Bottom ash from sludge cake as a barrier material to pollutant migration in landfills

Abstract

Treated urban sewage sludge, which had been dewatered and dried in an open bed, was locally burnt in an open drum and bottom ashes were formed. This work investigated whether these bottom ashes of dried sludge cakes (SC_bash)_' produced by local labour and equipment, could be used as landfill covers or liners, a function normally served by clay. Laboratory tests were performed to determine the particle size distribution, Atterberg limits, compaction characteristics, hydraulic conductivity and shear strength parameters of the sludge cake. The effects of desiccation and freeze-thaw processes on the hydraulic conductivity of SC_bash were also examined. It was found that properly compacted and stabilized SC_bash has the requisite properties for use as landfill covers or liners. The SC_bash can be compacted into a dense mass with a low hydraulic conductivity of the order of 1.15 X 10 ^-7 m s^-1 (as a comparison, the hydraulic conductivity of compacted clay is around 10^-9 m s^-1). The compacted SC_bash also showed good defence against the increases in hydraulic conductivity caused by desiccation and freeze-thaw processes compared with the data reported for compacted clays. The compacted SC_bash also has a greater shear strength than is typically expected of compacted clay and therefore is likely to remain stable on a typical landfill slope design based on the shear strength of clay.