Role of S(IV) in enhancing permanganate oxidation of emerging contaminants: pH dependence of reactive species generation

The enhanced degradation mechanism of micropollutants by sulfite (S(IV)) activated permanganate (Mn(VII)/S(IV)) process under different pH conditions were investigated in this study. The Mn(VII)/S(IV) process can significantly promote the degradation of sulfamethoxazole (SMX), ibuprofen (IBU), iohexol (IOX) and acetochlor (ACE). Compared with the permanganate (Mn(VII)) process alone, the degradation efficiency of SMX, IBU, IOX, and ACE in the Mn(VII)/S(IV) process increased by 51.6 %, 38.9 %, 43 % and 78.7 %, respectively. The pH value has a significant impact on the degradation of the four target pollutants. The mechanism of the Mn(VII)/S(IV) process was further explored using SMX as a model pollutant. Hydroxyl radicals (HO•), sulfate radicals (SO 4 •− ), and reactive manganese species (RMnS, Mn(III), and Mn(V)) were detected in the process. HO• plays an important role in the degradation of SMX under acidic conditions. At pH= 7, RMnS is the main reactive species. Under alkaline conditions, SO 4 •− plays an important role in the process. Mn(III) and Mn(V) can also be converted into other manganese species. In addition, the possible degradation pathway of SMX was proposed. This work reveals the important role of pH in the generation and transformation of reactive species, and demonstrates the enormous potential of the Mn(VII)/S(IV) process in controlling micropollutants. Considering the complexity of water matrix, future studies can explore the application of the Mn(VII)/S(IV) process in practical water treatment.