NEW YORK WATER ENVIRONMENT ASSOCIATION WINTER MEETING – FEBRUARY 10, 2003 MAXIMIZING CSO CAPTURE THROUGH WET WEATHER OPERATIONS AT WPCPS

Background Of Topic And Authors Topic NYC DEP Is Currently Establishing Wet Weather Capacities and Protocols For All Of Its WPCPs Which Service Combined Sewer Drainage Areas NYS Has Established Wet Weather Operating Guidelines and Technology Transfer Materials Authors James Mueller, Stephane Gobbons and Dorothy Chao New York City Department of Environmental Protection Bureau of Environmental Engineering Gary Grey HydroQual, Inc.

Why Maximize Treatment of Wet Weather Flows Minimize Water Quality Impairments Bathing Beach Closures (due to Coliform) Floatables Impacts (due to street litter and sanitary materials) CSO Sediments (due to settleable solids) Avoid or Minimize Need For New CSO Treatment Facilities Tanks, Screens, Nets, Skimmer Vessels Regulatory Compliance EPA Nine Minimum Controls NYS DEC 13 CSO BMPs SPDES Permits

Federal and State CSO BMPs EPA Nine Minimum Controls #4 Maximizing Flow to POTW Maximize sewer capacity through proper O&M Analyze records to correlate flow and plant performance Determine plants ability to accept incremental flow increases NYSDEC BMP #4 Maximizing Flow to POTW Particularly critical in treatment of first flush Collection system and headworks must be capable of delivering flow up to treatment process capacity during wet weather 2xDDWF+

SPDES Requirement for Maximizing Treatment of Wet Weather Flows Factors cited in Item 2. above shall also be considered in maximizing flow to the POTW. Maximum delivery to the POTW is particularly critical in treatment of first-flush. The _______ treatment plant shall be physically capable of receiving the peak design hydraulic loading rates for all process units. The _______ treatment plant shall be physically capable of receiving a minimum of _____ MGD through the plant headworks; a minimum of _____ MGD through the primary treatment works (and disinfection works if applicable; and a minimum of _____ MGD through the secondary treatment works during wet weather. The actual process control set points may be established by the Wet Weather Operating Plan required in BMP #4. The sewer collection system, regulating devices and head works must be capable to delivering these flows during wet weather.

How To Maximize Treatment of Wet Weather Flows Review Plant Performance for Significant Wet Weather Events Identify Critical Treatment Processes Establish Wet Weather Capacities and Wet Weather Operating Protocols Anticipate Wet Weather Events

Characterizing Plant Impacts Monitor influent characteristics and inter-process performance under wet weather conditions Monitor critical process operations during wet weather Develop a database to document plant response to wet weather flows Utilize data to make process decisions for wet weather events

Review Plant Flows

Review Performance for Significant Rain Events Average Peak Flow (MGD)

Review Plant Flow response to Wet Weather Conditions NYC produces ~ 3 mgd of Dry Weather Flow per 1 mi of rain over a 1mi 2 will produce >1.5 MG Average Dry Weather Flow Actual Flow

Is There Any Demonstrated Impact of Wet Weather Flow on WPCP Performance Plant Design 60 mgd

Are There Any SPDES Compliance Problems Associated With Wet Weather Flows Look at: BOD TSS Settleable Solids Fecal Coliform Cl 2 Residual

Anticipate Wet Weather

Operating and Design Issues Which Can Influence Wet Weather Capacity Ability to control flow accurately Process capacity Manual vs automatic controls Process bypass capability Flow meter accuracy Human factors

Impacts At Wastewater Treatment Facilities - First Flush High grit loading High screenings loading High BOD and suspended solids loading Short term increase in residuals handling Variable chlorine demand

Potential Impacts At Wastewater Treatment Facilities - Long Duration Excess grit passing through grit removal facilities Reduced primary clarifier efficiency Reduced hydraulic detention time in secondary treatment process Solids washout from secondary clarifiers Reduced contact time in disinfection processes

Operations Guidelines - General Assure that EVERYTHING is ready to go Place unused equipment & tankage in service Controlled bypassing Minor modifications for flexibility Reduce recycle flows Watch weather

Operations Guidelines - Pump Stations Modify pump control systems to: Maximize wet well storage Induce available collection system storage Dampen flow surges to treatment processes Bring stand-by pumps online REVISED PUMP-ON LEVEL TO TAKE ADVANTAGE OF PIPE STORAGE PUMP-ON LEVEL PUMP-OFF LEVEL

Operations Guidelines - Screening Place all screening units in service Increase screen cleaning frequency Prepare screenings containers NYS Guidelines

Operations Guidelines - Grit Removal Clean sewers, interceptors & catch basins regularly Place all grit removal units in service Shut off air to aerated grit chambers Increase grit removal rate Adjust velocity controlled grit chambers Prepare grit containers

Operations Guidelines - Primary Settling Place all units in service Maintain low sludge blanket levels Assure balanced flow Consider chemical addition Increase scum removal rate Monitor primary sludge concentration Discontinue secondary sludge wasting

Operations Guidelines - Activated Sludge Control sludge quality (avoid filamentous sludge) Adjust return sludge rate Manage aeration Change mode of operation Conserve biomass

Lower or Shut Off Air In Last Passes of Aeration Tanks NYS Guidelines

Operations Guidelines Secondary Settling Place all clarifiers in service Maintain low sludge blanket levels Balance flows to clarifiers Consider chemical addition to aid settling

Operations Guidelines - Disinfection Place all units in service Manage chlorination rates Chlorine demand will increase if bypassing primary effluent Clean solids from contact tank regularly Increase residual monitoring NYS Guidelines

Summary Analyze plant performance during wet weather and establish reasonable goals Establish operating procedures, follow them and and update them Preserve the integrity of the plant The benefits: Preserve designated uses (fewer beach closings) Compliance with CSO policies Avoid the need for additional facilities

More WWOP Information Click on Wet Weather Training