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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
iii
Use of contents on this sheet is subject to the limitations specified at the end of this document. Central Optimization - Executive Summary modified
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
ES iv
Use of contents on this sheet is subject to the limitations specified at the end of this document. Central Optimization - Executive Summary modified
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
v
Use of contents on this sheet is subject to the limitations specified at the end of this document. Central Optimization - Executive Summary modified
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
DRAFT for review purposes only. Use of contents on this sheet is subject to the limitations specified at the end of this document.