Biogas is produced through the breakdown of organic matter in the absence of oxygen, which is referred to as anaerobic digestion.
The whole process works like a big concrete stomach would: Organic materials like manure, food scraps, crop residue, or wastewater sludge (known as feedstock) are fed into the digester, where it’s heated to 38-40 degrees Celsius (temperature of a cow’s stomach) and stirred for 30-60 days, slowly producing a combination of methane, carbon dioxide and other gases (known as biogas).
The biogas can then be used for power generation, heating and cooling needs or piped into the natural gas grid.
Once biogas production is complete, the waste has transformed into a high-quality fertilizer (called digestate). Once it is removed from the digester, the process starts all over again.
Additional information about biogas can be found here:
Wikipedia
The Biogas Association
The Complete Biogas Handbook
