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Case Studies in Residual Use and Energy Conservation at Wastewater Treatment PlantsInteragency Energy and Environmental Research Report Presented By:MS. YVONNIE D. MANERA U.S. Environmental Protection Agency Office of Wastewater Management Washington, DCU.S. Department of Energy Efficiency, Conservation and Renewable Energy Washington, DC

Outline Introduction

I. County Sanitation Districts of Orange CountyII. City of Los Angeles Hyperion Wastewater Treatment PlantIII. Sunnyvale Water Pollution Control PlantIV. Sanford Big Buffalo Creek WWTP, North CarolinaV. Seattle Metro Renton Water Reclamation Plant

Other Promising TechnologiesFactors that Contribute to SuccessThe Influence of Financial FactorsConclusions

Introduction Founded this study for the U.S DOEEnvironmental Protection Agency (EPA)National Renewable Energy Laboratory (NREL)

For the purpose of:to document energy conservation activities and their effects on operation costs regulatory complianceprocess optimization

Background Wastewater treatment processes with the highest energy usage but also exhibit the greatest potential for energy savings.

activated sludgedewatering and conditioningbiosolids incinerationaerobic digestionadvanced wastewater treatmentaeration ponds

Basics of Biogas Generation and UseBiogas is the type of gas that is produced in an anaerobic digester.

produced from raw materials such as:agricultural wasteManuremunicipal waste PlantsSewagegreen wasteorfood waste

How does Biogas Produce?

Biogas In-plant uses are:

heating boilers in process heating operationsspace heating and coolingengine-driven machineryEngine generators for electricity generationsolids incinerators generation of electricity by steam turbines and fuel cells

*Biosolids: nutrient-rich organic materials resulting from the treatment of domestic sewage in a treatment facility

I. County Sanitation Districts of Orange County

Uses of biogas heat the digesters fuel engines that run pumps and blowers

In 1989, CSDOC codified formal energy conservation plans in the "2020 Vision Plan.The 2020 Vision Plan energy conservation activities lighting building heating and cooling generation of electricity onsite

Biogas: gaseous fuel, especially methane, produced by the fermentation of organic matter.

CSDOC PLANT 1

CSDOC PLANT 2

Financial Benefits

facility reduced electrical power purchases by:biogas fueling of engines, process changes, lighting energy conservation, peak load shifting, reduction of loadings to the secondary process.

With Central Gen on-line are able to fully use the biogas produced, the calculated savings in 1993-94 are substantial.

The plant staff estimates savings totaling 12,630 kilowatts, worth about $8,850,000

The $65 million cost for Central Gen and all associated projects will be recovered in about seven years because of the savings achieved by this project

II. City of Los Angeles Hyperion Wastewater Treatment PlantThe Hyperion Treatment Plant from the air.

The Hyperion Energy Recover System (HERS) came on-line in 1987. HERS generates energy from biosolids using two distinct methods:

Biogas from anaerobic digestion fuels three gas turbines. produce 4,500 kW of electricity (each).

Biosolids from the digesters are dehydrated powder is burned in a fluid bed gasification multi-stage combustion chamber. Ash from this combustion process is currently used in an offsite cement manufacturing process. total average electrical production is 20 megawatts.

The facility currently uses about 600,000 cubic feet per day of natural gas to supplement biogas production.

Location of Hyperion Treatment Plant

Coordinates 335531.44N,1182547.28W33.9254,-118.4298

III. Sunnyvale WaterPollution Control Plant

Facility Description

The plant was equipped with two 55-ft diameter anaerobic digesters two biosolids drying lagoons

Biogas produced by the anaerobic digestion Use to wastewater pump pre-aeration blower

power generation facility

7.5 MGD primary plant was designed to service a population of 10,000

to provide separate treatment for a seasonal cannery load of 4.0 MGD

Location of the Sunnyvale Water Pollution Control Plant

1444 Borregas Ave, Sunnyvale, CA 94089, United States

History 1956The Sunnyvale Water Pollution Control Plant (WPCP), in California incorporated use of biogas in its original plant construction1960Sunnyvale's population increased by 500 percent to 60,000 People1965Plant expansions1968increased the treatment plant's capacity to 15 MGD third 55ft-diameter anaerobic digester440-acre oxidation pond with a four-pump circulation pumping stationremote three-engine-generator facility to provide power for the pumps (use either natural or biogas as fuel)Addition of a third biosolids lagoon1972The City increased the plant capacityconstructed a fourth 70-ft diameter anaerobic digester

1978due to substantial upgrading of effluent discharge regulationsincluding the ammonia removal requirementsAdditional treatment:add fixed growth reactors (FGRs)air flotation units (AFTs)dual media filtersBreakpoint chlorination and dechlorination equipment1980increased treatment capacity to 22.5 MGD when the population exceeded 100,000 with a final upgrade to 30.0 MGD

Description of the TechnologiesA design goal for the Sunnyvale wastewater treatment plant was to make maximum use of biogas.

Waste Heat RecoveryUse of waste heat: digestion chlorination systemsspace heating for various buildings at the treatment plant

waste heat is recovered in three systems: pump-engine heat recovery, generator-engine heat recovery stack heat recovery

Heat from all sources is converted into hot water for use throughout the plant.

Operation and Maintenanceinfluent pumps were designed to pump min. flow (dry weather)= 1.0 MGDpeak flow (storm)=50 MGD

During installation in 1956, the pump engines used dual suction-type carburetors.

Biogas system Engine fuel use biogas when pressure built up to 4 inchesNatural gas fuel is use when the pressure in the biogas system fell two inches below

1) it combines gasoline and air creating a highly combustible mixture, 2) it regulates the ratio of air and fuel, and 3) it controls the engine's speed

Landfill Gas ProductionThe Sunnyvale WPCP is located next to the municipal landfill (closed). Landfill gas (LFG) is produced by bacterial decomposition of the organic portion of refuse in the absence of oxygen.

The proposed energy conservation project will collect LFG and use it together with biogas from the WPCP anaerobic digesters to fuel engines and generators that supply the WPCP with electricity.

The City projects savings in reduced purchases of electricity to be $826,400 in Year 94-95.

The total cost of the LFG project is estimated at $4.47 million.

The project has received a grant from the California Energy Commission for $500,000.

At the $ 826,400 annual savings in electrical costs, project payback is anticipated in approximately six years.

IV. Sanford Big Buffalo Creek WWTP , North Carolina

Facility DescriptionThe Big Buffalo Creek (BBC) WWTP provides wastewater treatment for a population of approximately 17,000 people.

average influent flow 3.52 MGDpeak flow 6.8 MGDmajor rainfall12 MGD

History of the Energy Conservation Programlate 1970several U.S. oil companies VioIated price controlsyears of 1983 to 1986NCDECD and Energy Division used part of the grant to conduct on-site energy audits of 15 wastewater treatment plants and three water treatment plants.

NCDECD-North Carolina Department of Economic and Community DevelopmentThe audit found that the plant components which consumed the major power were:

extended aeration (70%), influent pumping (1 7%), aerobic digestion (5%), sludge pumping (3%), small miscellaneous uses (5%).

Location of BBC WWTP

Description of the TechnologiesProcess control system consists of an Andover controller unit which communicates with a laptop computer.

controls the aeration basin aerators according to DO, high flow and low flow

A photo of Andover Control

During low flows, if the process is stable, the process control system continues to operate from the DO input.

monitors the tertiary fiIter for flow rate to determine optimal timing for backwashing.

An Allen Bradley controller was added to the influent pump station.

an automatic "Beck" valve was installed to maintain a constant head, of approximately ten feet, in the influent pump wet well.

A photo of Allen Bradley Controller

During the facility upgradeGasters Creek Pump Station pumpsreplaced with high efficiency, higher capacity centrifugal PumpThe Little Buffalo Creek Pump Station replaced with high efficiency submersible pumpRAS screw pumpsreplaced with centrifugal pumpsThe screw pump belt drivesreplaced with direct drive units to conserve energymercury vapor yard Lightingreplaced with energy efficient sodium vapor lighting, and installed energy efficient windows in the operations Building

Process ModificationsThe aeration basin were designed to treat 10 MGD

average flow is 4.56 MGD

Use of a single aeration basin allowed operators to match the flow volume with the design.

Financial BenefitsActual payback time for the process control system was less than the 1 year originally estimated.

before energy conservation the two-year average monthly electrical cost during 1982-83 was $8,755 at $ 0.044 per kilowatt hour).

Monthly electrical costs averaging $4,200 over the period July 1993 to April 1994 reflect the effects of energy Conservation measures on electrical costs at the BBC plant.

V. Seattle Metro RentonWater Reclamation Plant

Renton wastewater treatment plant built by Metro, 2000

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Outline Seattle Metro Renton Water Reclamation Plant Facility Description Energy Recovery from Biogas The Metro Therm Program Benefits of the Energy Conservation Program

Facility DescriptionSouth Plant, located in Renton, is part ofKing County's regional wastewater treatment system.

does not use its biogas onsite for heating and/or cooling.

to sell the gas for offsite use and replace its potential in-plant use with electrically operated heat pumps that remove heat from effluent.

feasible depend on the low prices for electricity in the Seattle area

Timeline1965Completed to built as a secondary treatment plant1986a new effluent discharge pipeline and outfall was completed to eliminate discharges to the Green/Duwamish River and carry treated wastewater 12 miles to a deep-water outfall in Puget 1997Plant began producingreclaimed water.2001 expanded to its current capacity of 115 million gallons per day of average wet weather flow and 325 MGD during peak storms

The Renton plant treats about 108 MGD of wastewater.

Plant processes consist of:primary settling, Aeration secondary settlingchlorinationDechlorination

Biosolids are treated in dissolved air flotation thickeners, followed by anaerobic digestion and belt filtration

Location of the WWTP

Energy Recovery from Biogasfour anaerobic digesters generate 1.2 million f/d of biogas

They scrubs the biogas to remove carbon dioxide, and sells the resulting 99 percent pure methane to the local gas utility.

receives $1,100/day for the scrubbed gas

The Metro Therm ProgramMetroTherm is designed to provide treated wastewater effluent for heating and cooling of buildings (WWTP)

1982the State of Washington began a "District Heating and Cooling" (DHC) program to encourage communities to develop centralized hot water production to serve various energy needs1994Provided grants and assistance and will continue to provide support to Metro with a $25,000 grant and $25,000 in services

Facilities can use effluent in three modes:

heating and cooling, cooling only, heating only

A heat pump or heat exchanger and a compatible heating or cooling system is necessary to use the effluent

Benefits of the Energy Conservation Program: Regulatory Compliance

Metro's energy conservation activities have positive environmental benefits.

By not burning biogas onsite, Metro avoids creating air emissions from such a process.

In addition, companies use heat exchangers rather than natural gas for heating purposes, additional reduced emissions would be expected.

Factors that Contribute to success

Factors that contribute to successCSDOCHyperionSanford's BBC WWTPAdvanced primary treatment Secondary treatmentLoading based limits for industrial usersidentified the importance of management and staff training, interest, and technical expertise to successfully carry out energy conservationidentified staff expertise as most important to the successtrained plant operators and instrumentation staff whose primary responsibilities are in wastewater treatment.

extended aeration basinsprocess control system identified the importance of management and staff training, interest, and technical expertise to successfully carry out energy Conservationcites the value of a comprehensive energy audit as an essential tool for cost-effective energy conservation.

The Influence ofFinancial Factors

BIOSOLIDS: Onsite Use versus Offsite Reuse1) If the cost of electricity purchased from the public power company were to increase by 45 percent or more, the onsite option becomes more economical.

2) If the cost to dispose of biosolids offsite were to at least double, it becomes more cost effective to process the biosolids onsite.

3. Hyperion staff show that the addition of steam dryers lowers the cost of onsite biosolids processing to $109 per dry ton, compared to $132 for offsite management

BIOGAS: Onsite Use versus Offsite SaleOnsite use:

to generate electricityto provide heat for digesters and buildings.

Conclusion

Energy recovery from biogas is universally cost effective and has gained widespread acceptance.

Recovery and use of biogas accomplish energy conservation and pollution prevention goals, and also cost savings.

Wastewater treatment plants located near municipal landfills, and could develop the landfill gas as an additional energy source