Nanoparticles formed in Fe(II)/KMnO₄-catalyzed ozonation to alleviate ceramic membrane fouling and improve membrane rejection performance of humic acid

Fe(II)/KMnO₄ has been identified as a moderate oxidation system capable of producing ferromanganese nanoparticles (NPs). However, previous studies on the catalytic impact of these formed NPs on ozone was limited. This study delved into the catalytic effects of NPs on controlling membrane fouling induced by humic acid (HA). In-situ NPs (I-NPs), formed during Fe(II)/KMnO₄ pretreatment for HA solutions, and ex-situ NPs (E-NPs), formed in DI water, combined with in-situ ozonation (5 mg O₃/L), resulted in a decrease TMP/TMP₀ from 2.32 to 1.85 and 1.20, respectively. Moreover, the membrane rejection performance of E-NPs/in-situ ozonation surpassed that of I-NPs/in-situ ozonation. The dissolved organic carbon (DOC) rejection ratio of 64.6% could be achieved at E-NPs [90 μM KMnO₄/270 μM Fe(II)]/5 mg O₃/L. Component analysis revealed that both I-NPs and E-NPs comprised Fe_xO_y, MnO₂ and FeOOH. Nevertheless, KMnO₄ was consumed by HA, and a portion of Fe(II) transformed into non-catalytic flocs during I-NPs preparation. E-NPs could decompose ozone into reactive oxygen species (ROSs), including ·OH, ·O₂⁻ and ¹O₂, contributing to higher membrane flux and rejection. Besides, E-NPs proved suitable for continuous-flow filtration resulting in a lower level of assimilable organic carbon (AOC) in the effluent. Therefore, the catalytic potential of Fe(II)/KMnO₄-formed NPs on ozone presents a promising potential for mitigating membrane fouling caused by HA.