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

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Presentation on theme: "Anaerobic Digestion Basics – Science, Systems and Benefits Building Your Biogas System Workshop Presentation prepared by: Anna Crolla, M.A.Sc. Chris Kinsley,"— Presentation transcript:

1 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. AgriEnergy Producers’ Association of Ontario 3rd Annual Growing the Margins Conference 1st Annual Canadian Farm & Food Biogas Conference London Convention Centre, London, ON March 10, 2009

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 40 o C –Thermophilic: 55 to 65 o C –Low temperature: 15 to 25 o C Nutrients going into the system equals the nutrients discharged from the system

3 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) Stage 1: Hydrolysis & Fermentation Stage 2: Acetogenesis & Dehydrogenation Stage 3: Methane Fermentation Complex Organics H 2, CO 2 Acetic Acid Methane (CH 4 ) + CO 2, H 2 S Volatile Fatty Acids 76% 24% 52% 72% 28%

4 Benefits of Anaerobic Digestion 1.Production of renewable energy – biogas usually contains a methane content of approximately 60%, which can be stored and used on demand. 2.Permits the addition of various substrates to increase biogas production, known as co-digestion. 3.Odour reduction – can be in the order of 80 to 90%. 4.Reduction of pathogens of up to 1 to 2 logs depending on configuration. 5.Reduction of greenhouse gas emissions. 6.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 CriteriaDry FermentationWet Fermentation Total Solids20-60 %TS< 13 %TS (pumpable) TechniqueRecirculation of leachate & need pre-mixing Substrates kept well mixed - homogeneous ProcessModular; single stage batch process Continuous process ConstructionConcreteConcrete or Steel

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

8 Interior Source: Böhni Digester Components of a Completely Mixed Digester System Impeller for AgitationHeating TubesWooden Ceiling

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

10 Bunker-style Plug-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 H 2 S (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 Source: Terryland Farms Inc. and Böhni Energy & Umwelt GmbH 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

13 Biogas Production Animal Biogas Potential (m 3 /animal/day) Energy Potential (Btu/animal/day) 1 Electricity Potential (kWh/animal/day) 2 Dairy (545kg) , Beef (454 kg) , Swine (68 kg) 0.275, Poultry (1.8 kg) Adapted from Schwart et al., Methane Generation, U.S. Dept. of Energy, Based on energy potential of Btu/m 3 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

14 Example: Dairy Farm with 250 cows 250 cows has the potential to produce: 312 m 3 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 Fepro Farm Digester – Manure Only (January 1, 2006 to June 30, 2007) Biogas (m 3 /day) Electricity (kWh/day) Heat (Btu/hr) Average ,000 STDEV n 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 Source: Adapted from Weiland et al., 2000 Biogas Potential of Manure and Co-substrates

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 m 3 per year and no more than 100 m 3 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 Off-farm Materials Must be materials listed in Schedule 1 or 2 and not listed in Schedule 3 Schedule 1Schedule 2 (requires pasteurization) 1. Waste products suitable to feed farm animals (contains animal product that has not been denatured) 1. Waste products suitable to feed farm animals (contains animal product that has been denatured) 2. Materials that previously would have been a product in 1. but no longer suitable for feeding animals for reasons that do not include contamination 3. Organic waste matter derived from drying or cleaning field crops 3. Paunch manure 4. Organic waste derived from production of ethanol and biodiesel Schedule 3 (requires C of A) 5. Aquatic plants1. Waste that contains cleaners 6. Organic waste matter from food processing2. Solvents (volatile organic compound) 7. Fruit and vegetable waste3. Petroleum products and hydrocarbon fuels 8. Leaf & yard waste / Raw sawdust & wood chips4. Resins and plastics 9. Organic waste material from greenhouse, nursery, garden centre etc. 5. Restaurant waste and airplane food waste

20 Electricity Production Example: Fepro Farm Digester, Cobden, ON Fepro Farm Digester - No GreaseFepro Farm Digester – With Grease (Grease added at 16% by volume) Biogas (m 3 /day) Electricity (kWh/day) Total Biogas (m 3/ day) Electricity (kWh/day) Flared Biogas (m 3 /day) Average STDEV n

21 No GreaseWith Grease Biogas (m 3 /day) Electricity (kWh/day) Biogas (m 3 /day) Electricity (kWh/day) Average STDEV n-- 51 Electricity Production Example: Terryland Farm Digester, St. Eugene, ON  Grease residue is added to manure digester at 20% by volume  Currently at capacity of 180 kW generator 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.

22 Odours  Odours: ammonia (NH 3 ), volatile fatty acids (VFA), phenolic compounds  98 % reduction of VFAs Example: Fepro Farm Digester, Cobden, ON Total VFA Concentrations (mg/L) Raw ManureDigested Manure Acetic Acid Propionic Acid Butyric Acid TVFAAcetic Acid Propionic Acid Butyric Acid TVFA Average <1 134 STDEV % Red

23 Pathogens E.coli in raw manure sample E.coli in digested manure sample  70-95% reduction in pathogens (~ 1-2 logs) Examples: Digesters at Fepro Farm, Cobden, ON & EEC, Thunder Bay, ON Pathogens Geometric Mean Bacteria Concentrations (CFU/100mL) Fepro DigesterTerryland Digester Raw Manure Digested Manure Log Reduction Raw Manure Digested Manure Log Reduction E.coli 4.33 E E E E Log STDEV Salmonella 2.04 E E E E Log STDEV C.perfringens 3.82 E E E E Log STDEV Enterococci 1.69 E E E E Log STDEV

24 Greenhouse Gases Greenhouse gases are reduced –Reduction of CH 4 in storage of manure –Reduction of N 2 O from manure application NH 3 may volatilise just after manure application Land application trials conducted at AAFC in Ottawa and Terryland Farm to measure NH 3 and N 2 O emissions after the application of raw and digested manure

25 CH 4 Emissions at Fepro Farms Source: Drs. Ray Desjardins, R. van Haarlem, Matthew McBain (AAFC – Ottawa) Summer 2007 Methane Emissions from Manure Type (kg CH 4 head -1 yr -1 ) Raw ManureDigested Manure% Reduction Mean STDEV

26 NH 3 Flux N 2 O Flux Gas Emissions from Land Application Trials of Application of Raw & Digested Manure Source: Dr. Elizabeth Pattey (AAFC – Ottawa) Raw Manure Application Digested Manure Application NH 3 Emission Factor (kg NH 3 per kg Inorganic-N applied) N 2 O Emission Factor (kg N 2 O per kg Inorganic-N applied) 0.026

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 Location Corn Yield (bu/ac) * Raw Manure Digested Manure Inorganic Fertilizer Alfred Campus * Corn yields are standardized to 15.5% moisture and 56 lbs per bushel

29 Land Application Trials Flow-weighted Mean NO 3 — N Concentrations (mg L -1 ) Surface Drains Subsurface Drains Surface Drains Subsurface Drains Spring 1 Fall 2 Raw Manure Digested Manure Inorganic Fertilizer Control 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 Nitrates in Drainage Waters E.coli in Subsurface Drains E.coliSalmonellaC.perfringensEnterococci Raw Manure2.3 ± ± ± ± 0.6 Digested Manure2.3 ± ± ± ± 0.6 Inorganic Fertilizer Control2.1 ± ± ± ± Year Log Geometric Mean of Pathogen Indicator Numbers in Subsurface Drains

30 Important Points 1.The technology is there to produce electricity on- farm 2.Ontario governments are working to make on-farm digesters economically feasible (i.e. electricity pricing & use of off-farm materials) 3.Need to consider other benefits of AD: –Pathogen removal –Odour removal –Treatment of off-farm sourced organics


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