Environmental Engineering Reference
As a generality, a typical dry landfill has an impermeable bottom liner, the wastes are
delivered to the landfill, spread out, compacted and covered at the end of the day with a thin layer
of soil, until a planned depth is reached, then the waste is covered with an impermeable cap. The
environmental barriers such as landfill liners and covers exclude moisture that is essential to waste
biodegradation. Consequently, wastes are contained in a “dry tomb” and remain intact for long
periods of time ranging from 30 to 200 years, possibly in excess of the life of the landfill barriers
and covers. Liner failure could happen in conventional dry landfill sometime in future, which can
cause serious groundwater and surface water contamination (Warith 2003).
Nowadays, siting new landfills has been very difficult and costly not only because
landfills can threaten the environment, but also because the public opposition, this often
called the NIMBY, or not in my back yard, syndrome. Therefore, the condition appeals to
investigators to make efforts to make landfills more economically sound and environmentally
friendly (Stessel and Murphy 1992).
Today, the “bioreactor landfill” is one idea that has gained significant attention. A
bioreactor landfill is a sanitary landfill that uses enhanced microbiological processes to
transform and stabilize the readily and moderately decomposable organic waste constituents
within 5 to 10 years of bioreactor process implementation. The bioreactor landfill
significantly increases the extent of organic waste decomposition, conversion rates and
process effectiveness over what would otherwise occur within the landfill (Pacey et al. 1999).
The “bioreactor landfill” provides control and process optimization, primarily through the
addition of leachate or other liquid amendments, the addition of sewage sludge or other
amendments, temperature control, and nutrient supplementation (Reinhart et al. 2002).
Beyond that, bioreactor landfill operation may involve the addition of air. Based on waste
biodegradation mechanisms, different kinds of “bioreactor landfills” including anaerobic
bioreactors, aerobic bioreactors, and aerobic-anaerobic (hybrid) bioreactors have been
constructed and operated worldwide. According to the survey conducted by the Solid Waste
Association of North America (SWANA) in 1997, there were over 130 leachate recirculation
landfills in USA (Gou and Guzzone 1997; Reinhart et al. 2002).
Generally, there are four advantages for employing bioreactor landfill technology
comparing to conventional dry landfills: (1) contain and treat leachate, (2) rapidly recover air
space, (3) accelerate waste stabilization and avoid long-term monitoring and maintenance and
delay siting of a new landfill, and (4) make more potential benefits from increased methane
generation in anaerobic bioreactor landfill. For aerobic bioreactor landfill, there are three
other advantages: (1) significant increase in the biodegradation rate of the MSW over
anaerobic processes, (2) a reduction in the volume of leachate, and (3) significantly reduced
methane generation and “anaerobic” odors. However, Costs for continuous supply of air are
excessively high for municipal solid waste treatment (Hanashima, 1999).
B. Bioreactor Landfills
There are three types of bioreactor technology:
Anaerobic Bioreactor Landfills
Aerobic Bioreactor Landfills
Aerobic-Anaerobic Bioreactor Landfills