Anaerobic Digester for Air Quality
In western Montana, the Northern Rocky Mountain RC&D Council helped the Huls Dairy, a 100-year old family dairy farm, build an anaerobic digester. The digester uses manure from the dairy’s 800 animals to create methane gas that is collected and burned to generate energy for the dairy. The remaining solids are separated and bagged for use as a soil amendment, and the remaining nutrient-rich liquid is used in the irrigation system as plant food for the farm’s corn and alfalfa crops.
Digestion occurs in two 30,000 gallon tanks, where the manure slurry is processed at over 100 degrees for 5 days. During this time the volatile solids are destroyed by bacteria, which creates methane. 20 cubic feet of methane is produced per minute, 24 hours a day. The gas then fuels a 50 KW generator connected to the grid providing electricity to power the dairy and, if surplus generating capacity exists, the community. Any methane not consumed by the generator is flared (i.e., burned) to prevent its escape to the atmosphere.
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