Landfill gas
A mixture of gases produced as organic material decomposes in a landfill.
Example
Methane and carbon dioxide commonly make up most of the mixture.
The catch
Composition varies with waste, age, moisture and operating conditions.
Related terms
Carbon dioxide, Methane, Anaerobic decomposition, Anaerobic digestion, Biogas, Biomethane
In more depth
Landfill gas, explained.
Landfill gas is both a climate hazard and a fuel, and how a site handles it decides which. Microbes break buried food, paper and garden waste down in stages. Once oxygen runs out, the mixture settles into methane and CO₂ in broadly similar proportions, with traces of hydrogen sulphide and other compounds that give landfills their smell. Waste ranks alongside agriculture and the energy sector as a main source of human-caused methane.
Collection starts with wells drilled into the waste and connected to blowers that keep the pipework under slight suction. The gas then goes to a flare, to engines under a methane-to-energy scheme, or to upgrading plant that strips out CO₂ for injection into the gas grid. Uncollected gas can also travel sideways through soil and gather in basements or drains, so safety checks at the site boundary matter as much as the climate account.
Inventories count the methane. They usually treat the CO₂ in landfill gas, and the CO₂ from burning it, as biogenic, because the carbon came from recent plant material. Burning collected methane therefore turns a potent gas into CO₂ that accounting places in the short carbon cycle. The best outcome still sits higher up the waste hierarchy, where less organic material reaches the landfill in the first place.