Modeling Coupled Hydromechanical Behavior of Landfilled Waste in Bioreactor Landfills: Numerical Formulation and Validation

Abstract

Bioreactor landfills involving leachate recirculation are emerging as the preferred option for managing municipal solid waste (MSW). Effective bioreactor landfill performance can be achieved by ensuring uniform and adequate moisture (leachate) distribution in landfilled MSW. This paper presents a numerical two-phase flow model as a tool to predict hydraulic behavior (moisture distribution and pore fluid pressures) in unsaturated MSW under leachate recirculation, mechanical response (stress-strain behavior), and coupled hydromechanical interactions of MSW in landfills. The selected mathematical model is the Fast Lagrangian Analysis of Continua (FLAC), which assumes leachate and landfill gas as two immiscible phases. The governing equations and numerical implementation are presented along with the general model implementation considerations. The model is validated by simulating the published laboratory studies, field studies, and published modeled studies. Overall, it is shown that the mathematical model is capable of providing information necessary for the design of effective bioreactor landfills by incorporating coupled hydromechanical processes.