Electrons from Manure

1. Electrons from Manure Philip Goodrich PE, Department of Biosystems and Agricultural Engineering, University of Minnesota

2. Methane ~ 60% Carbon Dioxide ~ 40% Hydrogen sulfide ~ trace What is Anaerobic Digestion? Conversion of Organic Matter by Anaerobic Microbes to Biogas and Manure Effluent

3. Anaerobic Digestion • Use a heated container to accelerate the degradation of the manure. • Microorganisms produce a fuel gas and degrade the manure. • Less odors are produced when compared to non controlled anaerobic digestion

7. Advantages of Digestion • Total waste management system • Pollution control • Odor control • Nutrient conservation • Greenhouse gas reduction

8. Advantages of Digestion • Energy Production • For use as heat • For conversion to electricity • Combination of both • For hot water needs

9. Disadvantages of Digestion • Is somewhat costly • Higher management levels required • Startup is sometimes difficult • Storage required • Cannot store methane as a liquid!! • Some risk of explosion

10. Uses of Methane Gas • Household cooking • House heating • Water heating • Electrical generation • Barn heat • Making of alcohol fuels

11. Benefits of Methane Generation • Reducing greenhouse gases • Only waste management system which generates some energy • Reduces odors • Reduces the solids to be disposed

12. Drawbacks to Digestion • More critical management of system • Some risks with fuel storage • Energy recovery system is complex • More subject to upsets

13. More Details on the Digestion Process Odor Acid forming bacteria Volatile Solids (VS) Volatile organic acids Methane forming bacteria Methane, carbon dioxide, water, trace gases

15. Covered Lagoon Flexible cover on lagoon or manure storage Lowest gas production Least “controlled” system Longest HRT

17. Background • Haubenschild Farms, near Princeton, Minnesota • 800-cow dairy farm, 1000 acres of crop land • Built plug-flow digester in 1999 • Biogas is being converted to electricity by 130 kW internal combustion engine generator • Have added a small fuel cell to test technology

18. Plug-Flow Digester - A small “plug” of slurry is pumped into one end each day, causing a comparable amount to flow out of the other end into the storage basin in the background.

20. Existing building on left houses internal combustion engine, new building on right will support the fuel cell and Stirling Engine

23. Fuel cell purchased from Plug Power, Inc. Latham, NY

25. How do fuel cells work • A simple electrochemical process. • The positive and negative plates allow for a flow of elections. An electrolyte, carries the hydrogen's protons from one electrode to the other. • an electrolyte, such as a polymer electrolyte membrane, separates an electron from the proton of a hydrogen atom. • The freed electron travels through a wire to power any electrical device. • A proton and electron reunite to form hydrogen and the hydrogen combines with oxygen to form water.

26. Challenges • Hydrogen sulfide removal • Initial concentration 3000-5000 ppm • Need concentration < 25 ppb • Moisture removal • Need dry gas • Carbon dioxide removal • Need concentration < 5 ppm

27. Environment and Economic Benefits • Reduced reliance on fossil fuels as an energy source • Reduced odors and emissions • Nutrient properties of the digested manure are unchanged • Distributed energy from a renewable resource support the rural economy while reducing reliance on fossil fuels and reducing emission of greenhouse gases.

28. Haubenschild Digester • Biogas production 93ft3/cow/day • (66 ft3/day/1000lb lw) • Electrical production 4 kWh/cow/day

29. Summary • Anaerobic treatment will reduce odors and produce some useful energy. • Systems are more complex than simple storage.

30. Questions • www.bae.umn.edu/extens/manure/

31. Advancing Utilization of Manure Methane Digester • Funding for this project was recommended by the Legislative Commission on Minnesota Resources from the Minnesota Environment and Natural Resources Trust Fund ($204, 375)

32. Other Key Facts • There is “no” reduction in manure volume • There is no reduction in manure nutrients • Some organic nitrogen is converted to ammonia nitrogen and could be volatilized in the manure storage • There is no increase in manure nutrients

33. History of Digestion • First plant built in India in 1859 • Fueled street lamps in England in 1985 • In 1998 an estimated 600 farm-based digesters were in use. • Estimated 31 digesters are currently in operation on farms in US

34. Terms to Know • Volatile Solids (VS) - A measure of the weight of solids that is combustible “volatilized” at a temperature of 600°C. It is reported as a percent of the total weight of the manure sample. Methane production is often based on the volatile solids portion of the manure.

35. Volatile Solids Production Dairy = 10 lbs VS per day Swine = 8.5 lbs VS per day Layer = 12 lbs VS per day (per 1000 lbs live weight) Approximately 50-70% of the VS can be converted. This depends on species and digester design.

36. Temperature considerations • Psychrophilic <68 ºF • Mesophilic 95-105 ºF • Thermophilic 125-135 ºF

37. pH considerations • Methane forming bacteria require pH of between 6.8 and 7.4

38. Biogas composition • Methane ~ 60% • Carbon Dioxide ~ 40% • Hydrogen sulfide ~ trace

39. Methane is a Fuel Source • Natural gas is 99% methane • Methane is about 900 BTU/ft3 • Propane is 2284 BTU/ft3

40. Typical Energy Production per1000 lbs live weight Species VS Biogas Energy lb/day ft3/day* BTU/day Dairy 10.0 39 23,400 Swine 8.5 28 16,800 Layer 12.0 37 22,000 Taken from MWPS-18 *Biogas production is typically much higher than these reported values (often more than twice).