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

entails the re-circulation of leachate or abstraction of gas within the fill. Kylefors (1997)
reported that leachate re-circulation affects landfill stabilization by removing the waste
products after degradation from the liquid phase, allowing the addition and distribution of
microorganisms and nutrients with the landfill and maintaining homogeneous conditions
within the fill.
Separation of Leachate: Different waste categories at municipal solid landfills will
generate leachate with varying characteristics. Since, this contributes to the complexity in
leachate treatment, it may be beneficial to sort waste in terms of the leachate characteristics
in order to improve the efficiency of the treatment (Kylefors, 1997). This can be achieved
by separation of leachate based on waste characteristics and by separation of leachate
based on degradation phases. Further, the composition of the waste landfilled can also be
altered by the addition of nutrients, seed and buffers to improve the microbial processes
within the fill. Generally, a combination of digested sewage sludge and alkaline ash is
added to enhance methanogenesis.
Bottom Liners and Top Covers: The bottom liners are selected to prevent seepage
of leachate into the groundwater sources, whilst top covers aid in maintaining moisture
within the fill as well as limiting infiltration, thus slowing down the degradation process.
2.8 Leachate Treatment
Most solid waste disposal sites do not have the proper leachate treatment system.
Though varied treatment processes are used for leachate treatment, most of them are not
properly designed to cope with quantity and characteristics of the generated leachate.
Therefore, the objective for leachate management in solid waste disposal should be to
develop leachate treatment system having low area requirement and which is also cost
effective, to identify significant factors which have to be considered in leachate treatment
system and finally to set up a suitable criteria and prepare guidelines for proper leachate
treatment in municipal solid waste disposal dump sites so as to reduce contamination and
environmental impacts.
Leachate treatment is dependent on the quality and quantity of the leachate input,
discharge limits or removal efficiency requirements, quantity of residual products and their
management, site location and economics. However, high ammonia concentrations and the
typical phosphorus deficiency in landfill leachate hamper the biological treatment
efficiencies. Therefore, a general consensus among researchers is high nitrogen levels
which are still hazardous to receiving waters and needs to be removed prior to discharge.
This is generally carried out through biological nitrification-denitrification processes for
young leachate and through physico-chemical processes for stabilised landfill leachate.
The success of treatment process depends on the characteristics of the leachate and age of
the landfill.
Several wastewater treatment processes have been generally used to treat landfill
leachate (Amokrane, et al., 1997). The major biological treatment processes comprises of
activated sludge (AS), sequencing batch reactor (SBR), rotating biological contactor
(RBC), etc and physical and chemical treatment processes comprises of oxidation,
coagulation-flocculation, chemical precipitation, activated carbon absorption and
membrane processes.
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