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Abstract: A new type of forward osmosis (FO) hollow fiber membranes with an antifouling nanofiltration (NF)-like selective layer has been developed in this work. The fabrication involves a step of porous poly(amide-imide) (PAI) ultrafiltration (UF) hollow fiber spinning via phase inversion, followed by simple polyelectrolyte post-treatments using positively charged polyethyleneimine (PEI) for cross-linking and negatively charged polystyrene sulfonate sodium salt (PSS) for deposition. The membranes are subsequently characterized by a series of standard protocols and evaluated in FO process. The PAI FO membranes possess a pure water permeability of 3.7–4.3Lm−2 h−1 bar−1 and Na2SO4 rejections up to 85% at 1bar. In the FO process, the membranes can achieve water flux of 17 and 12Lm−2 h−1 for active layer facing draw solution (AL-facing-DS) and active layer facing feed water (AL-facing-FW) configurations, respectively, using a 2000ppm Na2SO4 aqueous solution as the feed and 0.5M Na2SO4 as the draw solution. When the feed contained 1000ppm bovine serum albumin (BSA) and 2000ppm Na2SO4, a steady water flux of 11Lm−2 h−1 can be maintained using 0.5M Na2SO4 as the draw solution at ambient temperature of 23°C. The approach of making FO membranes developed in the present study offers the advantages of simple fabrication process, tailorable selective layer and promising membrane performance for protein-contained wastewater treatment by FO process. [Copyright &y& Elsevier]

Abstract: Hollow fiber membranes with a positively charged nanofiltration (NF)-like selective layer have been successfully fabricated by utilizing asymmetric microporous hollow fibers made of Torlon® polyamide–imide (PAI) material as the porous substrate followed by polyelectrolyte post-treatment using polyethyleneimine (PEI), which has not been reported previously. The reaction between PAI and PEI has been confirmed by experiments. The membrane structure and surface property are carefully tailored by adjusting polymer dope composition, spinning conditions and the post-treatment parameters. These membranes are, subsequently, characterized by a series of standard protocols in terms of membrane morphology, structure, permeability and salt rejection, and are applied in forward osmosis (FO) processes. The newly developed PAI hollow fiber membranes show a pure water permeability of 2.19–2.25L/m2 hbar and reasonable NaCl and MgCl2 rejections of 49% and 94% at 1bar, respectively. It is also found that in FO processes, when using 0.5M MgCl2 as a draw solution and DI water as the feed in the active layer facing feed water (AL-facing-FW) configuration at 23°C, the water fluxes of two PAI FO hollow fiber membranes are 8.36 and 9.74L/m2 h, respectively, and the J S /J V of the two membranes is smaller than 0.4g/L, which is lower than the data of 0.85g/L for commercial FO membrane from Hydration Technologies Inc. (HTI). Different from a neutral membrane, the positively charged FO membrane provides double electric repulsions to the salt transfer through the membrane in the AL-facing-FW configuration, leading to a reduction of salt penetration, while in the active layer facing draw solution (AL-facing-DS) configuration, the positive charges facilitate salt transportation. This study provides a simple and effective approach to make hollow fibers suitable for FO applications. [Copyright &y& Elsevier]