Controlled Study of Landfill Biodegradation Rates Using Modified Bmp Assays

Abstract

Biochemical Methane Potential (BMP) assays, typically used to assess anaerobic biodegradability of liquid wastes with added nutrients and bacteria, were adapted to compare gas production rates from solid landfill samples taken at sites in Illinois, Wisconsin, and Colorado, U.S.A. The technique involved incubation of 25 g ground samples in triplicate or quadruplicate under controlled anaerobic conditions. For the landfill assays, unamended samples were run as controls and compared with assays with added water or water plus nutrients (no anaerobic innoculum). In assays with added water, consistently higher gas production rates were obtained over unamended controls. In assays of samples with high soil:refuse ratios (soil was calcareous glacial till), there was little benefit to the addition of an aqueous nutrient media over addition of water alone. Higher percent biodegradation after 200 days incubation was a function of lower volatile solids loading which, for the controls, was associated with samples of high water content and high soil-refuse ratios. With both water and aqueous nutrient media additions, variability in rates was decreased relative to the controls. Anaerobic sample handling did not result in faster onset of methanogenesis in assay bottles relative to samples given a controlled aeration. Results suggest that alteration of current landfill practice to permit addition of liquids would result in higher, more consistent gas production rates and faster landfill stabilization for alternative land uses.