Improvement of sludge dewaterability and removal of sludge-borne metals by bioleaching at optimum pH

摘要

Bio-acidification caused by bio-oxidation of energy substances during bioleaching is widely known to play an important role in improving sludge-borne metals removal. Here we report that bioleaching also drastically enhances sludge dewaterability in a suitable pH level. To obtain the optimum initial concentrations of energy substances and pH values for sludge dewaterability during bioleaching, bio-oxidation of Fe~(2+) and S~0 under co-inoculation with Acidithiobacillus thiooxidans TS6 and AcidothiobaciUus ferrooxi-dans LX5 and their effects on sludge dewaterability and metals removal during sludge bioleaching were investigated. Results indicated that the dosage of energy substances with 2 g/L S~0 and 2 g/L Fe~(2+) could obtain bio-oxidation efficiencies of up to 100% for Fe~(2+) and 50% for S~0 and were the optimal dosages for sludge bioleaching. The removal efficiencies of sludge-borne Cu and Cr could reach above 85% and 40%, respectively, and capillary suction time (CST) of bioleached sludge decreased to as low as ～10s from initial 48.9 s for fresh sludge when sludge pH declined to ～2.4 through bioleaching. These results confirm the potential of bioleaching as a novel method for improving sludge dewaterability as well as removal of metals.