Decoding dual roles of Fe(II)/peroxymonosulfate (PMS) pretreatment in mitigating membrane fouling: Thermodynamic and molecular insights

Fe(II)/PMS pretreatment demonstrates substantial potential to improve ultrafiltration performance by controlling membrane fouling, though its underlying mechanisms remain incompletely understood. This study provides a detailed investigation of these mechanisms from thermodynamic and molecular perspectives, uncovering the dual roles of oxidation and coagulation in membrane fouling mitigation. Fouling tests revealed that Fe(II)/PMS pretreatment significantly reduced sodium alginate (SA) membrane fouling, achieving a 95.2 % decrease in specific filtration resistance (SFR) and a 27.8 % increase in flux recovery ratio (FRR). Quantum chemical simulations, coupled with experimental characterizations, indicated that oxidation predominated over coagulation, disrupting the SA crosslinked network and leading to an 87.3 % reduction in SFR. Flory-Huggins lattice theory analysis clarified that changes in chemical potential are linked to SA crosslinked structure disruption, highlighting its important role in reducing SFR. Additionally, limited floc formation through coagulation lowered SA viscosity by 65.5 %, thereby improving fouling resistance. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) modeling and SEM analysis demonstrated that the combined effects of oxidation and coagulation reduced the SA-membrane contact area by 53.6 % and decreased interfacial interaction energy by 38.8 %, significantly weakening SA adhesion. These findings provide critical insights into the dual mechanisms of Fe(II)/PMS pretreatment, offering a foundation for optimizing fouling control in ultrafiltration applications. [Display omitted] •Dual function of oxidation and coagulation significantly mitigates membrane fouling.•Oxidation dominates over coagulation, disrupting fouling layer and reducing filtration resistance by 87 %.•Flory-Huggins theory links fouling layer structure disruption to drastic reductions in filtration resistance.•SA-membrane contact area and adhesion energy decrease by 53 % and 39 % after Fe(II)/PMS pretreatment.•Mechanistic insights offer new perspectives for optimizing Fe(II)/PMS pretreatment process.