Environmental Engineering Reference
In-Depth Information
To gas collector system
Nutrients, inoculums, and/or buffer addition
Collector
Wastepile
Onoff
valve
Leachate outflow
MSW landfill
showing liner system
of compacted clay
overlain by HDPE liner
Leachate
treatment
Discharge
FIGURE 7.14
Schematic of a landill bioreactor. Leachate can be directly fed back to the wastepile in the landill without
treatment or after treatment in the leachate treatment facility. The use of on-off valves will facilitate choice
of treated or untreated leachate for recycling. (Adapted from Mulligan, C.N., Environmental Biotreatment ,
Government Institutes, Rockville, MD, 395 pp., 2002.)
the landill can serve as seeds for new areas. Ideally, other liquids will have to be added
to increase the moisture content to 30% to 40%. However, a balance must be made such
that organic acids or other components do not accumulate and inhibit methane produc-
tion (Pohland and Kim, 2000). Leachate and gas monitoring are integral to the success of
the process. In terms of heavy metal concentration in the leachate, pH is a major factor in
mobility of the metals. Mobility of the metals increases as the pH decreases. In addition,
organic and inorganic agents can serve as ligands, promoting metal transport. However,
the mechanisms of precipitation, encapsulation, and sorption ensure that the heavy metals
are captured in the waste.
Solubility, volatility, hydrophobicity ( k ow ), biodegradability, and toxicity inluence the
behavior of organic contaminants in the landill. Compounds such as dibromomethane,
TCE, 2-nitrophenol, nitrobenzene, PCP, and dichlorophenol tend to be highly mobile and
thus are found in the leachate and gas phase (Pohland and Kim, 2000). They will also be
biologically altered by reduction, complexation, complete, or partial degradation. Other
compounds such as hexachlorobenzene, dichlorobenzene, trichlorobenzene, lindane, and
dieldrin are more hydrophobic and thus will remain in the waste and are available for
biodegradation (Table 7.9).
The EPA (USEPA, 2007) reviewed the literature and evaluated ive full-scale operating
bioreactor landills. They found that the bioreactors complied with existing solid waste
regulations and technical guidance and that the addition of leachate and other liquids
requires appropriate design to allow the injection systems to distribute the moisture
 
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