Oregon’s Methane Project -Oregon’s Methane Project -Experience and PotentialExperience and Potential

Mike GamrothOregon State UniversityDept. of Animal Sciences

The processThe process• Anaerobic digestion – like the rumen

– Longer retention • Methane collection• Methane use

– Heat, hot water– Combustion engine electricity

“Methane digester”

Basic conceptsBasic concepts• Decomposition of organic material• Oxygen-free environment• Numerous strains of microorganisms• Biogas

– Methane 50-80%– CO2 20-50%– Other gases

• Ambient temperature– Covered lagoon– Lowest output

• Mesophilic– Around 100º F– More forgiving

• Thermophilic– Highest output, lower retention time

Digester typesDigester types• Plug flow

– Suited to scraped manure– Most common on dairies– Long rectangular tanks– Heat added, in-ground or insulated– Retention time (RT) 15 to 20 days

Digester typesDigester types• Complete mix

– Typically upright round tanks– Benefits from regular feeding– Can handle “wetter” manure– When co-digesting, mixing important

Digester typesDigester types• Covered lagoon

– Lowest cost, simplest to operate– Best suited to warm climates, wet manure– Lowest gas output– Often will be “seasonal”

Digester typesDigester types• Biofilm

– Can augment any digester– A place for bacterial activity– Reduces retention time

Economics 101Economics 101• A thrifty digester system can payback

in 7 to 10 years– Initial cost– Operation costs– Value of energy, tax credits– Other benefits – odor control, solids sales

Benefits of digestionBenefits of digestion• Generate energy from biomass• Odor reduction• More readily available nitrogen• Pathogen reduction

$65 $68 $80 $83

Why there aren’t more…Why there aren’t more…• Poor design• Lack of skills, time• Excessive maintenance, operation time• Diminishing returns over time• Lack of interest• Out of business

EPA and Meyer, et al

Keys to successKeys to success• Know your manure quality• Match the digester technology with the

manure• Select a tested design and keep it simple• Take advantage of incentives• Monitor the system daily• Line up operation and maintenance

backup

ResourcesResources

• http://www.epa.gov/agstar/index.html• Our project:

– Energy Trust of Oregon– Oregon Beef Council– Oregon Dairy Farmers Association

• Amanda Green (360) 751-4190 Amanda Green (360) 751-4190

A partnership of Cal-gon Farms A partnership of Cal-gon Farms and Portland General Electricand Portland General Electric

The systemThe system• Scraped manure• Piston pump to feed

digester• Digester effluent

through a screw-press screen

• Liquids stored in lagoon

• Solids in covered bunker

UsesUses• Lagoon liquids

mixed with water and irrigated onto field corn

• Solids are sold off the farm and used as bedding

• Recycling lagoon liquids through separator when not used for digester

Research projectResearch project• Questions about the farm’s nutrient

balance• Questions about the start-up and

stabilization of the digester• Received money from a grant program

to sample the digester during start-up and for a two month period during operation

• Evaluate solids as a soil amendment

Electrical OutputElectrical Output

Generation Record (based on PGE bills)

Cal-Gon Farms Biogas Project

6603362716778/3/2003

676291961411/27/2002

746312311510/29/2002

59630178869/28/2002

49430148178/29/2002

38432123017/30/2002

2753185275/30/2002

Avg kWh/day# DayskWhEnding Svc Date

Cal-Gon Anaerobic DigesterOrganic Acid Levels

0

500

1000

1500

2000

2500

3000

3500

1/9/

2002

1/16

/200

2

1/23

/200

2

1/30

/200

2

2/6/

2002

2/13

/200

2

2/20

/200

2

2/27

/200

2

3/6/

2002

3/13

/200

2

3/20

/200

2

3/27

/200

2

4/3/

2002

4/10

/200

2

4/17

/200

2

4/24

/200

2

5/1/

2002

5/8/

2002

5/15

/200

2

Sample Dates

(mg/

L)

Acetic Acid

Butyric Acid

Propionic Acid

Basic resultsBasic results

Lb. / 1000 gallons

DM % N P K CFU/100 ml E. coli

Raw manure 13.0 43 6 26 59 mill.

Digester effluent 4.6 27 4 19 1.2 mill.Solids 26.4 6.3/t 2.4/t 3.7/t

Exporting solids to reduce nutrient loadingExporting solids to reduce nutrient loading

Lb./cow-year (3.5 ton/cow)

N P K

Avg. separated solids1 17.1 3.0 6.5

Bernie’s separated

solids22.4 8.4 13

Bernie’s lagoon solids 31.1 14.6 9.4

1 Average of 51 separators, Willamette Valley, 1995

Solids plotsSolids plots

DAF separation

TS TSS

Raw 1.9

Sludge 3.3

Effluent 0.4 0.05

90%+ P removal