Environmental Engineering Reference
In-Depth Information
Moisture content is the single most important factor that promotes the accelerated
decomposition. The bioreactor technology relies on maintaining optimal moisture content
near field capacity (approximately 35 to 65%) and adds liquids when it is necessary to
maintain that percentage. The moisture content, combined with the biological action of
naturally occurring microbes decomposes the waste. The microbes can be either aerobic or
anaerobic. A side effect of the bioreactor is that it produces landfill gas (LFG) such as
methane in an anaerobic unit at an earlier stage in the landfill's life and at an overall much
higher rate of generation than traditional landfills.
D. Potential Advantages of Bioreactor Landfills
Decomposition and biological stabilization of the waste in a bioreactor landfill can occur
in a much shorter time frame than occurs in a traditional “dry tomb” landfill providing a
potential decrease in long-term environmental risks and landfill operating and post-closure
costs. Potential advantages of bioreactors include:
•
Decomposition and biological stabilization in years vs. decades in “dry tombs”
•
Lower waste toxicity and mobility due to both aerobic and anaerobic conditions
•
Reduced leachate disposal costs
•
A 15 to 30 percent gain in landfill space due to an increase in density of waste mass
•
Significant increased LFG generation that, when captured, can be used for energy use
onsite or sold
•
Reduced post-closure care
Research has shown that municipal solid waste can be rapidly degraded and made less
hazardous (due to degradation of organics and the sequestration of inorganics) by enhancing
and controlling the moisture within the landfill under aerobic and/or anaerobic conditions.
Leachate quality in a bioreactor rapidly improves which leads to reduced leachate disposal
costs. Landfill volume may also decrease with the recovered airspace offering landfill
operators an extension for the operating life of the landfill.
LFG emitted by a bioreactor landfill consists primarily of methane and carbon dioxide
plus lesser amounts of volatile organic chemicals and/or hazardous air pollutants. Research
indicates that the operation of a bioreactor may generate LFG earlier in the process and at a
higher rate than the traditional landfill. The bioreactor LFG is also generated over a shorter
period of time because the LFG emissions decline as the accelerated decomposition process
depletes the source waste faster than in a traditional landfill. The net result appears to be that
the bioreactor produces more LFG overall than the traditional landfill does.
Some studies indicate that the bioreactor increases the feasibility for cost effective LFG
recovery, which in turn would reduce fugitive emissions. This presents an opportunity for
beneficial reuse of bioreactor LFG in energy recovery projects. Currently, the use of LFG (in
traditional and bioreactor landfills) for energy applications is only about 10 percent of its potential
use. The US Department of Energy estimates that if the controlled bioreactor technology were
applied to 50 percent of the waste currently being landfilled, it could provide over 270 billion
cubic feet of methane a year, which is equivalent to one percent of US electrical needs.
