Anaerobic Digestion Basics Science, Systems and Benefits

Transcription

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 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 H 2, CO 2 28% 24% Complex Organics 76% Volatile Fatty Acids 52% Methane (CH 4 ) + CO 2, H 2 S 72% Acetic Acid Stage 1: Hydrolysis & Fermentation Stage 2: Acetogenesis & Dehydrogenation Stage 3: Methane Fermentation 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 2. Production of renewable energy biogas usually contains a methane content of approximately 60%, which can be stored and used on demand. 3. Permits the addition of various substrates to increase biogas production, known as co-digestion. 4. Odour reduction can be in the order of 80 to 90%. 5. Reduction of pathogens of up to 1 to 2 logs depending on configuration. 6. Reduction of greenhouse gas emissions. 7. 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 %TS < 13 %TS (pumpable) Technique Process Recirculation of leachate & need pre-mixing Modular; single stage batch process Substrates kept well mixed - homogeneous Continuous process Construction Concrete Concrete or Steel

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

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 Source: Michael Köttner, October 2008 Bunker-style Plug-flow Digester (dry fermentation)

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

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) , Poultry (1.8 kg) 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 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 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 Example: Fepro Farm Digester, Cobden, ON Daily Electricity Production (kwh/day) and 3 Daily Biogas Production /day) (m Dec Jan Feb Feb-07 Electricity Production 19-Mar Apr Apr May-07 Biogas Production 07-Jun Jun-07 Date Biogas (m 3 /day) Fepro Farm Digester Manure Only (January 1, 2006 to June 30, 2007) Electricity (kwh/day) Heat (Btu/hr) Average ,000 STDEV n

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 Biogas Yield (m 3 gas/t substrate ) Cow manure (9%TS) Pig manure (7%TS) Chicken manure (15%TS) Whey Beet chips Brewer's grain Thick stillage Green wastes Biowaste Flotation fat Used fat 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 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 1 Schedule 2 (requires pasteurization) 1. Waste products suitable to feed farm animals (contains animal product that has not 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 4. Organic waste derived from production of ethanol and biodiesel 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. Paunch manure 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 9. Organic waste material from greenhouse, nursery, garden centre etc. 4. Resins and plastics 5. Restaurant waste and airplane food waste

20 Electricity Production Example: Fepro Farm Digester, Cobden, ON Daily Electricity Production (kwh/day) and 3 Daily Biogas Production /day) (m Dec Jan Mar Mar Apr-07 Electricity Production Biogas Production Addition of FOG 30-May Jun Jul Aug-07 Date 27-Sep Oct Nov Dec Jan Feb-08 Fepro Farm Digester - No Grease Biogas Electricity (m 3 /day) (kwh/day) Fepro Farm Digester With Grease (Grease added at 16% by volume) Total Biogas (m 3/ day) Electricity (kwh/day) Flared Biogas (m 3 /day) Average STDEV n

21 Electricity Production Example: Terryland Farm Digester, St. Eugene, ON No Grease With Grease Biogas Electricity Biogas Electricity (m 3 /day) (kwh/day) (m 3 /day) (kwh/day) Average STDEV n 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 (NH 3 ), volatile fatty acids (VFA), phenolic compounds 98 % reduction of VFAs Acetic Acid Example: Fepro Farm Digester, Cobden, ON Raw Manure Propionic Acid Total VFA Concentrations (mg/l) Butyric Acid TVFA Acetic Acid Digested Manure Propionic Acid Butyric Acid TVFA Average <1 134 STDEV % Red

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

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 Heifers Calves Silos NH3 & CH4 Laser3 (06/29/07) Main Barn Road Open Barn - Dry Cow s Lagoon/ Biodigestor Background (Laser2) Laser1 (06/28/07) Laser4 (06/29/07) Sonic Anemometer N Summer 2007 Methane Emissions from Manure Type (kg CH 4 head -1 yr -1 ) Raw Manure Digested Manure % Reduction Mean STDEV Source: Drs. Ray Desjardins, R. van Haarlem, Matthew McBain (AAFC Ottawa)

26 Gas Emissions from Land Application Trials of Application of Raw & Digested Manure NH 3 Flux FG-TDL biodigested slurry FG-TDL raw slurry REA-DT bioigested slurry REA-DT raw slurry N 2 O Flux CFIA Field 14 Precipitation Raw Dairy Slurry Biodigested Dairy Slurry NH 3 Flux (mg NH 3 -N m -2 h -1 ) Raw slurry spread CD N 2 O Flux (mg N 2 O-N m -2 d -1 ) Precipitation (mm d -1 ) Digested slurry spread Calendar Day (2007) Calendar Day (2007) 0 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) 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 Raw Manure Corn Yield (bu/ac) * Digested Manure Inorganic Fertilizer Alfred Campus * Corn yields are standardized to 15.5% moisture and 56 lbs per bushel

29 Nitrates in Drainage Waters 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 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 ± ± ± ± 0.6 Digested Manure 2.3 ± ± ± ± 0.6 Inorganic Fertilizer Control 2.1 ± ± ± ± 0.6

30 Important Points 1. The technology is there to produce electricity onfarm 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