BIOLEACHING OF METALS FROM SEWAGE-SLUDGE - ELEMENTAL SULFUR RECOVERY

Heavy metal leaching by sulfur-oxidizing bacteria, one of the most pro mising sludge detoxification methods, uses elemental sulfur as a micro bial energy substrate. The addition of elemental sulfur in a powdered form makes it impossible to recover unused sulfur and can promote micr obial reacidification of disposed sludge. Hence, recoverable forms of sulfur are preferred. The purpose of the present study was to verify t he effect of sulfur forms, sulfur concentration, and the effect of sul fur recycling on the efficiency of microbial process. Powder, pastille , and sphere forms of sulfur were tested. Despite their relatively sma ller surface areas, the sphere and pastille sulfur forms did not affec t the consumption of sulfur substrate by the microbial process and wer e also comparable to the powder form in sludge acidification. Upon rec ycling in fresh sludge, the recovered elemental sulfur was as effectiv e in pH reduction as new sulfur. Elemental sulfur can therefore be add ed in a microbial leaching process in recyclable forms such as station ary blocks, small sulfur prills or suspended sulfur rods depending on the needs of a waste treatment plant.