Development of low pressure and high performance nf membranes for water softening

Abstract

Hard water poses several challenges for the industry and home application. Hence, water softening is required for water supply. This study examined the use of Polyelectrolyte Multilayer (PEM) hollow fibre membrane for water softening under low operating pressure of less than 2 bar. It aims to achieve a rejection of more than 90% for both Mg2+ and Ca2+. Using poly(ethersulfonate) (PES) Ultrafiltration (UF) hollow fibre membrane as substrate, Layer-by-Layer (LbL) technique was performed with alternate lumen deposition of Poly(styrene sulfonate) (PSS) and Poly(allylamine hydrochloride) (PAH). Finally, the PEM membrane is enhanced using Glutaraldehyde (GA) cross-linking which has not been evaluated for water softening yet. Membrane characterization was performed to determine the morphology and zeta potential of the PEM membrane and several deposition parameters were studied to determine the optimum deposition conditions. The PEM membrane is then subjected to performance testing to determine flux and rejection. Optimization results found that for complete coverage of substrate, 1.5 bilayer with 500K PSS and 15K PAH are required. For supporting electrolytes concentration, the optimum concentration was found to be 0.5 M for both PSS and PAH. Optimum cross-linked time was taken to be 5 mins. Performance of PEM membrane with single salt feed and mixed salt feed shows improvement in flux and rejection after GA cross-linking. This study suggests reduced pore size as possible reason for the result. Overall, the findings from this paper show that the membrane developed in this study is a promising development for water softening application.