Simultaneously promoted reactive manganese species and hydroxyl radical generation by electro-permanganate with low...

A novel water treatment process combining electrolysis, permanganate and ozone was tested in the laboratory. The combination showed synergistic effects in degrading various organic contaminants (like diclofenac, sulfamethoxazole, carbamazepine, etc.). A small amount of O₃ (1 mg L^-1, 60 mL min^-1) significantly improved the oxidation and mineralization ability of an electro-permanganate process by generating more reactive manganese species and hydroxyl radicals. The combination required less energy consumption than comparable processes. Mechanism experiments showed that the ·OH involved was mainly generated by cathode reduction, homogeneous manganese catalysis, and heterogeneous manganese catalysis of O₃ decomposition. Reactive Mn species were generated by electro-reduction, ·OH oxidation or/and O₃ activation. In situ generated Mn (Ⅳ)_s plays a vital role in generating ·OH and reactive Mn species. ·OH generated by O₃ catalysis could transfer colloid Mn (Ⅳ)_s to free Mn (Ⅴ)_aq and Mn (Ⅵ) _aq. And both the ·OH and RMnS played the dominant role for DCF removal. Increasing permanganate dosage, O₃ concentration, the current density, Cl^-, or humic acid, and decreasing the pH all enhanced the degradation of diclofenac, but the presence of PO₄^3- or HCO₃^- inhibited it. Supplementing electrolysis with permanganate and O₃ might be a practical, sustainable, and economical technology for treating refractory organics in natural waters.