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