Bioleaching of Metals from Sewage Sludge: Elemental Sulfur Recovery

Abstract

Heavy metal leaching by sulfur‐oxidizing bacteria, one of the most promising sludge detoxification methods, uses elemental sulfur as a microbial energy substrate. The addition of elemental sulfur in a powdered form makes it impossible to recover unused sulfur and can promote microbial reacidification of disposed sludge. Hence, recoverable forms of sulfur are preferred. The purpose of the present study was to verify the effect of sulfur forms, sulfur concentration, and the effect of sulfur recycling on the efficiency of microbial process. Powder, pastille, and sphere forms of sulfur were tested. Despite their relatively smaller surface areas, the sphere and pastille sulfur forms did not affect the consumption of sulfur substrate by the microbial process and were also comparable to the powder form in sludge acidification. Upon recycling in fresh sludge, the recovered elemental sulfur was as effective in pH reduction as new sulfur. Elemental sulfur can therefore be added in a microbial leaching process in recyclable forms such as stationary blocks, small sulfur prills or suspended sulfur rods depending on the needs of a waste treatment plant.