Anaerobic Digestion. Steve Baertsche. Mary Wicks

Anaerobic Digestion Steve Baertsche Mary Wicks

Anaerobic Digestion What is it? How does it work? Is it right for you?

What is it? An anaerobic digester is an air tight, oxygen free container that is fed an organic material, such as animal manure or food scraps. A biological process occurs to this mixture to produce methane gas, commonly known as biogas, along with an odor reduced effluent. Microbes break down manure into biogas and a nutrient rich effluent. (http://www.biogas.psu.edu/basics.html) It s what happens inside a cow s stomach after dinner.

What is it? Domed digester and channel for pig and human waste. Uncovered digester with influent port on left and effluent port on right. Over 37 million digesters operating in China in 2009. Using biogas for cooking. Source: http://www.cityfarmer.org/biogaspaul.html

What is it? ORGANIC MATERIAL manure food waste BACTERIAL DIGESTION BIOGAS ~65% methane ~35% carbon dioxide EFFLUENT solids liquids HEAT ELECTRICITY PIPELINE GAS BEDDING FERTILIZER

What is it? On farm digesters: Worldwide 20,000 U.S.* 157 (> 400,000 MWh equivalent per year) Ohio* 4 (> 16,000 MWh equivalent per year) *Source: U.S. EPA AgStar Average U.S. home uses 11,232 kwh/yr (DOE EIA 2007)

How does it work? Bacteria breakdown organic material in a series of stages. Carbohydrates Sugars Carbonic acids Fats Fatty acids and alcohols Hydrogen Carbon dioxide Hydrogen Acetic acid Carbon dioxide Methane Carbon dioxide Proteins Amino acids Ammonia The bacterial community changes throughout the process.

How does it work? Different factors affect how quickly the material breaks down and the volume of biogas produced: Feedstocks Type of digester Operating temperature

How does it work? Feedstocks contain different amounts of energy. Feedstocks Biogas Produced cubic meter/ton Waste grease 600 Molasses 469 Food waste 220 Potato peelings 68 Swine manure 35 Dairy manure 25 Source: Mathias Effenberger, 2006 Think about a cup of sugar vs. a cup of lettuce.

How does it work? Types of digesters: Characteristics Covered Lagoon Plug Flow Complete Mix Fixed Film Digestion vessel Deep lagoon Rectangular inground Round/square above/ in ground Above ground tank Level of technology Low Low Medium Medium Supplemental heat No Yes Yes No Total solids 0.5 3% 11 13% 3 10% 3% Solid characteristics Fine Coarse Coarse Fine Retention time 40 60 days 15+ days 15+ days 2 3 days Optimum climate Temperate & warm All All Temperate & warm (Source: http://www.epa.gov/agstar/pdf/handbook/chapter1.pdf )

How does it work? COVERED LAGOON Advantages Low cost (relative) Low tech/easy to construct Geo synthetic covers are readily available Disadvantages Cover maintenance/lifespan Solids/nutrient accumulation Miedema Dairy Circleville, OH Covered lagoon 1,000 dairy cows

How does it work? PLUG FLOW Advantages Good track record for dairy manure Works well with scrape systems Disadvantages Requires high solid feedstocks (11 14%) Sunny Knoll Farm Perry, NY Horizontal plug flow 1,800 dairy cows

How does it work? COMPLETE MIX Advantages High level of experience Works with wide range of influent total solids/moisture Fits well with most dairy/swine and food wastes Disadvantages Maintenance of mechanical mixing equipment Poor biomass immobilization OARDC Digester Wooster, OH Complete mix Feedstocks vary

How does it work? FIXED FILM Advantages Shorter retention time as microbes retained in system Smaller footprint Disadvantages Sensitive to solid load Faber PA Fixed film 100 dairy cows

How does it work? Operating temperature Thermophillic (120 140 F) Shorter processing time Smaller tank volume Less stable Mesophillic (95 105 F) Longer processing time Larger tank volume

Is it right for you? Benefits Create value added products: renewable energy (biogas) (heat, electricity, CHP, compressed gas for vehicles, pipeline gas) fertilizer fibers (bedding, mulch, hydroseeding, potting soil amendment) Reduce environmental impacts: odors pathogens greenhouse gases

Is it right for you? Considerations Is there a direct use for the biogas? What feedstocks are available? What is the biogas potential? Is there a need for nutrients (NPK) in the surrounding community? Is technical support available and reliable? Is it economically feasible?

Is it right for you? Resources U.S. EPA AgStar Program Voluntary outreach and educational program that promotes the recovery and use of methane from animal manure. Information about funding sources, decision making, other resources, and more. Available online at: www.epa.gov/agstar

Is it right for you? Resources AgStar Industry Directory, June 2010 Project designers and developers Energy service providers Equipment manufacturers Commodity organizations Available online at www.epa.gov/agstar/documents/agstar_industry_directory.pdf

Is it right for you? Incentives Rural Energy for America Program Grant assistance 25% of eligible costs $250,000 maximum for Energy Efficiency Projects $500,000 maximum for Renewable Energy Projects Loan guarantees 85% loan guarantee for loans under $600,000 $25,000,000 maximum load amount In Ohio contact: Randy.Monhemius@oh.usda.gov

Is it right for you? Incentives Renewable Energy Certificates (REC s) Electricity generated from renewable resources earns tradable REC s. 1 REC = 1,000 kwh or 1 MWh REC s are issued and can be sold to energy generators to help meet requirements for increased use of renewable energy. For more information, see http://www.epa.gov/greenpower/gpmarket/rec.htm

Is it right for you? Incentives Carbon Credits Credits given for reducing greenhouse gas emissions from livestock manure storage. For more information, see http://www.chicagoclimateexchange.com/ Other incentives Database for State Incentives for Renewable and Efficiency http://www.dsireusa.org/

Is it right for you? Questions?