Influence of Waste Temperatures on Long-Term Landfill Performance: Coupled Numerical Modeling

A coupled thermo-hydro-bio-mechanical (CTHBM) numerical model to simulate the long-term behavior of municipal solid waste in landfills is presented. Three numerical simulations—a conventional landfill simulation with no leachate injection (CONV) and two bioreactor landfill simulations involving leachate injection—were carried out by applying the CTHBM model to a typical two-dimensional (2D) landfill cell configuration to analyze the effect of temperature on the long-term performance characteristics of a landfill system. Of the two bioreactor landfill simulations, one (BIOR-T) incorporated temperature effects on the waste decomposition, while the other simulation (BIOR-NT) did not. For the waste conditions simulated, the CONV and BIOR-T had a maximum waste temperature of 54°C and 62°C, respectively. The temperatures at the bottom liner were determined to be in the range of 1°C–32°C and 1°C–39°C over the entire simulation time of the CONV case and BIOR-T case, respectively. The effect of waste temperatures on moisture distribution, methane gas production, and landfill surface settlement was also assessed. The surface settlement response for BIOR-T and BIOR-NT simulations suggests that incorporating the effect of waste temperatures on the waste decomposition is important for a realistic prediction of the waste settlement in landfills. The BIOR-T and BIOR-NT simulations had a similar interface shear response, suggesting that the changes in the stiffness and shear strength of waste, due to incorporating temperature effects on the biodegradation rate, have no noticeable impact on the interface shear response in the bottom liner system. Overall, the proposed CTHBM model can be used to predict long-term performance characteristics (e.g., moisture distribution, landfill gas production, settlement of waste, temperatures) relevant for effective design of bioreactor landfills.