Evaluation of Landfill Gas Emissions from an Instrumented Bioreactor Landfill Cell

Michigan State University, East Lansing MI

Investigators

Abstract

The key environmental impacts from a municipal solid waste (MSW) landfill are the discharge of leachate constituents into ground water and surface water; and emissions of landfill gases including methane and volatile organic compounds (VOCs) into the atmosphere. State and federal regulations (RCRA Subtitle D) require that a MSW landfill, upon closure, be capped with a final cover containing soil layers and a geomembrane - a flat geosynthetic product about 1 to 1.5 mm thick. Advective flux of liquid or gas through an intact portion of a geomembrane is negligible. However, contaminants can diffuse through an intact geomembrane, and gases or liquids can leak via advection through defects such as holes, punctures, and irregular welds. Currently, in the U.S. alone, there are over 2,000 MSW landfills in operation, and these will receive final caps progressively as they close. A bioreactor landfill operates to rapidly transform and degrade organic waste, and differs in concept from the traditional "dry tomb" municipal landfill approach. In order to operate a MSW landfill as a bioreactor, a key operational requirement is the addition of leachate or moisture to accelerates the decomposition of the organic fraction of waste, and hence accelerate gas generation. Moisture can be added using a leachate recirculation system, or by allowing controlled infiltration from the final cap of the landfill. However, under current regulations, use of a geomembrane virtually eliminates the moisture flux through the cap in the form of infiltration. In addition, the geomembrane is the most expensive component of the final cap. This action, to quantify landfill gas emissions from the final cap of a MSW landfill operated as a bioreactor, is supported under the Small Grants for Exploratory Research (SGER) program. The final cap of an existing field-scale bioreactor cell located in Michigan will be instrumented with: (1) gas probes to measure inorganic gas concentrations and pressure profile; and (2) flux chamber to measure inorganic and organic gas emissions from the surface. These gas emissions will be measured through a RCRA final cap containing a geomembrane. The gas emissions will be measured to evaluate these three scenarios of the cap: (1) intact condition; (2) 1 cm 2 hole made in the geomembrane; and (3) a relatively large size window cut in the geomembrane to simulate an earthen cap. The bioreactor cell has been instrumented below the final cap as part of an ongoing research project funded by the Department of Energy (DOE), and administered through Environmental Research & Education Foundation (EREF). The gas emissions data collected will be comprehensive and unique due to the extent of the instrumentation already installed in the field-scale (~1 acre) bioreactor cell. Such a comprehensive dataset will be used to test gas generation and gas emission models requiring comprehensive physical, chemical, and biological input. In addition, the project promotes teaching, training, and learning, and broadens the participation of undergraduate students in field data collection.