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Sources of Methane - Landfill

Household wasteGlobal methane emissions from landfill are estimated to be between 30 and 70 million tonnes each year. Most of this landfill methane currently comes from developed countries, where the levels of waste tend to be highest.

Landfills provide ideal conditions for methanogenesis, with lots of organic material and anaerobic conditions prevalent. The huge amounts of waste that are buried in landfill sites can mean that methane is produced for years after the site is closed, due to the waste slowly decaying under the ground.

Methane escapes from landfills either directly to the atmosphere or by diffusion through the cover soil. Highly active communities of methanotrophs can develop in these overlying soils and these can greatly reduce the amounts of methane emitted.

Human Impact

Our so called 'throw away society' in developed countries has led to a large increase in the amounts of domestic kitchen waste entering landfill sites. Not only does this increase in household waste lead to greater greenhouse gas emissions in the form of landfill methane, but the waste incurs further greenhouse gas costs in transporting waste to landfill sites. As the amounts of domestic waste increase in developing countries landfill methane could become an even greater source of global methane.

Potential for control

Landfill Strategies

In recent years, landfill methane emission has been identified by several world governments as a greenhouse gas source which can be both easily defined and reduced. Aside from the practice of covering landfills with a thick soil layer, to promote methane uptake by soil methanotrophs, more proactive strategies are also available.

Methane recovery systems are now commonly installed at landfill sites and these can reduce emissions to the atmosphere by more than half. Sometimes the recovered methane is flared off, producing the less powerful greenhouse gas, carbon dioxide. However, these methane recovery systems can also provide an economically viable energy source, with the collected methane being used in electricity generation.

Emission reductions of up to 90 per cent can also be achieved by the use of liners under landfill sites which stop leaching into nearby groundwater. Here in the UK large reductions in landfill methane emissions have been achieved in recent years by implementing strategies such as these.

Strategies for Individuals

Dave Reay's WormeryThough the direct reductions in landfill methane already discussed can be effective, a much greater impact can be made by reducing the amount of organic waste arriving at landfill sites in the first place.

By properly composting their kitchen waste, rather than having it transported to a landfill site, individuals can ensure that, as the waste decomposes, it forms carbon dioxide, rather than methane, and so has less of a greenhouse gas impact.

Several very effective composting methods are available for domestic use, with wormeries being particularly effective at quickly converting kitchen waste into good quality garden compost with a much reduced methane cost compared to that of landfills.

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