13.2.1 Solid Waste Disposal
The amount of methane emitted to the atmosphere from solid waste disposal depends
on the amount of waste that is disposed, its composition, and the nature of
the disposal mechanism. Mitigation technologies involve management techniques
that can be incorporated at any one, or a combination of these points. Furthermore,
greenhouse gases emissions can also be reduced by collecting and using the methane
Developed countries seek to reduce solid waste disposal by management techniques
that concentrate on waste minimisation and recycling (CEPA, 1992). Options to
reduce the amount of waste, in order of preference, are:
AVOID producing the waste (become more efficient).
REDUCE the amount of waste produced (substitute materials if possible).
RE-USE the materials instead of turning them into waste (internal recycling
by households and industry).
REPROCESS the materials during manufacture, instead of using new materials (community
Solid waste generated in less developed countries is considerably less, per
capita, than that in developed countries, because there is a relatively high
recycling rate through an active informal sector (Yhdego, 1995).
Solid waste composition can change as a result of increasing material consumption
(Wang, 1995). Active recycling techniques, such as composting, can be used to
minimise the unnecessary disposal of organic waste in landfills.
Solid waste disposal in less developed countries is often in tips or open dumps.
Such aerobic disposal tends to generate less methane than landfills (where operating
practices generally require that the waste be covered with dirt for odor control
and other environmental reasons). However, such tips can become anaerobic and
generate methane under certain conditions. Countries, such as Austria and Japan,
where the available land area is limited, use waste incineration for solid waste
disposal. This reduces methane emissions, but increases carbon dioxide (and
other air pollutant) emissions, and produces ash which must be disposed of.
Cogeneration, in which the heat from an incinerator is used for energy production
or district heating, further reduces GHGs (Fernwaerme Wien, 1994). Incineration
may be more widely applied in the future, although care must be taken to ensure
that waste composition and other factors are appropriate for effective combustion,
and attention should be given to improving combustion efficiency when possible.
Appropriate control of air emissions from a variable composition waste stream
is also of concern.
Because organic matter can generate methane over 10-30 years or more, methane
recovery programmes may be particularly appropriate to address the near and
mid-term GHG emissions in regions where large amounts of organic waste have
already been or are presently being landfilled. Depending on the site and the
type of gas collection system installed, upward of 50% of the emitted methane
can be recovered and used. Numerous projects have been developed throughout
the world, which use the gas for heat, electricity generation, vehicle fuel,
and purification and injection into gas systems.