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 Global
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
 Though
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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