loss of chloramine residual,
decrease in dissolved oxygen concentration, reduction in pH and alkalinity, and increased
microbial growth. Mitigation methods are discussed later in Section 11.4.4.4.
Additional information on the operation of water storage facilities to maintain water quality is
provided in Kirmeyer et. al. (1999).
Hydraulic and water quality models can also be used to evaluate the conditions in existing
storage facilities and for selecting locations for re-chlorination facilities, if needed.
11.4 DISTRIBUTION SYSTEM PIPING AND APPURTENANCES
11.4.1 Purpose and Types of Distribution System Facilities
Water distribution systems consist of pipes, valves, pumps, meters, fire hydrants, storage and
other pieces of equipment that are used to convey water to consumers. The distribution
system is designed to ensure that a sufficient volume of water at adequate pressure is
available, while maintaining the quality of the water from the treatment plant to the end user.
There are three main distribution system configurations, including arterial-loop systems, grid
systems and tree systems, as shown in Figure 11-1.
Most distribution systems are actually a combination of grid and tree systems. Arterial-loop
and grid layouts are generally preferable to tree layouts, as they generally have fewer dead-
end mains than tree systems.
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Figure 11-1 – Distribution Systems – Common Configurations
Adapted from Water Transmission and Distribution (AWWA, 1996)
11.4.2 Evaluating Performance
Distribution systems are designed to provide a balance between hydraulic water supply needs
and acceptable water quality.
The hydraulic performance of a distribution system is evaluated on the basis of the pressures
that exist at various points in the system under specific operating conditions. While pressures
must be high enough to serve consumers, provide fire protection, and prevent the intrusion of
contaminants, excessive pressures will increase pumping energy costs and can have adverse
effects on private plumbing. Excessive pressures may also increase the potential for main
breaks.
A minimum pressure of 140 kPa should be maintained at ground level at all points in the
distribution system under maximum day demand plus fire flow conditions. The normal
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operating pressure in the distribution system should be approximately 350 to 480 kPa and not
less than 275 kPa. Operating pressures outside of this range may be required based on
distribution system size and/or topography. The maximum pressures in the distribution
system should not exceed 700 kPa to avoid damage to household plumbing and unnecessary
water and energy consumption.
Additional information that can be used to evaluate the hydraulic capacity of distribution
systems is provided in the Design Guidelines for Drinking Water Systems, 2008 (MOE,
2008).
Water quality can deteriorate through interactions between the pipe wall and material on the
pipe wall and the water, and reactions within the bulk water itself. Depending on the retention
time in the system, water flow, treated water quality, pipe materials and condition, and
deposited materials (e.g. biofilms, iron, manganese, etc.), the water quality will change to a
greater or lesser extent.
Table 11-4 provides recommendations for monitoring, in terms of sampling locations and
analyses, in order to evaluate distribution system water quality.
Table 11-4 – Distribution Systems – Recommended Monitoring to Evaluate
Performance
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Treated Water
(at a location
where water
enters the
distribution
system)
Continuous monitoring Disinfectant residual
pH
Temperature
Turbidity
To monitor the
consistency of treated
water quality and for
comparison with
distribution system water
quality
Grab sample Bacteriological
parameters
Disinfection by-products
Metals (lead, copper,
aluminum, iron,
manganese)
Ammonia (for systems
using chloramination)
Colour, taste and odour
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Table 11-4 – Distribution Systems – Recommended Monitoring to Evaluate
Performance (cont’d.)
Location Types of Sample /
Measurement
Parameters / Analyses Comments
Distribution
System
Continuous monitoring
and/or grab samples Disinfectant residual
pH
Turbidity
Grab samples Bacteriological
parameters
Disinfection by-products
Ammonia, nitrate, nitrite
(if chloramination is
used)
Metals (lead, copper,
aluminum, iron,
manganese)
Colour, taste and odour
Note that the monitoring recommended in this table is in addition to the required regulatory
monitoring under the Drinking Water Systems Regulation (O. Reg. 170/03). The degree of
monitoring that is appropriate will depend on the size and complexity of the system, and the
variability in treated water quality.
11.4.3 Common Problems and Potential Impacts
There are several design and operational issues that can impact water quality in the
distribution system. Symptoms and causes of common problems encountered with
distribution systems are shown in Table 11-5.
Table 11-5 – Distribution Systems – Symptoms and Causes of Common Problems
Adapted from California State University (1996)
Problem Description
Mitigation
Cross Connections Physical connection between a
potable water supply with another
water supply of unknown or
contaminated quality
Can lead to contamination of the
potable water supply through
backflow or backsiphonage
Implement cross connection and/or
backflow prevention program or by-
law (see Section 11.4.4.10)
Maintain adequate system pressure to
prevent backflow or backsiphonage
Conduct regular water quality
sampling and testing to monitor for
indications of contamination
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Table 11-5 – Distribution Systems – Symptoms and Causes of Common Problems
(cont’d.)
Adapted from California State University (1996)
Problem Description
Mitigation
Corrosion Can lead to increased
concentrations of metals in water
supplied to consumers, causing
aesthetic and/or potential health
related problems
Can cause deterioration of
distribution system infrastructure
Implement internal corrosion control
program (Chapter 10)
Consider other corrosion control
techniques (e.g. cathodic protection),
if warranted (see Section 11.4.4.8)
Biological Growth
and Activity
(Biofilm formation)
Can accelerate corrosion in metal
pipes
Potential for reduced flow through
pipes as a result of greater
turbulence along pipe walls
Can cause taste and odour
problems as a result of sloughing
of biofilms and/or decay of
organisms
Potential loss of disinfectant
residual
Improve disinfection processes
during treatment (Chapter 9)
Maintain adequate secondary
disinfectant residual (see Section
11.4.4.3)
Nitrification For systems using chloramination
for secondary disinfection,
nitrification can lead to the
formation of nitrate and nitrite in
the distribution system, loss of
chloramine residual, decrease in
dissolved oxygen concentration,
reduction in pH and alkalinity,
and increased microbial growth
Control chlorine:ammonia dosage
ratio to reduce free ammonia levels
Monitor water temperatures and
other parameters to predict the onset
of nitrification events (see Section
11.4.4.4)
Improve operational practices to
prevent nitrification (see Section
11.4.4.4)
Changes in
Temperature Higher temperatures increase the
rate of chemical reactions,
biological growth and chlorine
demand, which can all result in a
loss of disinfectant residual
Very low temperatures can cause
freezing, potentially resulting in
more frequent main breaks and
loss of service
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Table 11-5 – Distribution Systems – Symptoms and Causes of Common Problems
(cont’d.)
Adapted from California State University (1996)
Problem Description
Mitigation
Changes in Flow Changes in velocity and flow
reversals can cause accumulated
sediment to be stirred up and
carried to consumers
Low flow and stagnation can
result in microbial growth,
deposition of sediment and
increased tastes and odours
Conduct hydraulic modelling to
evaluate flow conditions in a specific
area and identify options for
improving system flows (Chapter 4)
Conduct regular flushing and
periodic swabbing of distribution
system to remove sediment and
biofilm (see Section 11.4.4.5)
Excessive Water
Age and/or Presence
of Dead-End Mains
Excessive water age can lead to
increased DBP concentrations,
taste and odour problems, loss of
disinfectant residual and increased
microbial growth
Consider use of blow-offs or bleeders
on oversized mains or mains with
very low usage/flow
Conduct hydraulic modelling to
evaluate flow conditions in a specific
area and identify options for
improving system flows
Consider “looping” dead-end mains
to improve circulation (see Section
11.4.4.7)
Improve turnover in storage facilities
to minimize water age (see Section
11.3.4.3)
Excessive Water
Loss or
“Unaccounted for
Water”
Water loss results in additional
costs associated with treatment
and pumping (energy and
chemicals)
Small leaks can accelerate pipe
deterioration and lead to larger
breaks, which are more costly to
repair
Undetected leaks increase the
potential for contamination in the
distribution system
Conduct a water audit and/or
implement a leak detection program
(see Section 11.4.4.9)
11.4.4 Optimization Techniques
The operation and optimization of a distribution system can be very complex due to the size,
layout, construction and age of the system. The five step approach presented in Lauer (2005)
can be used to prevent or mitigate water quality problems. The five steps include:
1. Understanding the distribution system and defining the problem;
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2. Establishing water quality goals and preliminary performance objectives;
3. Evaluating alternatives and selecting the best approach;
4. Implementing good management practices and monitoring effectiveness; and
5. Finalizing performance standards and developing standard operating procedures.
Many of the approaches to optimizing distribution system water quality and solutions to
water quality problems involve improvements in water quality monitoring, operations and
maintenance, water treatment, management practices and/or system design (e.g. minor
modifications).
A discussion of all of the approaches that can be used to optimize distribution system
operation is beyond the scope of this manual. An overview of common optimization
techniques is provided in the following subsection. Additional information is available in
Lauer (2005), California State University (1996) and Friedman et. al. (2005).
11.4.4.1 Improving Treated Water Quality
In many cases, distribution system water quality can be improved by optimizing water
treatment. Improving nutrient removal (e.g. iron, manganese, sulphide, methane, assimilable
organic carbon (AOC), biodegradable organic carbon (BDOC), etc.) (see Chapter 10) and
disinfection (see Chapter 9), providing corrosion control (see Chapter 10) and maintaining an
adequate secondary disinfectant residual (see Section 11.4.4.3) can help to minimize
biological activity and regrowth in the distribution system. Similarly, improving the removal
of natural organic matter (see Chapter 6 and Chapter 10) during treatment can reduce DBP
formation and biological regrowth in the distribution system.
11.4.4.2 Enhancing Distribution System Monitoring
Under O. Reg. 170/03, drinking water systems are required to conduct regular monitoring
throughout the distribution system for a number of parameters. Additional monitoring can
also be conducted to identify the source and magnitude of a distribution system water quality
problem, such as nitrification or corrosion, by targeting specific parameters. A list of
parameters recommended for monitoring to identify a particular water quality issue was
presented in Table 11-4. Additional information is provided in Lauer (2005).
11.4.4.3 Disinfectant Residual Maintenance (Secondary Disinfection)
Secondary disinfection involves the maintenance of a disinfectant residual in the distribution
system. The maintenance of a persistent disinfectant residual protects the water from
microbiological re-contamination, reduces bacterial re-growth, controls biofilm formation
and serves as an indicator of distribution system integrity. Only chlorine, chlorine dioxide
and monochloramine provide a persistent disinfectant residual.
For drinking water systems that are required to provide secondary disinfection under O. Reg.
170/03, the system must be operated such that at all times and at all locations within the
distribution system there is a minimum free chlorine residual of 0.05 mg/L (at pH 8.5 or
lower), or chlorine dioxide residual of 0.05 mg/L, or a combined chlorine residual of 0.25
mg/L where chloramination is used.
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The Procedure for Disinfection of Drinking Water in Ontario (MOE, 2006) also establishes
operational targets for free chlorine residual and combined chlorine residual at 0.2 mg/L and
1.0 mg/L, respectively, at all locations in the distribution system.
The maximum disinfectant residual at any time and at any location within the distribution
system should not exceed 4.0 mg/L as free chlorine, 0.8 mg/L as chlorine dioxide and 3.0
mg/L as combined chlorine.
It should be noted that higher disinfectant residual concentrations (i.e. greater than the
operational objectives) may be needed to control microbial activity, nitrification and to
provide a persistent residual throughout the system, depending the size, and layout of the
distribution system and water quality characteristics. Higher free chlorine residuals may
increase the rate of DBP formation if organic precursors are present; therefore, the balance
between the need to ensure adequate secondary disinfection and minimizing DBP formation
should be considered.
In larger distribution systems, booster or re-chlorination systems may be needed at one or
more points in the distribution system to improve secondary disinfection.
11.4.4.4 Controlling Nitrification
Nitrification is a microbiological process by which ammonia is oxidized to nitrite and nitrate
by ammonia oxidizing bacteria (AOB) and archaea (AOA). The use of chloramine as a
secondary disinfectant and the presence of nitrifying bacteria in the distribution system are
the main causes of nitrification in water distribution systems.
Ammonia-nitrogen is converted to chloramine-nitrogen at the point of chloramine formation
during treatment. The chloramine-nitrogen is converted back to ammonia-nitrogen as
chloramines degrade in the distribution system.
There are several symptoms of nitrification that can impact water quality, including loss of
disinfectant residual, nitrite and nitrate formation, dissolved oxygen depletion, reduction in
pH and alkalinity, and an increase in heterotrophic plate count (HPC) bacteria, total coliforms
and ammonia-oxidizing bacteria and/or nitrite oxidizing bacteria.
A number of water quality factors contribute to nitrification, including the chlorine to
ammonia weight ratio, inadequate initial chloramine residual at the plant or booster station,
the availability of nutrients for nitrifying bacteria, and physical water quality characteristics
that may favour bacterial growth and/or hinder inactivation (e.g. temperature, pH and
alkalinity).
Operations and maintenance activities that can help to control nitrification events include:
Minimizing water age;
Improving turnover in storage facilities;
Flushing of distribution mains can be used to reduce water age, to maintain adequate
disinfectant residual concentrations and to remove accumulated biofilm or sediment;
and
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Periodic free chlorination either of the entire system or affected areas of the
distribution system.
If nitrification is a recurring problem in a drinking water system, consideration should be
given to the development of a site specific nitrification assessment and response plan.
Additional information on the causes, prevention and control of nitrification is provided in
AWWA (2006).
11.4.4.5 Improving Distribution System Operation and Maintenance
Three primary operational goals are used to maintain water quality: minimizing water
detention time in the system; maintaining positive pressure; and purposefully controlling the
direction and velocity of flow (Lauer, 2005). Table 11-6 provides a list of optimization
activities that can be undertaken in support of these objectives.
Table 11-6 – Operational Changes for Distribution System Optimization
Adapted from Lauer (2005)
Minimize Detention Time Maintain Positive Pressure Control Flow Direction and
Velocity
Hydraulic and water quality
modelling to predict water
age, DBP and disinfectant
residual concentrations
Improve reservoir turnover
(see Section 11.3.4.3)
Develop standard operating
procedures for reservoir
and system operation
Water quality monitoring
(see Section 11.4.4.2)
Looping of dead-ends (see
Section 11.4.4.7)
Hydraulic modelling to predict
water pressure
Implement cross connection
control program
Inspect valve positions
Avoid hydraulic surges
(improve control of pump
startup and shutdown; open
and close valves slowly)
Hydraulic modelling to evaluate
flow conditions in the system as
a result of power failure, fire
fighting and hydrant flushing
Control on/off cycles at well
pumping stations, if several
sources of supply are used in
the system
Avoid hydraulic surges
(improve control of pump
startup and shutdown; open and
close valves slowly)
Common distribution system maintenance activities include flushing, cleaning and repairs.
Watermain flushing is an important tool for helping to reduce the amount of sediment in the
distribution system and to remove stagnant water. Issues to consider when developing a
sampling program include: the type of flushing program (i.e. targeted flushing or system-
wide); unidirectional flushing versus conventional flushing of specific areas; the frequency of
flushing; the target velocity needed; monitoring of water quality before and after flushing; as
well as recording the procedures and results of the flushing program.
A variety of cleaning techniques can be used for watermains, including mechanical scraping,
pigging, swabbing, chemical cleaning and flow jetting. Each technique has advantages and
disadvantages that should be considered before being implemented. When a cleaning
technique is used, it may or may not be followed by relining of the pipe. If the pipe will not
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be relined following cleaning, special consideration should be given to the pipe material and
its condition so that corrosion of the newly exposed surface does not rapidly occur and
impact water quality.
11.4.4.6 Minor Modifications
Where limitations in distribution system performance are due to design factors,
reconfiguration of the existing system can be considered to improve system hydraulics and
water quality. The following measures can be implemented to optimize distribution system
performance:
Hydraulic and water quality models can be used to estimate water age and
disinfectant residuals at various points in the distribution system;
Pressure zones can be planned or reconfigured to reduce water age and maintain
water quality;
Consideration can be given to the installation of booster chlorination facilities;
Rehabilitation of deteriorated pipelines can be used to restore capacity and/or
improve water quality in targeted areas; and
Eliminating or looping of dead-end water mains (see Section 11.4.4.7).
11.4.4.7 Eliminating Dead-End Watermains
Dead-ends in a distribution system can be eliminated by making appropriate tie-ins or
looping whenever practical. Looping can provide increased reliability of service, and reduce
stagnation and loss of disinfectant residual.
Where dead-end mains cannot be avoided, a means for adequate flushing should be provided
that will help to prevent stagnation, such as the installation of a fire/flushing hydrant, or a
blow-off valve or “bleeder”.
Historically, bleeders have been used to prevent freezing in small diameter watermains or
service lines. The use of bleeders results in large volumes of water being wasted throughout
the year, increasing treatment and energy costs. Two options are available to reduce the
amount of water wasted from bleeders when their primary purpose is for preventing freezing:
1. Timers: Timers are used to turn bleeders on and off automatically. For example, they
can be set to clear water from a pipe before the water reaches ice-forming
temperatures. The capital cost is relatively low, but the system still wastes large
volumes of water.
2. Temperature sensors: These sensors are more expensive to install and maintain but
waste less water than bleeders with or without timers. The sensors should be installed
in the coldest sections of the supply pipes. When the sensor reads below a preset
temperature (usually just above freezing), the sensor triggers the opening of the
bleeder. The bleeder closes when the sensor reads above another preset temperature.
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Another alternative to providing a bleeder on a dead-end main is to install a recirculation
system, in which a pump and smaller diameter pipe are used to recirculate unused water in
dead-ends to prevent freezing and maintain water quality. The installation costs for
circulation systems are typically more expensive than for bleeders; however, there are
significant cost savings due to reduced water demand, energy consumption and wastewater
generation.
Site specific studies are needed to evaluate the various options available and select the
preferred alternative for improving water quality and preventing freezing in dead-end
watermains.
11.4.4.8 External Corrosion Control
Treatment processes commonly used for internal corrosion control are presented in Chapter
10. Other techniques that can be used to prevent corrosion in distribution systems include:
Coatings: These can be applied to the interior surface of watermains and tank surface
to protect against interior corrosion.
Cathodic Protection: This type of protection consists of a sacrificial anode made of
zinc or magnesium. These anodes are buried in the ground in close proximity to the
pipe and in areas that are prone to external corrosion. These metals deteriorate first
and thus protect the pipe material from deterioration. The anodes must be replaced on
a regular basis to maintain the desired level of protection.
Impressed Current Systems: These systems apply a low current through the pipe or
tank in a controlled circuit. This type of system is common for metal tanks and above
ground installations.
11.4.4.9 Leak Detection
Leaks may originate from any weakened joint or fitting connection, or from a damaged or
corroded part of the pipe. Leaks are undesirable not only because they waste water, but
because they can undermine pavements and other structures. Another undesirable effect of
leaks is that they create a potential for backflow contamination if pressure is lost in the pipe.
Leak detection programs are an effective means for water utilities to reduce operating and
maintenance costs. If a leak detection crew can reduce water loss and produce cost savings
greater than the cost of maintaining the field crew, then the leak detection program is
economically justified. Leak detection programs can also be justified in terms of the early
detection and repair of leaks while they are small, before serious failure occurs with resulting
property damage, crew overtime, delays of other projects and other similar problems.
Methods used to determine the location of leaks include sound rods, audio phones and
commercially available leak detection equipment, which intensifies the sound as a means of
locating leaks.
Water operators can also undertake a water audit of water supplied compared to the water
consumed in each area or zone of the system. The amount of “unaccounted for water” can be
compared against industry standards to identify the areas of the system that require a more
detailed street by street leak detection survey.
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Additional information is provided in AWWA (2009) and National Guide to Sustainable
Municipal Infrastructure (2003).
11.4.4.10 Backflow Prevention and Cross Connection Control
Backflow is the flow of any water, foreign liquids, gases or other substances, back into a
potable water supply. Two conditions that can cause backflow are backpressure and
backsiphonage.
A cross connection is any connection between a potable water system and any other water
source or system through which backflow can occur.
Cross connections must either be removed or some means provided to protect the potable
water supply from possible contamination. The preventive measure chosen depends on the
degree of hazard involved, the accessibility of the premises where the cross connection exists
and the type of water distribution system. Some commonly used backflow prevention devices
include:
Air gaps;
Reduced-pressure-zone backflow preventers;
Double check valve assemblies;
Vacuum breakers (atmospheric and pressure); and
Barometric loops.
When developing a cross connection control program, the owner/operator of a drinking water
system should consider provincial codes and regulations, municipal by-laws and the size of
the community. An effective cross connection control program should include the following
elements:
Adherence to or creation of plumbing and cross connection control by-laws;
Identification of an organization or agency with overall responsibility and authority
for administering the program, with adequate staff;
Systematic inspection of new and existing installations;
Follow-up procedures to ensure compliance;
Backflow prevention device standards, as well as standards for inspection and
maintenance;
Cross connection control training; and
A public awareness and information program.
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Additional information on the development of cross connection control and backflow
prevention programs is provided in AWWA (2004) and National Guide to Sustainable
Municipal Infrastructure (2005).
11.5 CASE HISTORIES
11.5.1 Region of Durham – Water Loss Control Strategy
The following case study is based on information presented in Hobbs & Dejan (2010).
System Description
The Region of Durham (the Region) operates and maintains six surface water treatment
plants, 25 groundwater wells, 22 reservoirs, 19 pumping and booster stations and almost
2,400 km of watermains.
The Region regularly undertakes a number of water loss management activities, including a
leak detection program, meter change-out program, hydrant inspections, valve inspection and
maintenance, service repairs and replacement, as well as a cathodic protection program.
In 2006, a Water Loss Control Strategy was developed to:
Assess existing Regional practices;
Evaluate data sources;
Understand the significance and scale of water loss;
Understand the economics of leakage;
Evaluate potential savings or maximized revenue;
Outline benefits to water loss control for maintenance, rehabilitation and demand
control; and
Recommend a strategy for water loss management.
The objective of the study was to incorporate the Region’s existing water loss activities into a
more comprehensive program.
Optimization Strategies
A water balance was conducted to quantify water losses. Conducting the water balance
before embarking on leakage detection or management projects allowed the Region to
determine if water loss reduction was economical. The water balance was conducted by
comparing the System Input Volume (production from the six surface water plants and eight
well systems) to authorized consumption. The difference, deemed water loss, was further
analyzed to determine apparent losses (e.g. meter inaccuracies) and real losses (i.e. leakage).
The results of the water balance indicated that, depending on the method used, real losses
accounted for up to 21 percent of the total system input. The estimated cost of real losses was
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Optimization Guidance Manual for Drinking Water Systems 2014
determined to be approximately $1 million per year. The total cost of apparent losses was
estimated between $513,400 and $657,700 per year. The Region determined that a potential
annual savings of approximately $760,000 could be achieved by reducing real losses.
As a result, several strategies were recommended to manage water loss, including the
implementation of:
Annual water loss assessment;
Improvements to metering strategies, including meter installations at system
interconnection points, sub-metering for larger zones, installation of Smart Meters
for large volume users, and at reservoir inlets;
Improving the billing database;
Customer meter replacement;
Calibration of meters at sources of supply;
Development of a Bulk Water Strategy; and
Improved tracking of unbilled authorized consumption.
Summary
As part of the water loss management study, the Region learned that detailed analysis of
water demands would require sub-metering on a district or pressure zone basis. In addition,
the accuracy of billing data and customer meter replacement would be required to more
accurately evaluate billed authorized consumption. Measures were also put into place to
investigate methods to reduce unauthorized consumption. The strategy will be reviewed on
an annual basis to evaluate the annual costs of the program versus the annual reduction in
water lost to recognize when it is no longer economical to further reduce leakage.
11.5.2 Region of Niagara – Treated Water Pumping & Storage Optimization
The following case study is based on information presented in Tracy (2009).
System Description
The Grimsby WTP is a conventional surface water treatment plant and supplies water to the
towns of Grimsby, Lincoln and West Lincoln. It is owned and operated by the Region of
Niagara (the Region).
Treated water storage facilities are typically sized to provide a portion of the maximum day
demand, water for fire protection and to provide balancing storage. In practice, operations
staff often maintain storage levels fairly high to keep pressures in the system and to maximize
emergency storage. This results in water treatment facilities having to operate towards peak
hour rates rather than maximum day rates, and frequent changes in the production rate are
often required. Ultimately, this operating scheme requires earlier expansion or upgrading of
WTPs earlier than planned or necessary.
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Optimization Strategies
The Region of Niagara conducted a pilot program applying OPIR® software to optimize
water treatment plant production and balance storage in the Grimsby drinking water system.
OPIR® is control software developed to optimize water system production through
intelligent control. The software continuously monitors actual diurnal demand by mass
balance calculations of consumption. It then forecasts the demand and sets the WTP
production rate to make full use of available balancing storage to minimize the number of
production set point changes.
The production rate set point is calculated using three steps:
1. Configuration: A database of storage capacities and operating levels, WTP
production increments, and flow and level instrumentation information is assembled.
2. Data capture: The software continuously calculates demand or consumption, derives
diurnal demand patterns for each day of the week based on the previous seven weeks,
and continuously moves the seven week window to capture seasonal variations.
3. Forecasting: The program forecasts demand in each control zone, forecasts levels in
all storage facilities, and displays historical performance and forecasts for the next
two days. It then derives cumulative demand and storage curves to determine a
“constant” production rate set point based on available WTP capacity increments.
By pumping at average day rates rather than peak rates, energy costs can be reduced by an
estimated 10 to 15 percent. The program can also be used to skew WTP production hours to
off-peak hydro hours, resulting in a potential energy savings of up to 20 percent.
Summary
Current energy costs at the Grimsby WTP are approximately $280,000 per year. It is
anticipated that by optimizing balancing storage and WTP production rates, the potential
energy savings would be between $30,000 and $50,000 per year. It should be noted that by
operating the WTP for average day demand rather than peak hour demand, the most
significant savings may be realized by delaying the expansion of the Grimsby WTP by
several years.
11.6 REFERENCES
American Water Works Association (1996). Water Transmission and Distribution –
Principles and Practices of Water Supply Operations. Second Edition. AWWA. Denver, CO.
ISBN 0-89867-821-8.
American Water Works Association (2004). Manual of Water Supply Practices M14:
Recommended Practice for Backflow Prevention and Cross Connection Control. Third
Edition. AWWA. Denver, CO. ISBN 1-58321-288-2.
American Water Works Association (2006). Manual of Water Supply Practices M56:
Fundamentals and Control of Nitrification in Chloraminated Drinking Water Distribution
Systems. Third Edition. AWWA. Denver, CO. ISBN 1-58321-419-4.
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American Water Works Association (2009). Manual of Water Supply Practices M36: Water
Audits and Loss Control Programs. AWWA. Denver, CO. ISBN 1-58321-631-6.
American Water Works Association Research Foundation and Japan Water Works
Association (1993). Instrumentation & Computer Integration of Water Utility Operations.
ISBN 0-89867-630-4.
California State University and USEPA Office of Drinking Water (1996). Water Distribution
System Operation and Maintenance. 3rd Ed. California State University, Sacramento
Foundation. ISBN 1-884701-16-7.
Friedman, M., G.J. Kirmeyer, G. Pierson, S. Harrison, K. Martel, A. Sandvig and A. Hanson
(2005). Development of Distribution System Water Quality Optimization Plans. AwwaRF.
Denver, CO. ISBN 1-58321-388-0.
Hobbs, E. and C. Dejan (2010). “A Systematic Approach to Undertaking Water Loss
Management”, presented at the OWWA/OMWA Joint Annual Conference, Windsor,
Ontario.
Kirmeyer, G.J. et. al. (1999). Maintaining Water Quality in Finished Water Storage
Facilities [Project #254]. AwwaRF & AWWA. Denver, CO. ISBN 0-89867-983-4.
Lauer, W.C. (2005). Water Quality in the Distribution System. AWWA. Denver, CO. ISBN
1-58321-323-6.
National Guide to Sustainable Municipal Infrastructure (2003). Water Use and Loss in
Distribution Systems. Federation of Canadian Municipalities and National Research Council.
National Guide to Sustainable Municipal Infrastructure (2005). Methodology for Setting a
Cross Connection Control Program. Federation of Canadian Municipalities and National
Research Council.
O’Connor, D. R. (2002). Part Two Report of the Walkerton Inquiry: A Strategy for Safe
Drinking Water. Toronto: Publications Ontario. ISBN: 0-7794-2621-5.
Tracy, H. (2009). “Water System Optimization & Energy Savings Using Predictive Control”,
presented at the OWWA/OMWA Joint Annual Conference, Toronto, Ontario.
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 12 RESIDUALS AND RECYCLE STREAMS
RESIDUALS AND RECYCLE STREAMS
12.1 Introduction .......................................................................................................... 12-1
12.2 Water Treatment Process Residuals ..................................................................... 12-1
12.3 Residuals Treatment Processes ............................................................................ 12-3
12.3.1 Sludge Thickening ................................................................................. 12-4
12.3.2 Sludge Dewatering ................................................................................. 12-8
12.4 Case Histories ..................................................................................................... 12-11
12.4.1 City of Brantford – Residuals Management Facility ........................... 12-11
12.4.2 Charleston, W.Va. – Kanawha Valley WTP Recycle Stream
Evaluation ............................................................................................ 12-12
12.5 References .......................................................................................................... 12-14
CHAPTER 12. Residuals and Recycle Streams 12-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 12
RESIDUALS AND RECYCLE STREAMS
12.1 INTRODUCTION
Most water treatment process residuals require treatment. The degree of treatment provided
depends on: regulatory requirements; the disposal method; the assimilative capacity of the
receiving water body in the case of discharge to the environment; and treatment/disposal
costs.
A discussion of all types of residuals and treatment technologies is beyond the scope of this
Manual, however, a brief overview of the types of plant waste residuals and treatment options
commonly used in Ontario is provided in this chapter.
Measures to optimize treatment processes to minimize the quantity of residuals produced are
presented elsewhere (e.g. Chapter 6 and Chapter 8). Reducing the quantity of residuals
requiring treatment and/or disposal will also decrease the costs associated with waste
handling.
12.2 WATER TREATMENT PROCESS RESIDUALS
Table 12-1 presents a summary of specific water treatment process residuals, as well as
treatment and/or disposal options. Additional information on the types of water treatment
plant wastes is provided in Cornwell et. al. (1987).
Table 12-1 – Specific Water Treatment Process Residuals Treatment and Disposal
Options
Process Type of Residual Treatment and/or
Disposal Options
Comments
Sedimentation/
Clarification
Sludge Mechanical dewatering
(centrifuges, rotary drum
thickeners, filter presses)
Disposal to sanitary
sewer1
Mechanical methods
are typically used for
larger treatment plants
Sewer and sewage
treatment plant
capacity need to be
considered
CHAPTER 12. Residuals and Recycle Streams 12-2
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-1 – Specific Water Treatment Process Residuals Treatment and Disposal
Options (cont’d)
Process Type of Residual Treatment and/or
Disposal Options
Comments
Chemically-
assisted Granular
Media Filtration
Backwash wastewater Surge/equalization tank
with disposal to sanitary
sewer1
Equalization/decant tank
with disposal of
supernatant to sanitary
sewer1 (or receiving
water body, where
acceptable) and sludge
removed for further
treatment
Recycling of supernatant
from backwash
treatment facilities to the
WTP intake or
headworks2
Sewer and sewage
treatment plant
capacity need to be
considered
Treatment may be
required when
discharging to a
receiving water body
Granular media may be
lost over time in
backwash waste
streams; impacts of
solids loading and
presence of media on
sludge thickening
equipment should be
considered
Membrane
Filtration
Membrane reject water May be discharged
without treatment to a
suitable surface water
body provided effluent
quality criteria are met
Membrane backwash
residuals Discharge to sanitary
sewer1
Treatment with
supernatant recycle and
solids disposal
Discharge of supernatant
to a suitable surface
water body if applicable
regulations or standards
are met
Membrane chemical
cleaning residuals On-site treatment
(quenching,
neutralization, etc.)
followed by discharge to
sanitary sewer1 or
holding tank for proper
disposal
The use of surfactants
or other proprietary
cleaning agents may
result in a requirement
for additional treatment
CHAPTER 12. Residuals and Recycle Streams 12-3
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-1 – Specific Water Treatment Process Residuals Treatment and Disposal
Options (cont’d)
Process Type of Residual Treatment and/or
Disposal Options
Comments
Iron and
Manganese
Removal
Backwash wastewater
and sludge Discharge to sanitary
sewer1
Holding tank with
supernatant recycle1 to
head of plant and solids
disposal
Ion Exchange Brine waste Discharge to sanitary
sewer1, where permitted
Holding tank for off-site
disposal
Discharge to sanitary
sewer may require use
of equalization tank
with discharge flow
control
Precipitative
Softening
Sludge Lagoons
Land application
Mechanical dewatering
Landfilling
Notes:
1. Discharges to sanitary sewers should meet all applicable local sewer-use bylaws.
2. Specific operating and monitoring requirements may apply when backwash water recycling is
practiced to minimize hazards associated with the potential for increased concentration of
pathogens in the water. Refer to the Design Guidelines for Drinking Water Systems, 2008
(MOE, 2008) for further information.
12.3 RESIDUALS TREATMENT PROCESSES
The type of residuals treatment process used at a water treatment plant will depend on the
type, quality and quantity of residuals produced as well as the discharge and ultimate disposal
requirements.
The recycling of waste streams can impact treated water quality or cause process upsets,
consideration of specific measures to minimize the concentrations of pathogenic organisms
and other contaminants in the recycle streams is required. Additional information is provided
in MOE (2008) and Cornwell & Lee (1993).
Processes commonly used in Ontario for handling water treatment process residuals include
flow equalization, sedimentation/clarification, sludge thickening and dewatering.
Methods for evaluating and improving the performance of equalization tanks and clarification
processes are presented in Chapter 7. Information on sludge treatment processes (thickening
and dewatering) is presented in the following subsections.
CHAPTER 12. Residuals and Recycle Streams 12-4
Optimization Guidance Manual for Drinking Water Systems 2014
12.3.1 Sludge Thickening
12.3.1.1 Purpose and Types of Sludge Thickeners
Sludge thickening is the process of removing free water not bound within the sludge flocs.
The result of removing a portion of the free water is a higher solid content, typically between
four (4) and 14 percent depending on the type of thickener. Thickening is typically
undertaken in order to reduce the volume of solids that will require subsequent treatment or
disposal.
There are a number of types of sludge thickeners that utilize different mechanisms to increase
the solids concentrations of the sludge including; gravity settlers, gravity belt thickeners
(GBTs), rotary drum thickeners (RDTs), thickening centrifuges, and DAF thickeners.
Gravity settlers use settling processes usually accompanied by a slowly revolving sludge
collector. GBTs thicken sludge by placing the sludge in between two fabric belts which move
and allow the water to separate from the sludge by gravity. RDTs act by straining free water
from the sludge through a rotating cylindrical screen.
Thickening centrifuges apply a strong centrifugal force to the sludge which separates the
sludge and water as a result of the density differences. The lighter liquids remain near the
center of rotation and exit by overflowing a weir. There are three types of centrifuges; basket,
solid-bowl and disc centrifuges. Basket centrifuges are rotating vertical chambers with a weir
at the top. Solid-bowl centrifuges bring sludge into a fast rotating bowl using a screw-type
conveyor. Within the bowl, the solids move to the walls while the liquid is decanted or
drawn-off. In disc centrifuges, the solids move toward the wall where stacks of discs are
located that collect the liquid. The collected liquid then flows to a discharge chamber. Solid
bowl centrifuges are most commonly used for sludge thickening.
Thickening of sludge using DAF occurs by introducing air to the sludge in a unit that has an
elevated pressure. When the sludge is depressurized, fine air bubbles are formed which, when
attached to the solid floc, carry thickened sludge to the top where it can be removed.
Further information on the purpose and type of thickeners can be found in MOE (2008),
Wang et al. (2007), and Metcalf & Eddy (2003).
12.3.1.2 Evaluating Process Performance
Typically, sludge thickener performance is evaluated based on the solids captured and the
total solids content achieved. Table 12-2 presents typical process performance results for the
various types of sludge thickeners.
CHAPTER 12. Residuals and Recycle Streams 12-5
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-2 – Sludge Thickening – Typical Process Performance
Adapted from MOE (2008) and Metcalf & Eddy (2003)
Thickening Method
Expected Performance
Total Solids (%) Solids Capture (%)
Basket centrifuges 8-10 1
80-90
Disc-nozzle centrifuges 4-6 1 80-90
Solid bowl centrifuges 5-8 1 70-90
GBT 4-8 ≥ 95
RDT 4-9 93-98
Gravity thickeners 5-10 n/a
DAF 4-6 ≥ 95 2
Notes:
1. Lower solids concentrations expected without use of polymers.
2. Using flotation aids.
Table 12-3 presents recommended monitoring, in terms of sampling locations and analyses,
in order to evaluate the performance of sludge thickeners.
Table 12-3 – Sludge Thickening – Recommended Process Monitoring to Evaluate
Performance
Location Types of Sample /
Measurement Parameters / Analyses Comments
Influent sludge Composite
recommended Flowrate
Sludge volume index
(SVI)
Total solids (TS)
Thickening units Continuous
monitoring Polymer dosage
Overflow rate
Underflow rate
For process control
CHAPTER 12. Residuals and Recycle Streams 12-6
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-3 – Sludge Thickening – Recommended Process Monitoring to Evaluate
Performance (cont’d)
Location Types of Sample /
Measurement Parameters / Analyses Comments
Centrate/supernatant/
subnatant
Composite
recommended Flowrate
Total suspended solids
(TSS)
Chlorine residual
Other parameters may
be required based on C
of A or DWWP/License
if discharged to the
environment or Sewer
Use By-Law limits if
discharged to the
municipal sewer system
Thickened sludge Composite
recommended Flowrate
TS
For performance
measurement
Figure 12-1 presents a process schematic of a sludge thickening process, along with
recommended sampling locations.
Thickeners
Centrate/Supernatant/Subnatant
Sample Location
Influent
Sludge
Influent Sludge
Sample LocationThickened Sludge
Sample Location
Thickening Unit
Centrate/
Supernatant
Thickened
Sludge
Figure 12-1 – Sludge Thickening – Process Schematic and Recommended Sampling
Locations
12.3.1.3 Common Problems and Potential Process Impacts
Symptoms and causes of common problems encountered with the sludge thickening process
are presented in Table 12-4.
CHAPTER 12. Residuals and Recycle Streams 12-7
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-4 – Sludge Thickening – Common Problems and Impacts
Problem Common Symptoms and
Potential Process Impacts Common Causes
Thickened sludge has
low solids content Lower than expected TS in the
thickened sludge
Higher than expected TS in the
centrate/supernatant/subnatant
Inadequate polymer dosing
(Section 12.3.1.4)
Inadequate sludge storage
Thickener is hydraulically
overloaded due to poor feed pump
controls
Short circuiting through the
thickener
Septic thickened
sludge Thickened sludge is odorous
High sludge blanket (gravity
thickeners)
Floating of sludge (gravity
thickeners)
Ineffective pump controls resulting
inconsistent or infrequent sludge
feeding
Low hydraulic overflow or
underflow rate
Long retention time of solids
within thickener
12.3.1.4 Options to Enhance Thickening
Optimizing the performance of thickeners begins with ensuring that the operation of the unit
is as close to the manufacturer’s recommended operating conditions as possible. Consultation
with the process supplier can be useful in ensuring the unit is operating optimally.
In addition, thickening can be improved by optimizing the use of polymers. Dosing polymers
can improve the solids capture and increase the solids content in the thickened sludge. Both
the polymer dosage and dosing point(s) should be reviewed as in some cases multiple dosing
points can improve performance. Jar testing can be used to optimize polymer type, dosage
and mixing. Full scale tests can be performed during plant operation to further optimize
polymer dosage. As polymer effectiveness depends on the polymer dose per unit of solids
(mg of polymer per kg dry solids in the sludge feed) not on dose per litre of sludge flow,
dosing polymer based on flow only will not be optimal unless sludge concentration is
relatively constant.
Thickening can be improved by ensuring that influent flows and concentrations are
maintained relatively constant which will prevent wide variations in solids load and polymer
dose. Minimizing the variability of feed flows and concentrations can be accomplished by a
number of ways including the implementation of online instrumentation and control systems
that can measure feed solids concentration and flow. In addition, implementation of mixed
storage tanks prior to mechanical thickening equipment can also be used to minimize
variability rather than feeding directly from clarifier underflows to thickeners.
Stress testing of the thickening process can be undertaken in order to determine the maximum
throughput, optimal operating settings, polymer dosage requirements, and the impact on the
CHAPTER 12. Residuals and Recycle Streams 12-8
Optimization Guidance Manual for Drinking Water Systems 2014
thickened sludge concentration and centrate quality. Procedures for stress testing are presented
in Chapter 4.
Further information on enhancing thickening processes can be found in WERF (2009).
12.3.2 Sludge Dewatering
12.3.2.1 Purpose and Types of Sludge Dewatering
The purpose of dewatering is to remove the floc-bound and capillary water from sludge prior
to further processing or off-site disposal. Sludge dewatering is similar to sludge thickening
(Section 12.3.1) but a much higher TS concentration in the dewatered sludge is achieved
compared to a thickening process. In order to improve sludge dewatering, chemical
conditioning is typically used to improve the solids capture and increase the solids content in
the dewatered sludge.
There are numerous dewatering processes available, a number of which can be employed to
increase the solids content of the sludge to between 10 to 50 percent depending on the
process. The processes include: solid bowl centrifuges, belt filters presses, filter presses, and
vacuum filters. Solids bowl centrifuges were described in Section 12.3.1.1.
Belt filter presses are continuously fed units that dewater chemically conditioned sludge first
in a gravity drainage section where the free water is removed. After the free water is
removed, low pressure is applied by porous belts to remove a portion of the bound water
from the sludge. Filter presses dewater by the application of high pressure to remove bound
water. Vacuum filters remove water from sludge by application of a vacuum.
Further information on the purpose and type of dewatering processes can be found in MOE
(2008), Wang et al. (2007), and Metcalf & Eddy (2003).
12.3.2.2 Evaluating Process Performance
Typically, sludge dewatering process performance is evaluated based on the solids captured
and the total solids content achieved. Table 12-5 presents typical process performance for the
various types of sludge dewatering processes.
CHAPTER 12. Residuals and Recycle Streams 12-9
Optimization Guidance Manual for Drinking Water Systems 2014
Table 12-5 – Sludge Dewatering – Typical Process Performance
Adapted from MOE (2008) and Fournier Inc. (2010)
Dewatering Method
Expected Performance
Total Solids (%)1 Solids Capture (%)
Solid bowl centrifuges 15-30 95-99
Belt filter press 10-25 85-95
Filter press 25-50 90-95
Vacuum filter 10-25 90-95
Notes:
1. Values presented in this table assume the use of conditioning chemicals (i.e. polymers). If no
conditioning chemicals are used, cake solids and solids capture values may be reduced.
Table 12-6 presents monitoring recommended, in terms of sampling locations and analyses,
in order to evaluate the performance of dewatering processes.
Table 12-6 – Sludge Dewatering – Recommended Process Monitoring to Evaluate
Performance
Location Types of Sample / Measurement Parameters / Analyses
Influent sludge Composite recommended Flowrate
TS
Centrate/filtrate Composite recommended Flowrate
TSS
Chlorine residual
Dewatered sludge Composite recommended Flowrate
TS
Figure 12-2 presents a process schematic of a dewatering unit, along with recommended
sampling locations.
CHAPTER 12. Residuals and Recycle Streams 12-10
Optimization Guidance Manual for Drinking Water Systems 2014
Thickeners
Centrate/Filtrate
Sample Location
Influent
Sludge
Influent Sludge
Sample LocationDewatered Sludge
Sample Location
Dewatering Unit
Centrate/
Supernatant
Dewatered
Sludge
Figure 12-2 – Sludge Dewatering – Process Schematic and Recommended Sampling
Locations
12.3.2.3 Common Problems and Potential Process Impacts
Symptoms and causes of common problems encountered with the sludge dewatering process
are shown in Table 12-7.
Table 12-7 – Sludge Dewatering – Common Problems and Impacts
Problem Common Symptoms and
Potential Process Impacts Common Causes
Dewatered sludge
has low solids
content
Lower than expected TS in the
dewatered sludge
Higher than expected TSS in the
centrate/filtrate
Inadequate polymer dosing
(Section 12.3.1.4)
Dewatering process is hydraulically
overloaded
Short circuiting through the unit
Septic dewatered
sludge Dewatered sludge is odorous
Inconsistent or infrequent sludge
feeding
Hydraulic overflow or underflow
rates lower than design rates
Long retention time of solids
within unit
CHAPTER 12. Residuals and Recycle Streams 12-11
Optimization Guidance Manual for Drinking Water Systems 2014
12.3.2.4 Options to Enhance Dewatering
As dewatering is a process similar to thickening, optimizing dewatering process performance
involves similar techniques. Possible techniques to enhance dewatering are listed below with
additional information available in Section 12.3.1.4:
Consultation with the process supplier to ensure that there are no equipment or
operating issues;
Jar testing to optimize polymer type, dosage and mixing rate;
Conducting full scale studies to optimize polymer dosing locations and dosage;
Installation of online instrumentation to measure and control the feed flow and solids
density to minimize feed fluctuations;
Implementation of mixed storage tanks prior to dewatering units to minimize feed
variability; and
Stress testing to determine optimal operating settings and maximum throughput.
Further information on enhancing dewatering processes can be found in WERF (2009).
12.4 CASE HISTORIES
12.4.1 City of Brantford – Residuals Management Facility
The following case study is based on information presented in Yohannes (2010).
System Description
The City of Brantford WTP process consists of an ActifloTM
high rate clarification process,
followed by dual media filtration and chlorination. In 2003, a new residual management
facility (RMF) was constructed to replace the existing lagoons.
Prior to the commissioning of the RMF, sludge was directed into a settling pond and the
supernatant overflowed into the Grand River. The bottom of the pond was dredged
periodically to remove the excess solids and maintain its effective settling capacity. Problems
associated with the operation of the lagoon included limited dredging time in winter months
because of ice formation, solids carryover into the Grand River during periods of heavy
rainfall, and disturbances in settling causing elevated suspended solids and aluminum levels.
Various studies were undertaken to evaluate waste handling systems for the wastewater
produced from filter backwashes and pretreatment processes (sludge from ActifloTM
process).
Both rotary drum thickeners and gravity settling thickeners were evaluated. Based on the data
obtained during the studies, gravity settling thickeners were selected as the preferred
alternative and two units were installed.
As part of the RMF operation, backwash water and pre-treatment sludge is collected into an
equalization tank before being pumped to the thickeners. An anionic polymer is applied to the
waste stream at the inlet of the thickeners in a flocculation tank. The supernatant from the
thickeners is dechlorinated and discharged to the Grand River. Thickened sludge is collected
CHAPTER 12. Residuals and Recycle Streams 12-12
Optimization Guidance Manual for Drinking Water Systems 2014
in a sludge storage tank until it is pumped to belt presses for dewatering. A cationic polymer
is added to the incoming sludge to enhance the dewatering process. Excess water is pumped
back into the equalization tank for further processing.
Upon commissioning of the RMF, it was determined that the thickeners did not perform
according to the design specifications because of significant problems with operation and
maintenance.
Optimization Strategies
To address the problems with the operation of the thickeners, full scale trials were undertaken
to determine if the thickeners could meet performance requirements for the overflow and
underflow when operated at the design loadings.
Several trials were conducted at various flow rates and at anionic polymer dosages of up to
3.0 mg/L. The results showed that the thickeners were challenged at the flow rate of 35 L/s
and were incapable of processing 52 L/s. It was determined that the units were overloaded
due to their small surface area. As a result, a third thickener was commissioned in 2006.
It was also noted that during winter months, turbidity levels in the raw water were very low,
resulting in low solids concentrations in the feed to the thickeners. Low solids in the residuals
process resulted in difficulties during the dewatering process, which caused the sludge to
become very “sloppy”. Careful monitoring and routine adjustments to belt speed, polymer
dose and sludge flow are required to ensure the proper operation of the belt presses.
Summary
The RMF had a number of advantages compared to the lagoon system, including an increase
in residuals treatment capacity and improvements in the discharge water quality (no chlorine
residual, lower suspended solids concentration, etc.). Proper operation of the RMF did
require additional monitoring and maintenance compared to the lagoon system.
12.4.2 Charleston, W.Va. – Kanawha Valley WTP Recycle Stream Evaluation
The following case study is based on information presented in Cornwell & Lee (1993).
System Description
The Kanawha Valley WTP is located in Charleston, W.Va., and draws water from the Elk
River. Treatment consists of polymer, lime and chlorine addition, followed by upflow
clarification and dual media filtration.
Sludge from the upflow clarifiers is discharged to the sanitary sewer. Spent filter backwash
water is pumped from an equalization tank into the raw water line upstream of the chemical
application point. Recycle pumping lasts for two to three hours and occurs one to three times
per day. The recycle flow typically ranges from 10 to 20 percent of the raw water flow.
CHAPTER 12. Residuals and Recycle Streams 12-13
Optimization Guidance Manual for Drinking Water Systems 2014
Optimization Strategies
A sampling program was undertaken to evaluate the impact of the recycle stream on finished
water quality, specifically in regards to turbidity, total THMs and THMFP concentrations.
Two rounds of sampling were performed. For each round, sampling was conducted over a
two-day period, with one set of samples collected each day. The water quality parameters
included in the study were: total THMs, THMFP, TOC, turbidity, chlorine residual and pH.
The following samples were collected:
Raw water
Mixed water without recycle
Settled water without recycle
Filtered water without recycle
Mixed water with recycle
Settled water with recycle
Filtered water with recycle
Recycle water (unsettled spent backwash)
The results of the sampling indicated that the introduction of the recycle stream to the
treatment process had a significant effect on total THM levels throughout the treatment
process. Filtered water total THM concentration increased from 73 to 95 µg/L during the first
round of sampling, and from 25 to 38 µg/L during the second round.
THMFP levels in the recycle water were found to be twice those of the raw water. The results
from this sampling showed a slight increasing trend of THMFP levels throughout the
treatment process during the recycle operation. The mixed, settled, and filtered water samples
all increased by similar percentages. The results also showed that settling the recycle water
could significantly reduce the THMFP values.
Sampling from both rounds of testing indicated that the recycle stream had substantial effects
on the turbidity of the mixed water; however, there was no impact on clarified or filtered
water. The treatment process was able to handle the increased turbidity loading without an
impact on finished water turbidity.
Summary
At the Kenawha Valley WTP, the influent water total THM concentration increased from 14
to 29 µg/L with the introduction of spent backwash water. This approximately 20 µg/L
differential was carried through the plant; such that the filtered water had a greater total THM
concentration with recycle than without.
CHAPTER 12. Residuals and Recycle Streams 12-14
Optimization Guidance Manual for Drinking Water Systems 2014
12.5 REFERENCES
Cornwell, D.A., M.M. Bishop, R.G. Gould and C. Vandermeyden (1987). Water Treatment
Plant Waste Management. AwwaRF & AWWA. Denver, CO. ISBN0-89867-404-2.
Cornwell, D.A. and R.G. Lee (1993). Recycle Stream Effects on Water Treatment. AwwaRF
& AWWA. Denver, CO. ISBN 0-89867-689-4.
Fournier Inc. (2010). “List of Advantages of the Rotary Press versus the Belt Filter Press”.
Metcalf & Eddy (2003). Wastewater Engineering: Treatment and Reuse, 4th ed. Toronto:
McGraw Hill. ISBN 0-07-041878-0.
MOE (2008). Design Guidelines for Sewage Works. ISBN 978-1-4249-8438-1.
Wang, L.K., N.K. Shammas, and Y-T Hung (2007). Volume 6 Handbook of Environmental
Engineering: Biosolids Treatment Processes. Humana Press Inc. ISBN: 978-59259-996-7.
Water Environment Research Federation (WERF) (2009). Integrated Methods for
Wastewater Treatment Plant Upgrading and Optimization. IWA Publishing. Document
Number: 04-CTS-5.
Yohannes, Y. (2010). “City of Brantford Residuals Management – An Environmentally
Friendly Process of Treating Sludge”, presented at the OWWA Spring Treatment Seminar,
“The Waste of Water”. Toronto, ON, March 2010.
CHAPTER 13 REPORTING RESULTS
REPORTING OF RESULTS
13.1 Introduction .......................................................................................................... 13-1
13.2 Interim Reports – Technical Memoranda ............................................................. 13-1
13.3 Workshops ............................................................................................................ 13-2
13.4 Final Report .......................................................................................................... 13-3
13.5 Implementation of Recommendations and Follow-up ......................................... 13-5
CHAPTER 13 . Reporting of Results 13-1
Optimization Guidance Manual for Drinking Water Systems 2014
CHAPTER 13
REPORTING OF RESULTS
13.1 INTRODUCTION
Reporting of results is an important part of an optimization study and can be used to present
findings and conclusions at key points during the study, and also to provide guidance for
facility administrators and operators and, if applicable, regulatory personnel. Internal studies
should be documented for future reference or in support of other activities.
The degree of detail and frequency of progress reports will vary with the scope of the study.
The following subsections present information on interim and final reports, as well as other
reporting tools, such as workshops, that can be developed as part of an optimization study.
13.2 INTERIM REPORTS – TECHNICAL MEMORANDA
Preparation of Technical Memoranda after completion of key activities are an effective
means of ensuring that all participants in the optimization study (owner, operations staff,
consulting team, etc.) are kept informed of project progress, have an opportunity to review
and understand project findings at an early stage, and provide input to the overall project
direction. Each Technical Memorandum (TM) should include:
An introduction describing the overall objective of the project;
The specific objective of the TM and how it relates to the overall project;
A discussion of the methodology, approach and key sources of information used;
The results of the specific activity described in the TM; and
Conclusions and recommendations.
Relevant data (e.g. modelling and simulation results, tracer test results, stress test results, etc.)
should be appended to the TM.
Table 13-1 presents some possible Technical Memoranda that could be prepared during a
comprehensive drinking water system optimization project. TMs prepared to describe the
findings of field investigations will depend on the specific field investigations undertaken.
These Technical Memoranda should be issued as drafts for review by the project team
responsible for the optimization study. Comments on the TM should be compiled and the TM
appropriately revised and issued as final. These Technical Memoranda can be incorporated
into the final report.
CHAPTER 13 . Reporting of Results 13-2
Optimization Guidance Manual for Drinking Water Systems 2014
Table 13-1 – Possible Technical Memoranda
TM Title TM Contents
#1: Existing Conditions Description of Drinking Water System.
Historic Data Review.
Desk-top Capacity Assessment.
#2: Field Investigations
Work Plan Outlines Work Plan for suggested field investigations based on
findings of TM#1.
Provides detailed description of test methodology, sampling and
analytical requirements, operations staff support requirements,
notification requirements, and any health and safety considerations.
#3: Filter Stress Testing Methodology, results and conclusions of filter stress testing to
determine filter performance efficiency and capacity.
#4: Tracer Testing to Verify
Clearwell Conditions Methods used for tracer testing for determination of actual hydraulic
detention time and test findings.
#5: Process and Distribution
System Modelling and
Simulation
Methodology used to calibrate and verify the simulation model,
conditions modelled, and the model outcomes.
#6: Options to Optimize
Plant Performance and
Distribution System
Operation
Description of options being considered.
Criteria considered in the assessment.
Evaluation of each option against the criteria.
Selection of preferred option and justification for selection.
13.3 WORKSHOPS
Workshops can be an effective means of communicating findings to all project participants,
including plant administration, management and operations staff, and regulators, at key
points in the project and soliciting input on key decisions.
The objectives and desired outcomes of the Workshop must be clearly communicated to the
participants. Important technical information that will be discussed at the Workshop should
be provided to the participants in advance to ensure that informed feedback and input can be
obtained.
Key points in the project where Workshops can prove useful are:
At project initiation, to introduce the project participants, review project background
and objectives, and provide a brief overview of the work plan to be executed and the
project schedule;
After completion of the historic data review, to present the findings of the desk-top
analysis, identify process or capacity limitations, and discuss the proposed field
investigations; and
CHAPTER 13 . Reporting of Results 13-3
Optimization Guidance Manual for Drinking Water Systems 2014
After the analysis of options, to present the findings of the field investigations,
proposed solutions to achieve the project objectives, the evaluation of options and to
obtain input to the selection of the preferred option(s).
Additional workshops may be beneficial depending on the study scope and duration.
Workshops should not replace regular project meetings with plant management and
operations staff to discuss specific activities, particularly field investigations.
Workshop notes should be compiled and included as an Appendix to the final project report.
13.4 FINAL REPORT
The outcome of an optimization study should be a comprehensive report that concisely
presents:
The project background and the rationale for the optimization study;
The project objectives;
A concise description of the drinking water system including a summary of the
design flows and water quality objectives, the process design of unit processes, a
process flow diagram, a distribution system schematic, and a summary of the
regulatory requirements that must be met or specific performance objectives that
have been set;
A summary of key information sources used during the investigation (e.g. historic
data; preliminary design reports, Certificate of Approval (C of A) or Drinking Water
Works Permit (DWWP) /Municipal Drinking Water Licence (Licence), MOE
inspection reports, annual reports, etc.);
A summary of historic operating conditions and performance for a period of at least
one year (refer to Section 3.3.3);
A desk-top analysis of the capacity and capability of each major drinking water
system component (refer to Section 3.2.1);
The methodology and findings of all field investigations such as stress tests, tracer
tests, jar tests, etc.;
An analysis of options to address capacity, performance or operational limitations, or
increase rated capacity to meet the project objectives;
The conclusions of the study; and
Any recommendations for follow-up investigations or implementation of the
findings.
Table 13-2 presents a suggested Table of Contents for a Drinking Water System Optimization
Final Report. The level of detail included in the final report should be consistent with the
project objectives and the target audience. For example, if an objective of the optimization
study is to support an application for a new C of A or DWWP/Licence to re-rate the plant
capacity, sufficient detail must be provided in the report for the MOE review engineer to
confirm that the proposed changes will consistently and reliably meet regulatory
requirements at the re-rated flow.
CHAPTER 13 . Reporting of Results 13-4
Optimization Guidance Manual for Drinking Water Systems 2014
Table 13-2 – Example Table of Contents for Drinking Water System Optimization
Report
Item Content
Executive Summary A concise (2 to 3 page) summary of the project objectives, key findings,
conclusions and recommendations.
Table of Contents Identifies key sections and subsections by title and includes a list of tables,
figures and appendices.
Introduction and
Background
Provides the rationale for the study and any background information
relevant to understanding the need for the process optimization. Should
include a list of key information sources used in the study.
Project Objectives Concisely states the key objective(s) of the study.
System Description Provides a process flow diagram of the WTP and/or distribution system,
including the locations of chemical addition points. Key design parameters
(e.g. average day flow, maximum day flow, CT requirements, etc.) and
sizing of key unit processes/mechanical equipment should be provided.
Historic Data Review A review of key operating and performance information for a period of at
least one year, including flows, raw water characteristics, treated water
quality, water quality at intermediate points in the process where available
and applicable (e.g. settled water, filtered water, etc.), and critical
operating parameters (e.g. surface overflow rates, settled water turbidity,
chemical dosages, etc.).
Desk-top Capacity
Assessment
Results of the desk-top analysis of the capacity of each major drinking water
system component study, based on the historic data and comparison to
typical design standards and guidelines, including a performance potential
graph (see Figure 3-2).
Results of Field
Investigations
Methodology and findings of any field investigations undertaken to
confirm the capacity assessment or determine the optimum approach to
achieve the project objectives.
Assessment of Options Identification and evaluation of alternative approaches to optimize the
system to meet the project objectives, including both operational and
design changes. Should include consideration of constructability,
integration with existing system, capital and operating costs, risks,
complexity, etc.
Conclusions Concise summary of the key findings.
Recommendations Recommendations for implementation of the conclusions or for further
investigations.
References Listing of key reference material.
Appendices Contains all supporting documentation such as Cs of A or
DWWP/Licence, modelling outputs, data from field investigations, details
of cost analysis if any, etc.
CHAPTER 13 . Reporting of Results 13-5
Optimization Guidance Manual for Drinking Water Systems 2014
13.5 IMPLEMENTATION OF RECOMMENDATIONS AND FOLLOW-UP
The time required to implement the recommendations from the optimization study will
depend on the nature of the recommendations. Operational changes such as increasing the
frequency of filter backwashing, increasing chemical dosage, or modifying sludge pumping
rates can be implemented quickly by operations staff. Design changes such as installing
baffles in clarifiers, retrofitting filters with new underdrains, or changing chemical dosage
points can be more time-consuming, likely requiring a detailed design phase, C of A or
DWWP/Licence amendment, tendering and construction.
Regardless of the nature of the upgrade, it is important to ensure that there is follow-up
monitoring to determine how effective the recommended upgrade was in achieving the
original optimization objective. If performance enhancement was the primary objective, a
post-implementation monitoring program should be undertaken to compare the performance
of the unit process after implementation with the performance achieved prior to
implementation. If cost reduction or energy efficiency was the primary objective,
comparative operating cost or energy use data, pre- and post-implementation, should be
collected.
Documentation of the success of the optimization project is critical to ensure on-going
support from management for further optimization activities.
APPENDICES
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDICES
APPENDIX A: Classification System, Factor Checklist and Definitions
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX A
CLASSIFICATION SYSTEM, FACTOR CHECKLIST AND DEFINITIONS
FOR ASSESSING PERFORMANCE LIMITING FACTORS
APPENDIX A: Classification System, Factor Checklist and Definitions A-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX A: CLASSIFICATION SYSTEM, FACTOR
CHECKLIST AND DEFINITIONS
CPE SUMMARY SHEET TERMS
Plant Type Brief but specific description of type of plant (e.g. conventional
with flash mix, flocculation, sedimentation, filtration and chlorine
disinfection or direct filtration with flash mix, flocculation and
disinfection).
Raw Water Source Brief description of water source (e.g. surface water including
name of river or ground water including geologic formation).
Plant Performance Summary Brief description of plant performance as related to desired water
quality.
Ranking Table A list of the major causes of decreased plant performance and
reliability.
Ranking Causes of decreased plant performance and reliability, with the
most critical ones listed first (typically only "A" and "B" factors
are listed).
Type A or B Identify factors as to A (major effect on a long term repetitive
basis) or B (minimum effect on a routine basis or major effect on a
periodic basis).
Performance Limiting Factors
and Category
Items identified from the Checklist of Performance Limiting
Factors. Identify factor category (e.g. administration, design,
operations, or maintenance).
APPENDIX A: Classification System, Factor Checklist and Definitions A-2
Optimization Guidance Manual for Drinking Water Systems 2014
CPE SUMMARY SHEET FOR RANKING PERFORMANCE LIMITING
FACTORS
Plant Name/Location: __________________________________________________
CPE Performed By: ______________________________Date: _________________
Plant Type: ___________________________________________________________
Raw Water Source: ____________________________________________________
Plant Performance Summary:
RANKING TABLE
RANKING TYPE A or B PERFORMANCE LIMITING FACTOR/CATEGORY
1 ____________ ______________________________________________________
2 ____________ ______________________________________________________
3 ____________ ______________________________________________________
4 ____________ ______________________________________________________
5 ____________ ______________________________________________________
6 ____________ ______________________________________________________
7 ____________ ______________________________________________________
8 ____________ ______________________________________________________
9 ____________ ______________________________________________________
10 ____________ ______________________________________________________
11 ____________ ______________________________________________________
12 ____________ ______________________________________________________
A – Major effect on a long term repetitive basis.
B – Minimum effect on a routine basis or major effect on a periodic basis.
C – Minor effect.
APPENDIX A: Classification System, Factor Checklist and Definitions A-3
Optimization Guidance Manual for Drinking Water Systems 2014
CHECKLIST OF PERFORMANCE LIMITING FACTORS
FACTOR RATING COMMENTS
A. Administration
1. Plant Administrators
a. Policies ____________ ____________________________________________
b. Familiarity with plant
needs ____________ ____________________________________________
c. Supervision ____________ ____________________________________________
d. Planning ____________ ____________________________________________
2. Plant Staff
a. Manpower
i) Number ____________ ____________________________________________
ii) Plant coverage ____________ ____________________________________________
iii) Workload distribution ____________ ____________________________________________
iv) Personnel turnover ____________ ____________________________________________
b. Morale
i) Motivation ____________ ____________________________________________
ii) Pay ____________ ____________________________________________
iii) Work environment ____________ ____________________________________________
c. Staff Qualifications
i) Aptitude ____________ ____________________________________________
ii) Level of education ____________ ____________________________________________
iii) Certification ____________ ____________________________________________
FACTOR RATING COMMENTS
d. Productivity ____________ ____________________________________________
APPENDIX A: Classification System, Factor Checklist and Definitions A-4
Optimization Guidance Manual for Drinking Water Systems 2014
3. Financial
a. Insufficient funding ____________ ____________________________________________
b. Unnecessary spending ____________ ____________________________________________
c. Indebtedness ____________ ____________________________________________
B. Maintenance
1. Preventive
a. Lack of Program ____________ ____________________________________________
b. Spare parts inventory ____________ ____________________________________________
2. Corrective ____________ ____________________________________________
a. Procedures ____________ ____________________________________________
b. Critical parts
procurement ____________ ____________________________________________
3. General ____________ ____________________________________________
a. Housekeeping ____________ ____________________________________________
b. References available ____________ ____________________________________________
c. Staff expertise ____________ ____________________________________________
d. Technical guidance ____________ ____________________________________________
e. Equipment age ____________ ____________________________________________
APPENDIX A: Classification System, Factor Checklist and Definitions A-5
Optimization Guidance Manual for Drinking Water Systems 2014
FACTOR RATING COMMENTS
C. Design
1. Raw Water
a. THM precursors ____________ ____________________________________________
b. Turbidity ____________ ____________________________________________
c. Seasonal variation ____________ ____________________________________________
d. Watershed management ____________ ____________________________________________
2. Unit Design Adequacy
a. Pretreatment
i) Intake structure ____________ ____________________________________________
ii) Presedimentation ____________ ____________________________________________
iii) Prechlorination ____________ ____________________________________________
b. Low lift pumping ____________ ____________________________________________
c. Flash mix ____________ ____________________________________________
d. Flocculation ____________ ____________________________________________
e. Sedimentation ____________ ____________________________________________
f. Filtration ____________ ____________________________________________
g. Disinfection ____________ ____________________________________________
h. Sludge treatment ____________ ____________________________________________
i. Residuals disposal ____________ ____________________________________________
j. Fluoridation ____________ ____________________________________________
APPENDIX A: Classification System, Factor Checklist and Definitions A-6
Optimization Guidance Manual for Drinking Water Systems 2014
FACTOR RATING COMMENTS
3. Miscellaneous
a. Process flexibility ____________ ____________________________________________
b. Process controllability ____________ ____________________________________________
c. Process automation ____________ ____________________________________________
d. Lack of standby units for
key equipment ____________ ____________________________________________
e. Flow proportioning to
unit processes ____________ ____________________________________________
f. Alarm systems ____________ ____________________________________________
g. Alternate power source ____________ ____________________________________________
h. Lab space/ equipment ____________ ____________________________________________
i. Sample taps ____________ ____________________________________________
j. Plant inoperability due to
weather ____________ ____________________________________________
k. Return process stream ____________ ____________________________________________
D. Operation
1. Testing
a. Performance monitoring ____________ ____________________________________________
b. Process control testing ____________ ____________________________________________
APPENDIX A: Classification System, Factor Checklist and Definitions A-7
Optimization Guidance Manual for Drinking Water Systems 2014
FACTOR RATING COMMENTS
2. Process Control Adjustments
a. Water treatment
understanding ____________ ____________________________________________
b. Application of concepts
and testing to process
control ____________ ____________________________________________
c. Technical guidance ____________ ____________________________________________
d. Training ____________ ____________________________________________
e. Insufficient time on job ____________ ____________________________________________
3. O&M Manual
a. Adequacy ____________ ____________________________________________
b. Use ____________ ____________________________________________
4. Distribution System ____________ ____________________________________________
E. Miscellaneous
1. ____________ ____________________________________________
2. ____________ ____________________________________________
3. ____________ ____________________________________________
4. ____________ ____________________________________________
5. ____________ ____________________________________________
6. ____________ ____________________________________________
7. ____________ ____________________________________________
8. ____________ ____________________________________________
APPENDIX A: Classification System, Factor Checklist and Definitions A-8
Optimization Guidance Manual for Drinking Water Systems 2014
DEFINITIONS OF PERFOMRANCE LIMITING FACTORS
A. ADMINISTRATION
1. Plant Administrators
a. Policies Do operating staff members have authority to make
required operation (e.g., adjust chemical feed),
maintenance (e.g. hire electrician), and/or
administrative (e.g. purchase critical piece of
equipment) decisions, or do policies cause critical
decisions to be delayed which in turn affect plant
performance and reliability? Does any established
administrative policy limit plant performance (e.g. non-
support of training; or plant funding too low because of
emphasis to avoid rate increases)?
b. Familiarity with plant needs Do administrators have a first-hand knowledge of plant
needs through plant visits or discussions with operators?
If not, has this been a cause of poor plant performance
and reliability through poor budget decisions, poor staff
morale, or limited support for plant modifications?
c. Supervision Do management styles, organizational capabilities,
budgeting skills, or communication practices at any
management level adversely impact the plant to the
extent that performance is affected?
d. Planning Does lack of long range plans for facility replacement,
alternative source waters, emergency response, etc.
adversely impact the plant performance?
2. Plant Staff
a. Manpower
i) Number
Does a limited number of people employed have a
detrimental effect on plant operations or maintenance
(e.g., not getting the necessary work done)?
ii) Plant coverage Is plant coverage adequate such that necessary
operational activities are accomplished? Can
appropriate adjustments be made during the evenings,
weekends or holidays? For example, is staff available to
respond to changing raw water quality characteristics
during periods of operation?
iii) Work load
distribution
Does the improper distribution of adequate manpower
(e.g. a higher priority on maintenance tasks) prevent
process adjustments from being made or cause them to
APPENDIX A: Classification System, Factor Checklist and Definitions A-9
Optimization Guidance Manual for Drinking Water Systems 2014
be made at inappropriate times, resulting in poor plant
performance?
iv) Staff turnover Does a high personnel turnover rate cause operation
and/or maintenance problems that affect process
performance or reliability?
b. Morale
i) Motivation Does the plant staff want to do a good job because they
are motivated by self-satisfaction?
ii) Pay Does a low pay scale or benefit package discourage
more highly qualified persons from applying for
operator positions or cause operators to leave after they
are trained?
iii) Environment Does a poor work environment create a condition for
more "sloppy work habits" and lower operator morale?
c. Staff Qualifications
i) Aptitude Does the lack of capacity for learning or understanding
new ideas by critical staff members cause improper O &
M decisions leading to poor plant performance or
reliability?
ii) Education Does a low level of education result in poor O & M
decisions? Does a high level of education cause needed
training to be felt unnecessary?
iii) Certification Does the lack of adequately certified personnel result in
poor O & M decisions?
d. Productivity Does the plant staff conduct the daily operation and
maintenance tasks in an efficient manner? Is time used
efficiently?
3. Financial
a. Insufficient funding Does the lack of available funds (e.g. inadequate rate
structure) cause poor salary schedules, insufficient stock
of spare parts that results in delays in equipment repair,
insufficient capital outlays for improvements or
replacement, lack of required chemicals or chemical
feed equipment, etc.?
b. Unnecessary spending Does the manner in which available funds are utilized
cause problems in obtaining needed equipment, staff,
etc.? Are funds spent on lower priority items while
needed, higher priority items are unfunded?
APPENDIX A: Classification System, Factor Checklist and Definitions A-10
Optimization Guidance Manual for Drinking Water Systems 2014
c. Indebtedness Does the annual debt payment limit the amount of funds
available for other items such as equipment, staff, etc.?
4. Water Demand Does excessive water use caused by declining rate
structure, concessions to industry, or high unaccounted
for use exceed the capability of plant unit processes and
therefore degrade plant performance?
B. MAINTENANCE
1. Preventive
a. Lack of Program Does the absence or lack of an effective scheduling and
recording procedure cause unnecessary equipment
failures or excessive downtime, which results in plant
performance or reliability problems?
b. Spare parts inventory Does a critically low or nonexistent spare parts
inventory cause unnecessary long delays in equipment
repairs that result in degraded process performance?
2. Corrective
a. Procedures Are procedures available to initiate maintenance
activities on observed equipment operating irregularities
(e.g. work order system)? Does the lack of emergency
response procedures result in activities that fail to
protect process needs during breakdowns of critical
equipment (e.g., maintaining disinfectant or coagulant
feeds during equipment breakdowns)?
b. Critical parts
procurement
Do delays in getting replacement parts caused by
procurement procedure result in extended periods of
equipment downtime?
3. General
a. Housekeeping Does a lack of good housekeeping procedures (e.g.
unkempt, untidy, or cluttered working environment)
cause an excessive equipment failure rate?
b. References available Does the absence or lack of good equipment reference
sources result in unnecessary equipment failure and/or
downtime for repairs (includes maintenance portion of
O & M Manual, equipment catalogs, etc.)?
c. Staff expertise Does the plant staff have the necessary expertise to keep
the equipment operating and to make equipment repairs
when necessary?
APPENDIX A: Classification System, Factor Checklist and Definitions A-11
Optimization Guidance Manual for Drinking Water Systems 2014
d. Technical guidance Does inappropriate guidance for repairing, maintaining,
or installing equipment from a technical resource (e.g.
equipment supplier or contract service) result in
equipment downtime that adversely affects
performance? If technical guidance is necessary to
decrease equipment downtime; is it available and
retained?
e. Equipment age Does the age or outdatedness of critical pieces of
equipment cause excessive equipment. downtime and/or
inefficient process performance and reliability (due to
unavailability of replacement parts)?
C. DESIGN
1. Raw Water Does the presence of raw water quality characteristics
over and above what the plant was designed for, or over
and above what is thought to be tolerable, cause
degraded process performance by any of the items (a-c)
listed below?
a. THM precursors
b. Turbidity
c. Seasonal variation
d. Watershed management Do facilities exist to control raw water quality entering
the plant (e.g. can intake levels be varied, can chemicals
be added to control aquatic growth, do watershed
management practices adequately protect raw water
quality)?
2. Unit Design Adequacy
a. Pretreatment Do the design features of any pretreatment unit cause
problems in downstream equipment or processes that
have led to degraded plant performance?
i) Intake structure Does the design of the intake structure result in
excessive clogging of screens, a build-up of silt, or
passage of solids that damages downstream processes?
ii) Presedimentation Does a deficient design cause poor sedimentation that
results in poor plant performance (e.g., inlet
configuration, size, type, or depth of the basin; or
placement or length of the weirs)?
iii) Prechlorination Does prechlorination cause excessive finished water
disinfection byproducts?
APPENDIX A: Classification System, Factor Checklist and Definitions A-12
Optimization Guidance Manual for Drinking Water Systems 2014
b. Low lift pumping Does the existence of high volume constant speed
pumps cause undesirable hydraulic loadings on
downstream unit processes?
c. Flash mix Does a lack of or inadequate mixing result in excessive
chemical use or insufficient coagulation to the extent
that it impacts plant performance?
d. Flocculation Does the performance of the flocculation unit process
contribute to problems in downstream unit processes
that have degraded plant performance? Does a lack of
flocculation time or flocculation stages with variable
energy input result in poor floc formation and degrade
plant performance?
e. Sedimentation Does a deficient design cause poor sedimentation that
results in poor filter performance (e.g., inlet
configuration, size, type, or depth of the basin; or
placement or length of the weirs)?
f. Filtration Does the size of filter, or the type, depth, and effective
size of filter media hinder its ability to adequately treat
water? Are the surface wash and backwash facilities
adequate to maintain a clean filter bed? Have the
underdrains or support gravels been damaged or
disturbed to the extent that filter performance is
compromised?
g. Disinfection Do the facilities have any design limitations that
contribute to poor disinfection (e.g. proper mixing,
detention time, feed rates, proportional feed, etc.)?
h. Sludge treatment Does the type or capacity of sludge treatment processes
cause process operation problems that degrade plant
performance?
i. Residuals disposal Are the sludge and backwash water facilities and
disposal area of sufficient size and type to ensure that
poor plant performance does not occur or applicable
permits regulating the discharge are not violated?
j. Fluoridation Do the fluoridation facilities have any design limitations
that result in an inability to achieve regulated fluoride
levels (e.g. feed rates, proportional feed, etc.)?
3. Miscellaneous The design "miscellaneous" category covers areas of
design inadequacy not specified in the previous design
categories. (Space is available in the Checklist to
accommodate additional items not listed.)
APPENDIX A: Classification System, Factor Checklist and Definitions A-13
Optimization Guidance Manual for Drinking Water Systems 2014
a. Process flexibility Do chemical feed facilities have various feed points to
optimize treatment (e.g. feed alum and cationic
polymers at flash mix, feed non-ionic or anionic
polymers at points where mixing is gentle)? Do
facilities exist to feed the types of chemicals required to
produce a high quality stable finished water (e.g.
coagulant aids, flocculant aids, filter aids, stabilization
chemicals)?
b. Process controllability Do the existing process control features provide
adequate adjustment and measurement of plant flow
rate, backwash flow rate, filtration rate, and flocculation
mixing inputs? Do chemical feed facilities provide
adjustable feed ranges that are easily set for operation at
all required dosages? Do chemical feed controls remain
set once adjusted or do they vary? Are chemical feed
rates easily measured?
c. Process automation Does the lack of needed automatic monitoring or
control devices (streaming current detector, continuous
recording turbidimeter, etc.) cause excessive operator
time for process control and monitoring? Does the
automatic operation of critical unit processes degrade
plant performance during startup and shut-down?
d. Lack of standby units for
key equipment
Does the lack of standby units for key equipment cause
degraded process performance during breakdown or
during necessary preventive maintenance activities (e.g.
backwash pumps and chemical feeders, etc.)?
e. Flow proportioning to
unit processes
Does inadequate flow proportioning or flow splitting to
duplicate units cause problems or partial unit overloads
that degrade effluent quality or hinder achievement of
optimum process performance?
f. Alarm systems Does the absence or inadequacy of an alarm system for
critical pieces of equipment or processes cause
degraded process performance (e.g. raw or finished
water turbidity)?
g. Alternate power source Does the absence of an alternate power source cause
problems in reliability of plant operation leading to
degraded plant performance?
h. Lab space/ equipment Does the absence of an adequately equipped laboratory
limit plant performance?
i. Sample taps Does a lack of sample taps on key process flow streams
(e.g. individual filters, sedimentation basin solids,
backwash recycle streams) for sampling prevent needed
APPENDIX A: Classification System, Factor Checklist and Definitions A-14
Optimization Guidance Manual for Drinking Water Systems 2014
information from being obtained?
j. Plant inoperability due to
weather
Are certain units in the plant extremely vulnerable to
weather changes and, as such, do not operate at all or do
not operate as efficiently as necessary to achieve the
required performance? Do poor roads leading into the
plant cause it to be inaccessible during certain periods
of the year for chemical or equipment delivery or for
routine operation?
k. Return process stream Does excessive volume and/or a highly turbid return
process flow stream (e.g. backwash return flow) cause
adverse effects on process performance, equipment
problems, etc.? Does the inability to measure or sample
these streams degrade plant performance?
D. OPERATION
1. Testing
a. Performance monitoring Are plant and distribution system monitoring tests truly
representative of performance?
b. Process control testing Does the absence or wrong type of process control
testing cause improper operational control decisions to
be made (e.g. does filter performance evaluation
support finished water turbidity data)?
2. Process Control Adjustments
a. Water treatment
understanding
Is the operator's lack of basic understanding of water
treatment (e.g. limited exposure to terminology, lack of
understanding of the function of unit processes, etc.) a
factor in poor operational decisions and poor plant
performance or reliability?
b. Application of concepts
and testing to process
control
Is the staff deficient in the application of their
knowledge of water treatment and interpretation of
process control testing such that improper process
control adjustments are made?
c. Technical guidance Does inappropriate operational information received
from a technical resource (e.g. design engineer,
equipment representative, regulatory inspector) cause
improper operational decisions to be implemented or
continued?
d. Training Does non-attendance at available training programs
result in poor process control decisions by the plant
staff or administrators?
APPENDIX A: Classification System, Factor Checklist and Definitions A-15
Optimization Guidance Manual for Drinking Water Systems 2014
e. Insufficient time on job Does the short time on the job and associated
unfamiliarity with plant needs result in the absence of
process control adjustments or in improper process
control adjustments being made (e.g., opening or
closing a wrong valve, turning on or off a wrong
chemical feed pump, backwashing a filter incorrectly,
etc.)?
3. O&M Manual
a. Adequacy Does inappropriate guidance provided by the O & M
manual/procedures result in poor or improper operation
decisions?
b. Use Does the operator's failure to utilize a good O & M
manual/procedures cause poor process control and poor
treatment that could have been avoided?
4. Distribution System Are distribution system operating procedures adequate
to protect the integrity of finished water quality (e.g.
flushing, reservoir management, etc.)?
E. MISCELLANEOUS
The "miscellaneous" category allows addition of factors
not covered by the above definitions. Space is available
in the Checklist to accommodate these additional items.
APPENDIX B. Data Collection Forms
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX B
DATA COLLECTION FORMS
APPENDIX B. Data Collection Forms B-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX B: DATA COLLECTION FORMS
FORM A – KICK OFF MEETING
A. MEETING OUTLINE
1. Purpose of CPE
a. Background
b. Assess plant potential for achieving compliance
c. Identify current factors limiting performance
d. Outline follow-up activities.
2. Schedule of Events DAY TIME
a. Kickoff Meeting _________________________ _________________________
b. Plant Tour _________________________ _________________________
c. Review Budget/User
Fees/Revenues _________________________ _________________________
d. Onsite Data Collection _________________________ _________________________
e. Personnel Interviews _________________________ _________________________
f. Exit Meeting _________________________ _________________________
3. Information Resources (availability):
As built drawings
O & M Manual
Monitoring records
Equipment literature
Process control records
Budget records
Design consultant
APPENDIX B. Data Collection Forms B-2
Optimization Guidance Manual for Drinking Water Systems 2014
FORM A – KICK OFF MEETING (cont’d.)
B. ATTENDANCE LIST
Municipality: ___________________________________________ Date: ____________________
Name Title/Dept. Telephone No.
1. ________________________ _________________________ _________________________
2. ________________________ _________________________ _________________________
3. ________________________ _________________________ _________________________
4. ________________________ _________________________ _________________________
5. ________________________ _________________________ _________________________
6. ________________________ _________________________ _________________________
7. ________________________ _________________________ _________________________
8. ________________________ _________________________ _________________________
9. ________________________ _________________________ _________________________
10. _______________________ _________________________ _________________________
11. _______________________ _________________________ _________________________
12. _______________________ _________________________ _________________________
13. _______________________ _________________________ _________________________
14. _______________________ _________________________ _________________________
15. _______________________ _________________________ _________________________
16. _______________________ _________________________ _________________________
17. _______________________ _________________________ _________________________
18. _______________________ _________________________ _________________________
19. _______________________ _________________________ _________________________
20. _______________________ _________________________ _________________________
APPENDIX B. Data Collection Forms B-3
Optimization Guidance Manual for Drinking Water Systems 2014
FORM A – KICK OFF MEETING (cont’d.)
C. PERSONNEL INTEVIEWS SCHEDULING SHEETINGS *
Name Title/Dept. Day Time
1. ________________________ _________________________ ___________ ___________
2. ________________________ _________________________ ___________ ___________
3. ________________________ _________________________ ___________ ___________
4. ________________________ _________________________ ___________ ___________
5. ________________________ _________________________ ___________ ___________
6. ________________________ _________________________ ___________ ___________
7. ________________________ _________________________ ___________ ___________
8. ________________________ _________________________ ___________ ___________
9. ________________________ _________________________ ___________ ___________
10. _______________________ _________________________ ___________ ___________
11. _______________________ _________________________ ___________ ___________
12. _______________________ _________________________ ___________ ___________
13. _______________________ _________________________ ___________ ___________
14. _______________________ _________________________ ___________ ___________
15. _______________________ _________________________ ___________ ___________
16. _______________________ _________________________ ___________ ___________
17. _______________________ _________________________ ___________ ___________
18. _______________________ _________________________ ___________ ___________
19. _______________________ _________________________ ___________ ___________
20. _______________________ _________________________ ___________ ___________
* Includes offsite administrators/owners, budgeting personnel, laboratory personnel,
maintenance personnel, plant administrators, shift personnel, operators, etc.
APPENDIX B. Data Collection Forms B-4
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA
A. NAME AND LOCATION:
Name of Facility _______________________________________________________
Owner _______________________________________________________
Administrative Office: _______________________________________________________
Mailing Address _______________________________________________________
Primary Contact _______________________________________________________
Title _______________________________________________________
Telephone No. _______________________________________________________
Treatment Plant:
Mailing Address _______________________________________________________
Primary Contact _______________________________________________________
Title _______________________________________________________
Telephone No. _______________________________________________________
APPENDIX B. Data Collection Forms B-5
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
B. ORGANIZATION:
1. Governing Body (Name and Schduled Meetings):
2. Structure:
From Governing Body to Plant:
Within Plant:
3. Staff Meetings (formal/informal):
APPENDIX B. Data Collection Forms B-6
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
B. ORGANIZATION (cont’d.):
4. Reporting Requirements (formal/informal):
5. Public Relations/Education:
6. Observations (openness, awareness of plant needs, management style, etc.):
APPENDIX B. Data Collection Forms B-7
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
C. PERSONNEL:
PLANT
No. Title/Name Certification Pay Scale % Time at
Plant
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
____ _________________________ _________________________ ___________ ___________
OFF SITE
No. Title/Name Pay Scale % Time Allocated to Plant
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
____ _________________________ ___________ ________________________________________
APPENDIX B. Data Collection Forms B-8
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
D. TRAINING:
Operator Training Budget _______________________________________________________
_______________________________________________________
_______________________________________________________
Training Incentives _______________________________________________________
_______________________________________________________
_______________________________________________________
Training Over Last Year _______________________________________________________
_______________________________________________________
_______________________________________________________
E. PLANT COVERAGE:
Weekdays (shift times/overlap/number per shift):
Weekends and Holidays:
Alarms (on what process? Auto-dailer?):
APPENDIX B. Data Collection Forms B-9
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
F. PLANT BUDGET/EXPENDITURES:
(Attach copy of actual budget and/or expenditures if available.)
Budget year _____________________ to ___________________________________
Expenditure period _______________ to ___________________________________
CATEGORY BUDGET AMOUNT EXPENDITURE AMOUNT
Administrative Salaries _________________________ _________________________
Plant Staff Salaries _________________________ _________________________
Utilities _________________________ _________________________
Electric _________________________ _________________________
Gas _________________________ _________________________
Chemicals _________________________ _________________________
Vehicles _________________________ _________________________
Training _________________________ _________________________
_________________________ _________________________ _________________________
_________________________ _________________________ _________________________
_________________________ _________________________ _________________________
_________________________ _________________________ _________________________
OPERATIONS TOTAL _________________________ _________________________
APPENDIX B. Data Collection Forms B-10
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
G. CAPITAL OUTLAYS:
1. Capital Improvement Reserve (Self-sustaining utility? Master Plan? Replacement philosophy?)
2. Capital Replacement Plan (Available? Items scheduled for replacement? Attach if available.)
3. Expansion History and Proposed Modifications (historical studies, current evaluations, long range
plans, etc.).
APPENDIX B. Data Collection Forms B-11
Optimization Guidance Manual for Drinking Water Systems 2014
FORM B – ADMINISTRATION DATA (cont’d.)
H. REVENUE:
1. User Charges:
2. Connection Fees:
3. Other Sources of Revenue (interest income, bulk water sales, etc.):
4. Total Revenue for Evaluation Period (compare to expenditures):
5. Miscellaneous:
Are rates and budget reviewed annually?
When was the last rate increase (how much)?
Proposed Increases?
APPENDIX B. Data Collection Forms B-12
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA
A. PLANT FLOW DIAGRAM
(Attach if Available, include solids handling and chemical addition points.)
B. FLOW DATA
Design Flow
Average Daily Flow = ____________ m3/d
Maximum Hydraulic Capacity = ____________ m3/d
Operating Flow
Peak Instantaneous Operating Flow = ____________ m3/d
APPENDIX B. Data Collection Forms B-13
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES
FLOW MEASUREMENT
Flow Stream Measured Meter Type Calibration
Frequency Comments
Raw Water:
Finished Water:
Backwash:
Other (Describe):
Accuracy Check During
CPE (Describe)
APPENDIX B. Data Collection Forms B-14
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
SCREENING
Travelling Bar Screen:
Bar Screen Width = ____________ cm
Bar Opening = ____________ cm
Screening Disposal:
Operation Problems:
Hand Cleaned Bar Screen:
Bar Screen Width = ____________ cm
Bar Opening = ____________ cm
Cleaning Frequency = ___________________________
Screening Disposal:
Operation Problems:
Other (Describe):
APPENDIX B. Data Collection Forms B-15
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
PUMPING
Flow Stream Pumped Pump Description # of Pumps Rated Capacity
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
Flow Control Method (Describe):
Flow Stream Pumped Pump Description # of Pumps Rated Capacity
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
Flow Control Method (Describe):
Flow Stream Pumped Pump Description # of Pumps Rated Capacity
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
________________________ _________________________ ___________ ___________
Flow Control Method (Describe):
APPENDIX B. Data Collection Forms B-16
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
PRESEDIMENTATION
Type (e.g. concrete or earthen) ___________________________________________
Number of Basins _____________ Surface Dimensions ______________________
Water Depth (shallowest) = _____________ m Water Depth (deepest) =_____ m
Weir Location ____________________ Weir Length = ____________ m
Total Surface Area = ____________ m2 Total Volume ____________ m
3
FLOW:
Design Flow = ________________ m3/d Operating Flow
*_________ m
3/d
DETENTION TIME:
At Design Flow = _______________ hr At Operating Flow* ________ hr
WEIR OVERFLOW RATE:
At Design Flow = _____________ m3/m/d Operating Flow
* = ___________ m
3/m/d
SURFACE OVERFLOW RATE:
At Design Flow = _____________ m3/m
2/d Operating Flow
* = __________ m
3/m
2/d
CHEMICAL FEED CAPABILITY:
Type of Chemicals: ____________________________________________________
Operating Range (Describe) _____________________________________________
Schematic:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-17
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
RAPID MIXING
RAPID MIX:
Type ________________________________________________________________
(mechanical, in-line mechanical, in-line static)
Number of mixers _____________ Power Rating ___________________________
Number of Basins _____________ Surface Dimensions = ____________________
Water Depth = ____________ m Total Volume = ___________________
m3
FLOW:
Design Flow = ________________ m3/d Operating Flow
* = _______ m
3/d
DETENTION TIME:
At Design Flow = _______________ hr At Operating Flow* = ______ hr
G VALUE (see Chapter 6 and Appendix G):
At Design Flow = _______________ s-1
At Operating Flow* =_______ s
-1
Operating Problems:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-18
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
FLOCCULATION
Type (e.g. paddle wheel, turbine, hydraulic) _________________________________
Control (e.g. constant or variable speed) ____________________________________
Stage Surface
Dimensions Depth Volume Power G Value
1 ________________ _____________ _____________ _____________ _____________
2 ________________ _____________ _____________ _____________ _____________
3 ________________ _____________ _____________ _____________ _____________
4 ________________ _____________ _____________ _____________ _____________
Total ________________ _____________ _____________ _____________ _____________
FLOW:
Design Flow = ________________ m3/d Operating Flow
*_________ m
3/d
DETENTION TIME:
At Design Flow = _______________ hr At Operating Flow* = ______ hr
Operating Problems:
Schematic:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-19
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
CLARIFICATION
Number of Basins _____________ Surface Dimensions ______________________
Water Depth (shallowest) = _____________ m Water Depth (deepest) = _____m
Weir Location ____________________ Weir Length = ____________ m
Total Surface Area = ____________ m2 Total Volume = __________ m
3
FLOW:
Design Flow = ________________ m3/d Operating Flow
* = _______ m
3/d
DETENTION TIME:
At Design Flow = _______________ hr At Operating Flow* = ______ hr
WEIR OVERFLOW RATE:
At Design Flow = _____________ m3/m/d Operating Flow
* = ___________ m
3/m/d
SURFACE OVERFLOW RATE:
At Design Flow = _____________ m3/m
2/d Operating Flow
* = __________ m
3/m
2/d
Inlet/Outlet Conditions (describe and/or schematic):
Operating Problems:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-20
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
FILTRATION
Type of Filters (media type, pressure, gravity, etc.) ___________________________
Number of filters _________________ Surface Dimensions __________
Total Surface Area ________________ m2
MEDIA CHARACTERISTICS:
Media Type Depth Uniformity
Coefficient Effective Size Specific Gravity
________________ _____________ _____________ _____________ _____________
________________ _____________ _____________ _____________ _____________
________________ _____________ _____________ _____________ _____________
________________ _____________ _____________ _____________ _____________
FLOW:
Design Flow = ________________ m3/d Operating Flow
* = _______ m
3/d
FILTRATION RATE:
At Design Flow = ______________ m/h At Operating Flow* = _____ m/h
Filter control (e.g. declining or constant rate/level, etc.): _______________________
Available Headloss = ____________ m
SURFACE WASH:
Type (e.g. rotary, fixed, manual) ____________________________________
Water Flow Rate = _______ m3/d Surface Wash Rate = ________m
3/m
2/d
Wash duration = ____________ min
BACKWASH:
Wash Water Rate:
At Design Flow = _______ m3/m
2/d At Operating Flow
* = ____ m
3/m
2/d
Wash duration = ____________ min
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-21
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
FILTRATION (cont’d.)
AIR WASH RATE :
At Design Flow = ___________ m3/m
2/d At Operating Flow
* = _______ m
3/m
2/d
CONTROL/OPERATING PROBLEMS:
Mud Balls:
Dirty media:
Uneven media:
Backwash rate control/Procedure (e.g. gradual start/stop):
Filter Rate Control/Procedure (e.g. gradual changes):
Hydraulic Loading During Backwash (e.g. reduce flow to remaining filters):
Air Bubbles During Backwash:
Surface Wash Control/Procedure:
Other:
Availability of Sample Taps (e.g. backwash and individual filters):
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-22
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
DISINFECTION
Contact Basin(s) Available (e.g. clearwell) __________________________________
Basin Surface Dimensions Depth Volume
____________________ ________________________ _______________ _______________
____________________ ________________________ _______________ _______________
____________________ ________________________ _______________ _______________
TOTAL: _______________
DETENTION TIME (see Chapter 9 and Appendix G):
Theoretical1 = ____________ min
Functional2 = ____________ min
1. Based on total available volume and peak instantaneous operating flow.
2. Based on evaluation of operating variables such as basin baffling, minimum operating depth
and transmission line length to first user.
CHLORINATORS:
No. of Chlorinators ___________________________________
Description (make/type, etc.) ___________________________
Capacity _______________ to __________________ kg/d
Flow Proportioned ___________________________________
FLOW:
Design Flow = ________________ m3/d Operating Flow
* = _______ m
3/d
MAXIMUM DOSAGE CAPABILITY:
At Design Flow = _____________ m3/d At Operating Flow
* = ____ m
3/d
Operating Problems:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-23
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
CHEMICAL FEED SYSTEMS
METAL SALTS
DRY:
Type Design Feed
Range (kg/h)
Dosage Range at Design Flow
(mg/L)
Dosage Range at Operating*
Flow (mg/L)
Min. Max. Min. Max.
________________ ___________ ___________ ___________ ___________ ___________
________________ ___________ ___________ ___________ ___________ ___________
LIQUID:
Type
Design Feed
Range
(mL/min)
Dosage Range at Design Flow
(mg/L)
Dosage Range at Operating*
Flow (mg/L)
Min. Max. Min. Max.
________________ ___________ ___________ ___________ ___________ ___________
________________ ___________ ___________ ___________ ___________ ___________
Dosage Control (describe):
Operating Problems:
Accuracy Check During CPE (describe):
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-24
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
CHEMICAL FEED SYSTEMS
POLYMERS
Type
Design
Feed
Range
(mL/min)
Stock1
Solution
(%w/v)
Recom-
mended1
Dilution
(%w/v)
Dosage Range at
Design Flow (mg/L)
Dosage Range at
Operating* Flow (mg/L)
Min. Max. Min. Max.
____________ _________ ________ ________ ________ ________ ________ ________
____________ _________ ________ ________ ________ ________ ________ ________
____________ _________ ________ ________ ________ ________ ________ ________
____________ _________ ________ ________ ________ ________ ________ ________
1. Obtain from manufacturer’s data sheet
Dosage Control (describe):
Operating Problems:
Accuracy Check During CPE (describe):
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-25
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
CHEMICAL FEED SYSTEMS
pH/ALKALINITY ADJUSTMENT:
Chemicals Used:
Dosage Control (describe):
Operating Problems:
FLUORIDATION:
Fluoride Compound Used:
Dosage Control (describe):
Operating Problems:
SOFTENING:
Chemicals Used:
Dosage Control (describe):
Operating Problems:
POWDERED ACTIVATED CARBON:
Dosage Control (describe):
Operating Problems:
OTHER:
APPENDIX B. Data Collection Forms B-26
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
SOLIDS HANDLING
PRESEDIMENTATION SLUDGE:
Description of Pumping Procedure (e.g. time clocks, variable speed pumps):
Method of Waste Volume Measurement:
Sampling Location:
Sampling Procedure:
Operating Problems:
CLARIFICATION SLUDGE:
Description of Pumping Procedure (e.g. time clocks, variable speed pumps):
Method of Waste Volume Measurement:
Sampling Location:
Sampling Procedure:
Operating Problems:
RETURN SLUDGE (Solids Contact Unit):
Description of Sludge Movement:
Controllable Capacity Range: Low = ___________ m3/d High = ____________ m
3/d
Method of Control:
Sampling Location:
Sampling Procedure:
Operating Problems:
APPENDIX B. Data Collection Forms B-27
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
C. UNIT PROCESSES (cont’d.)
SOLIDS HANDLING (cont’d.)
SLUDGE DRYING BEDS/LAGOONS:
No. of Beds/Lagoons ___________ Dimensions ____________________________
Total Volume _______________ Subnatant Drain To ______________________
Dewatered Sludge Removal:
Mode of Operation (depth of sludge draw, seasonal operation, schematic):
Operating Problems:
OTHER DEWATERING UNIT(S):
Type of Unit(s) __________________________________ No. of Units ________
Loading Rate:
At Design Flow = _____________ mg/L At Operating Flow* = __________ mg/L
Polymer Used ________________________ Dosage ________________ g/kg dry wt.
Cake Solids __________________________ % solids
Hours/Week of Operation
Design ___________________________ Operating ________________________
Operating Problems:
ULTIMATE SLUDGE DISPOSAL:
Description
_________________________________________________________________
Operating Problems:
* Peak instantaneous operating flow.
APPENDIX B. Data Collection Forms B-28
Optimization Guidance Manual for Drinking Water Systems 2014
FORM C – DESIGN DATA (cont’d.)
D. MISCELLANEOUS DESIGN INFORMATION
Process Automation (describe existing systems):
Standby Units (chemical feed, backwash pumps):
Flow Proportioning to Units:
Alarm Systems (description of systems, units covered):
Alternate Power Source:
Weather Inoperability:
Return Process Streams:
APPENDIX B. Data Collection Forms B-29
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA
A. PROCESS CONTROL STRATEGY AND DIRECTION
Who sets major process control strategies and decisions?
Who makes process control decisions when lead process control person is not at
plant?
Where is help sought when desired performance is not achieved?
Are staff members asked their opinions?
How is communication conducted between laboratory, operations and maintenance
staff?
B. SPECIFIC PROCESS CONTROL PROCEDURES
SAMPLING AND TESTING:
Sampling Locations (add to plant flow schematic):
PRESEDIMENTATION:
Sludge Removal (method of control/adjustment):
Performance Monitoring:
Other:
APPENDIX B. Data Collection Forms B-30
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
B. SPECIFIC PROCESS CONTROL PROCEDURES (cont’d.)
CLARIFICATION:
Performance Monitoring (tests used, solids balance):
Sludge Removal (method of control/adjustment):
Sludge Recycle (contact sedimentation):
Other:
FILTRATION:
Hydraulic Loading Rate Control (method of control/adjustment):
Backwash Control (test used, method of determining frequency):
Filter Monitoring:
Influent turbidity:
Effluent turbidity:
Headloss:
Loading rate:
Length of run:
COAGULATION:
Feed Rate Control (method of control/adjustment):
Performance Monitoring:
Jar testing:
Pilot filter:
Zeta meter:
Streaming current detector:
Turbidity:
APPENDIX B. Data Collection Forms B-31
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
B. SPECIFIC PROCESS CONTROL PROCEDURES (cont’d.)
DISINFECTION:
Performance Monitoring (tests used):
Feed rate Control (method of control/adjustment):
FLUORIDATION:
Performance Monitoring (tests used):
Feed Rate Control (method of control/adjustment):
pH/ALKALINITY ADJUSTMENT:
Performance Monitoring (tests used):
Feed Rate Control (method of control/adjustment):
SOFTENING/RECARBONATION:
Performance Monitoring (tests used):
Feed Rate Control (method of control/adjustment):
TASTE AND ODOUR:
Performance Monitoring (tests used):
Feed Rate Control (method of control/adjustment):
SLUDGE HANDING AND DISPOSAL:
Sludge Dewatering (monitoring, process control/optimization):
Sludge Disposal (meet requirement, monitoring, options):
APPENDIX B. Data Collection Forms B-32
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
C. PROCESS CONTROL REFERENCES
Specifically note sources (e.g. publications or personnel) that are the cause of poor
process control decisions or strategies, suspected or definitely identified.
D. OPERATIONS AND MAINTENANCE MANUAL
Adequacy:
Use:
APPENDIX B. Data Collection Forms B-33
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
E. LABORATORY CAPABILITY
1. Facilities
Adequate
Comments
Yes No
Bench space __________ __________ ______________________________
Storage space __________ __________ ______________________________
Floor area __________ __________ ______________________________
Lighting __________ __________ ______________________________
Electricity __________ __________ ______________________________
Potable water supply __________ __________ ______________________________
Compressed air __________ __________ ______________________________
Vacuum __________ __________ ______________________________
Chemical fume hood __________ __________ ______________________________
Air conditioning __________ __________ ______________________________
Desk __________ __________ ______________________________
Records storage __________ __________ ______________________________
2. Equipment & Instruments
Adequate
Comments
Yes No
Turbidimeter __________ __________ ______________________________
Core sampler __________ __________ ______________________________
pH meter __________ __________ ______________________________
Centrifuge __________ __________ ______________________________
Distilled water __________ __________ ______________________________
Drying oven __________ __________ ______________________________
FC water bath incubator __________ __________ ______________________________
Coliform water bath incubator __________ __________ ______________________________
Hot air oven __________ __________ ______________________________
APPENDIX B. Data Collection Forms B-34
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
E. LABORATORY CAPABILITY (cont’d.)
2. Equipment & Instruments
Adequate
Comments
Yes No
Refrigerator __________ __________ ______________________________
Autoclave __________ __________ ______________________________
Analytical balance __________ __________ ______________________________
Microscope __________ __________ ______________________________
Desiccator __________ __________ ______________________________
Automatic samplers __________ __________ ______________________________
Spectrophotometer __________ __________ ______________________________
Conductivity meter __________ __________ ______________________________
Jar test apparatus __________ __________ ______________________________
Titration burets __________ __________ ______________________________
Erlenmeyer flasks __________ __________ ______________________________
Volumetric flasks __________ __________ ______________________________
Beakers __________ __________ ______________________________
Evaporating dishes __________ __________ ______________________________
Zeta meter __________ __________ ______________________________
Particle counter __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
APPENDIX B. Data Collection Forms B-35
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
E. LABORATORY CAPABILITY (cont’d.)
3. Analytical Capability
Adequate
Comments
Yes No
Calcium __________ __________ ______________________________
Magnesium __________ __________ ______________________________
Hardness __________ __________ ______________________________
Sodium __________ __________ ______________________________
Alkalinity __________ __________ ______________________________
Temperature __________ __________ ______________________________
pH __________ __________ ______________________________
Turbidity __________ __________ ______________________________
Iron __________ __________ ______________________________
Manganese __________ __________ ______________________________
Chlorine __________ __________ ______________________________
Sulphate __________ __________ ______________________________
Nitrate __________ __________ ______________________________
Total coliform __________ __________ ______________________________
Heterotrophic plate count __________ __________ ______________________________
Conductivity __________ __________ ______________________________
Total dissolved solids __________ __________ ______________________________
Trace inorganics __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
APPENDIX B. Data Collection Forms B-36
Optimization Guidance Manual for Drinking Water Systems 2014
FORM D – OPERATIONS DATA (cont’d.)
E. LABORATORY CAPABILITY (cont’d.)
3. Analytical Capability
Adequate
Comments
Yes No
Organics __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
________________________ __________ __________ ______________________________
4. Miscellaneous
Quality Control:
Reference Standards:
Duplicate Tests (schedule, records, etc.):
Standard Procedures/References:
Standard Methods:
Site Specific Procedures:
Training:
APPENDIX B. Data Collection Forms B-37
Optimization Guidance Manual for Drinking Water Systems 2014
FORM E – MAINTENANCE DATA
A. PREVENTIVE MAINTENANCE PROGRAM
Program Description:
Method of Scheduling:
Method of Documenting Work Completed:
Method of Factoring Costs for Parts/Equipment Into Budgeting Process:
Spare Parts Inventory:
References:
O & M Manual:
Accurate Record Drawings:
Manufacturer’s Literature:
Adequacy of Following Resources:
Outside Support:
Tools/Lubricants:
Work Areas:
APPENDIX B. Data Collection Forms B-38
Optimization Guidance Manual for Drinking Water Systems 2014
FORM E – MAINTENANCE DATA (cont’d.)
B. EMERGENCY MAINTENANCE PROGRAM
Priority Setting (relationship to process control decisions):
Extent of On-Site Capability:
Method of Initiating Work Activities
Critical Parts Procurement (policy restrictions, sources):
Comments:
C. GENERAL
Equipment or Processes Out of Service Due to Breakdowns (identify equipment or
process, description of problem, length of time out of service, what has been done,
what remains to be done, estimated time before repair, how it affects performance) :
During the CPE (list and explain):
During the Last 12 Months (list and explain):
APPENDIX B. Data Collection Forms B-39
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA
A. SOURCE OF DATA:
(e.g. plant records, MOE DWSP reports)
B. FLOW DATA
Month/Year Minutes
Flow Operating
Time
Inst. Peak
Operating
Flow Average Maximum
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
____________ ____________ ____________ ____________ ____________ ____________
Average: ____________ ____________ ____________ ____________ ____________
Peak: ____________ ____________
Instantaneous plant operating flow is the peak flow rate that the unit processes
experience on a sustained basis. For example, if a plant treats 5,000 m3 during its
daily 12 hour (0.5 day) operating period, then the instantaneous peak operation flow
would be 5,000 m3 ÷ 0.5 d = 10,000 m
3/d. Judgment of the evaluator is essential in
selecting the instantaneous peak operating flow because of variations in flow that can
occur by operating different pumps or changing unit processes that are in service.
APPENDIX B. Data Collection Forms B-40
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA (cont’d.)
C. DEMAND EVALUATION
Number of Service Connections ____________ Population Served _____________
Major Industrial Users (include name and volume used):
Per Capital Consumption:
Average:
Peak:
Typical per capita water consumption values are shown below (Fair, Geyer and
Okun, 1971):
Type of Consumption Lpcd (range) Lpcd (average)
Domestic/Residential 76 – 340 208
Commercial 38 – 492 76
Industrial 76 – 303 189
Public 19 – 76 38
Unaccounted for Water 19 – 114 57
227 – 946 568
D. UNACCOUNTED FOR WATER EVALUATION
Total production of plant ____________ m3
Total metered water in system ____________ m3
Difference ____________ m3
% Unaccounted = Difference/Total Production x 100 = ____________ %
Typical unaccounted for water is approximately 10%.
E. BACKWASH WATER EVALUATION
Total volume filtered water _________ m3 Total volume backwash water _____ m
3
Difference ____________ m3
% BW Water = Difference/Total volume filtered water x 100 = ____________ %
Typical amount of backwash water is 2% to 6% for conventional plants. Direct
filtration plants often exceed this depending on raw water quality.
APPENDIX B. Data Collection Forms B-41
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA (cont’d.)
F. RAW WATER QUALITY
Month/Year
Turbidity
Temperature pH Alkalinity
Min. Ave. Max.
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
Average ________ ________ ________ __________ ________ __________
APPENDIX B. Data Collection Forms B-42
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA (cont’d.)
G. REPORTED OPERATING DATA FOR PREVIOUS 12 MONTHS
Month/Year
Settled Water Turbidity Finished Water Turbidity
Min. Ave. Max. Min. Ave. Max.
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
___________ ________ ________ ________ __________ ________ __________
Average ________ ________ ________ __________ ________ __________
APPENDIX B. Data Collection Forms B-43
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA (cont’d.)
H. CHEMICAL CONSUMPTION
Type of Chemical _____________________________________________________
Unit Cost _____________________________________
Month/Year Chemical Use per Month
(L or kg/month) Comments
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
Total ________________________
Type of Chemical _____________________________________________________
Unit Cost _____________________________________
Month/Year Chemical Use per Month
(L or kg/month) Comments
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
___________________ ________________________ ________________________________
Total ________________________
APPENDIX B. Data Collection Forms B-44
Optimization Guidance Manual for Drinking Water Systems 2014
FORM F – PERFORMANCE DATA (cont’d.)
I. MOE DRINKING WATER SURVEILLANCE PROGRAM (DWSP)
If available, review previous three years of DWSP data to identify water quality
concerns, including the distribution system, that are not evident from the review of
in-plant monitoring data.
J. PERFORMANCE ASSESSMENT
Develop graphs to depict plant performance, such as:
1. Plant effluent turbidity versus time for week or months with maximum
recorded turbidities. Isolate shorter time frames on graph after reviewing
dates.
2. Filter effluent turbidity versus time to assess recovery time following
backwashing a filter or starting a dirty filter.
3. Probability plots to show percentage of time turbidity exceeds desired
objective.
4. Long term plots of raw water and finished water turbidities to assess process
control.
5. Long term plots of finished water turbidity to assess stability of operation.
K. PERFORMANCE VIOLATIONS WITHIN LAST 12 MONTHS:
APPENDIX B. Data Collection Forms B-45
Optimization Guidance Manual for Drinking Water Systems 2014
FORM G – INTERVIEW DATA
A. INTERVIEW CONCERNS
Interviews are used to obtain feedback in the four categories of administration,
design, operation and maintenance. The following items are presented to assist the
interviewers in obtaining this feedback.
1. Administration
Owner Responsibility:
Attitude toward staff? Regulatory agency? Consultants?
Self-sustaining facility attitude?
Policies?
Communications (formal/informal)?
Performance Goal
Is plant in compliance?
o If yes, what’s making it that way?
o If no, why not?
Is regulatory pressure felt for performance?
What are performance requirements?
Administrative Support
Budget
o Within range of other plants?
o Covers capital improvements?
o Unnecessary expenditures?
o Sufficient?
o Attitude toward rates?
Personnel
Within range of other plants?
Allows adequate time?
Motivation, pay, supervision, working conditions?
Productivity? Turnover? Training support?
Involvement
Visits to treatment plant?
Awareness of facility performance?
Request status reports (performance and cost-related)?
Familiarity with plant needs?
APPENDIX B. Data Collection Forms B-46
Optimization Guidance Manual for Drinking Water Systems 2014
FORM G – INTERVIEW DATA (cont’d.)
A. INTERVIEW CONCERNS (cont’d.)
2. Design
Raw water quality problems?
Equipment problems?
Status of warranties?
Return process streams?
Preliminary treatment?
Coagulation/flocculation?
Sedimentation?
Filtration?
Chemical feed?
Advanced treatment techniques?
Disinfection?
Sludge handling and disposal?
Flow measurement?
Flow splitting?
Alarms or alternate power?
3. Operation
Communication of decisions?
Key control parameters?
Involvement of staff?
Laboratory quality?
Administrative support?
Staffing?
Performance problems?
Unit process optimization?
External support?
Process control testing/adjustments?
O & M manual/references?
4. Maintenance
How are priorities set?
Attitude toward program?
Emergency versus preventative?
Reliability (spare parts or critical part procurement)?
Staffing?
Equipment accessibility?
APPENDIX B. Data Collection Forms B-47
Optimization Guidance Manual for Drinking Water Systems 2014
FORM G – INTERVIEW DATA (cont’d.)
B. PERSONNEL INTERVIEWS
Name: _______________________________________________________________
Title:
____________________________________________________________________
Certification: _________________________________________________________
Years at plant: ____________ Years of experience: _____________________
Area of Responsibility: _________________________________________________
Training: ____________________________________________________________
Concerns/Recommendations (Administration, Design, Operation & Maintenance):
APPENDIX B. Data Collection Forms B-48
Optimization Guidance Manual for Drinking Water Systems 2014
FORM H – EXIT MEETING
ATTENDANCE LIST
Municipality: ___________________________________________ Date: ____________________
Name Title/Dept. Telephone No.
1. ________________________ _________________________ _________________________
2. ________________________ _________________________ _________________________
3. ________________________ _________________________ _________________________
4. ________________________ _________________________ _________________________
5. ________________________ _________________________ _________________________
6. ________________________ _________________________ _________________________
7. ________________________ _________________________ _________________________
8. ________________________ _________________________ _________________________
9. ________________________ _________________________ _________________________
10. _______________________ _________________________ _________________________
11. _______________________ _________________________ _________________________
12. _______________________ _________________________ _________________________
13. _______________________ _________________________ _________________________
14. _______________________ _________________________ _________________________
15. _______________________ _________________________ _________________________
16. _______________________ _________________________ _________________________
17. _______________________ _________________________ _________________________
18. _______________________ _________________________ _________________________
19. _______________________ _________________________ _________________________
20. _______________________ _________________________ _________________________
Attach copy of Exit Meeting Handouts
APPENDIX C. Example CPE Report
APPENDIX C
EXAMPLE CPE REPORT
APPENDIX C. Example CPE Report C-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX C: EXAMPLE CPE REPORT
RESULTS OF THE COMPREHENSIVE PERFORMANCE EVALUATION OF THE
ABC WATER TREATMENT PLANT
MUNICIPALITY OF XYZ
XYZ, ONTARIO
NOVEMBER 2010
APPENDIX C. Example CPE Report C-2
Optimization Guidance Manual for Drinking Water Systems 2014
INTRODUCTION
Composite Correction Program
The Composite Correction Program (CCP) is an approach developed by the U.S.
Environmental Protection Agency (USEPA) to improve surface water treatment plant
performance and to achieve compliance with their Surface Water Treatment Rule (SWTR).
The approach consists of two components, the Comprehensive Performance Evaluation (CPE)
and the Comprehensive Technical Assistance (CTA). A CPE is a thorough evaluation of an
existing treatment plant, resulting in a comprehensive assessment of the unit process
capabilities and the impact of the operation, maintenance, and administrative practices on
performance of the plant. A CTA is used to improve performance identified during the CPE.
Therefore, the CCP approach can be utilized to evaluate the ability of a water filtration plant
to meet turbidity and disinfection requirements and then to facilitate the achievement of cost-
effective compliance.
In recent years the CCP has gained in prominence as a mechanism that can be used to assist in
optimizing the performance of existing surface water treatment plants to levels of
performance that exceed regulatory requirements.
The Municipality of XYZ and the Ontario Ministry of Environment (MOE) recognized that
optimizing performance of its surface water treatment plants was an important safeguard that
could be pursued to ensure the protection of the public health. As such, they developed a
partnership to pursue the development of CCP capability within the municipality and the
Province. As a first component of this partnership effort, selected personnel are being trained
to conduct CPEs at two surface water treatment plants within the municipality. The training
that is being provided for the municipality and the MOEE was arranged by the project
consultant. The training was led by Process Applications, Inc. who developed the CCP
approach for the U.S. EPA. It is envisioned that use of CCP components will be an integral
part of the effort to optimize the performance of the municipality's surface water treatment
plants.
The following report documents the findings of a CPE conducted at the ABC water treatment
facility from September 18 - 21, 2010. The CPE was the first of the two training CPEs to be
conducted.
General Facility Information
The ABC WTP comprises two conventional treatment trains, essentially two plants, with a
common raw water source and treated water reservoir. Plant 1 was constructed around 1926;
Plant 2 was added in 1958 for an additional 25% capacity. The coagulation/sedimentation
process train in Plant 1 was modified in 1980 to provide more flocculation capacity.
Treatment includes coagulant chemical feed (alum or acidified alum and seasonal powdered
activated carbon (PAC», flocculation, sedimentation and dual media filtration - there is one
multimedia filter - and chlorination (prechlorination when PAC is not used and post
chlorination when the PAC is added).
The total design capacity is 109 ML/day with Plant 1, providing approximately 82 ML/day of
treatment capacity and Plant 2 providing about 27 ML/day of treatment capacity.
APPENDIX C. Example CPE Report C-3
Optimization Guidance Manual for Drinking Water Systems 2014
Raw water is supplied from an old canal which is basically a backwater of the "new" canal.
The old canal can act as a major raw water settling basin as the water flows from the new
canal to the plant and then into an adjacent river.
Raw water quality is generally good with more variability in the winter months, when
turbidities average 4 NTU with periodic excursions to a maximum between IS and 20 NTU.
The summer months have more stable raw water quality with turbidities around 2-3 NTU.
A flow schematic of the plant is presented in Figure 1.
Figure 1 – Plant Flow Schematic
APPENDIX C. Example CPE Report C-4
Optimization Guidance Manual for Drinking Water Systems 2014
FACILITY DESIGN DETAILS
Key design data were collected during the three-day CPE and are presented in Table 1. The
plant was evaluated against the 102 ML/day Peak Instantaneous Operating Flow (PIOF) as
identified from the records for the last ten years. It is worth noting that the plant's PIOF over
the previous 12 months had been 86.5 ML/day and that the design flow is higher than the
PIOF at 109 ML/day.
Table 1 – Facility Design Details
Type of Flow Design Parameters
Design Flow 109 ML/d
PIOF 102 ML/d
Raw Water Intake Five (5) Pumps: 32.7 ML/d
26 ML/d
39 ML/d
14.4 ML/d
34 ML/d
For a total of 146.1 ML/d
Raw Water Flow Measurement Venturi meters to each plant
Flocculation Plant 1 Two identical trains for a total volume of 1200 m3
Flocculation Plant 2 388 m3
Sedimentation plant 1 Two identical trains for a total surface area of 625.54 m2
Sedimentation plant 2 Two “stacked” basins with an effective settling area of 446 m2
Filtration Plant 1 Six dual media filters with a total area of 343 m2
Filtration Plant 2 One dual media and one multi-media (with garnet sand) filters with a
total area of 96 m2
Backwash Two pumps each rated at 56.16 ML/d (650 L/s)
Reservoir Volume of 3241 m3; serpentine baffled basins
Treated Water Pumps Seven (7) Pumps: Two 19.6 ML/d
Two 5.42 ML/d
2.75 ML/d
34.66 ML/d
32.7 ML/d
For a total of 120.15 ML/d
Chemical Feed Pumps (duty and
standby)
Liquid alum
Liquid hydrofluosilicic acid
Liquid sodium hypochlorite
Powdered activated carbon slurry
PERFORMANCE ASSESSMENT
APPENDIX C. Example CPE Report C-5
Optimization Guidance Manual for Drinking Water Systems 2014
During the CPE the capability of the ABC was evaluated to assess whether the facility, under
existing conditions, could comply with the turbidity and disinfection requirements that are
used to define optimized performance. Optimized performance, for purposes of this CPE,
represents performance criteria that exceed the Ontario Drinking Water Standards, Objectives
and Guidelines. A preliminary definition of optimized performance was established by the
project Partners during a Protocol Development Workshop held in August 2010.
The optimized performance values were as follows:
1. Sedimentation:
< 2 NTU as average
< 5 NTUs as peaks
2. Filtration
< 0.1 NTU as average
< 0.2 NTUs as peaks
3. Disinfection
To be based on CT concept described in the Procedure for Disinfection of Drinking Water in
Ontario.
Based on this preliminary protocol, optimized performance would require that the facility take
a raw water source of variable quality and consistently produce a high quality, finished water.
Multiple treatment processes (flocculation, sedimentation, and filtration) are provided in
series to remove turbidity, cysts, and other microorganisms followed by disinfection to
inactivate any remaining microorganisms. Each of these processes represents a barrier to
prevent the passage of cysts and other microorganisms through the plant. By providing
multiple barriers, any microorganisms passing one process will be removed in the next,
minimizing the likelihood of microorganisms passing through the entire treatment system and
surviving in water supplied to the public. All treatment processes in the plant must be capable
of providing a barrier at all times because even temporary loss of a barrier could result in the
passage of microorganisms into the distribution system and represents a potential health risk
to the community.
A major component of the CPE process is an assessment of past and present performance of
the plant. This performance assessment is intended to identify if specific unit treatment
processes are providing multiple barrier protection through optimum performance. The
performance assessment is based on data from plant records and data collected during special
studies performed during the CPE.
The ABC operations staff measures the turbidity of the raw, settled, and finished waters
throughout each day and records this information on daily log sheets. The data then serves as
the basis of the monthly monitoring reports. During the CPE, raw water turbidity values from
the monthly reports for the most recent twelve months (e.g., September 1, 2009 through
August 31, 2010) were used to assess raw water quality. Performance out of the combination
APPENDIX C. Example CPE Report C-6
Optimization Guidance Manual for Drinking Water Systems 2014
sedimentation units and filtered water from the plant c1earwells were also evaluated based on
data from the daily log sheets. Individual filter performance is not routinely monitored. It is
noted that the evaluation of settled and finished water quality was based on the maximum
turbidity values measured each day. Maximum values were used to assess if these unit
processes were providing the consistent performance needed for optimized performance and
maximum public health protection.
The raw water turbidities for the most recent twelve months show that the average raw water
turbidity was less than 5 NTU, which indicates that the plant routinely receives a relatively
good quality raw water. However, variability in raw water quality was noted, which requires
process control adjustments to maintain consistent treatment.
The daily maximum settled turbidity for the sedimentation basins associated with each plant
are also varied widely for each of the units. Often the turbidity values were in excess of the
desired maximum of 2 NTU. The variability in settled water also seemed to trend with the
variability of the raw water indicating that process adjustments are not optimized.
The daily maximum finished water turbidity also shows variability. The level of performance
depicted meets the Provincial Drinking Water Objectives but does not meet the optimized
performance goal of 0.1 NTU or less on a consistent basis.
Since the end of March 2010, the raw water turbidity improved from that of the winter
months, averaging less than 4 NTU. This improved raw water quality was again reflected in
the treated water with values of filtered water averaging less than 0.2 NTU. From the end of
June 2010, the treated filtered water was consistently less than 0.05 NTU. This excellent
performance coincides with a number of recent changes to the plant operation. Firstly, a new
laboratory turbidimeter was purchased; secondly the coagulant used was changed from alum
to acidified alum (Clarion A7) and, as already discussed, the raw water quality improved
significantly. Therefore, it is difficult to attribute one specific reason for the consistent high
quality treated water nailed performance over the four months from June to September.
A study of the turbidity output of Filter #7 was carried out during the three week period
before the CPE. The filter effluent was passed through a continuous monitoring turbidimeter
(Hach 172OC) and the results recorded on a circular 7-day chart. The data on the recordings
indicated that a turbidity spike up to 0.35 NTU occurred immediately after each backwashing
of the filter.
The week before the CPE filtered water data indicated that following backwashing the filtered
water peaked to 0.15 NTU with a duration of perhaps 15 to 20 minutes before dropping below
0.1 NTU; often these peaks only reached 0.1 NTU. This represents excellent filtration
operation. During this period the raw water turbidity averaged 1.3 NTU.
Prior to June 2010, the plant performance suggests that there is opportunity for performance
optimization to achieve a more consistent, higher quality finished water (i.e. 0.1 NTU which
minimizes public health risk) at a potentially lower operating cost.
APPENDIX C. Example CPE Report C-7
Optimization Guidance Manual for Drinking Water Systems 2014
MAJOR UNIT PROCESS EVALUATION
The capacities of the major unit processes were determined based on recognized design
criteria. Disinfection capacity was determined based on the requirements of the Procedure for
Disinfection of Drinking Water in Ontario (MOE, 2006) with respect to Giardia cyst
inactivation. The capacity assessment applies the concentration*time (CT) concept for the
cyst inactivation. The standard required reduction for a reasonable quality raw water source is
3 logs (99.9% removal/inactivation) and it was judged that the conventional treatment at the
ABC WTP would receive a removal "credit" of 2.5 logs for Giardia. This results in the
requirement for the ABC WTP achieve a further 0.5 log reduction through inactivation.
Since the plant's treatment processes must provide an effective barrier at all times, a peak
instantaneous operating flow (PIOF) was also determined. The PIOF represents those
conditions where the treatment processes are the most vulnerable to the passage of cysts and
microorganisms.
If the treatment processes are adequately sized to operate at the PIOF and are within
performance goals, then the major unit processes are likely capable of providing the necessary
effective barriers at lower flow rates. A peak instantaneous operating flow rate of 102 ML/day
was used to assess the plant's physical facilities.
The design criteria on which the estimated unit process capacities were based were as follows:
1. Flocculation
estimated capacity based on 20 minute Hydraulic Detention Time (HDT)
2. Sedimentation
estimated capacity based on 58 m3/m
2/d Surface Overflow Rate (SOR)
3. Filtration
estimated capacity based on 290 m3/m
2/d Hydraulic Loading Rate (HLR)
4. Disinfection
3 log removal/inactivation required
plant 2.5 log removal credit
pH 8.0
Temp 0.5°C
Assumes 90% plug flow (0.9 X usable volume) and 1.85 m effective depth in
reservoir
1.5 mg/L free chlorine residual is max. allowed at clearwell outlet
APPENDIX C. Example CPE Report C-8
Optimization Guidance Manual for Drinking Water Systems 2014
Required CT = 54.5 mg/L min. (need at least 36.3 minutes detention at the
PIOF)
Unit process capability was assessed using a performance potential graph format where the
estimated treatment capacity of each major unit process was compared against the current
PIOF rate. The calculations that were conducted to complete the graph and major unit process
evaluation are shown below.
Flocculation
Plant 1 Flocculation Tanks Total Volume = 1200 m3
Rated by evaluator for HDT = 20 min (see Chapter 6)
Rated Capacity = 1200 m3 ÷ 20 min x (60 min/h x 24 h/d) = 86,400 m
3/d = 86.4 ML/d
Plant 2 Flocculation Tank Volume = 388 m3
Rated by evaluator for HDT = 20 min (see Chapter 6)
Rated Capacity = 388 m3 ÷ 20 min x (60 min/h x 24 h/d) = 27,936 m
3/d = 27.9 ML/d
Sedimentation
Plant 1 Settling area = 625.54 m2
Rated by evaluator at 59 m3/m
2/d or 2.45 m/h (see Chapter 7)
Rated Capacity = 59 m3/m
2/d x 625.54 m
2 = 39,907 m
3/d = 39.9 ML/d
Plant 2 Settling area = 446 m2
Rated by evaluator at 59 m3/m
2/d or 2.45 m/h (see Chapter 7)
Rated Capacity = 59 m3/m
2/d x 446 m
2 = 26,314 m
3/d = 26.3 ML/d
Filtration
Plant 1 Filtration area = 343 m2
Rated by evaluator at 290 m3/m
2/d or 12 m/h (see Chapter 8)
Rated Capacity = 290 m3/m
2/d x 343 m
2 = 99,470 m
3/d = 99.5 ML/d
Plant 2 Filtration area = 96 m2
Rated by evaluator at 290 m3/m
2/d or 12 m/h (see Chapter 8)
Rated Capacity = 290 m3/m
2/d x 96 m
2 = 27,840 m
3/d = 27.8 ML/d
APPENDIX C. Example CPE Report C-9
Optimization Guidance Manual for Drinking Water Systems 2014
Disinfection
Plants 1 & 2 Combined Calculate required detention time
Required HDT = 54.5 mg/L·min ÷ 1.5 mg/L = 36.3 min
Calculate effective volume of clearwell
Effective volume = 3,241 m3 x 0.9 = 2,917 m
3
Calculate rated capacity at required detention time
Rated capacity = 2,917 m3 ÷ 36.3 min x (60 min/h x 24 h/d)
= 115,716 m3/d = 116 ML/d
The performance potential graphs prepared for the two plants are shown in Figures 2 and 3.
The combined disinfection performance potential graph is shown in Figure 4. The unit
processes evaluated are shown on the left side of the graphs and the various flow rates against
which the processes were assessed are shown across the top.
Figure 2 – Plant 1 Performance Potential Graph
APPENDIX C. Example CPE Report C-10
Optimization Guidance Manual for Drinking Water Systems 2014
Figure 3 – Plant 2 Performance Potential Graph
Figure 4 – Combined Plant Disinfection Performance Potential Graph
Horizontal bars on the graph represent the estimated peak capability of each unit process that
would support achievement of desired process performance. These capabilities were estimated
based on the combination of the CPE team's experience with. other similar processes, industry
design guidelines, and regulatory standards. The shortest bar represents the unit process which
limits plant capability relative to achieving the desired plant performance.
APPENDIX C. Example CPE Report C-11
Optimization Guidance Manual for Drinking Water Systems 2014
The unit processes were assigned a rating indicated by the number at the end of the bar. Each
major unit process was then categorized as indicated below:
Type 1 – Are Adequate
A Type 1 unit process is adequately sized. Any necessary performance improvement is
most likely to be achieved through implementation of non-construction oriented
follow up technical assistance.
Type 2 – Are Marginal
Type 3 – Are Inadequate
From the performance potential graphs, it can be seen that Plant 1, which processes 75 % of
the raw water flow, has adequately sized Type 1 flocculation and filtration facilities with the
sedimentation unit process being about half the size theoretically needed. The 1980 plant
upgrade used some of the sedimentation tankage, assuming that the plant could operate in the
direct filtration mode – there is a by-pass directly from the flocculation to the filters. As a
result, the Plant 1 sedimentation process was not considered to be a major performance
limiting impact.
In Plant 2, which processes 25% of the raw water flow, all processes were categorized as
Type 1.
The common disinfection facility was also adequate and categorized as Type 1.
A special study was carried out to determine backwash efficiency and filter media depth. The
backwash rate supplied by the backwash pumps was sufficient to expand the bed by about
20% and adequately clean the bed. Filter media depth was as indicated in plant design
specifications.
PERFORMANCE LIMITING FACTORS
The areas of design, operation, maintenance, and administration were evaluated in order to
identify factors which limit performance. These evaluations were based on information
obtained from the plant tour, interviews, performance and design assessments, special studies,
and the judgment of the evaluation team. Each of the factors were classified as A, B, or C,
according to the following guidelines:
A – Major effect on a long-term, repetitive basis
B – Minimal effect on a routine basis or major effect on a periodic basis
C – Minor effect.
Of the five factors identified, three were "B" factors and two were "Cs". These ratings reflect
the relatively high level of performance of the plant. The "B" factors were prioritized in terms
of relative importance; "C" factors are merely listed. Of the four categories evaluated, there
was one "B" Factor each in the areas of administration, operations and design. Maintenance
factors were not felt to impact on the plant performance.
APPENDIX C. Example CPE Report C-12
Optimization Guidance Manual for Drinking Water Systems 2014
The factors identified were prioritized as to their relative impact on performance and are
summarized below:
1. Administrative Policies (B-1)
Issues in this category were noted in. several areas including:
The performance target or goal of 0.1 NTU is not clearly established for plant staff
nor clearly communicated to them by plant management. As a result, there is no
commitment from staff to ensure that this goal is consistently met.
There is no incentive to try to continue to improve the plant operation in terms of
producing the highest quality of finished water at the lowest cost.
There is no procedure to ensure that new operating staff have opportunity to
acquire sufficient skills from knowledgeable staff before being given operating
responsibility.
2. Operator Application of Concepts and Testing to Process Control - Operations (B-2)
This factor relates to the ability of operations staff to apply their water treatment
knowledge to interpret process test results and adjust process conditions to support
optimum performance. This factor was demonstrated in a number of ways:
Very high quality raw water has led to complacency on the part of plant staff in
terms of process control. There is little need to adjust conditions to produce a high
quality finished water. As a result, technical skills such as jar testing, to respond to
even small changes in raw water quality are not used. As such the capability to
respond to process changes may not be adequate.
Filtered water turbidimeters are not repaired or replaced so that the ability to
optimize or even to monitor performance of this key barrier does not exist.
The link between turbidity spikes from key unit processes, especially filtration,
and potential public health impact, does not appear to be clearly understood.
The plant staff could not discern whether low raw water turbidities, changes in
coagulant or different turbidity reading from a new turbidimeter led to improved
performance in June 2010.
3. Lack of Process Flexibility - Design (B-3)
There is no ability to independently control chemical feed rates to different filters, no
ability to apply a filter aid or to dose chlorine at different rates to the two plants. The
fact that there are two plants with different designs make control more difficult, but at
the same time more necessary. Operation of the two plants at the optimum is difficult
to establish.
APPENDIX C. Example CPE Report C-13
Optimization Guidance Manual for Drinking Water Systems 2014
The final two factors are both "C" factors, those having a minor effect. Both are design factors
which are not presented in any particular order.
The sedimentation capacity is limited in Plant 1 which results in floc carryover to
the filters under peak hydraulic loading;
There is a lack of sludge treatment processing to permit routine cleaning of the
sedimentation tanks which can lead to sludge accumulation and consequent solids
carryover to the filters.
In developing this list of factors limiting performance, 65 potential factors were reviewed and
their impact on the performance of the ABC Water Treatment Plant was assessed. These
factors are outlined in Optimization Guidance Manual for Drinking Water Systems (this
Manual). Five factors were identified, and numerous other factors were not felt to be
impacting plant performance. Most notably, the administration acted in a professional manner
and was genuinely committed to learning about methods to optimize existing plant
performance. This type of attitude represents a solid foundation for future plant optimization
activities.
SUMMARY
Comprehensive Technical Assistance (CTA) is a formal and comprehensive program that
systematically addresses the factors identified in a CPE as limiting the plant's performance.
Activities during a CTA normally focus on improving performance through the transfer of
process control capabilities to the plant operators. Administrative and minor design factors are
also resolved as they relate to their impact on plant performance. Typically, all changes
during a CTA are implemented by local personnel under the guidance of a facilitator external
to the plant staff. The facilitator can be a consultant or other qualified person.
Many of the factors identified by this CPE could be addressed by a CTA. For example, as the
municipal administration moves to address the first B factor identified – In the area of
administrative policies – it will be expected that the enthusiasm and tenacity to achieve the
higher operational standard will positively affect the second B factor, the operator application
of concepts and testing to process control.
The finished water at the ABC WTP meets Ontario drinking water objectives. The plant
performance since June of 1995 suggests that there is capability for performance optimization
to achieve more consistent, higher quality finished water (i.e. less than 0.1 NTU, which
minimizes public health risk) at a lower operating cost. This capability represents a viable and
worthwhile challenge for ABC WTP staff.
APPENDIX D. Example CPE Scheduling Letter and Letter to MOE
Regarding Project Approval
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX D
EXAMPLE CPE SCHEDULING LETTER AND LETTER TO MOE REGARDING
PROJECT APPROVAL
APPENDIX D. Example CPE Scheduling Letter and Letter to MOE
Regarding Project Approval D-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX D: EXAMPLE CPE SCHEDULING LETTER AND
LETTER TO MOE REGARDING PROJECT APPROVAL
EXAMPLE CPE SCHEDULING LETTER
(From CPE Team)
Date
Address of Municipality
Re: Evaluation of the XYZ Drinking Water Treatment Plant on Month/Day/Year
Dear Official:
This letter is intended to provide you with some information on the evaluation and
describe the activities in which you will be involved. We expect that this evaluation
will enable your water plant to attain significantly improved performance.
The evaluation procedure that will be used is the first phase of the Composite
Correction Program (CCP) approach. The CCP approach has been successfully used
in Ontario and the United States to bring existing plants into compliance with their
regulations. In this first phase, which is known as the Comprehensive Performance
Evaluation (CPE), all aspects of the design, operation, maintenance, and
administration of the plant will be reviewed and evaluated with respect to their
impact on performance.
The CPE will begin with a brief kickoff meeting on _______________ at
approximately 8:00 a.m. or 4:00 p.m. The purpose of the kickoff meeting is to explain
to the operations staff and plant administration the methods used in conducting the
evaluation and the types of activities which will occur during the three days. Any
questions and concerns regarding the CPE can also be raised at this time. It is
important that the plant administrators and those persons responsible for plant
budgeting and planning be present because the CPE will focus a significant effort in
reviewing these aspects of the plant. Following the kickoff meeting, which should last
approximately 30 minutes, the plant staff will be requested to take the CPE team on
an extensive plant tour. After the plant tour, the team will begin collecting
performance and design data. Please make arrangements so that the operating records
and any design information for the plant are available. These activities will be
continued through the second day.
As far as the types of information and records that will be reviewed during the CPE,
we will first need to review your monitoring reports for the last 12 months. Any
laboratory and plant log sheets covering this same period will be useful as well as any
drawings and specifications for the treatment plant. We will also need budget and
financial information. This will centre around the budget for the treatment plant and
information on salaries, operating funds available, etc. It is our experience that the
information we need is usually readily available from existing reports. We usually
APPENDIX D. Example CPE Scheduling Letter and Letter to MOE
Regarding Project Approval D-2
Optimization Guidance Manual for Drinking Water Systems 2014
work with the information available and do not request the administration staff
prepare additional summaries of the information.
On the third day the CPE team will be involved in several different activities. The
major involvement of the plant staff will be in individual interviews. The plant
administrators will also be interviewed and the financial records of the plant
reviewed. Several special studies may also be completed by the CPE team to
investigate the performance capabilities of the plant's different unit treatment
processes. We request that each member of the operations staff be available some
time during the day for the interviews. We would also appreciate having an operator
available to answer questions about the plant and to operate the plant during the
special studies. We will be flexible in working these interviews and special studies
around the other required duties of you and your staff.
The last day of the CPE will consist of an exit meeting. During the exit meeting the
results of the evaluation will be discussed with all of those who participated. The
performance capabilities of the treatment processes will be presented and any factors
found to limit the performance of the plant discussed. The CPE team will also answer
any questions regarding the results of the evaluation. The results presented in the exit
meeting will form the basis of the final report, which will be provided in about six
weeks. We expect to begin the exit meeting at 8:00 a.m. on and it should last
approximately one hour.
Yours Very Truly,
APPENDIX D. Example CPE Scheduling Letter and Letter to MOE
Regarding Project Approval D-3
Optimization Guidance Manual for Drinking Water Systems 2014
EXAMPLE LETTER TO MOE REGARDING PROJECT APPROVAL
(From CPE Team or Municipality/Utility. Please note that this letter is written as if a
CPE has already been completed and a CTA is planned. If contact is made with MOE
before the CPE begins, the letter must be changed to reflect the timing.)
Date
Addresses of MOE District Office and MOE Approvals Branch
Re: Certificate of Approval Requirements for Technical
Assistance Program at the XYZ Water Treatment Plant
Dear District Manager/Water and Wastewater Manager:
This letter is intended to provide you with general information on the evaluation that
was done at the XYZ plant on and the follow-up technical assistance that is planned.
The evaluation procedure that was used at the XYZ plant was the Comprehensive
Performance Evaluation (CPE) approach, which has been successfully used
elsewhere to bring existing plants into compliance. During this evaluation, all aspects
of the design, operation, maintenance, and administration of the XYZ plant were
reviewed and evaluated with respect to their impact on performance.
The next phase of our work will involve on-site technical assistance to address the
maintenance, administrative, operations, and design-related factors that are adversely
affecting finished drinking water quality. This work will likely require us to make
some equipment and/or operational changes, and the on-site assistance should last for
six months. We anticipate the following changes will be made:
(List here in bullet format)
Please respond soon and let us know which changes will require an amended
Certificate of Approval and what we are responsible for. I can be reached at (xxx)
yyy-zzzz if you require more information.
Yours Very Truly,
APPENDIX E. Example Special Study
Optimization Guidance Manual of Drinking Water Systems 2014
APPENDIX E
EXAMPLE SPECIAL STUDY
APPENDIX E. Example Special Study E-1
Optimization Guidance Manual of Drinking Water Systems 2014
APPENDIX E: EXAMPLE SPECIAL STUDY
TITLE: Reduce Plant Flow
HYPOTHESIS: A reduction in peak instantaneous operating flow will decrease
finished water turbidity.
APPROACH:
1. Reduce peak instantaneous operating flow to plant to 3,000 L/min by
adjusting valve at raw water pump.
2. Relocate pressure gauge to location upstream of throttling valve.
3. Reduce chemical feed rate in proportion to flow.
4. Measurements: (One week prior to change/one week after change.)
a. Raw water turbidity every four hours during operation.
b. Settled water turbidity every four hours during operation.
c. Effluent turbidity from each filter every four hours during operation.
d. Continuous measurement of finished turbidity with existing
turbidimeter.
e. Influent water temperature on daily basis.
DURATION: One week under current conditions and one week under
changed conditions. If raw water quality changes dramatically,
repeat.
EXPECTED RESULTS:
1. Reduction in settled water turbidity and in variations.
2. Reduction in filter water turbidity and in variations.
3. Reduction in finished water turbidity to <0.1 NTU on continuous basis.
4. Increase in filter run time.
CONCLUSIONS: To be completed after study.
IMPLEMENTATION: To be completed after study.
APPENDIX F. Example CTA Summary Report
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX F
EXAMPLE CTA SUMMARY REPORT
APPENDIX F. Example CTA Summary Report F-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX F: EXAMPLE CTA SUMMARY REPORT
SUMMARY REPORT
WATER TREATMENT PLANT X
COMPREHENSIVE TECHNICAL ASSISTANCE
(Note: this report was written for a CTA conducted at a U.S water plant in the early
1990s, hence the reference to the Surface Water Treatment Rule)
APPENDIX F. Example CTA Summary Report F-2
Optimization Guidance Manual for Drinking Water Systems 2014
INTRODUCTION
The CCP approach is a proven procedure for improving performance of water
treatment plants. This approach consists of two components, the CPE phase and the
CTA phase. A CPE is a thorough review and analysis of a plant's design capabilities
and associated administrative, operation, and maintenance practices. It is conducted to
identify factors that may be adversely impacting a plant's capability to achieve optimal
performance. Its major objective is to determine if significant improvements in
performance can be achieved without major capital improvements. A CTA is a
performance improvement phase that may be implemented if results from the CPE
indicate that improved performance can be achieved. During the CTA phase, factors
identified by the CPE are systematically eliminated. The major benefit of a CTA is
that it optimizes the capability of existing facilities without the expense of major
capital improvements.
A CPE was conducted at plant X on August 21-24. It revealed that the plant had some
performance problems and that the top ranked factors identified were process control
related. It was felt that operator training, conducted as a portion of a CTA, would
improve plant performance. This report summarizes the results of the CTA, which was
initiated in the following April.
CPE RESULTS
A CPE was conducted August 21-24 at water treatment plant X. The plant is a direct
filtration facility constructed in 1978. Treatment includes coagulant chemical feed
(alum and cationic polymer), flocculation in a reaction basin, non ionic polymer filter
aid feed, filtration through four dual media filters, post chlorination, and gravity flow
from the plant to storage and distribution. Raw water is supplied from a multiple use
lake located several miles northwest of the plant. Raw water quality is generally good
in winter months, with turbidities in the 5 to 10 NTU range; but prevailing westerly
winds often stir up sediments in the relatively shallow lake in other seasons, resulting
in peak raw water turbidities as high as 50 to 280 NTU.
A review of operating data for the previous year revealed that the plant was generally
producing water of less than 1.0 NTU, but would not meet the Surface Water
Treatment Rule (SWTR) (USPEA, 1989) requirements of 0.5 NTU 95 percent of the
time. Further performance evaluation included a special study to determine the
turbidities before and after backwashing. Results indicated that filter effluent
turbidities increased to 3.2 NTU and did not drop below 1.0 NTU for over two hours.
Optimum performance would be a 0.2 NTU increase for less than 10 minutes and a
return to operating turbidities of less than 0.1 NTU.
A performance potential graph projected that the design-rated 11,400 m3/d facility
would have to be de-rated to 5,700 m3/d because of a severe air binding problem
identified with the filters. This problem was exacerbated by the design of the filter
effluent header, which allowed the formation of negative pressure in the filter
underdrains. A short detention time in the reactor/flocculation basin also resulted in a
projected capacity less than design for this unit process. A longer time was felt to be
necessary because of the longer reaction time needed with cold water during winter
operation.
APPENDIX F. Example CTA Summary Report F-3
Optimization Guidance Manual for Drinking Water Systems 2014
The plant's performance limiting factors were assessed and prioritized in order of
significance as follows:
1. Operator Application of Concepts and Testing to Process Control – Operation
The plant had no formal process control program to provide information from
which operational decisions could be made. Although the operators had a good
understanding of water treatment, they were not applying their knowledge to
operation of the plant. Because of the highly variable raw water quality it was
essential that the plant be monitored continuously and coagulant dosages
changed to maintain a consistent high quality finished water.
2. Process Control Testing – Operation
The lack of process control testing resulted in insufficient data being collected
to properly assess plant performance (e.g. jar testing was not being conducted
to optimize the coagulation process).
3. Filtration – Design
Turbidity measurements taken at the time of the evaluation demonstrated that
the filters were not performing optimally. The presence of filter media in the
clearwell was an indication that the filters may have been damaged by
backwashing or the release of air from the severely air-bound filters. More
involved evaluations were felt to be necessary to determine if the support
gravels were damaged. Filter capacity was also being affected by air binding
and periodic high raw water turbidities, necessitating frequent backwashing.
4. Raw Water Turbidity – Design
The turbidity of the raw water often exceeded that normally recommended for
the direct filtration process. During periods of high turbidity it was projected
that it would be necessary to reduce plant flow rates to produce an acceptable
water.
5. Plant Coverage – Administration
The plant was not attended on weekends and the operators were often
conducting other duties away from the plant during weekdays. It was assessed
that this practice would result in undetected periods of poor finished water
quality.
6. Lack of Standby Units – Design
There were no standby alum and polymer feed pumps. Failure of one of the
units would result in poor plant performance.
7. Reactor/Flocculation Basin – Design
The reactor basin was too small to provide adequate time for flocculation
during cold water conditions in winter months. It was projected that the plant
APPENDIX F. Example CTA Summary Report F-4
Optimization Guidance Manual for Drinking Water Systems 2014
flow rate would have to be reduced during winter to ensure adequate
flocculation.
8. Plant Inoperability Due to Weather – Design
Drought severely impacted the availability of water from the lake in 1985. An
engineering study had been completed to assess relocation of the intake to a
deeper part of the lake.
The CPE report recommended that a follow-up CTA be conducted because the top
ranked factors identified were process control related and it was felt that operator
training would improve plant performance. Also, since the historical peak day demand
was only about 5,700 m3, it was concluded that the plant could be operated at a lower
flowrate for a longer period to address the design-related limitations of the filters and
reactor/flocculation basin.
CTA SIGNIFICANT EVENTS
The CTA was initiated in the following April. Major activities are briefly summarized
below.
Consultant Initial Site Visit (April 3-6)
Implemented a process control sampling and testing schedule and developed a
daily data sheet to record results.
Implemented policies/procedures approach.
o Developed procedures for calibrating chemical feeders and calculating
chemical dosages so that chemicals could be accurately applied.
o Developed procedures for calibrating effluent turbidimeter.
o Developed procedure for process control testing and sampling.
Initiated a special study to determine the effect of operating the plant at a
reduced flow rate and operating the filters without a negative pressure. At the
conclusion of the visit, the plant was operated at 4,000 L/min (~5,700 m3/d)
rather than at 7,900 L/min (~11,400 m3/d) and a plug was removed from the
filter effluent header to allow the negative pressure to be released from the
filter.
Identified special studies to be conducted in the future including: analysis of
dissolved oxygen and temperature in raw water including transmission line to
determine causes of filter air binding, evaluation of effect of rapid mix on
coagulant feed, an analysis of effect of alum and polymer feed points.
Developed action/implementation plan and made assignments to the operating
staff and administrators with due dates to ensure activity continued until next
site visit.
APPENDIX F. Example CTA Summary Report F-5
Optimization Guidance Manual for Drinking Water Systems 2014
Chemical feed rates were not changed during the visit because it was desirable
to have the plant staff operate the plant following feeder calibration to evaluate
plant performance with the newly calculated dosages.
Evaluation Period (April – July)
Continued process control testing on plant as presented in sampling and testing
schedule procedure.
Operated plant at reduced flow rate (4,000 L/min) and without negative
pressure on filter effluent header.
Initiated weekly transmission of data to consultant and initiated weekly phone
calls between plant staff and consultant.
Consultant developed computer spreadsheet to analyze plant data.
Installed accurate pressure gauges on lake intake pumps to relate pump
discharge pressure to pump output.
Sent finished water turbidimeter to factory service centre for repair.
Plant staff modified daily data sheet based on operating experience.
Purchased dissolved oxygen meter for special study on filter air binding.
Welded sample taps and chemical feed taps on plant influent line before and
after orifice plate in preparation for chemical feed special study. The plant staff
hired a local welder to make the welds.
Consultant Site Visit (June 26-27)
Conducted jar tests using filter paper and established new chemical feed rates
for alum and cationic polymer. Plant performance improved dramatically prior
to the end of the site visit.
Developed a procedure for jar testing using filter paper to correlate results with
plant performance. Explained the conduct and interpretation of the jar
testing/filter paper procedure to the operating staff.
Expanded process control program to include jar testing/filter paper testing to
establish chemical feed rates.
Reviewed chemical feed calculations with plant staff.
Investigated filter backwash and determined that additional wash time would
be required to adequately clean the filters.
APPENDIX F. Example CTA Summary Report F-6
Optimization Guidance Manual for Drinking Water Systems 2014
Updated the special study on relocation of alum and cationic polymer feed
points.
Updated the action-implementation plan.
Evaluation Period (July – October)
Implemented full plant process control program including evaluating raw water
quality and determining the correct coagulant and filter aid feed rates. Jar tests
were used to determine required chemical doses when raw water quality
changed.
Continued weekly transmission of data to consultant and weekly phone calls
between plant staff and consultant.
Consultant developed monthly data sheet to analyze plant data.
Relocated the feed points for alum and cationic polymer addition to take
advantage of a hydraulic flash mix at the orifice plate located in the influent
piping. Completed special study on relocation of the chemical feed points.
Convinced administrators to allow time for the operating staff to remain at the
plant to conduct process control testing and to make plant adjustments.
Purchased additional laboratory supplies for conducting jar tests.
Extended filter backwash time to allow more complete cleaning of filters.
Staff investigated cost of monitoring raw water quality with a turbidimeter and
alarm at raw water pumping station, an alarm on the existing turbidimeter at
the plant, and a streaming current monitor with automatic control of coagulant
feeders.
Consultant Site Visit (October 17 - 19)
Reviewed process control program.
Conducted jar tests to evaluate alum replacement products.
Reviewed chemical feed calculations.
Completed CTA assistance.
CTA RESULTS
Significant improvement in plant performance was achieved during the conduct of the
CT A. This is depicted graphically in Figure 1. It is noted that while plant operation
improved after reducing the plant flow rate and eliminating the negative pressure on
APPENDIX F. Example CTA Summary Report F-7
Optimization Guidance Manual for Drinking Water Systems 2014
the filters in April, performance remained erratic until process control, including
chemical adjustments, was implemented in July. After July, plant finished water
turbidities remained very consistent at about 0.1 to 0.2 NTU through the duration of
the project. This consistent performance was achieved even though raw water
turbidities, shown in Figure 2, varied widely. Plant finished water quality remained
below 0.3 NTU even when the raw water turbidities reached 70 NTU because the
operating staff consistently monitored varying raw water quality and responded by
changing chemical feed rates. The plant performance is especially impressive since
influent turbidities frequently exceeded values thought to be treatable with direct
filtration (e.g. > 50 NTU). Another indication of improved performance was that filter
effluent turbidity following a backwash did not exceed 0.3 NTU and returned to 0.15
NTU within minutes after the wash.
The improved performance was achieved primarily through improved process control
activities and lowering plant loadings that were more in line with unit process
capability. The primary process control tool utilized was the jar test, which proved to
be valuable in allowing the operators to predict chemical doses required when raw
water quality varied. The jar test was used in conjunction with filter paper to correlate
results with the direct filter plant conditions. The test provided a very accurate
indication of required chemical dose.
Figure 1 – Finished Water Turbidity for Plant X
APPENDIX F. Example CTA Summary Report F-8
Optimization Guidance Manual for Drinking Water Systems 2014
Figure 2 – Raw Water Turbidity for Plant X
The plant staff became very adept at evaluating raw water quality and adjusting
chemical feed rates to produce a high quality finished water on a continuous basis. The
staff exhibited a great deal of expertise and professionalism during the CTA, and
quickly learned chemical feed calculations and implemented the necessary process
control activities.
The process control activities took additional operator time at the plant. Prior to the
CTA, operators would check the plant daily; however, during the CTA, operators were
at the plant a minimum of four hours each day. If plant raw water quality was
changing rapidly operators would be at the plant making adjustments whenever the
plant was operating. Administrators had to be convinced that the additional time was
necessary to achieve and maintain improved plant performance.
Only minor physical plant modifications were required to improve plant performance.
The modifications included removing a threaded plug from the filter effluent header to
relieve negative pressure on the filters, and adding additional alum and cationic feed
points prior to an orifice which was used as a flash mix. All minor modifications were
made by the plant staff.
The administrators were favourably impressed by the level of performance achieved
by the plant. Major plant (e.g. construction of a sedimentation basin) and raw water
intake modifications were being planned prior to the successful implementation of the
CTA. These major modifications were placed on hold based on the ability of the plant
to perform within the SWTR requirements. The intake modifications may eventually
be made because they will potentially reduce the turbidity load (e.g. draw water from
deeper points in the lake) to the direct filtration plant allowing it to operate at higher
hydraulic loading rates.
APPENDIX F. Example CTA Summary Report F-9
Optimization Guidance Manual for Drinking Water Systems 2014
CONCLUSIONS
Implementation of a CTA at water treatment Plant X was highly successful. The CTA
proved that the plant could achieve compliance with SWTR turbidity requirements
without major capital improvements. City administrators had planned on spending an
estimated one million· dollars on construction of sedimentation basin facilities and
related improvements. After the CTA they decided to delay any construction until
water demands required the plant to be operated at higher rates. The plant staff
developed increased confidence that excellent quality water could be produced despite
high raw water turbidities, and they developed a level of pride that did not allow them
to accept marginal finished water quality. In addition, the jar test/filter paper
procedure proved to be a valuable process control tool that allowed accurate selection
of coagulant doses. The City will have to continue the commitment to water treatment
in order to sustain the level of performance obtained during the CTA. Continued
production of high quality water will require a commitment to allowing adequate
operator time at the plant to make necessary chemical feed adjustments. If operators
are not at the plant whenever it is operating, a turbidimeter with alarm should be
installed at the raw water pumps to give the operators continuous notice of raw water
changes. The use of a streaming current monitor that would automatically adjust the
alum feed rate if raw water quality changes could be investigated.
APPENDIX G. Equations and Calculations
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX G
EQUATIONS AND CALCULATIONS
APPENDIX G. Equations and Calculations G-1
Optimization Guidance Manual for Drinking Water Systems 2014
APPENDIX G: EQUATIONS AND CALCULATIONS
A. COAGULATION AND FLOCCULATION CALCULATIONS
Velocity Gradient, G
21
V
PG
Where:
P = power input to the fluid (J/s)
V = volume of the flocculator (m3)
µ = dynamic viscosity of the water (N·s/m2)
Dynamic Viscosity of Water versus Temperature
Temperature (°C) Dynamic Viscosity (kg/m*s)
0 1.794 x 10-3
5 1.519 x 10-3
10 1.308 x 10-3
15 1.140 x 10-3
20 1.005 x 10-3
25 8.940 x 10-4
30 8.010 x 10-4
Jar Testing – Sampling Time
)(
000,1min
440,1)(dim1.0
(min)3
2
dLrateflowplant
m
L
dmareasurfaceentationsem
timeSampling
APPENDIX G. Equations and Calculations G-2
Optimization Guidance Manual for Drinking Water Systems 2014
B. DISINFECTION CALCULATIONS
Required Detention Time, T
)/(Retansin
)min/((min)
LmgsidualtfecDi
LmgCTT
req
req
Where:
Treq = Required detention time in post-disinfection unit process
CTreq = CT requirements from tables in Disinfection Procedure for post-
disinfection conditions
Disinfectant Residual = Selected operating residual maintained at the discharge
point from the disinfection unit process
Flow Rate, Q (Post-Disinfection)
(min)
)(min)/(
3
3
req
post
T
mVmQ
Where:
Q = Flow rate where required CT can be met
Vpost = Effective volume for post-disinfection unit processes
Treq = Required detention time in post-disinfection unit process, as determined
using equation shown in Section 9.6.1
Flow Rate, Q (Pre- and Post-Disinfection)
(min)
)(
(min)
)(min)/(
33
3
postreq
post
prereq
pre
T
mV
T
mVmQ
Q = Flow rate where required CT can be met
Vpre = Total effective volume for pre-disinfection unit processes
Vpost = Total effective volume for post-disinfection unit processes
Treq = Required detention time in pre- or post-disinfection unit process, as
determined using equation shown in Section 9.6.1