From Visualization to Mechanism: Uncovering Early Fouling Dynamics in Nanofiltration through LIF Experiments

Early fouling in nanofiltration membranes critically impacts long-term performance and operational efficiency, yet its dynamic evolution remains poorly understood due to limitations in real-time characterization. This study employs laser-induced fluorescence (LIF) technology to visualize and quantify the spatiotemporal development of early fouling during the initial 120 min of filtration. Combined with discrete phase model (DPM) simulations, the work reveals how cross-flow velocity and transmembrane pressure modulate early fouling behavior. Higher velocity (10 mL/s) significantly mitigated foulant accumulation, stabilizing the surface concentration at 28.9 ± 0.22 mg/L and reducing the fouling layer thickness to 5.8 ± 0.76 μm. In contrast, low velocity (0.1 mL/min) and high pressure (5 bar) promoted rapid accumulation, with local concentrations exceeding 250 mg/L within 3 min. Flux derivative analysis, supported by LIF imaging, captured the transition from intermediate blocking to cake-like deposition under varying conditions. DPM simulations highlighted Saffman lift and permeation drag as the dominant forces governing particle transport. This integrated experimental–computational framework offers new insights into the mechanisms of early fouling, offering a foundation for optimizing nanofiltration systems to enhance fouling control and operational efficiency in water treatment applications.