Improvements to Reduce Energy Costs

at the Downers Grove Sanitary District

FVOA 2010 Mini-ConferenceAugust 19, 2010

Nick MenningaGeneral Manager

– 11/22 MGD average/peak full treatment capacity

– Primary clarification

– Single-stage nitrification

– Tertiary sand filtration

– Anaerobic digestion

– Sludge dewatering and aging

– Excess flow primary and disinfection to 110 MGD total

Downers Grove Sanitary District, Illinois

Areas of Opportunity

• Aeration• Pumping• Digester Gas• HVAC• Funding Sources

Aeration Project

• 50-60% of an activated sludge plant electrical usage from aeration

• Traditional efficiency improvement: fine bubble diffused air

• Many other opportunities exist for improved efficiency in aeration system

Legacy Aeration System

• Various work-horse blowers

• Various aeration tank/diffuser arrangements

• Limited instrumentation and control

Improvements Identified

• New diffusers• New high-efficiency blower• Smarter use of tankage• I&C improvements• Potential electrical savings: 20%?

Blower Addition

ABS-HST Turbo-compressor– 2400 – 6000 cfm turn-

down, matches existing process demand

– low maintenance– fits in the room– reasonable sound levels– adiabatic efficiency

improved from 50% to 80%

– old blowers used as backup or for additional air if needed

New DiffusersSanitaire membrane plate

diffusers– Full-floor coverage – not

tapered– 9” circular plates– 10 drops per tank typical,

each with manual air-flow control

– Oxygen transfer efficiency (OTE) improved from 8% to >12%

Better Use of Tankage

• Convert deep aerobic digester tank to activated sludge service

• Remove shallow aeration tanks from service, reserve for use during excess flow or future process modifications

• Difficult channel interconnection required• Part of diffuser OTE improved efficiency

Instrumentation and Control

• LDO probes (Fluoroprobes) in each tank• Blower variable speed control• Air flow meters (2 total)• Manual butterfly valves on the drops• Dissolved oxygen feedback control in

plant SCADA (Allen Bradley PLCs/Ifix)

Control Screens

Project Costs

• Total project cost $1.4M

• Illinois Clean Energy Community Foundation grant of $250,000

Electricity Savings

• Average whole plant energy usage tracking:– before: 1,833 kWh/MG– after: 1,305 kWh/MG– reduction: 1/3 of plant total electricity use/volume treated

• Payback at $0.08 per kwh: < 7 years

Pumping

Flo-Matchers– Liquid rheostat– 1970’s technology– Lower flow = lower efficiency– Similar efficiency characteristics to

throttling discharge valve– 2 Lift stations

Recommended Improvements

• VFDs• Level control through

SCADA (Allen Bradley PLC/iFix)

• Expected Efficiency Improvements: 50%?

Project Costs

• Wroble Lift Station: 2 pumps, each at 150 hp, Project Cost $44,500

• Hobson Lift Station: 4 pumps, each at 250 hp, Project Cost $78,500 (no need to re-wind motors)

• Illinois Department of Commerce and Economic Opportunity (IDCEO) Grant: $36,127

Electricity Savings

• Wroble: 40% reduction• Hobson: 30% reduction• Payback at $0.08 per kwh: 3 years

Digester Gas

• Used first for digester heat• Previously had engine-driven blower

– No siloxane removal– Lost cost-effectiveness after 20 years of

operation

• Desiccant dehumidification in sand filter building

• Beginning to take restaurant grease trap waste to bolster production

Desiccant Dehumidifier

• Displacing 30 tons (50 hp) of electric-driven dehumidification

• Displacing gas-fired heat (8,500 therms/yr)

• Indirect fired• Solid-wheel desiccant media -

Munters

X 3

Project Costs

• Pilot project – equipment rental $15,000

• Equipment purchase - $120,000• Installation (duct work) - $33,000• Total $168,000

Energy Savings

• Natural gas use reduction measured: 868,000 cf

• Electricity reduction estimated from audit: 350,000 kwh/yr

• Payback at $1/therm and $0.08/kwh: 4 years

HVAC• As heat and AC package units are

replaced, upgrading to heat pumps that use effluent water as heat sink/supply– Grant from Illinois Clean Energy

Community Foundation for $38,400 approved this year

– Purchasing 3 units with total capacity of 30 tons, net cost around $36,000

– Expect $9,000 annual savings, 4 year payback

• Evaluating potential for digester gas fired unit heaters/absorption chillers

Funding Sources

• Illinois Clean Energy Community Foundation (ICECF) www.Illinoiscleanenergy.org

• Illinois Department of Commerce and Economic Opportunity (DCEO) www.commerce.state.il.us/dceo

• Illinois Environmental Protection Agency Revolving Loan Fund (IEPA SRF)

www. epa.state.il.us/water/financial-assistance/economic-stimulus/index.html

Conclusions

• Opportunities Exist for Any Budget• Grant Funding is Abundant and Will

Improve Cost-effectiveness of Projects

• Projects Stand on Economic Merit Alone: Green is Green

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Questions?

nmenninga@dgsd.org