The landfill deposition of organic materials such as food waste, yard trimmings, paper and wood results in the generation of landfill gas. Anaerobic bacteria degrade these materials to produce landfill gas, which primarily contains methane and carbon dioxide. Landfill gas is typically a combination of methane (50-55%), carbon dioxide (45-50%) and non-methane organic compounds. In addition, oxygen and nitrogen are also observed in landfill gas, which are present mainly as a result of air infiltration.
The decomposition of organic matter (such as food waste, leaf and yard waste and paper), whether in a landfill, through composting, via digestion in an anaerobic reactor, in a waste to energy facility or through natural pathways results in its carbon content to be released as carbon dioxide. This carbon dioxide is not counted as an anthropogenic greenhouse gas emission because it is carbon dioxide that would have eventually been released under natural conditions. This is referred to as biogenic carbon dioxide.
These biogenic (organic) materials (including paper and wood products, yard trimmings and food discards) are made from carbon in plants and have been produced as a result of the photosynthetic capture of carbon from the atmosphere. In the natural carbon cycle this carbon is returned to the atmosphere when the plant dies and decays (aerobically) on the earth’s surface. Therefore, international conventions do not include biogenic CO2 from waste treatment as anthropogenic.
Landfill gas can be combusted in boilers or other equipment that can be modified to utilize landfill gas, such as dryers, space heaters, kilns, furnaces, reformers, gas chillers and other thermal applications. Landfill gas use is well suited for operations that have a steady and continuous demand for fuel. Boilers use landfill gas as a fuel to produce steam or hot water. The steam produced by the boiler can be used for space heating, process heating or electricity generation via a steam turbine. Furnaces, dryers and kilns can use landfill gas as a replacement for or supplement to conventional fuels in cement, brick and ceramics, iron and steel, wood products manufacturing and other sectors. For small applications (such as local brick or pottery plants), LFG landfill gas may supply all or most of the energy needs. Landfill gas can also be used directly to evaporate leachate, which reduces leachate treatment and hauling costs by evaporating this liquid to a more concentrated and more easily disposed of effluent volume.
Landfill gas can be used as a fuel in internal combustion engines or combustion turbines driving either an electrical or gas-powered generator. The generated electricity can be used to power on-site needs such as the blowers for the active gas collection system or leachate treatment system or, more typically, be sold to the local electricity grid. Electricity generation from landfill gas accounts for the majority of landfill gas to energy projects globally.