Gradient purification of surface water and ultrafiltration membrane fouling mitigation based on Fe(VI) multifunctional integration characteristics: Is a sedimentation unit necessary?

Ferrate (Fe(VI)) can provide oxidation and in-situ coagulation/adsorption for the removal of emerging contaminants and natural organic matter, and can be used in conjunction with ultrafiltration (UF) membrane to enhance the removal of composite contaminants and mitigate UF membrane fouling. Based on the Fe(VI) multifunctional integration characteristics, the study objectively and comprehensively verified the gradient purification of surface water and the UF membrane fouling mitigation by Fe(VI)-UF and sulfite (S(IV)) activated Fe(VI) (S(IV)/Fe(VI))-UF, elucidated the effect of sedimentation unit on the UF mechanism and the membrane fouling behaviors, and revealed the free energy changes throughout the UF process. The experimental results demonstrated that S(IV)/Fe(VI)-UF showed superior purification performance and UF membrane fouling mitigation than Fe(VI)-UF. S(IV)/Fe(VI)-UF achieved removals of sulfamethoxazole, DOC, and UV up to 77.73 %, 61.86 %, and 86.33 %, and was able to significantly mitigate UF membrane fouling by prolonging the transition stage and positively shifting the interfacial free energy. Innovatively, the absence of a sedimentation unit was found to adversely affect the initial stages of Fe(VI)-UF and S(IV)/Fe(VI)-UF by lowering the energy barriers, while negligibly affecting cake filtration. Additionally, the water treatment cost of S(IV)/Fe(VI) was 0.3 yuan per ton, indicating notable economic benefits and engineering potential. While deepening the understanding of Fe(VI) multifunctional integration characteristics, the above results provided theoretical and data support for S(IV)/Fe(VI)-UF and Fe(VI)-UF treatment of surface water, and enriched the application scenarios of Fe(VI)-related technologies.