Novel 3D printed feed spacers based on triply periodic minimal surfaces (TPMS) to enhance reverse osmosis and ultrafiltration performance

Abstract

In this proof of concept study, 3D printed feed spacers with complex geometries based on triply periodic minimal surfaces (TPMS) were designed and tested in reverse osmosis (RO) and ultrafiltration (UF) processes. The spacers showed flux enhancement of 15.5% and 38% in brackish water RO and UF tests with sodium alginate solution, respectively, in comparison to a commercial feed spacer. Moreover, lower feed channel pressure drop was also observed for the TPMS spacers. Biofouling tests were performed and the membranes were characterized using total organic carbon (TOC) and fluorescence microscopy. The TPMS spacers yielded a reduction in biofouling when compared to commercial feed spacers. Fouling patterns on the membranes were visualized for the different spacers using crystal violet stain, which also revealed a significantly reduced biofilm deposition using the TPMS spacers. The TPMS-based feed spacers have shown great promise in enhancing both RO and UF membrane processes, both in terms of flux enhancement and fouling reduction. An ideal feed spacer balances induced flow channel turbulence with a minimal formation of scaling and biofouling. Feed spacers with complex triply periodic minimal surface (TPMS) geometries have been shown to reduce biofouling while maintaining pressure across membrane structures. Several feed spacer geometries were designed and fabricated using 3D printing technology. Additive manufacturing processing were employed to vary porosity, directionality as well as increasing thickness along the length of the spacers. The fabricated spacers were tested to determine mass transfer and pressure drop parameters and critical flux in ultrafiltration setup. Dimensionless number analysis was done with Dextran filtration and critical flux was determined by the flux-stepping method by filtration of bovine serum albumin (BSA). All the tested spacers displayed an increase in mass transfer, with the Gyroid spacer (84% porosity) exhibiting a lower pressure drop and a 67% improvement in Sherwood number when compared to the commercial spacer design. The Gyroid design also showed an 8% improvement in critical flux. By increasing the porosity of the Gyroid to 90%, a 23% improvement in mass transfer was observed over the 84% porosity Gyroid, with an even lower pressure drop.

Date of Award	Dec 2017
Original language	American English