EFFECT OF VERTICAL WELL CONFIGURATION ON LEACHATE DISTRIBUTION IN BIOREACTOR LANDFILLS

摘要

Uniform and elevated moisture distribution in a bioreactor landfill is of utmost importance to enhance the biodegradation of municipal solid waste (MSW). This is accomplished by recirculating leachate through MSW using a leachate recirculation system (LRS). Currently, the selection and design of LRS is based on limited laboratory and field observations, which often leads to widely varying performance. Our research goal is to develop a rational method for the design of LRS for bioreactor landfills. This paper investigates the effectiveness of different configurations of vertical wells (VW) as LRS. Initially, MSW is under an unsarurated condition where the pores between the solid particles are filled by leachate and landfill gas. Therefore, a two-phase flow mathematical model is implemented in this study by considering the recirculated leachate as wetting fluid and the generated landfill gas as non-wetting fluid. The hydraulic properties of MSW, which include the relative permeabilities for wetting and non-wetting fluids, are computed by the van Genuchten model based on the soil water characteristic curve. Flow of wetting and non-wetting fluid in a porous media is computed by Darcy's law. A typical bioreactor cell of 30 m high compacted in ten layers of 3 m each is considered for this study. MSW is modeled as inhomogeneous and anisotropic material. Saturation level, wetted area, accumulated pore water pressure, and outflow rate (from the leachate collection system located at the bottom of the landfill) are computed for a selected leachate injection rate of 55m3/day. Results show that a VW configuration involving close spacing with staggered injection screen locations is effective for uniform elevated moisture distribution in the landfill. When leachate is injected continuously for four weeks, uniform moisture distribution with a maximum saturation of 100% is achieved throughout most of the landfill, and the maximum pore water pressure of 120 kPa is found near the injection screen locations.