Physical, geotechnical and biochemical behaviours of municipal solid waste in field and laboratory bioreactors.

This paper investigates the effects of degrees of compaction (initial dry unit weights), recirculation liquid and rate, and environmental temperature on the long-term physical, geotechnical, and biochemical properties of municipal solid wastes (MSWs) biodegraded for approximately 800 days. Four field bioreactors were filled with fresh MSWs collected from a landfill site. Three laboratory bioreactors were filled with synthetic MSWs with the composition same as that used in the field bioreactors. The bioreactors were recirculated with water or leachate at different rates. Compared to water recirculation, leachate recirculation further promotes the settlement of the MSWs and methane generation. Increasing the recirculation rate does not significantly increase the settlement of the MSWs. The biocompression ratio increases with the environmental temperature. The MSWs with lower dry unit weights are more sensitive to the change in temperature, especially with leachate recirculation. However, opposite to common sense, the decomposition of MSWs may not significantly contribute to the settlement after analysing the relationship between the degrees of biodegradation and settlement of the MSWs. Over 90 % of the settlement during the test period was completed within 25 % degrees of biodegradation. The major change in the physical, geotechnical, and biochemical properties occurs at low (less than20 %) degrees of biodegradation. A new equation is proposed to describe the nonlinear variation in the methane generation rate. The modelled methane generation rate and accumulated volume of methane well match the test results from the laboratory scale bioreactors and other studies.