Effects of Unsaturated Hydraulic Properties of Municipal Solid Waste on Moisture Distribution in Bioreactor Landfills

Moisture distribution in a bioreactor landfill depends on various parameters such as the leachate recirculation system and its geometric configuration, hydraulic properties of municipal solid waste (MSW), and others. Hydraulic properties of MSW are the most important parameters that govern leachate distribution. Studies on the effect of saturated hydraulic properties of MSW on moisture distribution are documented in literature; however, studies on the effect of unsaturated hydraulic properties are scarce. The main objective of this paper is to model the effect of unsaturated hydraulic properties of MSW on leachate distribution. Since MSW is unsaturated, flow of two immiscible fluids (leachate and landfill gas) is expected; therefore, a mathematical model that accounts for a two-phase system is implemented which considers leachate as wetting fluid and landfill gas as non-wetting fluid. This model is validated based on reported laboratory test results and mathematical modeling studies. The effect of unsaturated hydraulic properties of MSW indicates significant variations in leachate distribution under steady state and gravity drainage conditions, which shows that its consideration is essential in the design of leachate recirculation systems in bioreactor landfills.