System Effects on Bioreactor Landfill Performance Based on Coupled Hydro-Bio-Mechanical Modeling

A newly developed and validated numerical model that accounts for the coupled hydro-bio-mechanical processes in municipal solid waste (MSW) landfills, was employed to assess influence of various field conditions and system variables on the performance of bioreactor landfills. The numerical model integrates a hydraulic two-phase flow model which assumes landfill leachate and gas as two immiscible phases, a mechanical model based on plain-strain formulation of Mohr-Coulomb constitutive law, and a first-order decay biodegradation model for modeling coupled hydro-bio-mechanical processes in bioreactor landfills. The influence of typical field conditions and system variables, namely, the landfill slope configuration, geometric configuration of the leachate recirculation system, and the mode of leachate injection on the bioreactor landfill performance were evaluated. The bioreactor landfill performance was investigated with regards to hydraulic behavior (e.g., moisture distribution, waste saturation, pore water and capillary pressures), extent of biodegradation and mechanical response (e.g., slope stability, landfill settlement, in-plane shear behavior of composite liner system) during the operation of leachate injection. Overall, this parametric study concluded that various field conditions and system variables significantly influence the performance of bioreactor landfills. Therefore, these system variables must be properly accounted for when optimizing the performance of bioreactor landfills undergoing coupled hydro-bio-mechanical processes during the leachate injection operations.