Permeability and leachability of solidified sewage sludge

Solidification/stabilization is considered as a technically sound and cost-effective approach to treat sewage sludge. The results of stabilization are typically evaluated with leaching tests on particles obtained by drying and grinding of treated samples. However, limited research has been focused on the monolithic features of the samples. This technical paper reports the results of permeability and leachability tests (i. e., leaching of organics, zinc and copper) on monolithic samples performed in a flexible wall permeability test apparatus. The samples were prepared by solidifying sewage sludge with ordinary Portland cement and calcium bentonite. This study considered three mixing levels with different amounts of calcium bentonite. The environmental effects of acid rain and microbial activities on permeability and leachability were also evaluated. Hydrochloric acid was used to simulate acid rain, while glucose solution was used to simulate microbial activities in the sludge. The test results indicated that (1) an increase in calcium bentonite content helped to reduce the permeability and leachability; (2) lower permeability helped to maintain a lower leaching level of organics (zinc and copper); and (3) an acid condition increased the permeability and leachability, but microbial activities had a minor effect on them.