Manganese(II) Enhanced Ferrate(VI) Pretreatment: Effects on Membrane Fouling and Pollutants Interception

To mitigate membrane fouling in the ultrafiltration process of surface water, this study focused on the source water from the Songhua River, systematically investigating the efficacy and mechanism of combined ferrate(VI) (Fe(VI)) and manganese(II) (Mn(II)) pretreatment in controlling ultrafiltration membrane fouling. Emphasis was placed on analyzing the impacts of pretreatment on membrane fouling performance, physicochemical properties of influent and effluent, membrane surface characteristics, and interfacial interactions. The results showed that the combined pretreatment with Fe(VI) and Mn(II) outperformed individual pretreatments and the untreated group significantly. When Fe(VI)/Mn(II) was 2/3, the normalized flux reached 0.66, a 35% increase compared to the untreated group; meanwhile, the pollutants retention was enhanced to 41.5%, with reversible and irreversible fouling resistances reduced by 75% and 77%, respectively. At this optimal ratio, the reaction products of Fe(VI) and Mn(II) coagulation acted as the core mechanism. It enhances pollutant particle repulsion, reduces particle size to form a loose structure, leading to a porous, hydrophilic membrane surface fouling layer with low roughness, thus minimizing membrane pore blockage. The combined pretreatment maintained a repulsive total interaction energy between pollutants and the membrane throughout the process, significantly reducing irreversible adsorption, which further verified the effectiveness of fouling mitigation. This study demonstrated that combined Fe(VI)/Mn(II) pretreatment at a molar ratio of 2:3 could efficiently control ultrafiltration membrane fouling by regulating pollutant characteristics and interfacial interactions, providing a theoretical basis and technical support for advanced treatment of surface water.