A MODEL TO PREDICT SETTLEMENTS AND LANDFIL GAS GENERATION IN BIOREACTOR LANDFILLS

摘要

Current practice of landfill settlement modeling is predominantly empirical, thus most of the available techniques make no attempt to simulate the real mechanisms of waste settlement. Although a landfill is an interacting multiphase medium there is limited research on landfill gas generation and dissipation as an integral part of the landfill settlements. This research describes a model which couples settlements of a bioreactor landfill with the generation and dissipation of landfill gases. The major mechanisms of waste settlement were identified as mechanical compression and biodegradation-induced strain. Mechanical compression was modeled with the help of laboratory simulations. To model the biodegradation-induced settlements, it was assumed that waste degradation obeys the first order kinetic equation. The mass balance was used to link settlement with gas pressures. The mass balance of the landfill gas was used to link settlement with gas pressures and the Richard's equation was used to simulate the distribution of moisture. The proposed mathematical model was solved numerically to predict the settlements, and gas pressures in a bioreactor landfill using landfill geometry and waste properties. To test the mathematical formulations, a numerical exercise was performed using a hypothetical bioreactor landfill. The model predicted higher strains as expected. It was also found that the high gas pressure values made a higher contribution to the total settlement. The model was capable of predicting landfill density, and the density values predicted for 25 years matched with those reported in literature.