Edinburgh Napier University

  Municipal solid waste (MSW) is biodegradable in landfills under anaerobic conditions. The evolution of the biochemical, physical and mechanical characteristics of MSW are interdependent and is investigated first through an experiment and subsequently via a constitutive model. Specifically, a well-characterized MSW specimen was reconstituted with waste constituents obtained from Sauk Trail Hills Landfill in Michigan and was biodegraded in a large-scale experimental setup that enabled simultaneous characterization of the processes with time. A 42-L column accompanied by a system to recirculate and store leachate, and a system to monitor the long-term waste degradation process was constructed. The specimen unit weight, settlement, biogas composition, volume and leachate chemistry were measured with time to assess the progress of waste degradation. The experiment was completed after 1100 days of operation, when degradation appeared to have been complete. This closely-monitored process is modelled using the modelling framework proposed by McDougall (2007), with a focus on biodegradation. A two-stage degradation model is used to describe the anaerobic process and account for hydrolysis of degradable matter in relation to moisture content, product inhibition, cellulose digestibility and microbial controls. To investigate how solid mass loss caused by biodegradation is reflected into settlement, a void change parameter is used that describes the loosening or densification during degradation. The model performed fairly well in predicting the biochemical (volatile fatty acids concentrations) and physical (solid degradable matter) behaviour; however, for the assumptions made in this study, it significantly over-predicted biogas production.