Unveiling the Hidden Role of Feed Spacer Filament Microstructure in Membrane Fouling

Membrane fouling is a persistent problem that impairs the performance of spiral wound membrane (SWM) modules used for water treatment. While the feed spacer, which creates feed channels and governs hydrodynamic properties, is essential in SWM modules, the role of its filament microstructures in membrane fouling remains poorly understood. Here, we delved deeply into how the filament's concave and torsion features influence local hydrodynamic behavior and thus membrane fouling. The findings reveal that the membrane fouling rate could be significantly correlated with both the low-velocity region fraction (r) and the average mass transfer coefficient (k_ave). Increasing torsional angle (θ) from 0 to 180° reduces r by 30%, enhances k_ave by 6.1%, and diminishes fouling rate by 13.2%, whereas a further increase of θ to 540° yields insignificant improvements. The enhanced antifouling performance with torsion characteristics comes from a reduced hydraulic stagnant zone and enlarged recirculation region with stronger turbulence. Nonetheless, concave features tend to generate stagnant zones with solute accumulation, resulting in severe membrane fouling, and this detrimental effect is exacerbated with increasing concave depth, even when combined with torsion characteristics. We propose a macro-to-micro path for optimizing feed spacer to combat membrane fouling and enhance the performance of SWM modules for environmental applications.