Effects Of Ratio Of Substrate Dosage To Solid Content During Sewage Sludge Bioleaching

Large volume, complex components of excess activated sludge from full-scale municipal wastewater treatment plants have been restricted the reuse and disposal of sludge. Sludge resource utillzation reflects the thinking of the economic cycle. However, heavy metals from urban wastewater to some industrial discharges can accumulate in the waste sludge in wastewater treatment plants, leading to a sludge disposal problem concerned worldwide. And whether the content of heavy metal come up to the standard is also an important target of sludge resource utilization.The aim of this work was to study the effect of ratio of substrate dosage to solid content (Sd/SC) on the removal efficiency of heavy metals(Cu, Zn, Pb) from sewage sludge from wastewater treatment plant by bioleaching technique was studied adopting cultivation with order-batch type shaking bed. In this work, sulphur powder was substrate and the inocula—indigenous sulfur-oxidizing bacteria were enriched and cultured from the fresh activated sludge to a wastewater treatment plant. The results showed that Sd/SC significantly influenced the sludge bioleaching process. With increase in Sd/SC the sludge bioleaching was enhanced, which was represented by the acceleration of sludge acidification, oxidizing environment formation, and substrate (sulfur) utilization. Higher Sd/SC was more efficient to solubilize the heavy metals than lower Sd/SC. The solubilization patterns of copper and zinc were similar. Zinc and copper were efficiently bioleached because of sludge acidification and sludge oxidation, but lead was bioleached with a low efficiency because of the formation of low soluble PbSO₄ precipitates. The optimal Sd/SC ratio was 2.50, under which 30.8% of Pb was leached out on the 16th day and the solubilization of copper and zinc began from the 4th day, reached the maximum of 66.2-63.9%, respectively, on the 8th day, and then decreased a little. Readsorption of soluble copper and zinc to the sludge and/or the complexation of the soluble copper and zinc with the organic compounds in the sludge may decrease the heavy metal solubilization. To sum up, after bioleaching the biotoxicity of sewage sludge greatly reduced.