The critical role of feed spacer channel porosity in membrane biofouling: Insights and implications

Membrane biofouling is a major hindrance limiting the efficiency of spiral wound membrane (SWM) module for water treatment. Feed spacer is an imperative component of SWM module which creates feed channels, determines fluid field and thus influences biofilm development via its geometry. Yet, the role of feed spacer channel porosity in biofilm development remains unclear. In this study, 16 feed spacers of varied geometric parameters and thus different channel porosities were used for both numerical simulations and biofouling experiments. Results showed that the hydraulic and anti-biofouling performances were more sensitive to the variation of filament diameter and spacer thickness. Feed channel porosity as a gross parameter played a pivotal role in biofouling development. The high-porosity (> 0.85) feed spacer channels exhibited a slower increase of feed channel pressure drop when biofouling occurred, but with more biomass accumulated in the middle of spacer meshes because of lower shear stress. For the low-porosity (< 0.75) channels, biofilm incipiently developed from the interspace region between spacer filaments and membrane surface due to “block effect”, which aggravated “narrow channeling” and induced a larger area of dead zone, leading to more severe biofouling ultimately. An appropriate channel porosity was suggested at ∼0.85 based on the hydraulic and anti-biofouling performances conjointly in this study.