Numerical modeling of settlement and gas generation in biodegrading municipal solid waste: a systematic review for...

The short- and long-term behavior of municipal solid waste (MSW) in sanitary landfills is governed by coupled hydraulic, mechanical, thermal, and biochemical processes. Among these, settlement due to biodegradation and landfill gas (LFG) generation are critical for assessing structural stability, environmental safety, and energy recovery during both operation and post-closure. Following the guidelines established by the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) in 2020, this study systematically reviews numerical models implemented in computational frameworks to simulate settlement and/or gas generation in biodegrading MSW. A structured search in the Scopus database covered peer-reviewed journal articles and conference papers published between 2000 and May 2025. The reviewed works address different combinations of coupled processes, mainly implemented using finite element or finite difference formulations. While one-dimensional domains remain common, nearly half of the studies employed two-dimensional models. First-order kinetics is the predominant approach for representing biodegradation and its coupling to volumetric strain and gas generation, although some models incorporate more detailed biochemical processes. Earlier approaches used the secondary compression index to capture long-term MSW settlement, whereas a few recent studies implemented physically based creep models. Waste heterogeneity and its time-dependent mechanical response have been considered in some studies, although temperature effects on waste properties remain rarely implemented in computational frameworks. This review highlights critical research gaps and emphasizes the need for unified numerical frameworks capable of integrating biodegradation, multiphysical coupling, temperature effects on MSW properties, large-strain kinematics, and parameter variability to realistically simulate the evolving behavior of MSW in landfills.