Anaerobic digestion is a biological process that produces biogas - which is principally composed of 55 to 65 percent methane (CH4) and carbon dioxide (CO2) as the balance.

Methane gas is an odorless, colorless, flammable gas and is the primary constituent of natural gas.

Biogas contains trace amounts of hydrogen sulfide and nitrogen gas. At 65% methane, biogas has a heat value is 650 Btu per cubic foot compared to natural gas at 1,000 Btu per cubic  foot.