Coupled Thermo-Hydro-Bio-Mechanical Model for Holistic Performance Assessment of Municipal Landfills

Currently, the design, construction, and operation of engineered landfills to effectively contain the municipal solid waste (MSW) and its byproducts from contaminating the environment is well-established. However, the relatively dry conditions with the waste in the conventional landfills presents unfavorable conditions for rapid microbial decomposition of waste to occur. Bioreactor landfills, which involve recirculation of landfill leachate/other liquids through leachate recirculation systems (LRS), have emerged as a promising option to accelerate waste decomposition rates and achieve early waste stabilization with numerous other benefits (e.g. high biogas generation and settlement rates, reduced leachate treatment and disposal costs, reduced long-term landfill monitoring costs). However, there is no rational approach to design safe and effectively operating bioreactor landfills due to a lack of adequate understanding about the influence of coupled interactions between the fundamental landfill processes under rapid waste decomposition conditions on the short-term and long-term performance of bioreactor landfills (e.g. moisture distribution, landfill settlement, evolution and distribution of temperatures, landfill gas generation rates and volumes). This research presents a comprehensive coupled thermo-hydro-bio-mechanical (CTHBM) model to fundamentally characterize and mathematically simulate the coupled interactions between the hydraulic, mechanical, biochemical, and thermal processes observed in MSW landfills. After successful validation with simulated long-term laboratory experiments on representative field-waste samples, the proposed CTHBM model was applied to a typical full-scale landfill cell configuration to assess the holistic short-term and long-term performance of the landfill cell under simulated conventional and bioreactor landfill conditions. A parametric study was also conducted to assess the effects of different LRS variables on the long-term performance of bioreactor landfills, and aid in developing design recommendations for effective operation of bioreactor landfills. Finally, a probabilistic analysis using Monte Carlo simulations approach was performed by considering spatial variability in the hydraulic, mechanical, biochemical, and thermal properties of waste to assess the influence of waste heterogeneity on the reliability of the predicted long-term performance of bioreactor landfills in comparison to a deterministic analysis.