Gas is mainly produced in landfills through the bacteriological and chemical breakdown of organic substances in the waste. It consists of methane (CH4) and carbon dioxide (CO2). Nitrogen (N2) and oxygen (O2) do not occur in this anaerobic environment. The landfill gas can be collected via gas wells or horizontal drainage lines. A pumping station then feeds it to a gas engine, which burns the gas with almost no residue.