Hydraulic and Mechanical Characteristics of a Compacted Municipal Solid Waste Compost

Abstract

Results of a laboratory study are presented that describe hydraulic and mechanical properties of a compacted compost derived from a mixture of municipal solid waste and treatment plant sludge. The objective of the study was to determine if compacted compost has properties desirable of a hydraulic barrier used in liners and final covers of landfills. Ordinarily, the hydraulic barrier is constructed with compacted clay and/ or a geomembrane. Laboratory tests were performed to determine the particle size distribution, compaction characteristics, hydraulic conductivity and shear strength of the compacted compost. Tests have also been conducted to evaluate: (1) the resistance of compost to changes caused by desiccation and freeze-thaw, (2) the effects of extended permeation and (3) the concentration of contaminants leached during permeation. The results of the study show that compost can be compacted into a dense mass with low hydraulic conductivity (2 x 10-10 m s-1). It is also more resistant to increases in hydraulic conductivity caused by desiccation and freeze-thaw than compacted clay. Compacted compost also has greater shear strength than compacted clay and therefore is likely to remain stable on typical landfill slopes. However, contaminants considered hazardous, such as heavy metals, were leached from the compost at levels exceeding United States drinking water standards. The results suggest that the compost used in this study has hydraulic and mechanical properties desirable of a hydraulic barrier and further detailed study of its use is warranted.