Build your own biogas generator

Biogas is actually a mixture of gases, usually carbon dioxide and methane. It is produced by a few kinds of microorganisms, usually when air or oxygen is absent. (The absence of oxygen is called “anaerobic conditions.”) Animals that eat a lot of plant material, particularly grazing animals such as cattle, produce large amounts of biogas. The biogas is produced not by the cow or elephant, but by billions of microorganisms living in its digestive system. Biogas also develops in bogs and at the bottom of lakes, where decaying organic matter builds up under wet and anaerobic conditions