This study aims to develop a high-efficiency radical oxidation process for enhancing the dewaterability of waste activated sludge (WAS). Radical scavenging studies combined with electron paramagnetic resonance (EPR) were carried out for the direct radical identification and effectiveness evaluation of radical oxidation. The results indicated that Fe(II)-activated CaO2 can pose a superior effect on dewatering WAS due to its distinctive capacity of stable •OH production and the high reaction efficiency of regulated-released •OH with water-holding organics. The mechanism for the enhanced dewatering performance was also explored. The rupture of sludge colloidal flocs and the reduction of hydrophilic functional groups in loosely bound extracellular polymeric substances (LB-EPS) were found to be mainly responsible for the release of interstitial water and improved dewaterability, respectively. In addition, an inference about the relationship between interfacial water and zeta potential of different EPS fractions was established by the simultaneous measurement of the binding affinities of Ca2+ and Fe2+/Fe3+ for EPS and bound water content. All these results provide the direct evidence that Fe(II)-activated CaO2 is a promising pretreatment reagent for sludge disposal.
Implications: Fe(II)-activated CaO2 was first proposed to be highly effective in enhancing the dewaterability of waste activated sludge. Electron paramagnetic resonance (EPR) spectroscopy provided the direct evidence for the specific advantages of CaO2, especially the capacity of durable and efficacious •OH production leading to the excellent conditioning performance.