Defect-free outer-selective hollow fiber thin-film composite membranes for forward osmosis applications

This study presents the successful fabrication of a novel defect-free outer-selective hollow fiber (OSHF) thin-film composite (TFC) membrane for forward osmosis (FO) applications. Thin and porous FO membrane substrates made of polyether sulfone (PES) with a dense and smooth outer surface were initially fabricated at different air-gap distances. A modified vacuum-assisted interfacial polymerization (VAIP) technique was then successfully utilised for coating polyamide (PA) layer on the hollow fiber (HF) membrane substrate to prepare OSHF TFC membranes. Experimental results showed that the molecular weight cut-off (MWCO) of the surface of the membrane substrate should be less than 88 kDa with smooth surface roughness to obtain a defect-free PA layer via VAIP. The FO test results showed that the newly developed OSHF TFC membranes achieved water flux of 30.2 Lm(-2) h(-1) and a specific reverse solute flux of 0.13 g L-1 using 1 M NaCl and DI water as draw and feed solution, respectively. This is a significant improvement on commercial FO membranes. Moreover, this OSHF TFC FO membrane demonstrated higher fouling resistance and better cleaning efficiency against alginate-silica fouling. This membrane also has a strong potential for scale-up for use in larger applications. It also has strong promise for various FO applications such as osmotic membrane bioreactor (OMBR) and fertilizer-drawn OMBR processes.