(best examples and good practices) on household organic waste ...

57
3.3.5. Leachate collection <strong>and</strong> removal system
Leachate is a noxious, mineralized liquid capable of transporting bacterial
pollutants produced when water moves through the refuse (Botlin., 1995).
Leachate generated in the solid waste passes through a filter layer which
underlines the waste. It is supposed to keep the solid waste from infiltrating to
leachate collection system. This system usually consists of gravel. It allows
leachate to flow across the top of the liner to the top of the HDPE liner. Then it
flows across to the top of the liner to a collection pipe <strong>and</strong> is transported to a
container, where the leachate can be pumped from the l<strong>and</strong>fill. Lower
composite liner represents a leak detection system for the upper liner. It is
located between the two composite clay liners. It is suggested that geosynthetic
liners should be used as an add-on to the regular clay liner. Geosynthetic liners
are thin layers of bentonite clay which is encased in a woven material. Together
with clay liners they minimize leachate formation through infiltration or
ground water intrusion (Fred Lee., 2010).
3.3.6. L<strong>and</strong>fill cover
The l<strong>and</strong>fill cover is designed with a sloping surface as to enhance surface
runoff. Runoff is then collected by drainage channels constructed at the
surrounding edge of the l<strong>and</strong>fill. Materials (geomembranes) usually used for
waste cover are: low-permeability plastic sheeting layer, HDPE, very flexible
polyethylene (VFPE), or polyvinyl chloride (PVC) (Zanzinger, 1999, pp. 2-3).
Above the layer there is a drainage layer. Above there is topsoil that serves as
vegetation layer. It is designed to promote the growth of vegetation that will
reduce the erosion of the l<strong>and</strong>fill cover. L<strong>and</strong>fill covers should be monitored as
to detect when moisture leachate through the cover occurs. Usually it is a visual
inspection of the vegetative soil layer. All the cracks <strong>and</strong> depressions that are
observed are then filled with soil (Fred Lee., 2004).
3.3.7. L<strong>and</strong>fill gas
The anaerobic decomposition of organic materials in a municipal solid waste
l<strong>and</strong>fill will generate a combination of gases, mainly methane <strong>and</strong> carbon
dioxide. The migration of l<strong>and</strong>fill gas underground can pose safety risk for
l<strong>and</strong>fill construction. In smaller l<strong>and</strong>fills the gas venting layer provides the
effective collection <strong>and</strong> dispersion of l<strong>and</strong>fill gas. The gas is passively released
through vents installed in a l<strong>and</strong>fills cover system. The gas venting layer in
larger l<strong>and</strong>fills is eliminated <strong>and</strong> the gas is actively collected via horizontal
trenches <strong>and</strong> collection wells then burned in flares or utilized in projects that
make use of the energy value of the methane component of the l<strong>and</strong>fill gas.
L<strong>and</strong>fill gas collection system should be installed. It should be designed to have
at least 95% probability of collection all l<strong>and</strong>fill gas generated at the l<strong>and</strong>fill
(Fred Lee., 2010).