Secondary Compression of Municipal Solid Wastes and a Compression Model for Predicting Settlement of Municipal Solid Waste Landfills

The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.