The transformation behaviors of heavy metals and dewaterability of sewage sludge during the dual conditioning with Fe2+-sodium persulfate oxidation and rice husk

This study focused on the behavior of heavy metals (HMs) in sewage sludge after conditioning based on total HMs concentration, fractionation and leaching tests. Fe2+-sodium persulfate (SPS) oxidation was applied as chemical conditioner and rice husk (RH) was added as a physical conditioner to improve the dewaterability of sewage sludge. Combined the response surface methodology analysis and our previous research, the capillary suction time (CST) and the water content of sludge cake reduced by 93.8% and 25%, respectively, after conditioned by 125 mg g−1 dry solid (DS) SPS, 33 mg g−1 DS Fe2+, 333 mg g−1 DS RH at original pH of sludge. The HMs analysis indicated that the concentrations of Cu, Pb, Cd, Zn and Cr were increased in liquid phase after conditioning process. And after conditioned by Fe2+/SPS with RH, the leaching toxicity reduction are 79%, 100%, 93%, 80% and 68% for Cu, Pb, Cd, Zn and Cr, respectively. Results showed that RH combined with Fe2+/SPS oxidation has a synergistic effect on risk reduction and immobilization of HMs. The chemical species of HMs were redistributed and the risk of Pb was reduced from medium risk to no risk after sludge conditioning process according to the risk assessment.