Sewage Sludge Conditioning and Dewatering by Bioleaching

摘要

Treatment of large quantities of sewage sludge is one of challenges for wastewater treatment plants. Influencing factors of sewage sludge bioleaching were optimized to enhance sludge dewaterability and to find reasons for sludge conditioning. The indigenous inocula for sewage sludge bioleaching was cultured and enriched with abundant substrates. Specific resistance to filtration (SRF), pH and water content of the filter cake were used to explain the sludge dewaterability improvement effect by bioleaching. Considered both sludge dewaterability improvement and operation cost, the optimum conditions of sludge bioleaching were found 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 h were needed for pH value decrease to about 2.0; the sludge SRF decreased from 1.26×1014 m/kg to 8.14×1012 m/kg with a SRF reduction of 93.54%, and the water content of filter cakes decreased from 98.39% to 73.68%. After adjusting the pH of bioleaching sludge back to 6, the sludge SRF further decreased to 8.27×1011 m/kg with a total SRF reduction of 99.34%, and the sludge was regarded easy to be dewatered. Species of iron ion and zeta potential of sludge flocs were measured to analyze the mechanisms of sludge dewaterability improvement by bioleaching. Fe2+ions added as bioleaching substrate were converted to Fe3+through microorganism oxidation, and the flocculation effect of Fe3+may be one of the important mechanisms of sludge conditioning. The sewage sludge bioleaching may have potential application for sludge conditioning and dewatering because of short treatment time, low operation cost, and simultaneous heavy metal removal.