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Anaerobic Digestion Basics – Science, Systems and Benefits Building Your Biogas System Workshop

Anaerobic Digestion Basics – Science, Systems and Benefits Building Your Biogas System Workshop. Presentation prepared by: Anna Crolla, M.A.Sc. Chris Kinsley, M.Eng., P.Eng.

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Anaerobic Digestion Basics – Science, Systems and Benefits Building Your Biogas System Workshop

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  1. Anaerobic Digestion Basics – Science, Systems and BenefitsBuilding Your Biogas System Workshop Presentation prepared by: Anna Crolla, M.A.Sc. Chris Kinsley, M.Eng., P.Eng. 3rd Annual Growing the Margins Conference1st Annual Canadian Farm & Food Biogas ConferenceLondon Convention Centre, London, ON March 10, 2009 AgriEnergy Producers’ Association of Ontario

  2. Anaerobic Digestion (AD) • Conversion of organic matter to biogas (methane and carbon dioxide) by anaerobic microorganisms • Biogas can be used to run a generator producing electricity and heat, or it can be burned as a fuel in a boiler or other burner • AD works well with liquid manures with a dry matter content between 6 and 14% • Temperature: • Mesophilic: 35 to 40oC • Thermophilic: 55 to 65oC • Low temperature: 15 to 25oC • Nutrients going into the system equals the nutrients discharged from the system

  3. H2, CO2 28% 24% Methane (CH4) Complex Organics Volatile Fatty Acids 76% + CO2, H2S 52% 72% Acetic Acid Stage 1: Hydrolysis & Fermentation Stage 2: Acetogenesis & Dehydrogenation Stage 3: Methane Fermentation Fundamentals of Anaerobic Digestion • AD is a biological process where microorganisms metabolize the organic material (i.e. volatile solids) in manure and produce biogas as a by-product • Controlling environmental factors is crucial to keeping microorganisms healthy and producing biogas (i.e. acid formers and methane formers should be kept in balance)

  4. Benefits of Anaerobic Digestion • Production of renewable energy – biogas usually contains a methane content of approximately 60%, which can be stored and used on demand. • Permits the addition of various substrates to increase biogas production, known as co-digestion. • Odour reduction – can be in the order of 80 to 90%. • Reduction of pathogens of up to 1 to 2 logs depending on configuration. • Reduction of greenhouse gas emissions. • Improves the immediate fertilizer value of the manure.

  5. Scale of Digester Systems • On-Farm • Typically for one farm’s manure or manure from several nearby small farms • Lower capital cost and a much lower level of complexity and control • Successfully adopted throughout North America • Centralized • Manure is hauled to a centralized digester • High organic wastes are often added to increase biogas production • Transportation costs can be significant (in Europe radius is < 8 km) • Bio-security issues • Popular throughout Europe

  6. Types of Digester Systems • Wet Fermentation • Completely Mixed Digester • Plug-flow digester • Dry Fermentation • Plug-flow digester: Bunker-style digester

  7. Components of a Completely Mixed Digester System Exterior Expandable gas storage roof Generator Room Generator Room Location: Fepro Farms, Cobden, ON Location: Terryland Farms, St. Eugene, ON Agitator Motors Agitator Motor

  8. Components of a Completely Mixed Digester System Interior Impeller for Agitation Heating Tubes Wooden Ceiling Source: Böhni Digester

  9. Plug-flow Digester (wet fermentation) Source: AgStar, 2005 with paddle mixing Source: Michael Köttner, October 2008

  10. Bunker-stylePlug-flow Digester (dry fermentation) Source: Michael Köttner, October 2008

  11. Electricity and Heat Production(Co-generation) • Biogas: • 60-65% methane • 35-40% carbon dioxide • Trace amounts of H2S (0.2 to 0.4%) • Methane is used to run a generator to produce electricity (generator typical runs on methane and other fuel) • Electricity and heat are produced

  12. Co-generation Motor Heat exchanger system for heat recovery from engine cooling water and engine exhaust Controls for digester temperature, agitation, de-sulphuring biogas, and gas analysis Source: Terryland Farms Inc. and Böhni Energy & Umwelt GmbH

  13. Biogas Production 1 Based on energy potential of 21180 Btu/m3 for biogas containing 60% methane 2 Assume a 35% cogeneration efficiency for electricity production, where 1 million Btu is equivalent to 293 kWh of electricity Adapted from Schwart et al., Methane Generation, U.S. Dept. of Energy, 2005

  14. Example: Dairy Farm with 250 cows 250 cows has the potential to produce: • 312 m3 of biogas per day • 6.6 million Btu of energy per day: • Electricity = 675 kWh per day (assuming 35% cogeneration efficiency for electricity production) • Waste heat recovery = 3 million Btu per day (assuming 70 % efficiency for waste heat recovery)

  15. Electricity Production Example: Fepro Farm Digester, Cobden, ON

  16. Co-digestion • Substrates rich in organic matter (agricultural and non-agricultural sources) • Increases biogas production (up to 2-4 times) • Possibility of obtaining tipping fees – good source of revenue for producer • Agricultural producers already manage high organic wastes • Popular in Europe • Disadvantage: farm could be designated a waste disposal site • Regulations are being finalized by OMAFRA and MOE

  17. Biogas Potential of Manure and Co-substrates Source: Adapted from Weiland et al., 2000

  18. Co-substrate Materials • At least 75% (by volume) of total material in digester must be on-farm materials • Maximum amount of off-farm materials is 25% (by volume) of total material in digester • At least 50% (by volume) of total material in digester must be manure • Off-farm materials cannot exceed 5,000 m3 per year and no more than 100 m3 of off-farm materials can be received in any one day (unless it is farm feed) • Minimum hydraulic retention time of materials treated in digester is 20 days (other HRTs must be specified by engineer)

  19. Must be materials listed in Schedule 1 or 2 and not listed in Schedule 3 Off-farm Materials

  20. Electricity Production Example: Fepro Farm Digester, Cobden, ON

  21. Electricity Production Example: Terryland Farm Digester, St. Eugene, ON 1 Calculated values based on 280 animal units 2 Calculated biogas production based on daily electricity production and assumed 35% efficiency for the methane to electricity conversion. • Grease residue is added to manure digester at 20% by volume • Currently at capacity of 180 kW generator

  22. Odours • Odours: ammonia (NH3), volatile fatty acids (VFA), phenolic compounds • 98 % reduction of VFAs Example: Fepro Farm Digester, Cobden, ON

  23. Pathogens • 70-95% reduction in pathogens (~ 1-2 logs) Examples: Digesters at Fepro Farm, Cobden, ON & EEC, Thunder Bay, ON E.coli in raw manure sample E.coli in digested manure sample

  24. Greenhouse Gases • Greenhouse gases are reduced • Reduction of CH4 in storage of manure • Reduction of N2O from manure application • NH3 may volatilise just after manure application • Land application trials conducted at AAFC in Ottawa and Terryland Farm to measure NH3 and N2O emissions after the application of raw and digested manure

  25. CH4 Emissions at Fepro Farms Source: Drs. Ray Desjardins, R. van Haarlem, Matthew McBain (AAFC – Ottawa)

  26. Gas Emissions from Land Application Trials of Application of Raw & Digested Manure NH3 Flux N2O Flux Source: Dr. Elizabeth Pattey (AAFC – Ottawa)

  27. Fertilizer Value of Digested Manure • Nutrients going into the digester system = nutrients discharged from the system • just present in different forms • Organic nitrogen is transformed into ammonia during digestion – ammonia is more readily available for plant uptake • May have nutrient losses if plants are not present for the uptake of nutrients • Crop yields and the movement of nutrients in the soil and water (surface and subsurface) are being studied at the Campus d’Alfred

  28. Corn Yields * Corn yields are standardized to 15.5% moisture and 56 lbs per bushel

  29. Nitrates in Drainage Waters 1 Land application trials were designed to deliver approximately 110 kg ha-1 of total nitrogen to fields 2 Land application trials were designed to deliver approximately 75 kg ha-1 of total nitrogen to fields E.coli in Subsurface Drains 2 Year Log Geometric Mean of Pathogen Indicator Numbers in Subsurface Drains

  30. Important Points • The technology is there to produce electricity on-farm • Ontario governments are working to make on-farm digesters economically feasible (i.e. electricity pricing & use of off-farm materials) • Need to consider other benefits of AD: • Pathogen removal • Odour removal • Treatment of off-farm sourced organics

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