The methane potential of landfills is the projected energy value of methane produced by the decomposition of organic matter in landfill sites, if this methane were to be used for the generation of power such as electricity. Large landfill sites often produce very significant quantities of methane. This flammable gas usually simply seeps out of the landfill site into the atmosphere, where it contributes to pollution problems including global warming. Methane is one of the most damaging pollutants in terms of global warming, and as a greenhouse gas; it is up to 20 times more damaging than equivalent volumes of carbon dioxide. The attraction of methane from landfills as a source of energy is partly in order to prevent atmospheric pollution, and partly due to it having the potential of a cheap source of energy.
Landfill methane potential depends upon many factors, including the proportion of decomposable material that makes up the garbage disposed of in the site. Non-decomposable matter, such as non-biodegradable plastics, does not contribute to the production of methane. The chemical reactions that create methane in landfills are similar to natural processes that also generate methane. These processes are the result of the activity of microorganisms, and are typically anaerobic fermentation processes, that is to say that they occur in places that are not aerated with oxygen. Natural methane production occurs during the decay of manure, when organic matter decays in waterlogged areas such as wetlands, and in the stomachs of cows and other ruminants when cellulose from plants is digested.
Gas that is produced by landfills is in fact typically a mixture of a number of different gases, of which methane usually makes up about 50% of the volume. While the methane potential of landfills in terms of an alternative energy source is very significant, and indeed in some countries is already used as a viable source of power, there are other ecological factors to consider when evaluating landfills for their potential energy production. Landfill gas typically contains many contaminants, which are released into the atmosphere when the gas is burned for energy. These contaminants also affect the efficiency of energy generation methods that may be used, as boilers or turbines utilizing landfill gas may need high levels of maintenance and cleaning.