Fabrication of thin film composite forward osmosis hollow fiber membranes

• Main Author: Fang, Wangxi
• Other Authors: Wang Rong
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/38895
• Institution: Nanyang Technological University

Forward osmosis (FO) has received intensive studies recently for a range of potential applications such as wastewater treatment, water purification and seawater desalination. One of the major challenges to be overcome is the lack of an optimized FO membrane that can produce a high water flux comparable to commercial reverse osmosis (RO) membranes. The objective of the project is to fabricate thin film composite (TFC) hollow fiber membranes which are suitable for FO applications. Specifically, the ultra-filtration hollow fiber substrate was spun using polyethersulfone (PES) by phase inversion method. The substrate is single-skinned on the lumen side. The thin film active layer was formed on the inner surface of the hollow fiber substrate through interfacial polymerization (IP). The two monomers of the polymerization used are M-phenylene-diamine (MPD) and M-phenylene-diamine (TMC). Several IP experimental variables including involvement of additives, MPD concentration in the aqueous solution, polymerization reaction time, etc. were optimized. Hollow fiber substrates and FO membranes were characterized using different analytical methods including scanning electron microscope observation, molecular weight cut-off test, porosity measurement and mechanical strength test, etc. Water and solute permeability of the FO membrane were also measured in an RO setup. It was found that two different chemicals can successfully work together as the additives of aqueous solution to achieve a better performing membrane than applying each additive separately. It was also deduced that, within a feasible range, higher MPD concentration in the aqueous solution is considered more desirable in FO hollow fiber membrane fabrication. The water flux achieved during lab-scale FO test for two membrane orientations using different draw solution concentrations were benchmarked against commercial FO and nanofiltration (NF) membranes. For the fabricated membranes with optimized preparation conditions, water flux can reach 42.6 L/h•m2 using 0.5M NaCl as draw solution and deionized water as feed for the active layer facing draw solution orientation. The performance of the in-house made FO hollow fiber is believed to be superior to all FO membranes reported in the open literature.