Breaking through the traditional water purification mechanism of ultrafiltration technology by coupling “Aluminum salt coagulation and Fenton-like” dexterously: Achieving the long-term adsorption of organic compounds by flocs and cake layers, membrane anti-fouling and in-situ cleaning

Transforming the cake layer into a valuable resource offers an innovative alternative to expensive membrane materials. This study integrated nano-Fe₃O₄@SiO₂ with Al-salt coagulation and Fenton-like treatment to address water containing complex natural organic matter (NOMs) and small-molecule micropollutants, based on ultrafiltration. The cake layer was reconstructed to improve water flux, adsorb pollutants, and facilitate in-situ membrane cleaning. We investigated three processes: Fe₃O₄@SiO₂ loading-coagulation/oxidation-ultrafiltration (F-C/O-UF), Fe₃O₄@SiO₂ loading-coagulation-oxidation-ultrafiltration (F-C-O-UF), and Fe₃O₄@SiO₂ loading-oxidation-coagulation-ultrafiltration (F-O-C-UF). We assessed responses to organics at different stages of the pre-ultrafiltration to identify key mechanisms for removal. Results indicated that F-C/O relies on adsorption complexation, F-C-O utilizes oxidative mineralization, while F-O-C is mainly dependent on micro-flocculation. The formation of the cake layer then began. In the temporal domain, the rapid formation of a mature cake layer hindered irreversible fouling caused by membrane pore blockage. The cake layers exhibited a highly porous multidimensional spatial morphology. Meanwhile, theoretical calculations and physicochemical analyses of the cake layer revealed that F-C/O and F-O-C altered the hydrolysis pathway of aluminum salt coagulation, enhancing the formation of octahedral Al that complexes more readily with organic matter. The cake layer also exhibited a high hydroxyl concentration and an increased lattice oxygen ratio, reducing adhesion to the membrane surface. The introduction of •OH facilitates electron transfer-mediated hydrogen bonds and van der Waals forces, improving the adsorption persistence of organics by floc and cake layers. Moreover, numerous catalysts in the cake layer enable in-situ membrane cleaning. These strategies transformed the traditional ultrafiltration separation mechanism, achieving a broader and more profound performance enhancement.