Full-scale evaluation of bioreactor landfill technology

US regulations require landfills to be designed with very low permeability composite liners and leachate collection systems to prevent groundwater contamination, a low permeability cap to prevent infiltration after closure, and a landfill gas extraction system to prevent air emissions. Because the degradation process proceeds at a slow rate in a "dry tomb" landfill, it can be biologically active for hundreds of years, producing air and water emissions that must be monitored, controlled, and treated. As an alternative to the current practice, several research studies have concluded that landfills managed as "bioreactors" promote waste degradation in an environmentally sound manner. This is accomplished by installation of a leachate, recirculation system designed to ensure that sufficient moisture is added to promote anaerobic processes. The approach would be analogous to that used in wastewater management - degradation is promoted in a controlled environment for the purpose of preventing the negative effects when these reactions occur in receiving waters. The claimed advantages of bioreactor landfills include a) shorter time period over which air and water emissions are generated, b) accelerated production of methane making recovery and energy generation more cost-effective, c) a shorter post-closure monitoring period because the waste stabilizes more quickly, d) increased active life (pre-closure) of the landfill due to increased waste volumes resulting from faster compaction, and e) faster return of the landfill property to a productive end-use. A number landfills or portions of landfills have been operated as bioreactors, but only a limited number of scientific studies have been performed. In this research, a 1.5-acre bioreactor cell for municipal solid waste (MSW) was designed and constructed to evaluate performance and to understand how this relates to basic chemical, biological and physical processes occurring within the cell. A three-dimensional monitoring system was developed and installed to measure moisture content, gas composition, chemical characteristics of the leachate, and the settlement of the waste. TDR (time-domain reflectometry) probes were used to measure in-situ moisture content and temperature at each of 48 sampling points. A gas sampling point and leachate collection basin were also installed at each point, and samples are being analyzed for a comprehensive set of chemical and biological parameters. Three leachate recirculation methods are also being evaluated for the distribution of the moisture.