Environmental and Landfill Operational Aspects of Co-disposal of Dewatered Sewage Sludge and Municipal Solid Waste

The co-disposal of dewatered sewage sludge and municipal solid waste may cause significant impacts (such as total and differential settlement, slope stability of the waste, and leachability) on landfill operations and the subsurface environment. The objectives of this study were to investigate the co-disposal of dewatered sewage sludge and municipal solid waste with respect to their consolidation characteristics, vane shear strength, and leachability. The results of the consolidation tests show that, for a given stress increment, the deformation (the change in the void ratio) of the dewatered sewage sludge is larger than the deformation of its sludge mixtures. When the sludge ratio in the mixture increases, the compressibility of the mixture increases. The total consolidation settlement taking place in landfilling of dewatered sewage sludge alone would be much greater than that for co-disposal of sludge with solid waste. The results of the shear stress strength tests of the sludge and its mixtures imply that side slopes of 20o can probably be constructed in a landfill site without causing a sliding problem. Based on the results of the column leachability tests, Fe, Cu and nitrogen leached out from the sludge and its mixture might cause groundwater pollution.