Landfill gas is generated in landfill sites by the anaerobic decomposition of domestic refuse (municipal solid waste). It consists of a mixture of gases and is colourless with an offensive odour due to the traces of organosulphur compounds. Aside for its unpleasantness, it is highly dangerous as methane is explosive in concentrations in air between 5 per cent, the Lower Explosive Limit (LEL), and the Upper Explosive Limit (UEL) of 15 per cent. Landfill gas must be controlled at all operational landfill sites, whether actively or passively vented or both especially in the case of deep sites.
Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons. Landfill gases have an influence on climate change. The major components are CO2 and methane, both of which are greenhouse gasses. Methane in the atmosphere is a far more potent greenhouse gas, with each molecule having twenty-five times the effect of a molecule of carbon dioxide. Methane itself however accounts for less composition of the atmosphere than does carbon dioxide. Landfills are the third-largest source of methane in the US. Because of the significant negative effects of these gases, regulatory regimes have been set up to monitor landfill gas, reduce the amount of biodegradable content in municipal waste, and to create landfill gas utilization strategies, which include gas flaring or capture for electricity generation.
