Animal manure, human sewage, or food waste can produce methane during anaerobic digestion. Here, an animal scientist measures a cow for respiration of oxygen and carbon dioxide and production of heat and methane.

Biogas is a renewable natural gas containing approximately 70 percent methane (CH4) and roughly 30 percent carbon dioxide and trace amounts of other gases. Potential agricultural feedstocks for biogas production include manure (hog, dairy, beef, and poultry), food processing (byproducts of meat processing, potato, dairy, cheese whey, sugar beet, and vegetables), and energy crops cut as silage (wheat, barley, triticale, clover, alfalfa, ryegrass, turnips, and corn). Commercial products from biogas production include methane, electricity, heat, steam, fertilizer, chemical recovery, odor reduction, water recycling, carbon dioxide, and, potentially, carbon credits and greenhouse gas credits.

Anaerobic ...