Limited anti-biofouling effect of surface-patterned membranes in spacer-filled feed channels over longer time periods

Topographical membrane surface patterns are a promising approach for increasing transmembrane flux and reducing foulant deposition. In this study, we investigated the anti-biofouling propensity of TFC membranes with micrometer-scale patterns. Unlike most studies in literature, where biofouling of patterned membranes was investigated without feed spacers and in short-term tests, we considered a) spacer-filled channels and b) advanced biofouling stages. We thereby addressed an important knowledge gap regarding the interaction between membrane surface patterns, spacer geometry, and biofouling dynamics. We found no substantial differences between surface-patterned and reference flat membranes regarding anti-fouling propensity in biofilm growth and membrane cleaning. Differences were marginal to modest ( < 10 % ) for most and not significant for all assessment methods (feed channel pressure drop, active/total biomass in final biofilms, and camera image data). To explain these findings, we suggest that the anti-fouling effects of micrometer-scale membrane surface patterns may be a) overridden by millimeter-scale feed spacers that dominate flow characteristics and biofouling dynamics and b) ultimately hindered by biofilm coverage in advanced biofouling stages. Besides, image-based fouling monitoring of advanced biofouling stages was critically assessed. Although no substantial differences between flat and surface-patterned membranes were observed for the geometries (micrometer-scale line-and-groove patterns and millimeter-scale conventional spacers) and conditions (accelerated biofouling tests without permeation) tested, anti-fouling effects of patterned membranes in spacer-filled channels may occur under alternative operating conditions and geometry scales. We therefore recommend further biofouling tests, incorporating permeation, real desalination feed waters, adapted cleaning procedures, different pattern scales, and novel feed spacer geometries.