Micro-nano bubbles enhance the Fe(II)/persulfate process for ultrafiltration membrane fouling control: Performance and mechanisms

Abstract

The persistent challenges of membrane fouling and insufficient removal of emerging pollutants remain significant barriers to the widespread adoption of ultrafiltration processes. Therefore, a pre-oxidation system combining Fe(II)-activated persulfate with micro-nano bubble enhancement (MBs/Fe(II)/PS) was developed to alleviate membrane fouling and efficiently remove acetochlor (AC). The results demonstrated that, under conditions where Fe(II) and persulfate (PS) were applied at concentrations of 15 μM and 30 μM respectively, the MBs/Fe(II)/PS pre-oxidation system outperformed the Fe(II)/PS pre-oxidation system in mitigating both reversible and irreversible membrane fouling caused by natural organic matter (NOM) mixture. The superior fouling mitigation capabilities of the MBs/Fe(II)/PS system can be primarily attributed to the coagulation effect of in-situ generated Fe(III) and the oxidation mechanisms involving free radicals. Furthermore, the MBs/Fe(II)/PS pre-oxidation process effectively reduced foulant accumulation on the membrane surface while decreasing interfacial free energy between foulants and the membrane. This transition facilitated a shift from cake filtration to complete blocking or intermediate blocking modes. Additionally, the MBs/Fe(II)/PS pre-oxidation system exhibited optimal performance in degrading NOM and AC due to the presence of SO₄^•–, •OH, and ¹O₂. This study introduces a novel pre-oxidation strategy for mitigating membrane fouling and eliminating emerging pollutants, providing a theoretical basis for the practical application of MBs-based pre-oxidation technology.