A Jenbacher J312 biogas engine from GE now generates 633 kW of electricity on a Wisconsin farm. It can power the farm, a factory on-site, and over 300 homes. In the process of generating fuel, cow manure is circulated and anaerobic, or oxygen-free, digestion takes place in a big vat. Microorganisms break down the organic waste, ultimately producing gas — mainly methane with some carbon dioxide. This gas can be burned just like natural gas, thus generating energy. This page from the GE site contains several short videos describing the whole thing.
Knee-deep in _____ ; Up close with a biogas generator
A biogas-powered engine runs a Wisconsin farm and sends power back to the local grid.