A Novel First-Order Kinetic Model for Simultaneous Anaerobic–Aerobic Degradation of Municipal Solid Waste in Landfills

A first-order kinetic model for the simultaneous anaerobic–aerobic degradation of municipal solid waste (MSW) is presented in the study. The model incorporates the effect of oxygen concentration on anaerobic degradation, enabling the coexistence of anaerobic and aerobic processes within specific oxygen ranges. The model can thoroughly consider the impacts of temperature, moisture content, oxygen concentration, and free air space (FAS) on the degradation rates of five substrates, i.e., holocellulose, non-cellulosic sugars, proteins, lipids, and lignin. The model was successfully verified against two experimental results. The sequential model underestimates both compression strain and degradation ratio, with peak underestimation ratios of 8.7% and 9.2%, respectively. Using the simultaneous model, the effects of anaerobic age, temperature, and aeration rate on landfill aerobic remediation efficacy are quantitatively assessed. Two evaluation criteria, namely the advance rate of aerobic remediation stabilization time (Rt) and the degradation rate after 100 days of aerobic remediation (λ100a), are adopted. The results indicate the following: (1) Rt is more sensitive to anaerobic age and temperature, while λ100a is more affected by anaerobic age and aeration rate; (2) under optimal conditions, Rt and λ100a can reach 86.3% and 70.9%, respectively. The present model provides a crucial theoretical framework for evaluating aerobic remediation effectiveness in both anaerobic sanitary landfills and informal landfills, offering valuable insights for practical implementation and management.