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Novel composite forward osmosis (FO) hollow fiber membranes with two selective skin layers were developed in the present work. The polyethersulfone (PES) hollow fiber substrate was firstly fabricated by a phase inversion method. The RO-like polyamide skin layer was then prepared on the inner surface of the hollow fiber substrate via interfacial polymerization (IP), while the NF-like outer skin layer was prepared via polyelectrolyte layer-by-layer (LBL) assembly. Three double-skinned membranes with negative (DS#1.5), positive (DS#2.0) and minimal (DS#2.5) outer surface charges under neutral pH environment were evaluated for their capabilities against organic fouling in the FO process. The newly developed double-skinned membranes possess water permeability greater than 2 l/m 2 h bar and NaCl rejection higher than 95% under 2 bar pressure, and have superior water flux and less salt leakage than the commercial HTI FO membranes as well as all the reported double-skinned FO membranes with RO-like selective layers. Most importantly, the double-skinned DS#2.5 hollow fiber membrane exhibits exciting organic fouling resistance because of its highly hydrophilic NF-like secondary layer with minimal surface charge and tightened surface structure to mitigate possible substrate pore clogging and fouling layer formation. A stable water flux of around 25 l/m 2 h was attained for DS#2.5 membrane using <0.5 M NaCl as the draw solution and a water containing 200 ppm dextran (DEX) or Aldrich humic acid (AHA), or lysozyme (LYS) and 10 mM NaCl as the model feed in the active layer against the draw solution (AL-DS) configuration, suggesting its great potential for practical FO applications. [ABSTRACT FROM AUTHOR]

Abstract: The performance of a forward osmosis (FO) system may be characterised by the assessment parameters: FO–RO flux ratio (J w/J w(RO)), apparent FO water permeability (J w/(π ds − π ml)), and the newly developed flux efficiency factor (J w,ob/J w,re). The former two parameters offer information on extent of internal concentration polarisation and driving force utilisation, respectively. The J w,ob/J w,re factor has practical relevance, and reveals the inevitable trade-off between flux and recovery (φ) for a FO system. The derived J w,ob/J w,re factors corresponded well to experimental observations. High water permeability, low salt-to-water permeability ratio, and large mass transfer coefficient improve the performance of a FO system, but these may also be influenced by operational and fouling effects, such as draw solute transmission, fouling resistance and cake-enhanced concentration polarisation. It was shown that membrane properties also play a significant role in fouling behaviour. Fouling amelioration factors include aeration and osmotic backwash. A thin-film composite membrane showed potential for FO application with favourable intrinsic transport parameters. It was demonstrated that a FO system could achieve stable water production with both relatively high flux efficiency (J w,ob/J w,re =0.8) and high recovery (φ =95.8%), which attested to the technology potential. [Copyright &y& Elsevier]