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Bioreactor Landfills State-Of-The Practice Review
Citation:
Benson, C., M. Barlaz, AND T. M. TOLAYMAT. Bioreactor Landfills State-Of-The Practice Review. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/071.
Impact/Purpose:
To examine six full-scale bioreactor projects with the objective of providing a perspective of current practice and technical issues that differentiate bioreactor landfills from conventional landfills.
Description:
Recently approved regulations by the U.S. Environmental Protection Agency (EPA) give approved states the power to grant landfill variance under Subtitle D by allowing these landfills to introduce bulk liquids into the solid waste mass. These types of landfills are called bioreactor landfills. The study presented here examines six full-scale bioreactor projects with the objective of providing a perspective of current practice and technical issues that differentiate bioreactor landfills from conventional landfills. For the purpose of this study only, bioreactor landfills were defined in a broad sense as "landfills where liquids are intentionally introduced into the waste mass in an effort to degrade the waste in a controlled fashion". The definition presented here includes landfills recirculating leachate with the intention of enhancing degradation as well as landfills controlling liquids and gases in a manner intended to optimize degradation. The analysis showed that bioreactor landfills operate and function in much the same manner as conventional landfills, with designs similar to established standards for waste containment facilities. Recirculation of leachate appeared to have little effect on the integrity or the perfornance of the containment system. Leachate generation rates, leachate head on the liner, leachate temperatures, and liner temperatures appeared to be essentially the same in bioreactor and conventional landfills Data from leakage detection systems indicated liners used for bioreactors were discharging liquid no different from that discharged by conventional landfills. A definitive assessment regarding the effectiveness of degrading waste using current bioreactor operations was not possible, although analysis of gas data indicates that biodegradation probably was accelerated at one or two sites. This does not imply that waste was not being degraded at an accelerated rate at bioreactor landfills. Rather, ambiguities in the data precluded definitive inferences regarding the effect of bioreactor operations on waste degradation and methane generation. More detailed and carefully collected data are needed before reliable conclusions can be drawn. Analysis of leachate quality data showed that bioreactors generally produce stronger leachate than conventional landfills during the first two to three years of recirculation. However, after two-to-three years, leachate from conventional and bioreactor landfills were similar, at least in terms of conventional wastewater parameters (BOD, COD, and pH). The exception was ammonia, which tended to remain elevated in bioreactor landfills due to the absence of biological mechanisms for removing ammonia under anaerobic conditions. Analyses were not conducted to determine if bioreactor operations affect concentrations of metals, volatile organic compounds, or other constituents in leachate. Settlement data collected from two of the sites indicate that settlements were larger and occurred at a faster rate in landfills operated as bioreactors. Anecdotal reports and visual observations at the other sites were consistent with the settlement data. Thus, the waste mass in a bioreactor can be expected to settle more quickly than in a conventional landfill. However, the results were inconclusive about the nature of the primary settlement, caused by the increase in the mass by the liquid introduced, or secondary, caused by an increase in degradation of solid waste mass. An important finding of this study is that insufficient data are being collected to fully evaluate whether bioreactor methods used in practice at commercial and municipal landfills are effective in enhancing waste degradation, stabilization, and gas generation. Future studies should include more detailed monitoring and evaluation schemes that can be used to form definitive conclusions regarding the effectiveness of bioreactor operational methods. Data from such studies would also be useful in identifying more efficient and effective methods for operating bioreactor landfills.