Converting Dairy Manure into Energy. An introduction to anaerobic digestion of farm waste Stefan Grimberg Associate Professor Dept. Civil Environ. Eng Clarkson University

Thank you to Floyd Schanbacher

Anaerobic Digester Potential Benefits Odor Control Reduced liability Manure stabilization Help with nutrient management Soil stability Energy generation Offset farm electricity requirements from grid Sale of extra energy Heat generation to reduce fuel required Reuse of bedding solids Offset bedding cost

Plug Flow Digesters Little mixing Few mechanical parts Simple

Mixed Digesters Mechanical mixing in tank More gas production Slightly higher capital cost

Behringen co-fermentation plant in Germany Community Digester

Digester Feed

Large-scale Digester Performance

Capital Cost of Manure Management Technology Source: AgStar Publication:

Digester economics Dr. Fick’s estimated fixed of $660 per cow is a little low for the farms we are looking at. Tinesdale farm (in Minnesota), with1800 cows, invested about $1,000 per head. Good estimate $1,000 per cow? At this capital assumption AD system become economical based on sold energy alone at power sale price of $0.09/kWh. (Mehta, 2002)

Case Study Gordondale Farms, Nelsonville, WI 750 head dairy Sell biogas to utility that generates electricity on site, utility owns and operates generator Sell at $/kWh generated Martin, J.H., An evaluation of a mesophilic, modified plug flow anaerobic digester for dairy cattle manure. Final report for EPA contract GS10F-0036K

Summary

Martin, 2005

Economic Evaluation Capital costs with co/gen: $748,000 Annual sale of power: $18,396 Avoided annual bedding cost: $60,000 Sale of extra solids: $8,600 Total benefits: $86,996 Payback period: Approx 6 years.

Digester Systems Model DigesterSolids Sep. Cogen Manure Other Input Biogas Electricity offset Surplus electricity Surplus heat Spread liquid fraction Solids for bedding Sale of solids Solids field application Heat

Example 500 cow dairy Free stall barn Scraped manure Include flush from milking parlor Northern NY

Model Estimate: 500 cow dairy ItemCost/Benefit Capital CostDigester/Cogen system $656,180 Total Annual Cap. Cost over 10 yrs $68,774 Annual Operating CostsMaintenance, Repair $23,553 Potential Annual Benefits Fiber sales$9,133 Electric Sales (surplus)$17,707 Thermal Sales (surplus)$12,368 Methane Credit$7,646 Renewable Energy Tax Credit$4,203 Farm savings-Electric (internal)$25,171 Farm savings-Thermal (internal)$8,495 Tax Offset$16,739 Onsite Fiber value$10,000 Total Annual Benefits$111,463 Annual Net Benefit per Cow $38.27 Annual Net Benefit per Cow if excess heat cannot be sold $13.54 Annual Net Benefit per Cow without excess heat and methane credits -$1.8

Run Digester Model Demonstrate: Effect of size Power cost Bedding off set Any scenarios of interest?

Conclusions Anaerobic digestion of manure has significant potential to decrease fossil fuel use in rural areas. Community digesters may be very cost effective due to larger scale and mixed feed composition