Effects of gas and moisture on modeling of bioreactor landfill settlement.

This manuscript describes a model that can predict settlement at variable moisture and pressure conditions as encountered in bioreactor landfills. In this model mechanical compression of municipal solid waste (MSW) was accounted with the help of laboratory compression tests. To model biodegradation-induced settlement, biodegradation of MSW was assumed to obey a first order decay equation. Richards equation was used to model moisture transport in the waste mass and mass balance was used to link settlement with gas pressure. The functionality of the numerical formulation was examined using a hypothetical bioreactor landfill. Four scenarios were analyzed to demonstrate how the proposed model can be used to analyze the settlement behavior of bioreactor landfills as well as dry landfills. The model predicted higher strains when moisture and gas pressures were incorporated into the settlement process. Results also indicated that the prediction capability of a MSW settlement model can be improved by coupling the settlement mechanisms with the generation and dissipation of gas pressure and the moisture distribution. The model is also able to predict landfill density values, and the predicted MSW wet density after 25 years agreed reasonably with those reported in literature.