Enhanced dewaterability of sewage sludge in the presence of Fe(II)-activated persulfate oxidation

► First scientific attempt to apply sulfate radicals to sludge dewatering. ► 88.8% CST reduction efficiency was obtained within 1min. ► Both soluble EPS and viscosity played negative roles in sludge dewatering. ► No correlation was established between dewaterability and bound EPS. ► Soluble EPS were degraded and flocs were ruptured, inducing the dewaterability improvement. The potential benefits of Fe(II)-activated persulfate oxidation on sludge dewatering and its mechanisms were investigated in this study. Capillary suction time (CST) was used to evaluate sludge dewaterability. Both extracellular polymeric substances (EPS) and viscosity were determined in an attempt to explain the observed changes in sludge dewaterability. The optimal conditions to give preferable dewaterability characteristics were found to be persulfate (S2O82-) 1.2mmol/gVSS, Fe(II) 1.5mmol/gVSS, and pH 3.0–8.5, which demonstrated a very high CST reduction efficiency (88.8% reduction within 1min). It was further observed that both soluble EPS and viscosity played relatively negative roles in sludge dewatering, whereas no correlation was established between sludge dewaterability and bound EPS. Three-dimensional excitation–emission matrix (EEM) fluorescence spectra also revealed that soluble EPS of sludge were degraded and sludge flocs were ruptured by persulfate oxidation, which caused the release of water in the intracellular pace and subsequent improvement of its dewaterability.