Effects of Leachate Recirculation System Variables on Long-Term Bioreactor Landfill Performance Using Coupled Thermo-Hydro-Bio-mechanical Model

Abstract

This study will apply a newly developed coupled thermo-hydro-bio-mechanical (CTHBM) numerical model to a typical full-scale landfill cell geometry with horizontal trenches (HTs) as the leachate recirculation system (LRS) and will evaluate the effect of the leachate injection pressure (IP), the horizontal spacing of the leachate injection locations (IS), and the mode of leachate injection (IM), on some of the major long-term hydraulic (e.g., wetted area), mechanical (e.g., differential waste settlement), biochemical [e.g., methane (CH4) gas production], and thermal (e.g., elevated temperatures) characteristics of bioreactor landfills. Based on the results from a series of numerical simulations with different IP, IS, and IM, it was determined that the variable IP had the most significant impact on the landfill performance compared with IS or IM. Higher IPs lead to a linear increase in the wetted area and a corresponding increase in the degraded waste area, thereby reducing the time taken for waste stabilization. However, an increase in IP leads to larger elevated temperature zones within the landfill and larger differential settlements on the landfill surface. Larger IS caused significantly higher differential waste settlements due to the formation of unwetted zones within the landfill cell. Increasing the duration of gaps between the intermittent injection periods significantly reduced the extent of elevated temperature zones formed within the landfill. The relative shear displacements in the geosynthetic interface in the bottom liner and final cover system were mainly influenced by the IP.