Characteristics of Gas and Leachate at an Elevated Temperature Landfill

Data from a municipal solid waste (MSW) landfill with elevated temperatures are evaluated to assess how characteristics of landfill gas and leachate evolved as the landfill temperature increased from ranges typically associated with methanogenic decomposition (40 - 50 degrees C) to more than 100 degrees C. The MSW landfill was deep (similar to 100 m), unlined, and most of the waste was saturated and below the water table. Temporal trends in landfill gas temperature measured at the wellhead indicate that the gas temperatures increased abruptly and systematically following a shutdown to address a concern about the potential for subsurface combustion. Temperature profiles collected subsequently indicated that the highest temperatures were substantially below the leachate level, making combustion an unlikely mechanism for the elevated temperatures. Temporal trend analysis indicated that the primary gas ratio (CH4: CO2) decreased systematically and substantially when the gas temperature increased abruptly. Leachate chemistry also changed significantly after the gas temperature increased abruptly, with BOD, COD, and the BOD: COD ratio increasing rapidly, pH dropping more than one unit, and total suspended solids increasing more than two orders of magnitude.