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348 Waste Management Practices: Municipal, Hazardous, and Industrial
Research conducted at Georgia Tech and elsewhere indicate that there is some potential for
metal mobilization in bioreactors; however, there are multiple mechanisms for attenuation of all
metals and therefore the metals generally precipitate within the waste mass. In addition, a review of
data from 12 landfills indicated that heavy metals were not an issue for a fully stabilized anaerobic
landfill. Over a pH range of 7 to 9, as are typically encountered in these landfills, the metals were
immobilized. While metals are present in the landfill leachate, all values were below drinking water
standards (U.S. EPA, 2000).

10.7.6.5 Advantages of Bioreactor Landfills

As was the case for the conventional sanitary landfill, gases emitted from a bioreactor landfill con-
sist primarily of methane and carbon dioxide along with lesser amounts of volatile organic chemi-
cals and hazardous air pollutants. Use of a bioreactor is expected to generate landfill gas earlier and
at a higher rate compared with a conventional landfill. The bioreactor landfill gas is also generated
over a shorter period of time because emissions decline as the accelerated decomposition process
depletes the microbial substrates faster than in a traditional landfill. According to the U.S. EPA
(2003), the bioreactor produces more landfill gas overall than the traditional landfill.
Some studies indicate that the bioreactor increases the feasibility for cost-effective landfill gas
recovery, which in turn reduces fugitive emissions. This presents an opportunity for beneficial reuse
of bioreactor gas in energy recovery projects. Currently, the use of landfill gas (in traditional and
bioreactor landfills) for energy applications is only about 10% of its potential use. The U.S.
Department of Energy estimates that if the controlled bioreactor technology were applied to 50%
3
of the waste currently being landfilled, it could provide over 270 billion ft of methane per year,
which is equivalent to 1% of electrical needs in the United States. Other potential advantages of
bioreactor landfills include (U.S. EPA, 2003):

● Decomposition and biological stabilization in years vs. decades in conventional landfills
(‘dry tombs’)
● Lower waste toxicity and mobility due to both aerobic and anaerobic conditions
● Reduced leachate disposal costs
● A 15 to 30% gain in landfill space due to an increase in density of waste mass
● Reduced postclosure care

10.7.6.6 Summary of Bioreactor Landfills
Bioreactor landfills are engineered systems that incur higher initial capital costs and require addi-
tional monitoring and control during their operating life, but are expected to involve less monitor-
ing over the duration of the postclosure period than conventional ‘dry tomb’ landfills.
Moisture content is the single most important factor that promotes the accelerated decomposi-
tion. 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. Issues that need to be addressed during both design and operation of a bioreactor land-
fill include:

● Increased gas emissions
● Increased odors
● Physical instability of waste mass due to increased moisture and density
● Instability of liner systems
● Surface seeps
● Landfill fires