Central Wastewater Treatment Plant

Optimization Study Prepa red fo r

Met ropo l i ta n Gove rnm ent o f Nash v i l le a nd Dav id son Cou nty

DRAFT

Central Wastewater Treatment Plant Optimization Table of Contents

Table of Contents List of Figures ........................................................................................................................................................... iv

List of Tables ............................................................................................................................................................. iv

List of Abbreviations .................................................................................................................................................. v

Executive Summary .................................................................................................................................................. 1

APPENDICES IN VOLUME 2

Appendix A: Tasks 1 and 2 Evaluation of Wastewater Flows and Loads

TM 1: Flows and Pollutant Loading Analysis

Appendix B: Task 3 Plant Hydraulic Evaluation

TM 3: Plant Hydraulic Evaluation

Appendix C: Task 4

TM 4.2: Wastewater Characterization Study Results

TM 4.3: Process Model Calibration and Validation

Appendix D: Task 5

TM 5.1: Plant Hydraulic Capacity Assessment and Alternatives Evaluation

TM 5.2: Potential Improvements at South Grit Facility

TM 5.4: Process Capacity Assessment and Alternatives Analysis of CWWTP

TM 5.5: Low Pressure Aeration System Upgrades

Appendix E: Task 6

TM 6.1: Wet Weather Treatment Alternative Analysis

Appendix F: Task 7

TM 7: Disinfection Feasibility Study

Appendix G: Task 9

TM 9.1: Preliminary Cost Estimate

Appendix H: Task 10

TM 10: Plant Operations Review and Support

Appendix I: Task 15 Quick Fixes

TM 15: Quick Fixes

Appendix J: Project Meetings and Presentations

Brainstorming Meeting 12/15/11

Cold Weather Sampling Kickoff 01/19/12

Project Kickoff 02/16/12

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Central WWTP Optimization Study

Disinfection Kickoff 05/07/12

Results Workshop 08/02/12

Brainstorming Workshop 08/29/12

Stormwater Phase 12 Kickoff 10/19/12

Alternatives Development 12/12/12

Central Disinfection Results & Alternatives Review 05/30/13

List of Figures Figure 1. Summary of Capacity Results .................................................................................................................. 8

Figure 2. Conceptual Aeration Tank Configuration .............................................................................................. 12

Figure 3. Potential Return Splitter Box Configurations ........................................................................................ 13

Figure 4. Existing Mixed Liquor Slide Gate ........................................................................................................... 13

Figure 5. SC Flow Meter Discharge Piping Existing Conditions ........................................................................... 14

Figure 6. SC Flow Meter Discharge Piping with 45-bend Removed .................................................................... 14

Figure 7. Existing Pipe Chase North Chlorine Area............................................................................................... 15

Figure 8. Potential EFTU Configuration including Old South Plant Tankage...................................................... 18

List of Tables Table ES-1. Summary of Existing and Achievable Optimized Capacities .............................................................. 2

Table ES-2. Scope of Work and Description of Tasks for the Central Optimization Study................................... 2

Table ES-3. Summary of Future Influent Flows and Pollutant Loadings for the Central WWTP .......................... 4

Table ES-4. Modeling Tools and Field Testing Utilized for the Central Optimization Project ............................... 5

Table ES-5. Summary of Existing Hydraulic and Process Capacities .................................................................... 8

Table ES-6. Comparison of Peak CWWTP Capacities Assumed by the LTCP and Achievable via the COPT Project ..................................................................................................................................................... 17

Table ES-7. Summary of Proposed Alternatives and Costs ................................................................................. 23

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Central Wastewater Treatment Plant Optimization Table of Contents

List of Abbreviations AT Aeration Tank

BC Brown and Caldwell

CCT Chlorine contact tank

cf cubic foot

CFD Computational Fluid Dynamics

cfm Cubic feet per minute

COPT Central Optimization

CPS Central Pump Station

CSO Combined sewer overflow

CSS Combined sewer system

CWWTP Central Wastewater Treatment Plant

DAFT Dissolved Air Flotation Thickener

DO Dissolved Oxygen

DoJ Department of Justice

dtpd Dry tons per day

EPA Environmental Protection Agency

EFTU Excess flow treatment unit

F Fahrenheit

FOG Fats, oils and grease

ft Foot

FM Forcemain

hr Hour

kW Kilowatt

lb Pound

LF Linear foot

LTCP Long Term Control Plan

MLSS Mixed liquor suspended solids

MGD Million gallons per day

MWS Metro Water Services

NGF North Grit Facility

NPDES National Pollutant Discharge Elimination System

O&M Operations and maintenance

psi Pound per square inch

PS Pump station

PST Primary settling tank

SGF South Grit Facility

SC Secondary clarifier

sq ft Square foot

TM Technical Memorandum

TDEC Tennessee Department of Energy and Conservation

TS Total solids

VFD Variable frequency drive

VS Volatile solids

VSR Volatile solids reduction

WWTP Wastewater Treatment Plant

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Central WWTP Optimization Study Executive Summary

Central Biosolids Facility

Central Wastewater Treatment Plant

Executive Summary

Metro Water Services (MWS) selected Brown and Caldwell (BC) to perform an optimization study for the Central Wastewater Treatment Plant (CWWTP) in Nashville, TN. The purpose of the MWS Central Optimization (COPT) Project is to determine the current plant hydraulic and process capacities, identify and eliminate capacity limitations, and increase the peak wet weather secondary treatment capacity of the CWWTP while minimizing construction of new process tankage. An evaluation of the Central Biosolids Facility is also being performed to

identify necessary improvements of the solids process to achieve the optimized capacity. Additional goals include improving plant operability, maintainability, reliability and energy efficiency. Recommendations from this study will be used to develop a scope of work for design and implementation of the improvements, a portion of which may be performed in conjunction with the COPT Project.

In accordance with the Consent Decree enacted by the Environmental Protection Agency (EPA), Department of Justice (DoJ) and the Tennessee Department of Environment and Conservation (TDEC) in March 2009, and the Long Term Control Plan (LTCP) submitted by MWS to these agencies in September 2011, MWS has committed to a reduction in combined sewer overflow (CSO) frequency at the Kerrigan CSO. MWS proposed a combination of treatment at the CWWTP and equalization (EQ) storage to achieve the committed CSO control frequency. Increased CWWTP treatment capacity identified as part of this optimization study will reduce the amount of EQ storage required.

Summary of Optimization Study Results Based on the results of the COPT project and through the recommended process and hydraulic improvements at the CWWTP, it was determined that the CWWTP has an achievable optimized secondary treatment capacity of 350 million gallons per day (MGD), with an additional 80 MGD of wet weather treatment through the Excess Flow Treatment Unit (EFTU), for a total peak wet weather treatment capacity of 430 MGD.

As discussed further throughout this report, plant improvements are recommended that will increase secondary treatment capacity, reduce energy usage, minimize reliance on complicated automation and also optimize process control which will result in a more reliable and operable WWTP.

Table ES-1 below provides the existing and achievable flow through secondary treatment at the CWWTP, based on different biological treatment options and hydraulic capacity determined as part of this study. As can be seen from the total achievable plant flow through secondary treatment, the hydraulic capacity of the existing infrastructure is the limiting factor for overall plant capacity.

ES 1

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