Mechanistic insights for DOM removal and membrane fouling mitigation: Optimizing Ferrate(VI)/AlCl₃ pretreatment and revealing the synergistic effect

Membrane fouling is a significant obstacle for ultrafiltration application in the water treatment field. This study investigates the synergistic effects of ferrate (Fe(VI)) oxidation and aluminum chloride (AlCl₃) coagulation on dissolved organic matter (DOM) removal and ultrafiltration membrane fouling alleviation. Four pretreatment strategies, coagulation (AlCl₃), oxidation (K₂FeO₄), coagulation followed by oxidation (C O), and oxidation followed by coagulation (O C) were compared. Results showed that the interaction between oxidation and coagulation generated more active species, including Al 13 , Al 30, and Fe 3+ . The collaboration of these species during the coagulation-oxidation-ultrafiltration (C-O-F) process achieved the highest DOM removal (73.6 % DOC and 80 % UV 254 ) and the lowest total membrane fouling. Specifically, DOM with high and medium-molecular-weight components could be effectively removed. Furthermore, the C O process formed larger and looser flocs with a diameter of 1100 μm and a fractal dimension of 1.32. With better DOM removal and floc properties, a porous cake layer without gel-like structure would accumulate on the ultrafiltration membrane surface during the C-O-F process, and fewer DOM deposited in the membrane pores, leading to lower physically reversible fouling and chemically reversible fouling. These results were verified by the SEM image of the fouled membrane, and the membrane pore diameter after physiochemical cleaning could be restored to 0.0117 ± 0.0086 μm. This study innovative reveals the mechanisms of synergistic effects between AlCl 3 and K 2 FeO 4 , which provides new insights for the sustainable development of ultrafiltration technology.