Comparison of solid, liquid and powder forms of 3D printing techniques in membrane spacer fabrication

Feed channel spacers in a spiral wound membrane module are net-like structures that influence the hydrodynamics of the feed channel to improve the mass transfer, thus reducing the effect of concentration polarization. Common issues associated with feed channel spacers include the trade-off between mass transfer and pressure loss as well as their impact on membrane fouling. Prior studies mainly focused on optimizing the geometry and orientation of spacers. 3D printing techniques have been used to fabricate novel spacer with complex geometries that were limited by conventional manufacturing methods. Nevertheless, 3D printing is not perfect, for example, not all design features can be additive manufactured with accuracy. 3D printing can also inadvertently result in different surfaces and geometry deviations of the spacers. This study investigates different 3D printing techniques that result in spacer geometry and surface differences and their effect on membrane performance and fouling. All 3D printed spacers by FDM, SLS and Polyjet showed better performance in terms of mass transfer at fixed power consumption and critical flux than the commercial spacer. Polyjet was found to give the most accurate representation of the intended design while FDM produced spacers that showed the greatest deviation from the specifications. The design considerations for additive manufactured spacers in geometric printability, model to part accuracy and surface finish are recommended. The implication of this research is that factors to be considered in spacer fabrication by 3D printing technique or other methods shall not be limited to the geometry parameter, the accuracy and surface finish associated with the fabrication methods are equally important.