Biofouling behavior and control in metallic membrane treatment of algae-laden water: exploring the diverse impacts of oxidation.

Membrane biofouling remains a critical challenge in ultrafiltration (UF) systems for algae-laden water treatment, particularly in corrosion-resistant metallic membranes where oxidant-algae interactions dictate fouling dynamics. This study systematically evaluates the divergent impacts of potassium permanganate (KMnO) and sodium hypochlorite (NaClO) pre-oxidation on biofouling control, integrating multi-scale characterization (3D fluorescence, SEM, flow cytometry) with mechanistic modeling. While both oxidants achieved high algal removal (>86 %), KMnO demonstrated superior fouling mitigation via dual oxidation-coagulation functionality. At low doses (0.01-0.05 mmol/L), KMnO selectively degraded free organic matter without compromising algal cell integrity, forming a permeable MnO-organic composite layer that reduced irreversible fouling resistance (R, 0.12 for KMnO vs. 0.31 for NaClO). Higher KMnO concentrations (0.05-2 mmol/L) triggered controlled oxidation of intracellular organics, encapsulating debris into a porous MnO-rich cake layer with enhanced reversibility (flux recovery >95 %). In contrast, NaClO induced dose-dependent cell lysis, releasing recalcitrant <3 kDa organics that exacerbated irreversible pore blockage (R up to 0.40 at 2 mg/L). Mechanistic modeling revealed KMnO shifted fouling from pore-blocking (n = 2.2) to cake-dominated regimes (n < 0), while NaClO amplified standard-blocking dynamics. Metallic membranes' inherent oxidative stability further amplified KMnO's efficacy, avoiding organic membrane degradation observed in polymeric counterparts. This work pioneers the linkage between oxidant-driven algal cell fate (lysis vs. encapsulation) and metallic membrane fouling behavior, offering a paradigm for sustainable algae-rich water treatment through MnO-mediated self-protective fouling layers. The findings redefine pre-oxidation strategies, emphasizing dual-function oxidants that harmonize algal inactivation, organic retention, and operational longevity.