Biological Biogas

There is some confusion between “biogas” and “producer gas”, “syngas”, “pyrolysis gas” and similar gaseous products obtained from biological or organic materials by thermal processes. (1) Biogas (a mixture of methane (CH₄—natural gas) and carbon dioxide (CO₂), also known as marsh gas) is obtained from moist organic material by microbial processes, in fact it is so natural it occurs in our own stomachs as well as in other animal’s digestive systems (particularly ruminants like cattle), marshes, mud, the Arctic Tundra and even volcanoes—anywhere air is absent. (2) Thermal processes can also be used to gasify combustible material in reduced oxygen, resulting in a mixture of gases that often includes carbon monoxide (CO)—a very toxic gas. Gasification is better applied to dry materials like wood and was used in World War Two, when petrol was rationed, to power vehicles by fitting a “gasifier” to the car/truck to make “producer gas”. In this chapter, we will look briefly at the long history of biogas, take an overview of the microbial process, cover some of the different types of digesters and look at building, starting and operating a simple type of digester, including fault finding.