Synergistic effects of permanganate and chlorination on the degradation of Benzophenone-3: Kinetics, mechanisms and toxicity evaluation

To obtain utilization efficiency of low permanganate (KMnO4), it is available to combine with other chemical agents. This work found the synergistic effects of adding KMnO4 and sodium hypochlorite (NaClO) simultaneously on the efficient degradation of benzophenone-3 (BP-3). The synergy factors of the combined method were increased with increasing concentrations of KMnO4 and NaClO. Neutral and alkaline conditions were more favorable for BP-3 removal. Methyl phenyl sulfoxide (PMSO) was used as the probe to detect high-valence Mn species (e.g., Mn(VI), Mn(V)). Results indicated that the reactivity of KMnO4 was improved by NaClO by increasing the content of high-valence Mn species. Cl- converted from NaClO was oxidized by KMnO4 to generate Cl2, also promoting the degradation of BP-3. The oxidative mechanisms of BP-3 in the system of KMnO4 coupling with NaClO (KMnO4/NaClO) mainly included oxidative ring-opening, carboxylation, Bayer-Villiger oxidation, electrophilic chlorination, hydroxylated reactions and cleavage, but oxidative ring-opening products were detected only in the combined system. Due to the reduced dosage of chlorine and the decreased toxicity in the combined process, KMnO4/NaClO decreased the environmental risk of the reaction process largely. Comprehensively analyzing the degradation efficiency and environmental risk in treatment of BP-3 by the combined process, KMnO4/NaClO oxidation is a promising technology for water treatment.