Biogas
A gas mixture created through biological breakdown of organic matter, usually rich in methane and CO₂.
Example
A digester can collect this mixture for heat, electricity or upgrading.
The catch
The word describes an origin, not a guarantee of low life-cycle emissions.
Related terms
Methane, Anaerobic decomposition, Anaerobic digestion, Biomethane, Composting, Destruction efficiency
In more depth
Biogas, explained.
Biogas only becomes a dependable fuel after cleaning. Raw gas from a digester carries hydrogen sulphide, which smells of rotten eggs and corrodes engines, plus water vapour and other impurities that operators remove before use. Landfill gas is a type of biogas with extra trace contaminants from mixed waste.
Burning it releases CO₂ that plants drew from the air recently, and the GHG Protocol requires companies to report that biogenic CO₂ outside their scope totals. Unburned biogas is another matter. Escapes from a leaking cover or an open relief valve release mostly methane, and modest losses can cancel a large part of the benefit. Methane that passes through an engine unburned is called methane slip.