MUNICIPAL LANDFILL BIODEGRADATION AND SETTLEMENT

Landfills are frequently considered for urban development, but have limited end uses due to large differential settlements, leachate generation, and gas emissions. Current landfill design with top- and bottom-liner systems minimize entry of moisture and increase the period required for stabilization of the refuse to occur. The objective of this study is to test the ability of biological enhancement to reduce the time to reach biological stabilization of the waste to nondegradable matter, and to determine the effects of biodegradation on settlement. To accomplish this, six landfill test cells were constructed to model both settlement and decomposition over extended periods. Three cells were designed to simulate bioreactor landfills, while another three were designed to simulate secure vaults. Results demonstrate that secondary settlement is linear with the logarithm of time, and decomposition is well represented by a first-order model. Comparisons indicate that in the short term there is no significant increase in the settlement rate due to biodegradation; however, extrapolation suggests that in the long term the settlement rate will likely increase as the effects of decomposition become more significant.