Environmental Engineering Reference
In-Depth Information
intrusion will be greatly affected by the type of cover on the landfill. A landfill with a low
permeability (geomembrane) cover will be more resistant to air intrusion than a landfill with a
soil cover.
E. LFG Production Enhancement Methods
The biodegradation of MSW and LFG production in bioreactor landfills can be enhanced
through different methods. In all cases, the purpose is to control and manipulate the
influencing factors in a positive manner in order to accelerate the biodegradation of MSW and
increase the amount of LFG produced. There are many advantages to enhancing the
biodegradation of MSW, including more rapid waste stabilization and increased gas
production; lower leachate treatment costs through recirculation to the landfill; reduced length
and cost of post closure activities; and greater landfill airspace availability due to increased
settlement during the operation rather than the post closure stage, as is the case in
conventional landfills (Reinhart et al., 2002).
The technologies used to enhance the biodegradation of MSW are studied by San et al.
(2001), Laquidara et al. (1986), Chan et al. (2002), Chiemchaisri et al. (2002), Warith (2003),
Bae et al. (1998), Pacey (1989), Klink et al. (1982), Stegmann (1983), and reviewed by
Barlaz et al. (1990), Warith et al. (1998), Komilis et al. (1999a), Christensen et al. (1992),
Stegmann et al. (1996).
These technologies are leachate recycle, pH buffering, sludge addition, temperature
control, reduced waste particle size, improved cell design, daily cover and waste compaction,
and pre-treatment of MSW. They will all be discussed in the following sections.
1. Leachate recirculation
Leachate recirculation is the process by which the leachate collected at the base of the
landfill is recycled or reintroduced in the landfill in order to control the moisture content.
The advantages and impacts of leachate recirculation on the degradation of MSW were
covered by Barlaz et al. (1996), San et al. (2001), Ham et al. (1982, 1989), Baldwin et al.
(1998), Warith et al. (1998, 2002, 2003), Reinhart et al. (1996, 2002), and Sponza et al.
(2004). The advantages of leachate recirculation lay both in the rapid reduction of the organic
content present in the leachate itself which reduces the cost of treatment; and the potential
transformation of waste into energy, as it increases the rate of methane production.
Leachate recirculation provides optimum conditions for enhancing biodegradation by
increasing the moisture content and movement, and by distributing the nutrients throughout
the landfill. Both moisture content and moisture movement are necessary settings for bacteria
growth and the establishment of methanogenic conditions. They also provide better contact
between insoluble substrates, soluble nutrients and microorganisms (Klink et al., 1982).
Ham et al. (1982) and Baldwin et al. (1998) studied the effect of moisture content on the
biodegradation of MSW and concluded that moisture content has a positive effect on gas
production. Also, leachate recirculation treats the leachate through the landfill (in situ
treatment) because the organic compounds in the leachate are reduced with the recirculation
due to the biological activity within the landfill (Sponza et al., 2004).
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