Chlorine Disinfection Validation Protocol · 2018-06-22 · tables referenced in this protocol are...

Chlorine disinfection

Validation protocol

About Australian WaterSecure Innovations Ltd

Australian WaterSecure Innovations Ltd (trading as WaterSecure) was established in 2016 to oversee the implementation of national research outcomes, including the WaterVal™ program, one of the flagship outcomes developed by the Australian Water Recycling Centre of Excellence (the Centre), an independent research organisation established in 2009 by Commonwealth funding.

About WaterVal™

WaterVal™ is a framework that provides national consistency in the validation of water treatment technologies for the water industry. The framework, jointly developed by the Centre, regulators, water utilities, researchers and the private sector, is underpinned by protocols and agreed methods to validate pathogen removal by treatment technologies. The framework and protocols are applicable to a broad range of water sources, and give effect to key objectives of the Australian guidelines for water recycling and the Australian drinking water guidelines.

Acknowledgements

WaterSecure is grateful for the contributions made by the WaterVal™ Protocol Development Group (in particular John Mieog, David Cunliffe Andrew Lanchbery and Luc Richard), Viridis Consultants Pty Ltd (Karen Pither), Karl Linden and Cedric Robillot, and input received from external reviewers.

WaterSecure acknowledges the contribution of the Smart Water Fund of Victoria and their funding of the study by Keegan et al. (2012) Chlor(am)ine disinfection of human pathogenic viruses in recycled waters whose data underpins this validation protocol.

Citation

WaterSecure 2017, Chlorine disinfection, WaterVal validation protocol, Australian WaterSecure Innovations Ltd, Brisbane.

Date of publication

February 2017

Publisher

Australian WaterSecure Innovations Ltd Level 16, 333 Ann Street, Brisbane, Queensland 4000 www.watersecure.com.au

© Australian WaterSecure Innovations Ltd

This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of it may be reproduced for any purpose without written permission from the publisher. Requests and inquiries concerning reproduction rights should be directed to the publisher.

Disclaimer

While every effort has been made to ensure the accuracy of the information contained in this document, Australian WaterSecure Innovations Ltd cannot guarantee that it is entirely accurate and error-free.

This document is intended to be used in conjunction with the WaterVal™ framework. Australian WaterSecure Innovations Ltd does not accept any legal liability or responsibility whatsoever for any injury, loss or damage, due to or arising out of any use of this document independent of that framework.

It is the responsibility of the user to determine the suitability and appropriateness of the information and its specific application.

201702_WaterVal_Validation Protocol_Chlorine Disinfection 1

Contents

1. Background and scope ............................................................................................................................... 2

2. Identification of pathogen removal mechanisms ....................................................................................... 3

3. Identification of target pathogens.............................................................................................................. 4

4. Influencing factors ...................................................................................................................................... 5 4.1. Dose–response relationship ........................................................................................................... 5 4.2. Chlorine exposure .......................................................................................................................... 5

4.2.1. Exposure concentration..................................................................................................... 5 4.2.2. Exposure time .................................................................................................................... 5

4.3. pH ................................................................................................................................................... 6 4.4. Water temperature ........................................................................................................................ 6 4.5. Turbidity (suspended solids and particles in water) ....................................................................... 6 4.6. Disinfection demand ...................................................................................................................... 6

5. Operational monitoring parameters .......................................................................................................... 7

6. Validation method ...................................................................................................................................... 8 6.1. CT calculation ................................................................................................................................. 8

6.1.1. Residual concentration ...................................................................................................... 8 6.1.2. Contact time ...................................................................................................................... 8 6.1.3. Disinfection segments ....................................................................................................... 9

6.2. Other methods for validation ......................................................................................................... 9

7. Data collection and analysis ..................................................................................................................... 10

8. Operational monitoring ............................................................................................................................ 11 8.1. Determination of critical limits ..................................................................................................... 11

9. Method to determine the LRV for each pathogen group ......................................................................... 12

10. Triggers for revalidation ........................................................................................................................... 13

Glossary and abbreviations ............................................................................................................................... 14

References ........................................................................................................................................................ 15

Tables

Table 1 CT values for 1- to 4-log removal values of viruses at a range of turbidity, pH and temperature ............... 12


1. Background and scope

Chlorine disinfection is used widely to limit waterborne disease by inactivating pathogenic organisms in water supplies and wastewater, and is often seen as the final barrier in a multiple-barrier system. Chlorine disinfection is a cost-effective and well-established technology for wastewater treatment. It is also considered reliable because control of the process is relatively straightforward.

This protocol provides guidance for validating chlorine disinfection. The method presented is based on demonstrating that appropriate CT values are achieved for the log reduction value (LRV) claimed. The protocol is underpinned by the United States Environmental Protection Agency (US EPA) guidance outlined in the Disinfection profiling and benchmarking guidance manual (US EPA 1999a), but prescribes specific CT values (distinct from US EPA CT values) based on recent studies conducted using the pathogen target coxsackievirus B5.

The inactivation of viruses is the main focus of this protocol, because viruses are more resistant to chlorine than bacteria. Chlorine is considered to be ineffective for the inactivation of Cryptosporidium at the operating conditions normally expected for water treatment, and LRVs for protozoa cannot be claimed under this protocol.

This document is consistent with the WaterVal validation Protocol template (AWRCE 2015), which provides a recommended approach to validation that is based on nine elements:

identification of the mechanisms of pathogen removal by the treatment process unit

identification of target pathogens and/or surrogates that are the subject of the validation study

identification of factors that affect the efficacy of the treatment process unit in reducing the target pathogen

identification of operational monitoring parameters that can be measured continually and are related to the reduction of the target pathogen

identification of the validation method to demonstrate the capability of the treatment process unit

description of a method to collect and analyse data to formulate evidence-based conclusions

description of a method to determine the critical limits, as well as an operational monitoring and control strategy

description of a method to determine the LRV for each pathogen group in each specific treatment process unit performing within defined critical limits

provision of a means for revalidation or additional onsite validation where proposed modifications are inconsistent with the previous validation test conditions.

Formation of disinfection by-products and other health impacts have not been considered as part of this protocol; they should be considered case by case, depending on the proposed use of the water.


2. Identification of pathogen removal mechanisms

Chlorine inactivates pathogens through oxidation reactions that attack and lyse cell walls, and damage genetic material, so that the organism cannot reproduce and is no longer capable of causing illness. A chlorine residual is obtained by adding chlorine gas or hypochlorite to water. The hypochlorite ion (OCl–), hypochlorous acid (HOCl) and chlorine gas (Cl2) species are known as free available chlorine or free chlorine residual. The ratio of HOCl to OCl– is a function of pH. HOCl is a stronger oxidant and more effective in inactivating viruses than OCl– (Engelbrecht et al. 1980).

Enteric viruses are generally more resistant to free chlorine than enteric bacteria. Although how chlorine inactivates viruses is not well understood, studies into virus resistance to chlorine have determined that reoviruses are the least resistant to chlorine treatment (Engelbrecht et al. 1980, Liu et al. 1971). Adenoviruses and echoviruses are relatively more resistant, whereas polioviruses and coxsackieviruses have been found to be the most resistant (Engelbrecht et al. 1980, Liu et al. 1971).


3. Identification of target pathogens

The target pathogen is the pathogen that is the subject of a validation study and is the most resistant to the treatment process. Generally, a target pathogen should be selected from each pathogen group.

Black et al. (2009), Keegan et al. (2012) and more recently Canning et al. (2015) undertook investigations to determine the most suitable virus target pathogen for calculating the LRVs achieved by chlorine disinfection. For free chlorine, the literature indicated that coxsackievirus B5 was the most resistant virus between pH 6 and pH 10, and is considered to be the most suitable target pathogen for validating log reductions. The CT tables referenced in this protocol are based on validation studies using coxsackievirus B5 as the target pathogen for chlorine disinfection.

Because bacteria are more sensitive to chlorination, the log inactivation for viruses will also apply to bacteria, and a separate target pathogen for bacteria is not required. Where validation of bacterial inactivation alone is proposed, Escherichia coli is considered to be the most suitable target pathogen for validating log inactivation by chlorine disinfection (Victorian Department of Health 2013).


4. Influencing factors

The principal factors that influence disinfection efficiency are residual chlorine concentration, contact time, temperature and pH. Turbidity can also indirectly influence the effectiveness of chlorine disinfection. In general, the highest levels of pathogen inactivation are achieved with high chlorine residuals; long contact times; high water temperature, with good mixing; low pH; low turbidity; and the absence of interfering substances.

4.1. Dose–response relationship

Inactivation of organisms is described using a linear Chick–Watson model for the specific disinfection regime, assuming a constant chemical residual (Li et al. 2001)

𝐿𝑜𝑔10 (𝑁𝑂

𝑁𝐼) = −𝑘𝐶𝑡 (equation 1)

where: NO is the initial number of organisms NI is the number of organisms that remain viable after treatment k is the pathogen inactivation rate constant (or lethality constant) C is the average concentration of chlorine, or residual, in the water t is the exposure time The pathogen inactivation rate constant (k) incorporates coefficients that account for the organism, the form of chlorine, the extent of inactivation, and the dependence of disinfection on physicochemical attributes of water, such as pH and temperature.

4.2. Chlorine exposure

As described in equation 1, the germicidal efficacy of chlorine is correlated with the product of the chlorine dose applied or residual (mg/L) and the contact time (min), also referred to as CT. Increasing either the chlorine residual or the contact time will increase the CT value and the log inactivation of target pathogens.

4.2.1. Exposure concentration

To produce free chlorine available for disinfection, the concentration must exceed ‘breakpoint’, below which chlorine is consumed by inorganics (e.g. oxidising iron and manganese or reacting with ammonia to form chloramine) as well as organics. Once breakpoint is reached, the chlorine remaining in the system is free chlorine available for disinfection. When the concentration of free chlorine increases, the effectiveness of pathogen inactivation increases, resulting in less time required to achieve the desired log inactivation.

Studies by Mallmann and Schalm (1932; cited in Block 2001) and Rudolph and Levine (1941; cited in Block 2001) demonstrated that, when pH and temperature were kept constant, the time required to inactivate bacteria decreased when the concentrations of hypochlorite solutions increased.

4.2.2. Exposure time

Thurston-Enriquez et al. (2003) found that, at constant temperature, pH and free chlorine residual, the inactivation of adenovirus type 40 and feline calicivirus increased as exposure time increased.


4.3. pH

The relative concentration of chlorine species present in water is affected by pH (Keegan et al. 2012). As the formation of oxidising chlorine species is pH dependent, the Chick–Watson pathogen inactivation rate constant (k) (equation 1) is affected by pH. Keegan et al. (2012) and Canning et al. (2015) demonstrated that, as pH increases from 7 to 9, a greater CT is required to achieve the desired log inactivation by chlorine.

4.4. Water temperature

Chlorine disinfection is more effective at higher temperatures, which results in faster chemical reactions and more effective inactivation of pathogens (US EPA 1999b), with the pathogen inactivation rate constant (k) in the dose–response model (equation 1) increasing with water temperature (Li et al. 2001). Canning et al. (2015) demonstrated that, as temperature increases, a lower CT is required to achieve the desired log inactivation by free chlorine.

4.5. Turbidity (suspended solids and particles in water)

Chlorine is only effective when it comes into contact with the pathogen to be inactivated. Therefore, substances in the water, such as sand, dirt, iron or manganese particles, can ‘shield’ or protect pathogens from contact with chlorine and reduce its germicidal effectiveness (US EPA 2008). Keegan et al. (2012) found that higher turbidities may protect viral particles by creating a chlorine demand or by shielding the virion.

US EPA chlorine log inactivation CT values for viruses have been set based on drinking water systems with a turbidity of less than 1 nephelometric turbidity unit (NTU). Keegan et al. (2012) found that, using seeded organisms, higher CT values lead to effective disinfection of coxsackievirus B5 in wastewater with turbidity as high as 20 NTU. Because these results were obtained using seeded particles, they may not be directly applicable to indigenous organisms.

4.6. Disinfection demand

Because chlorine can react with all the organic and inorganic material in the water, the chlorine available to inactivate pathogens is reduced when other material is present. The chlorine demand is defined as the difference between the amount of chlorine added and the amount remaining (chlorine disinfection residual) after a given contact time. Where water quality is poor, higher chlorine dosages will be required to account for the additional chlorine demand and ensure that an adequate concentration of free chlorine is available for disinfection.


5. Operational monitoring parameters

Selection of operational monitoring parameters to inform the initial CT and log inactivation calculations, and to provide ongoing confirmation of operational efficacy is based on the factors that can influence disinfection efficiency. The operational monitoring parameters needed to validate log inactivation by chlorine are:

flow rate

chlorine dose

chlorine disinfection residual (measured at, or downstream of, the point at which the contact time is achieved)

temperature

pH

turbidity.

Requirements for collecting data for these parameters and their application in determining log inactivation are provided in the following sections.


6. Validation method

Under this protocol, the log inactivation of pathogens by chlorine disinfection is validated by calculating and confirming CT values.

6.1. CT calculation

As discussed in Section 4, the CT value – expressed in min·mg/L – is determined by multiplying the residual chlorine concentration by the contact time

𝐶𝑇 = 𝐶 × 𝑡 (equation 2)

where: C is the residual chlorine concentration in mg/L measured at, or downstream of, the point at which the

contact time is achieved t is the time, measured in minutes, that the water is in contact with chlorine

6.1.1. Residual concentration

The chlorine residual is to be measured at, or downstream of, the point at which the contact time is achieved. The residual disinfectant concentration must be measured for each disinfection segment (see Section 6.1.3) and should be measured continuously.

6.1.2. Contact time

Chemical reactions can occur in many reactors or vessels, which can be designed in a variety of shapes, sizes and configurations. In water treatment systems, reactors are typically flow-through systems (e.g. tanks, pipes), and the hydraulic mixing and short circuiting in these reactors has to be considered when determining a representative contact time. A disinfection contact reactor should be designed to provide adequate exposure to free chlorine to achieve the required CT (Gualtieri & Guelfo 2007).

Many indices of hydraulic performance have been developed for various chemical reaction purposes (Teixeira & Siqueira 2008), such as the baffling factor (BF), Morril index, short circuiting index and dispersion index. The measure most appropriate for water treatment is the BF, which is described in more detail in the US EPA Disinfection profiling and benchmarking guidance manual (US EPA 1999a).

The BF is defined as

𝐵𝐹 = 𝑇10

𝑇𝐷𝑇 (equation 3)

where: TDT is the theoretical hydraulic detention time, or reactor volume divided by flow rate T10 is the time taken for 10% of the incoming water to exit the tank. This measure ensures that 90% of the

incoming water to a given reactor remains in the reactor and is exposed to chlorine. The contact time to be applied is T10, measured from the point of chlorine injection to a point where the residual is measured before the first customer (or the next disinfection application point), and is measured in minutes. Flow-through process units require T10 to be determined through a tracer study.

New schemes should consider estimating T10 based on computational fluid dynamic modelling in the design


phase and subsequently confirm the value in a tracer study. Whichever design tool is used in the design phase, the actual performance of the reaction vessel needs to be tested to validate the assumed or designed performance. This requires full-scale testing of the completed installation to consider factors such as construction and modification of the design, non-ideal construction, upstream and downstream hydraulic influences from pipework configurations, and other assumptions made in the design process.

Appendix D of the US EPA Disinfection profiling and benchmarking guidance manual (US EPA 1999a) provides further guidance on the use of tracer studies. Since T10 is inversely proportional to the flow rate, tracer studies conducted at only one flow rate must use the highest flow rate to give a conservative T10 value. To give more operational flexibility, tracer studies can be carried out at various flow rates (minimum of three) to derive a relationship between T10 and flow, from which interpolation can be used to derive the appropriate T10 and BF for the given operational flow conditions.

Where tracer testing is not completed, a default BF of 0.1 is to be applied, which will result in the reactor volume being 10 times larger to achieve a given CT than a reactor of ideal configuration.

6.1.3. Disinfection segments

Every disinfectant injection point is the start of a new disinfection segment. Every injection point must have an associated monitoring point. A disinfection segment is a section of a treatment system beginning at one chlorine injection or monitoring point and ending at the next chlorine injection or monitoring point. The US EPA has detailed instructions on how to identify disinfection segments and calculate the contact time. Chlorine residual, pH, temperature and turbidity are measured for each disinfection segment.

Chlorine residuals tend to decline as water moves through the treatment plant. The reason for monitoring the chlorine residual at multiple locations is to obtain additional credit for the higher chlorine levels that exist at intermediate points in the plant.

6.2. Other methods for validation

This protocol does not propose challenge testing to validate LRVs where published CT tables are consistent with the scheme operating envelope. Specific challenge testing may be undertaken where LRVs are being claimed for systems that operate outside the scope of CT tables identified in this protocol.

Where specific challenge testing is proposed for chlorine disinfection of viruses and bacteria, coxsackievirus B5 should be used as the challenge testing organism. The LRVs claimed for viruses will also apply to bacteria. Where challenge testing is proposed for chlorine disinfection of bacteria only, Escherichia coli should be used as the challenge testing organism.


7. Data collection and analysis

Data collected during the validation testing program must be representative and reliable. To ensure that quality data are collected:

appropriate sampling methods and techniques must be consistent with the Standard methods for the examination of water and wastewater (Rice et al. 2012)

National Association of Testing Authorities (NATA)–accredited methods must be used, where available. Where NATA-accredited methods are not available, the laboratory must

o demonstrate that the method used is consistent with a standard method, where this is available

o document the method used for the analysis

o retain documentation and appropriate quality assurance data

o engage independent expert(s) to peer review and endorse the method

field and laboratory equipment must be maintained and calibrated

limits of detection must be appropriately measured

all procedures must be completed by qualified personnel and be subject to quality assurance or quality control procedures.

The monitoring program for the validation study must ensure that the data collected are relevant and sufficient for a statistically valid analysis. The raw data and their analysis must be appended to the validation report. If data are excluded from the analysis, the rationale must be provided.

In analysing data, validation uncertainty needs to be taken into account, including biases and errors in measurements, laboratory equipment, experimental design and analytical techniques. The measurement of validation uncertainty must be included, to the extent practicable, when attributing an LRV to the treatment process unit.

Under the ISO standard to which NATA accredits laboratories – ISO/IEC 17025-2005 – General requirements for the competence of testing and calibration laboratories – accredited laboratories are required to estimate the uncertainty associated with the results they produce (known as the measurement of uncertainty). Measurement of uncertainty data must be provided when reporting analytical results. This information will show the variability in the analytical data and will assist in formulating evidence-based conclusions.

Furthermore, during validation testing, all equipment must be carefully selected and calibrated to minimise uncertainty. Measurements must be traceable to a registered standard method, where this is available.

Increasing the sample number and/or sample volume, and using more accurate and precise measuring devices will provide the best estimate of the capability of a treatment process unit to remove or inactivate pathogens.


8. Operational monitoring

Operational monitoring is necessary to enable adequate control over the system and to continuously confirm that the system is operating within the validated operational envelope. Where operational parameters are found to be outside the validated operating envelope, the log inactivation may not be achieved, resulting in supply of water that is not fit for use. Action should be taken to bring the system back into the envelope and/or stop the supply of potentially unsuitable water.

The requirements for operational monitoring are as follows:

Use of a flow meter can confirm that the flow rate through the system or disinfection segment is consistently below the maximum flow used to calculate the log inactivation.

Both the dosed and the residual chlorine concentrations should be measured in real time. The chlorine residual is to be measured at, or downstream of, the point at which the contact time is achieved.

Temperature, pH and turbidity should be measured in real time or at a frequency that can identify conditions under which the system is operating outside the validated operational envelope.

Where the system does not allow monitoring of a disinfection segment, it may be useful to install a sidestream chamber, which has the same theoretical detention time and where a monitoring point can be located to measure the operational parameters.

8.1. Determination of critical limits

Critical limits are defined in the Australian guidelines for water recycling (NRMCC et al. 2008) as a prescribed tolerance that must be met to ensure that a critical control point effectively controls a potential health hazard; this criterion separates acceptability from unacceptability (adapted from the Codex Alimentarius Commission). Put simply, a critical limit is a value that defines the condition where hazards are no longer controlled to the level defined as the validated LRV.

Some systems may have the instrumentation to monitor key parameters and calculate CT in real time, and can therefore manage disinfection efficacy by applying a critical limit to CT. Systems that do not calculate CT in real time should set critical limits for disinfection based on the operational parameters used to calculate CT and determine the log inactivation.

Recommended parameters that will require a critical limit to be set are:

chlorine residual measured at, or downstream of, the point at which the contact time is achieved (minimum)

flow rate (maximum)

water temperature (minimum)

pH (maximum)

turbidity (maximum).


9. Method to determine the LRV for each pathogen group

Table 1 can be used to determine the LRV by chlorination for viruses and bacteria for turbidity ranging from

0.2 to 5 NTU, pH ranging from 7 to 9 and temperature ranging from 5 C to 25 C.

The CT values at a temperature of 10 C and a pH of 7, 8 or 9 are determined by linear regression, based on the experimental CT values in Keegan et al. (2012) and by rounding up to the next integer. The CT values for

intermediate pH values are linearly interpolated. The CT values for temperatures other than 10 C are based

on the CT values at 10 C adjusted for temperature, using the relationships described in Appendix C, Table C-7 of the US EPA Disinfection profiling and benchmarking guidance manual (US EPA 1999a). Using the US EPA data for pH 6 to 9 (validation protocol pH range is 7 to 9), a relationship with temperature can be

established according to equation 4. This relationship can be applied to the CT values at 10 C before rounding, assuming that the same relationship applies for all LRVs, and conservatively rounding up to the next integer.

𝐶𝑇(𝑇) = 𝐴 ∗ 𝑒(−0.071∗𝑇) (equation 4)

where 𝐴 = 𝐶𝑇(10℃)

𝑒(−0.071∗10)

Table 1 CT values for 1 to 4 log reduction values of viruses at a range of turbidity, pH and temperature

pH Log10

inactivation

≤0.2 NTU ≤2 NTU ≤5 NTU

5 °C

10 °C

15 °C

20 °C

25 °C

5 °C

10 °C

15 °C

20 °C

25 °C

5 °C

10 °C

15 °C

20 °C

25 °C

≤7 1 4 3 2 2 1 4 3 2 2 1 4 3 2 2 1

2 5 4 3 2 2 5 4 3 2 2 6 4 3 2 2

3 7 5 4 3 2 7 5 4 3 2 7 5 4 3 2

4 8 6 4 3 2 9 6 4 3 2 9 7 5 3 3

≤7.5 1 7 5 4 3 2 7 5 4 3 2 8 6 4 3 2

2 10 7 5 4 3 10 7 5 4 3 13 9 6 5 4

3 13 9 7 5 4 13 9 7 5 4 16 12 9 6 5

4 16 11 8 6 4 16 11 8 6 4 21 15 11 7 6

≤8 1 9 7 5 3 3 10 7 5 4 3 12 9 6 4 3

2 14 10 7 5 4 15 10 7 5 4 19 13 9 7 5

3 18 13 9 7 5 19 13 10 7 5 25 18 13 9 7

4 23 16 12 8 6 23 16 12 8 6 32 23 16 11 8

≤8.5 1 11 8 6 4 3 12 9 6 5 4 14 10 7 5 4

2 17 12 9 6 5 19 13 9 7 5 21 15 11 8 6

3 23 16 12 9 6 25 17 13 9 7 29 21 15 10 8

4 29 21 15 10 8 31 22 16 11 8 37 26 18 13 9

≤9 1 13 9 6 5 3 14 10 7 5 4 15 10 7 5 4

2 20 14 10 7 5 22 16 11 8 6 23 16 12 8 6

3 28 19 14 10 7 30 21 15 11 8 32 23 16 11 8

4 35 25 17 12 9 38 27 19 13 10 41 29 20 14 10

For systems that operate outside the values for pH, temperature and turbidity identified in the CT table, specific challenge testing must be undertaken to determine the log inactivation.


10. Triggers for revalidation

Processes should be revalidated when variations occur that may affect the performance of processes (e.g. impacts of changes to primary or secondary treatment processes on downstream filtration or disinfection). Any new processes should be tested using benchtop, pilot-scale or full-scale experimental studies to confirm that the required results are produced under conditions specific to the individual water supply system.

Significant changes to the validated disinfection process are defined as changes that are likely to significantly affect CT calculations and/or lead to the disinfection system operating outside the validated envelope. Such changes may include:

changes to the point of disinfection

changes to the disinfectant(s) used in the treatment plant

changes to baffles in contact tanks

changes to the disinfection process (including changes to plant hydraulics or piping schemes that affect CT)

changes to the operating envelope.

Where the operating envelope is altered, the CT should be recalculated and the log inactivation for the new operating conditions identified.


Glossary and abbreviations

BF baffling factor The ratio of the actual contact time to the theoretical detention time.

chlorine (free) The concentration of residual chlorine in water that is present as dissolved gas (Cl2), hypochlorous acid (HOCl) and/or hypochlorite ion (OCl–). The three forms of free chlorine exist together in equilibrium, and their relative proportions are determined by pH and temperature.

chlorine (residual) The level of free chlorine remaining in the water after the initial chlorine dosing.

CT Disinfectant residual concentration (C, in mg/L), multiplied by contact time (t, in minutes) at the point of residual measurement; a measure of disinfection effectiveness.

LRV log reduction value A log10 reduction value is used in the physical–chemical treatment of water to characterise the removal or inactivation of microorganisms such as bacteria, protozoa and viruses (1-log10 = 90% or a 10-fold reduction, 3-log10 = 99.9% or a 1000-fold reduction, and so on).

LRV = log10 (N0) – log10 (N), where N0 = concentration of infectious microorganisms before treatment and N = concentration of infectious microorganisms after treatment.

NATA National Association of Testing Authorities

NTU nephelometric turbidity units

T10 contact time The detention time experienced by 90% of the water passing through a process unit (contactor).

TDT theoretical detention time Determined by dividing the volume of a process unit (contactor) by the peak hourly flow rate.

tracer study An experimental procedure for estimating hydraulic properties of the distribution system, such as contact time.

US EPA United States Environmental Protection Agency


References

AWRCE 2015, Protocol template, WaterVal validation, Australian Water Recycling Centre of Excellence, Brisbane.

Black S, Thurston JA & Gerba CP 2009, Determination of CT values for chlorine of resistant enteroviruses, Journal of Environmental Science and Health, part A, 44(4):336–339.

Block SS 2001, Disinfection, sterilization, and preservation, 5th edn, Lippincott, Williams and Wilkins, Philadelphia.

Canning A, Wati S, Keegan A, Middleton D, Shilito D & Bartkow M 2015, Validation of relationship between free chlorine dose and pathogen inactivation in drinking water, Water 42(4):65–70.

Engelbrecht RS, Weber MJ, Slate, BL & Schmidt CA 1980, Comparative inactivation of viruses by chlorine, Applied and Environmental Microbiology 40:249–256.

Gualtieri C & Guelfo PD 2007, Residence time distribution and dispersion in a contact tank. In: G Di Silvio & S Lanzoni (eds), Harmonizing the demands of art and nature in hydraulics, 32nd congress of IAHR, the International Association of Hydraulic Engineering & Research, 1–6 July 2007, Venice, Italy, IAHR.

Keegan A, Wati S & Robinson B 2012, Chlor(am)ine disinfection of human pathogenic viruses in recycled waters, Smart Water Fund, Melbourne.

Li H, Finch GR, Smith DW & Belosovic M 2001, Sequential disinfection design criteria for inactivation of Cryptosporidium oocysts in drinking water, AWWA Research Foundation & American Water Works Association, Denver.

Liu OC, Seraichekas HR, Akin EW, Brashear DA, Katz EL & Hill WJ 1971, Relative resistance of twenty human enteric viruses to free chlorine in Potomac water. In: Virus and water quality: occurrence and control, proceedings of the 13th Water Quality Conference, Urbana-Champaign, Engineering Publications Office, Urbana, 171–195

Mallmann WL & Schalm O 1932, The influence of the hydroxyl ion on the germicidal action of chlorine in dilute solutions, Michigan Engineering Experiment Station Bulletin 1932:44.

NRMCC, EPHC & NHMRC 2008, Australian guidelines for water recycling: managing health and environmental risks, Natural Resource Management Ministerial Council, Environment Protection and Heritage Council & National Health and Medical Research Council, Canberra.

Rice EW, Baird RB, Eaton AD & Clesceri LS (eds) 2012, Standard methods for the examination of water and wastewater, American Public Health Association, American Water Works Association & Water Environment Federation, Washington, DC.

Rudolph AS & Levine M, 1941, Factors affecting the germicidal efficiency of hypochlorite solutions, Iowa Engineering Experiment Station Bulletin 150:1–48.

Teixeira EC & Siqueira RN 2008, Performance assessment of hydraulic efficiency indexes, Journal of Environmental Engineering 134:851–859.

Thurston-Enriquez JA, Haas CN, Jacengelo J & Gerba CP 2003, Chlorine inactivation of adenovirus type 40 and Feline calicivirus, Applied and Environmental Microbiology 69(7):3979–3985.

US EPA 1999a, Disinfection profiling and benchmarking guidance manual, United States Environmental Protection Agency, Washington, DC.

US EPA 1999b, Alternative disinfectants and oxidants guidance manual, US EPA, Washington, DC.

US EPA 2008, Sanitary survey guidance manual for ground water systems, US EPA Office of Ground Water and Drinking Water, Washington, DC.

Victorian Department of Health 2013, Guidelines for validating treatment processes for pathogen reduction: supporting class A recycled water schemes in Victoria, State of Victoria, Department of Health, Melbourne.

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