Mn-Fe bimetallic oxide catalytic oxidation combined with ultrafiltration for treating secondary effluent: EfOM molecular transformation and membrane fouling control mechanism

Despite extensive application and research of membrane technology in secondary effluent treatment, fouling induced by effluent organic matter (EfOM) remains a challenge. Herein, a pretreatment strategy involving Mn-Fe bimetallic oxide-activated peroxymonosulfate (MnFeO/PMS) was used before ultrafiltration to decompose EfOM and tackle membrane fouling. Results showed that membrane fouling was effectively alleviated, with reductions in reversible and irreversible fouling resistances of 88.3 % and 58.9 %, respectively. Theoretical analyses illustrated a more pronounced adsorption energy and decomposition tendency of PMS on the MnFeO surface. The generated [rad]OH and SO₄^[rad]− played a key role in the degradation of EfOM. The parallel factor analysis along with self-organizing maps revealed the preferential oxidative degradation of humic acids and fulvic acids over tryptophan-like substances, which contributed to the reversible fouling mitigation. In addition, MnFeO/PMS transformed high and middle molecular weight organics into low molecular weight compounds. The primary molecular reactions involved in the degradation of EfOM included oxygen addition, dealkylation and deamination, which changed the properties of EfOM and contributed to the mitigation of membrane fouling. Morphology analysis further indicated that the fouling layer on the membrane surface was inhibited when filtering the MnFeO/PMS-pretreated sample. This study offers revelations for integrating oxidation with ultrafiltration in secondary effluent treatment to alleviate EfOM-induced membrane fouling.