Evaluating the effects of the preoxidation of H2O2, NaClO, and KMnO4 and reflocculation on the dewaterability of sewage sludge

Abstract The preoxidation effects of H 2 O 2 , NaClO, and KMnO 4 on the dewaterability of sewage sludge were compared by analyzing the changes in specific resistance to filtration (SRF), filter cake moisture content (FCMC), extracellular polymeric substance (EPS) fractions and components, and floc properties. The three oxidants varied in oxidation efficiency and exhibited distinctive mechanisms. NaClO not only destroyed sludge flocs and EPSs but also effectively caused cell lysis, resulting in release of a considerable amount of organic matters and subsequently significant deterioration of dewatering performance. The oxidation of H 2 O 2 and KMnO 4 was relatively mild and occurred mainly on the outer layers of the sludge flocs and cell-bound EPSs. By contrast, the SRF and FCMC of the sludge conditioned with a low dose of KMnO 4 were slightly improved, and a fraction of soluble EPS was compressed because of the coagulation effect of the oxidation product MnO 2 . The pH of the sludge conditioned with H 2 O 2 and KMnO 4 had no considerable change. Meanwhile, NaClO evidently increased the alkalinity of the sludge because of the hydrolysis effect. After the pH of the NaClO-treated sludge was readjusted to 7.0, the partial protonation efficiency slightly alleviated the deterioration of sludge dewatering performance. The preoxidized sludge was then subjected to reflocculation treatment using FeCl 3 , polyacrylamide, and a cationic starch-based flocculant, respectively. The combined treatment of preoxidation and reflocculation showed a high dewatering efficiency owing to their synergistic effect.