Synergistic degradation of sulfamethoxazole in an oxalate-enhanced Fered-Fenton system: The critical heterogeneous solid-liquid interfacial mechanism and an insight in practical application.

It was demonstrated in this study that appropriate concentrations of oxalate (Ox) would lead to greatly accelerated electro-generation of Fe2+ but obviously lower power consumption in the Fered-Fenton system. Depending on the Ti electrode with pristine TiO2 layer, effects of important parameters on the SMX degradation were investigated in the Fered-Fenton-Ox system. It was found that the heterogeneous interfacial electrochemically reduction of FeIII was critical in the Fered-Fenton-Ox system relying on the surface hydroxyl bonding FeIII-Ox and formation of FeOTi bonds. A heterogeneous-homogeneous reaction mechanism was therefore proposed. It included the heterogeneous interfacial electrochemical generation of FeII-Ox and the heterogeneous-homogenous Fenton oxidation of pollutants. The promotional role of Ox would be also homogenous and heterogeneous, i.e. maintaining ferric at higher pH and forming specific FeIII-Ox complex as well as accelerating the solid-liquid interfacial heterogeneous iron cycle. Furthermore, a continuous-flow pilot study was conducted in treating a printing and dyeing industrial wastewater. As compared to conventional Fenton and Fered-Fenton systems, the Fered-Fenton-Ox system could achieve more efficient COD removal with a relative low cost/△COD, suggesting great advantages in its practical applications for treating real industrial complex wastewaters.