Environmental Benefits of Landfill Gas Extraction and Generation

Landfill gas if produced in a landfill site where organic compounds are broken down by bacteria in the absence of oxygen. Typically for most of the gas produced it is comprised of 60% methane and 40% carbon dioxide. Methane is a greenhouse gas twenty one times more potent than carbon dioxide. If the landfill gas can be collected and the methane combusted in a flare (and turned into carbon dioxide) then the greenhouse gas emissions from a landfill site can be reduced dramatically. Since the carbon source is biomass the resultant carbon dioxide emissions have no net impact on the environment. If all the methane gas a landfill site produces can be collected that landfill site will make no net impact on global warming. A typical tonne of waste will produce between 100 and 200 Nm3 of landfill gas.

If the methane is collected and, instead of being burnt in a flare, is fed to an electricity generating set then useful power can be produced from the biodegradable waste in the landfill. Each Nm3 of landfill gas may produce approximately 1.75 kWh of electricity. Each tonne of waste placed in the landfill may therefore produce between 175 and 350 kWh of electrical power. A landfill site may produce at any one time between 300 kW of electricity for a small site up to 20 MW for a large site. 300 kW is enough to power approximately 450 homes and 20 MW enough for 30,000 homes in the UK.

The electricity produced offsets electricity produced from fossil fuel sources and thus both displaces fossil fuel consumption and prevents the carbon dioxide emission associated with this. 1 MW of electricity generation from landfill gas over a period of ten years prevents the release of 35,000 tonnes of carbon dioxide emissions from fossil fuel power stations over the same period. To put this into perspective a single 1 MW scheme can displace the same amount of carbon dioxide as produced by 3,700 households.