Two-Phase Modeling of Leachate Recirculation Using Drainage Blankets in Bioreactor Landfills

A drainage blanket (DB) is a recently introduced leachate recirculation system (LRS) in bioreactor landfills, which involves the use of a blanket of high permeable material that is spread over a large area of the municipal solid waste (MSW). Based on the laboratory and field observations documented in the literature, the results of the performance and efficiency of bioreactor landfills vary greatly due to the empirical method followed to design the LRS. Therefore, a rational LRS design methodology that achieves an efficient bioreactor landfill and creates an optimal and safe environment is necessary. Two-phase flow modeling was performed in this study by representing the relative permeabilities of leachate and landfill gas with the van Genuchten function and fluid flow with Darcy's law. The effects of heterogeneous-anisotropic MSW, the leachate injection rate, and the saturated and unsaturated hydraulic conductivities of the MSW on the moisture distribution in a typical bioreactor landfill cell using a DB as the LRS were modeled. Those results included saturation levels, maximum pore water and gas pressures, maximum influenced lateral spread (wetted width), maximum influenced wetted area, and outflow collected at leachate collection and removal system at the bottom of the landfill. The results indicate that the variation in the different parameters assumed has a significant influence on the successful distribution of the moisture. Unsaturated hydraulic properties considerably affect moisture flow and distribution in landfilled MSW. And, the intermittent mode of leachate recirculation has the potential for the development of gas pressures that must be considered to evaluate the stability of the landfill slopes.