Effect of decomposition, stress, and water content on thermal properties of municipal solid waste

Abstract

Recent studies of elevated temperature landfills (ETLFs) demonstrate the importance of managing heat and temperature in municipal solid waste (MSW) landfills. Predicting heat transfer within the MSW and across landfill boundaries is necessary when developing and evaluating thermal management strategies. This study evaluated how the thermal conductivity and specific heat of synthetic MSW vary with composition, water content, dry unit weight, and decomposition. Methods to estimate thermal conductivity and specific heat based on MSW composition were also evaluated. Synthetic waste was created to mimic the average MSW composition reported in the United States Environmental Protection Agency’s 2015 solid waste database. Degraded waste was created by anaerobic decomposition of the fresh waste. Thermal properties of fresh and decomposed synthetic MSW were measured at water contents of 6 to 60 % (by dry mass) and confining stresses ranging from 2 to 400 kPa. Thermal conductivity of the waste increased with an increase in water content and with higher confining stress, the latter contributing to higher dry density. Specific heat capacity of the waste was larger at higher water content due to the higher specific heat capacity of the water phase. Comparisons were made between measured thermal conductivities and thermal conductivities predicted using serial, parallel, and geometric mean volume-weighted models. Similar comparisons were made between measured specific heat capacities and specific heat capacities predicted with a mass-weighted model. Thermal conductivity was under-predicted by the serial and geometric-mean thermal conductivity models, and over-predicted by the parallel model. A new mixing model over-predicted thermal conductivity modestly in the low range, and was comparable in the high range. The mass-weighted model predicted specific heat capacity accurately.