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Presentation prepared by: Anna Crolla, M.A.Sc.

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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. 3rd Annual Growing the Margins Conference 1st Annual Canadian Farm & Food Biogas Conference London 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 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 H2, CO2 Acetic Acid Methane (CH4) + CO2, H2S Volatile Fatty Acids 76% 24% 52% 72% 28%

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 Criteria Dry Fermentation Wet Fermentation Total Solids 20-60 %TS < 13 %TS (pumpable) Technique Recirculation of leachate & need pre-mixing Substrates kept well mixed - homogeneous Process Modular; single stage batch process Continuous process Construction Concrete Concrete or Steel

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-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 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 Dairy (545kg) 1.25 26,400 2.7 Beef (454 kg) 0.85
Animal Biogas Potential (m3/animal/day) Energy Potential (Btu/animal/day)1 Electricity Potential (kWh/animal/day)2 Dairy (545kg) 1.25 26,400 2.7 Beef (454 kg) 0.85 18,000 1.8 Swine (68 kg) 0.27 5,700 0.6 Poultry (1.8 kg) 0.03 635 0.07 1 Based on energy potential of 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 Fepro Farm Digester – Manure Only (January 1, 2006 to June 30, 2007) Biogas (m3/day) Electricity (kWh/day) Heat (Btu/hr) Average 391 699 300,000 STDEV 77 80 -- n 300

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 Schedule 2 (requires pasteurization) Schedule 3 (requires C of A)
Off-farm Materials Must be materials listed in Schedule 1 or 2 and not listed in Schedule 3 Schedule 1 Schedule (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 plants 1. Waste that contains cleaners 6. Organic waste matter from food processing 2. Solvents (volatile organic compound) 7. Fruit and vegetable waste 3. Petroleum products and hydrocarbon fuels 8. Leaf & yard waste / Raw sawdust & wood chips 4. 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 Grease Fepro Farm Digester – With Grease (Grease added at 16% by volume) Biogas (m3/day) Electricity (kWh/day) Total Biogas Flared Biogas Average 391 699 1133 1213 382 STDEV 77 80 478 329 114 n 300 155 175 99

21 Electricity Production
Example: Terryland Farm Digester, St. Eugene, ON No Grease With Grease Biogas (m3/day) Electricity (kWh/day) Average 3501 7561 16222 3684 STDEV -- 800 n 51 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 Total VFA Concentrations (mg/L) Raw Manure Digested Manure Acetic Acid Propionic Acid Butyric Acid TVFA Average 4988 1432 734 7154 92 42 <1 134 STDEV 1231 649 413 1221 38 35 6 73 % Red. 98 97 99.8

23 Pathogens 70-95% reduction in pathogens (~ 1-2 logs)
Geometric Mean Bacteria Concentrations (CFU/100mL) Fepro Digester Terryland Digester Raw Manure Digested Manure Log Reduction Digested Manure E.coli 4.33 E+08 2.26 E+05 3.29 2.10 E+08 7.53 E+05 2.44 Log STDEV 0.82 0.57 0.64 0.34 Salmonella 2.04 E+04 2.43 E+03 0.92 4.71 E+05 2.47 E+04 1.28 0.94 0.67 0.88 0.43 C.perfringens 3.82 E+06 6.71 E+05 0.75 7.50 E+05 2.75 E+05 0.44 0.54 0.47 0.37 0.19 Enterococci 1.69 E+07 1.53 E+06 1.05 2.46 E+06 2.66 E+05 0.97 0.29 0.31 0.36 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
Summer 2007 Methane Emissions from Manure Type (kg CH4 head-1 yr-1) Raw Manure Digested Manure % Reduction Mean 25.19 13.82 45 STDEV -- 3.71 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 Raw Manure Application Digested Manure NH3 Emission Factor (kg NH3 per kg Inorganic-N applied) 0.22 0.32 N2O Emission Factor (kg N2O per kg Inorganic-N applied) 0.026 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 Location Corn Yield (bu/ac) * Raw Manure Digested Manure
Inorganic Fertilizer Alfred Campus 128 196 179 * Corn yields are standardized to 15.5% moisture and 56 lbs per bushel

29 E.coli in Subsurface Drains
Nitrates in Drainage Waters Land Application Trials Flow-weighted Mean NO3—N Concentrations (mg L-1) Surface Drains Subsurface Spring 1 Fall 2 Raw Manure 6.62 8.20 2.18 4.03 Digested Manure 12.02 14.97 4.31 4.77 Inorganic Fertilizer Control 10.36 11.52 4.01 3.99 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 E.coli Salmonella C.perfringens Enterococci Raw Manure 2.3 ± 1.3 1.9 ± 1.2 1.1 ± 1.3 0.9 ± 0.6 Digested Manure 2.3 ± 1.2 1.9 ± 1.3 1.1 ± 0.9 Inorganic Fertilizer Control 2.1 ± 1.1 1.1 ± 1.0 0.8 ± 0.6

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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