Plug Flow Digesters

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Plug Flow Digesters

• Peter Wright, Manure Treatment Specialist
• Scott Inglis, Research Associate
• Department of Biological and Environmental
  Engineering
• Cornell University

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Reasons to adopt Methane Generation in 1970s

• Energy prices went up and were expected to go
  higher
• Guaranteed price for electricity produced
• Technology was demonstrated successfully
• Problems in 1970s
• Biological systems management on farms was
  primitive
• Peak energy demands on farm
• Few large farms
• High capital costs
• High maintenance costs
• Cows on pasture

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Electricity use profile for 100 and 600 cow
dairies (Jewell)
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Electric Cost / Cow / Year
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Reasons to adopt Methane Digestion in 2004

• Odor control is a real need
• More larger farms with economies of sale
• Management ability of biological systems on farms
  has increased
• Electric demand on some farms is continuous
• Liquid manure handling systems are more advanced
• Solid separation
• Problems in 2004
• High capital costs
• Support industry not developed
• Wholesale electric price is low

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Percent of Time Cows are out of the Barn
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Plug Flow

• No Mixing
• Inflow Outflow, HRTSRT
• HRT 20-25 days

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Plug Flow advantages

• Perfect for scraped dairy manure
• Many successful examples
• Slug loads?

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Plug Flow Disadvantages

• Total solids need to be close to 12
• Short Circuiting

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Solid Settling
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Manure characteristics and estimated amounts per
cow from Anaerobic Digestion System
(Wright and Perschke)
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Farm ML Schematic
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Benefits

• Electric sales off farm 12,000
• Tipping fee for handling food wastes 210,000
• Bedding material replacement, separated,
  partially composted (2 weeks) used as bedding
  15,600
• Compost sales, potential markets still being
  developed 6,000
• Hot water, heat recovered from the engine used in
  calf barn and milking center 6,000
• Odor control, avoided cost of additives and
  management time to resolve complaints
  5,100
• Gas sales to drying operation 100,000
• Total annual benefits 392,785

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Food waste benefits

• Profits from tipping fees
• More energy
• Small nutrient increase
• Heated waste
• Pays for odor control
• Pays for pathogen reduction
• Liquefies the manure stream
• Reduction of solids

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Food Waste Disadvantages

• Foam
• Too much gas
• Potential contamination
• Regulatory constraints

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Anaerobic Digestion Systems

• Biological
• Manure and Effluent Handling
• Separation
• Gas Collection
• Conditioning
• Engine
• Electric
• Heat
• Management

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Benefits

• Energy production
• Odor Reduction
• Nutrient Management
• Solid Sales
• Bedding use
• Liquefy Manure
• Integration with other enterprises
• Profit Center

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Loss (left) and resultant availability relative
to fertilizer N (right) of ammonium nitrogen from
manure as a function of manure dry matter content
and time after spreading.

Bill Jokela, VT
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Choosing a Manure System

• Minimize environmental damage
• Maximize nutrient value
• Minimize neighbor problems
• Minimize damage to the land
• Minimize cost
• Minimize frustration

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Anaerobic Digestion Systems

• Management
• Dedicated
• Safety
• Gas
• Electric
• Mechanics
• By-Product Utilization
• Electric
• Heat
• Nutrients
• Solids

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Conclusions

• Alternative Systems depend on farm situation
• Maximize By-Product Use
• Maximize Profits
• Integrate with other enterprises
• More Research is Needed

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Questions?