Anaerobic Digestion Basics – Anaerobic Digestion Basics – Science, Systems and BenefitsScience, Systems and Benefits

Building Your Biogas System WorkshopBuilding 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

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

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%

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.

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

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

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

Interior

Source: Böhni Digester

Components of a Completely Mixed Digester System

Impeller for Agitation Heating Tubes Wooden Ceiling

Plug-flow Digester (wet fermentation)

Source: Michael Köttner, October 2008

Source: AgStar, 2005

with paddle mixing

Bunker-style

Plug-flow Digester (dry fermentation)

Source: Michael Köttner, October 2008

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

Co-generation

Source: Terryland Farms Inc. and Böhni Energy & Umwelt GmbH

MotorHeat exchanger system for heat recovery from engine cooling water and engine exhaust

Controls for digester temperature, agitation, de-sulphuring biogas, and gas analysis

Biogas Production

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

Adapted from Schwart et al., Methane Generation, U.S. Dept. of Energy, 2005

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

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)

Electricity Production

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 300 300 --

Example: Fepro Farm Digester, Cobden, ON

0

100

200

300

400

500

600

700

800

900

1000

Date

Daily E

lectr

icit

y P

rod

ucti

on

(kW

h/d

ay)

an

d

Daily B

iog

as P

rod

ucti

on

(m

3/d

ay)

Electricity Production Biogas Production

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

Source: Adapted from Weiland et al., 2000

Biogas Potential of Manure and Co-substrates

30

36

58

55

75

75

80

110

120

400

800

0 100 200 300 400 500 600 700 800 900

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

Biogas Yield (m3gas/tsubstrate)

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)

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)

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

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

Electricity ProductionExample: Fepro Farm Digester, Cobden, ON

0

500

1000

1500

2000

2500

3000

Date

Daily E

lectr

icit

y P

rod

ucti

on

(kW

h/d

ay)

an

d

Daily B

iog

as P

rod

ucti

on

(m

3/d

ay)

Electricity Production Biogas Production

Addition of FOG

Fepro Farm Digester - No Grease Fepro Farm Digester – With Grease(Grease added at 16% by volume)

Biogas

(m3/day)

Electricity

(kWh/day)

Total Biogas

(m3/day)

Electricity

(kWh/day)

Flared Biogas

(m3/day)

Average 391 699 1133 1213 382

STDEV 77 80 478 329 114

n 300 300 155 175 99

No Grease With Grease

Biogas

(m3/day)

Electricity

(kWh/day)

Biogas

(m3/day)

Electricity

(kWh/day)

Average 3501 7561 16222 3684

STDEV -- -- -- 800

n -- -- -- 51

Electricity ProductionExample: 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.

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 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 98

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 Digester Terryland Digester

Raw Manure

Digested Manure

Log Reduction

Raw Manure

Digested

Manure

Log Reduction

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

Log STDEV 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

Log STDEV 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

Log STDEV 0.29 0.31 0.57 0.36

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

CH4 Emissions at Fepro Farms

Source: Drs. Ray Desjardins, R. van Haarlem, Matthew McBain (AAFC – Ottawa)

5061850

5061900

5061950

5062000

5062050

5062100

359050 359100 359150 359200 359250 359300 359350

RoadOpen Barn - Dry Cow s

Lagoon/Biodigestor

Main Barn

Silos

Background (Laser2)

Laser1(06/28/07)

Laser4 (06/29/07)

NH3 & CH4 Laser3 (06/29/07)

8 Heifers

Calves

Sonic Anemometer

NN

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 --

CFIA Field 14

-20

-15

-10

-5

0

5

10

15

20

25

30

127 132 137 142 147 152 157 162 167 172 177 182 187 192 197 202 207

Calendar Day (2007)

N2O

Flu

x (m

g N

2O-N

m-2

d-1

)

0

10

20

30

40

50

60

70

80

90

100

Pre

cipi

tatio

n (m

m d

-1)

Precipitation

Raw Dairy Slurry

Biodigested Dairy Slurry

-20

0

20

40

60

80

100

120

140

160

180

200

220

240

260

134 135 136 137 138 139 140

Calendar Day (2007)

NH

3 Fl

ux (

mg

NH

3-N

m-2

h-1

)

FG-TDL biodigested slurryFG-TDL raw slurryREA-DT bioigested slurryREA-DT raw slurry

Raw slurry spreadCD 137-138

Digested slurry spread

NH3 Flux

N2O 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

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 0.026

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

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

Land Application Trials

Flow-weighted Mean NO3—N Concentrations (mg L-1)

Surface Drains

Subsurface Drains

Surface Drains

Subsurface Drains

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

Nitrates in Drainage Waters

E.coli 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 0.9 ± 0.6

Inorganic Fertilizer Control 2.1 ± 1.1 1.9 ± 1.3 1.1 ± 1.0 0.8 ± 0.6

2 Year Log Geometric Mean of Pathogen Indicator Numbers in Subsurface Drains

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