Page 30 - Materials Chemistry, Second Edition

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1.5 Landfill Current Practice and Future Sustainability 11
Solid waste and/or ash produced from the incineration process should be
landfilled. Most people think of landfills as dumpsites, just an open hole in
the ground where solid waste is put with all kinds of animals and insects
wandering around. This is not true. A landfill is a very complicated struc-
ture, very carefully designed and positioned either into or on top of the
ground in which solid waste is isolated from the surrounding environment.
There are many steps before starting to construct a landfill. The first step is
to choose a suitable site. Site location is one of the very important steps to
avoid any impacts on the surrounding environment. After choosing the appro-
priate location for a landfill, the designing process starts. Beside the design
of the lining and coverage of the landfill, a leachate collection system, biogas
collection system and a storm water drainage system should also be designed
and planned for implementation during operation.
The bottom liner isolates the solid waste from the soil preventing
groundwater contamination. The liner is usually some type of durable,
puncture-resistant synthetic plastic (polyethylene, high-density polyethyl-
ene, polyvinyl chloride). In landfills constructed below surface level, a side
liner system is used which maintains mechanical resistance to water pres-
sure, drainage of leachate and prevention of lateral migration of biogas.
The landfill size is directly related to the capacity and the lifetime of
the landfill. To maximize the landfill’s lifetime, solid waste is compacted
into areas, called cells. Each cell contains only one day’s solid waste. Each
cell is covered daily with 15 cm of compacted soil. This covering seals the
compacted solid waste from the air and prevents pests (birds, rats, mice, fly-
ing insects, etc.) from getting into the solid waste.
It is impossible to totally exclude water from the landfill. The water
percolates through the cells in the landfill. As the water percolates through
the solid waste, it picks up contaminants (organic and inorganic chemicals,
metals, biological waste products of decomposition). This water with the
dissolved contaminants is called leachate and is typically acidic. It is then
collected into a pond by means of perforated pipes and sent for treatment.
Bacteria in the landfill break down the solid waste in the absence of
oxygen (anerobic) because the landfill is airtight. A byproduct of this aner-
obic breakdown is landfill gas, which contains approximately 60% methane
and 40% carbon dioxide with small traces of other gases. This presents a
hazard because the methane can explode and/or burn if it is not collected
and utilized. So, the landfill gas must be removed or collected for utilization
through a pipe network embedded within the landfill. After the landfill has
been closed a layer of soil is put above it to prepare it for landscaping.
Disadvantages of landfill:
• Landfill construction requires high capital cost.
• Mismanagement of landfill may cause soil contamination, water
contamination as well as air pollution.