Evaluation of waste sludge compatibility for landfill cover application

The objective of this paper is to examine the material properties of paper sludge (PS) and construction sludge (CS) as landfill cover materials. Compaction, shear strength, consolidation, and hydraulic conductivity tests are carried out to evaluate the material properties as well as the engineering behaviors of PS and CS. Furthermore, the long-term behavior of these two types of sludge is evaluated by centrifuge tests. The basic properties of PS and CS indicate their suitability for use as cover materials, and the PS results agree well with previously documented data. The leaching properties of heavy metals from both types of sludge satisfy the Japanese Environmental Quality Standards for reusing them as cover materials. The compacted CS shows hydraulic conductivity in the range of 1.2 × 10^-8 to 6.5 × 10 ^-8 cm/s, which can satisfy the requirements for hydraulic conductivity of landfill covers distributed by USEPA. In the case of compacted PS, there is no remarkable difference in the hydraulic conductivity (in the range of 3.5 × 10^-7 to 9.0 × 10^-7 cm/s) for a wide variation of water contents ranging from 50 to 150%. Compacted PS and CS maintain a hydraulic conductivity of 10^-7 and 10^-8 cm/s order of magnitude, respectively, under a centrifugal field of 60 G over 24 hours. Thus, the PS and CS can maintain these levels of hydraulic conductivity for about 9.86 years when used as barrier materials.