Combined Heat and Power Systems Using Biogas in Wastewater Treatment Plants

North Dakota Water and Pollution Control Conference

Grand International Inn Minot, ND

October 16, 2012

Tracy Ekola, Principal | Regional Practice Center Leader

John Fisher, Principal | Senior Design Leader

Did You Know? US EPA Reports • CHP systems are engine-generators that use biogas as fuel to

produce electricity or as boiler fuel to produce heat. • There are over 75,000 wastewater treatment plants (industrial

and municipal) in the US.

• Most of these treatment plants use aerobic digestion and about 5,000 currently contain anaerobic digesters.

• Energy costs can account for 30 percent of the total operation and maintenance (O&M) costs of WWTPs (Carns 2005).

• WWTPs account for approximately 3 percent of the electric load in the United States.

US EPA - Combined Heat and Power (CHP) Partnership Report

As of June 2011, CHP systems using biogas were in place at 104 WWTPs, representing 190 megawatts (MW) of capacity. CHP systems are technically feasible at 1,351 additional sites Nationwide, WWTFs have the potential to provide more than 400 MW in generating capacity and 38,000 million Btu per day of thermal energy. 3 million metric tons of carbon dioxide emissions could be prevented annually, which is the equivalent of emissions from 596,000 vehicles.

WWTPs Use Electricity! Process Energy Breakdown

4

Building Systems 2%

Prelim/Primary Treatment 7%

Biological System 37%

Secondary/RAS Pumps 9%

Sludge Thickening/Dewatering 12%

Digestion 14%

Sludge Drying 11%

Plant Water & Disinfection 8%

How Do Treatment Plants Work?

Solids Can Be Digested 2 Ways Aerobic Digestion Aerobic organisms need oxygen and mixing Typically used in plants with small population (less than

15,000) and low industrial load

Anaerobic Digestion Anaerobic organisms function without oxygen Typically used in plants with large populations and high

industrial load

Anaerobic digestion offer many potential benefits. Less solid waste is left over – 1 lb solids in, ½ lb solids out Biogas (methane) is produced and reused

Biogas 101

Biogas is a by-product of the anaerobic decomposition of organic solid waste

300 scfm of biogas = ~ 800 kW electricity

Biogas–~ 65% methane (CH4)–~ 35% carbon dioxide (CO2)

By using the energy from biogas, a WWTP can save $1,000’s of dollars per year in heating costs and reduce greenhouse gas emissions.

A Look Inside an Anaerobic Digester

A large covered tank which is mixed and heated

Operates biologicially without air

Biogas accumulates at the top of the digester

Sludge volume is reduce by ½ within 15 days

Biosolids become beneficial and are applied to farmland

One WWTP that Uses Bio Gas to Heat Sludge and Plant Buildings

Austin, MN 2 separate WWTPs with combined flow of 4.5 mgd City population 23,000 Hormel Foods waste load has population equivalent to

115,000 BioGas produced is estimated at 250,000 scfm per day and

is burned through large boilers Remaining biosolids are stored then land applied in

Spring and Fall

Austin Municipal WWTP

Trickling Filter

Clarification

Excess BioGas is Flared – Normally in Summer

Austin Industrial WWTP

Industrial WWTP - Anaerobic Digesters

Industrial Plant – Boiler / Heat Exchangers

2 WWTPs That Use BioGas to Generate Electricity and Heat Ames, IA Population 56,700 Generating electricity and thermal energy for 22

years 20% electrical savings annually

Owatonna, MN Population 25,600 and has some large industries Generating electricity and thermal energy for 25 years Also recovering heat from wastewater effluent Biogas provide 30% electrical savings annually =

$200,000

Ames, Iowa

Trickling Filters

Anaerobic Digester Cover

BioGas Powered Engine Generator

Thermal Heat Piping

Thermal Heating System

Sludge is Land Applied

Owatonna, MN

Activated Sludge Process

Anaerobic Digester Complex

Anaerobic Digester – Biogas Cover

BioGas Piping

BioGas Powered Engine Generator

Controls

Hot Water Recirculation System

Digester Sludge Heat Exchanger

Effluent Heat Recovery System

Non-Municipal Anaerobic Digestion

Anaerobic digestion is gaining poplularity One of the oldest processes used for solids stabilization at wastewater treatment plants

Increased use due to driving factors - Energy costs as well as decreasing loading limits

Many variations developed over the last several decades as a result of anaerobic digestion being more closely evaluated by industry and agriculture

Food processors (dairy, vegetable, brewing, meat packers) Ag/manure digesters Co-digestion

Motivations For Agriculture:(as size increases so does problem/opportunity)

1) Public pressure for reduced odor 2) Increased environmental scrutiny –

greenhouse gas emissions/nutrient issues 3) Energy generation 4) Digested solids used for bedding

For Industry: 1) Cost avoidance – WW charges, electricity charges,

natural gas usage, waste disposal 2) Interest in renewable energy or corporate

sustainability

For Co-digestion: Energy Generation

Feasibility Factors

Feedstock Characteristics, strength and availability

Technical Feasibility – inhibitory/toxic components, C:N ratio

Regulatory Issues

Site Constraints

Economics – Payback period

Funding Assistance

Motivation

Anaerobic Digestion Differences Municipal • Uniform waste composition • CSTR

Non-Municipal • Variable waste composition • Many types & configurations

CHP Technology is at Work Everywhere

Number of Installed Ag Systems

Some Energy Stories Found on the Web McDonalds successfully transformed waste into

electricity earlier this year at several United Kingdom restaurants

Chrysler is converting used paint solids from two St. Louis assembly plants into electricity.

Heinz is working on a program to transform used potato peels into energy.

Kraft - Two cheese plants in New York will turn used whey into energy in a move that will supplant a third of the facilities' natural gas purchases. The company also will avoid the expense of hauling the waste away.

SEH AD Case Studies

• Village of Turtle Lake, WI

• Southern MN Community

• Northeastern MN Community

• Potato Industry, MN

• Dairy, WI

AD Project Success Factors By-product disposal/reuse

options available

Strong motivating factor

Ownership model/Cohesive team

High current operational costs (WW treatment, energy, propane)

Pima County Arizona Wastewater Treatment Plant – CHP

Seven Waukesha engine/generator packages

Produces 243 cfm biogas @ 60% methane

Provides 35 percent of energy needs

Thermal energy: Digester heat, HVAC, domestic hot water

Electricity generation = 5 cents/KWh (includes maintenance) rebuild 28-year-old engines, each with 40,000 hours of operation

San Francisco, CA East Bay Municipal Utility District

• Nine Communities send 75 mgd of sewage to the WWTP.

• Located in the San Francisco Bay area - cogenerating electricity and thermal energy anaerobic digester gas (biogas)

• Generates enough energy for approximately 125 % of its energy needs resulting in cost savings estimated $1.7 million annually

Metropolitan Council Environmental Services

Maintains approximately 600 miles of sewers that collect flow from 105 communities.

Treats an average of 250 million gallons of wastewater daily at 7 regional treatment plants.

Energy use is a major expense -- approximately $15 million per year.

MCES 2015 Energy Goal is to reduce purchased of energy by 25%

Europe’s Vision is for WWTPs to Become Energy Neutral

• Why? – Gasoline costs over $8.00 per gallon – Power costs are $0.26 per kwh – Government initiatives and funding incentives in place to

reduce carbon footprint – Beneficial reuse is part of social framework – Photos of a BioGas Refueling Station in Germany

Questions?

Combined Heat Projects in Wastewater Plants Have Worked Very Well in the Past and Will

Become Even Better in the Future!

tekola@sehinc.com jfisher@sehinc.com