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NEW YORK WATER ENVIRONMENT ASSOCIATIONWINTER MEETING – FEBRUARY 10, 2003

NEW YORK WATER ENVIRONMENT ASSOCIATIONWINTER MEETING – FEBRUARY 10, 2003

MAXIMIZING CSO CAPTURE THROUGH WET WEATHER OPERATIONS AT WPCP’S

Background Of Topic And AuthorsBackground Of Topic And Authors

Topic NYC DEP Is Currently Establishing Wet Weather Capacities and

Protocols For All Of Its WPCP’s Which Service Combined Sewer Drainage Areas

NYS Has Established Wet Weather Operating Guidelines and Technology Transfer Materials www.dec.state.ny.us/website/dow/bwcp/foas_main.html

Authors James Mueller, Stephane Gobbons and Dorothy Chao

New York City Department of Environmental Protection Bureau of Environmental Engineering

Gary GreyHydroQual, Inc.

Why Maximize Treatment of Wet Weather Flows

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 BMP’s SPDES Permits

Federal and State CSO BMP’sFederal and State CSO BMP’s

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 plant’s 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

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

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 FlowsReview Plant Flows

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Flo

w (

MG

D)

Daily Avg Dry Flow Hourly Peak Hourly Min Aeration Flow Bypass Flow

Design Dry Weather Flow = 150 MGD

Plant Peak Design Flow = 300 MGD

Review Performance for Significant Rain EventsReview Performance for Significant Rain Events

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Review Plant Flow response to Wet Weather Conditions

Review Plant Flow response to Wet Weather Conditions

• NYC produces ~ 3 mgd of Dry Weather Flow per 1 mi 2

• 0.1” 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

Is There Any Demonstrated Impact of Wet Weather Flow on WPCP Performance

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Peak Hourly Flow (mgd)

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nt

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Current 7-Day Arithmetic Average Limit 45 mg/L

Current 30-Day Arithmetic Average Limit 30 mg/L

Future Daily Maximum Limit 50 mg/L(does not apply when wet weather flows exceed 2xDDWF)

Plant Design 60 mgd

Are There Any SPDES Compliance Problems Associated With Wet Weather Flows

Are There Any SPDES Compliance Problems Associated With Wet Weather Flows

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Conc Load_DWF Load_TotalFlow

Permit Limit = 45 mg/L, 22,518 lb/d

Look at:BODTSS Settleable SolidsFecal ColiformCl2 Residual

Anticipate Wet WeatherAnticipate Wet Weather

www.weather.com

www.accuweather.com

www.intellicast.com

Operating and Design Issues Which Can Influence Wet Weather Capacity

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 loadingHigh screenings loadingHigh BOD and suspended solids loadingShort term increase in residuals handlingVariable chlorine demand

Potential Impacts At Wastewater Treatment Facilities - Long Duration

Excess grit passing through grit removal facilitiesReduced primary clarifier efficiencyReduced hydraulic detention time in secondary

treatment processSolids washout from secondary clarifiersReduced contact time in disinfection processes

Operations Guidelines - General

Assure that EVERYTHING is ready to goPlace unused equipment & tankage in

serviceControlled bypassingMinor modifications for flexibilityReduce recycle flowsWatch 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

REVISEDPUMP-ON LEVEL

TO TAKEADVANTAGE OFPIPE STORAGE

PUMP-ONLEVEL

PUMP-OFFLEVEL

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

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

SummarySummary

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 InformationMore WWOP Information

www.dec.state.ny.us/website/dow/bwcp/foas_main.html

Click on Wet Weather Training