Landfill Gas

Landfill gas is the mixture of gases produced when microorganisms decompose organic waste, such as food and paper, buried within a landfill; it is a form of biogas, running roughly 40 to 60 percent methane with most of the remainder carbon dioxide, plus trace hydrogen sulfide and other compounds. Gas generation typically begins about six months after waste is deposited, peaks around twenty years later, and then declines gradually over subsequent decades. In the United States the number of landfill gas energy projects grew from 399 in 2005 to 594 by 2012, and waste-management company Waste Management alone operates 110 facilities converting landfill gas to energy, offsetting an estimated two million tons of coal a year and supplying power equivalent to about 400,000 homes. Because methane is a potent greenhouse gas and landfills are the third largest source of methane emissions in the United States, federal regulations require large landfills to monitor and control gas migration for thirty years after closure.