Thesis - faculty.ait.ac.th - Asian Institute of Technology

2.7.3 Composition of the Waste Dumped
The leachate quality is greatly affected by refuse composition. Organic material
present in the waste mainly comprises of kitchen waste while the inorganic constituents
consists of the plastic, glass, metal, etc. The leachate composition depends upon the ratio
of organic and inorganic components present in the waste disposed in the landfill. It is
estimated that approximately one half of the municipal solid waste is typically composed
of cellulose and hemicellulose (Fairweather and Barlaz, 1988; Barlaz, et al., 1989), which
are considered readily degradable in the environment. The organic content leached into the
leachate is as a result of hydrolysis and degradation of higher molecular weight organic
compounds by the microorganisms present in the waste. However, it has been shown that
readily degradable refuse components can sometimes persist for surprisingly long periods
of time in landfills owing to several environmental factors that limit the microbial growth
(Suflita, et al., 1992; Gurijala and Suflita, 1993). The other factors which influence the
leachate are the moisture content, nutrients and organic loading in the solid waste disposed.
2.7.4 Geological Characteristic
As the leachate percolates through the underlying strata, many of the chemical and
biological constituents originally contained in it will be removed by filtering and
adsorptive capacity of the material composing the strata. In general, the extent of this
action depends on the characteristics of the soil and especially the clay content. With this
potential, it can allow the leachate to percolate into the landfill for elimination or
contamination, thereby playing a role in affecting the leachate quantity. The influence of
soil particle size, the type of soil in the underlying ground and cover material are factors
that further influence leachate production and strength.
2.7.5 Filling Technique
Various factors during the filling of the municipal solid waste in the landfill
influence the leachate quality and quantity to a great extent.
Filling Height: The surface to volume ratio of the waste in landfill has an impact
over the infiltration, heat transfer and gas exchange occurring within the landfill. It is
expected that an increase in landfill height may limit the affect of seasonal variation in the
leachate composition and can preserve the heat from the microbial action to enhance
further degradation. However, aerobic conditions can be hindered due to limitations in gas
transfer, thereby converting it into anaerobic conditions, thus affecting the leachate quality.
Density: Waste with low density results in a larger volume of air infiltrating through
the landfill and thus promoting aerobic degradation process. This enhances the degradation
of easily degradable waste fractions and complex organic and also elevates temperature
within the landfill which can in turn improve conversion into inorganic constituents. A
prolonged aerobic phase can lead to a drought condition within the fill and reduce
degradation rates.
Enhanced Stabilization: In order to reduce the time required for leachate treatment,
it is necessary to enhance leachate stabilization. Stabilization can be accomplished by two
ways namely, pre-treatment by size reduction, mixing and pre-composting or by using flow
systems to influence the environmental conditions within the landfill. Continuous flow
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