Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water

Abstract

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)–activated ferrate (Fe(VI)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(VI) could generate active species (Fe(V), Fe(IV), ˙OH and O₂˙⁻) to degrade pollutants, while the in situ produced Fe(III) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(VI) system, dissolved organic carbon was reduced by 49.38%, while UV₂₅₄ was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J₀ was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(VI) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.