| Because of large quantities of excess sewage sludge produced from wastewater treatment plants, which has brought great pressure to wastewater treatment plants due to high operation cost of sludge treatment and disposal, sludge dewatering has become one key of sludge treatment.Sewage sludge bioleaching was optimized to improve sludge dewaterability. Sludge dewaterability was evaluated with specific resistance to filtration (SRF), water content of filter cake and ratio of water volume to total sludge volume with centrifugal separation.Considering both sludge dewaterability improvement and operation cost, the optimum conditions of sludge bioleaching were as follows:sulfur powder addition of 3 g/L, Fe2+ addition of 4 g/L and inocula addition of 0.4. Under the optimum bioleaching conditions,36-48 hours were needed for pH value decrease to about 2.0; the sludge SRF decreased from 1.26x 1014 m/kg to 8.14x 1012 m/kg with a SRF reduction of 93.54%, the water content of filter cakes decreased from 98.39% to 73.68% and the ratio of water volume to total sludge volume with centrifugal separation increased from 72% to 83%. After adjusting the pH of bioleached sludge back to 6.0, the sludge SRF further decreased to 8.27×1011 m/kg with a total SRF reduction of 99.34%, and the sludge can be regarded easy to be dewatered.Change of iron species in sludge system and sludge flocs properties were measured to analyze the mechanisms of sludge dewaterability improvement by bioleaching. Fe2+ ions added as bioleaching substrate were quickly converted to Fe3+ through microorganism oxidation. Flocculation effect of Fe3+ may be the main mechanisms of sludge dewaterability improvement.
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