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Sulphonated polyethersulfone (SPES) has been synthesized for developing high performance thin film composite (TFC) forward osmosis (FO) membranes with enhanced hydrophilic support layer. Sulphonated substrate not only affects the membrane performance but also changes the membrane morphology from finger-like structure to a sponge-like morphology at higher degree of sulphonation thereby affecting the mechanical strength of the FO membrane. Non-sulphonated TFC-FO membrane with 12 wt % polymer concentration shows a faint finger-like structure while sulphonated samples at a similar polymer concentration show a fully sponge-like structure with much higher performance. For example, a water flux of 35 Lm-2 h-1 and 0.28 gL-1 specific reverse solute flux was achieved with sulphonated TFC-FO membrane sample (50 wt% SPES) under the FO mode using 2 M NaCl as the draw solution and deionised water as feed. Substrate sulphonation also considerably decreased the membrane structural parameter from 1096 µm without sulphonation to 245 µm at 50 wt% sulphonation. This study therefore shows that, besides surface morphology, the water flux of the FO membrane can also be enhanced by improving its substrate hydrophilic property.

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TFC membrane supported on backing fabric was fabricated for PAO process.• RO and FO membrane casting methods were investigated. • PAO membrane had a higher S value compared to FO membranes. • PAO membrane had a higher water permeability compared to FO membranes. • Developed PAO membrane can sustain applied hydraulic pressure.The water flux in forward osmosis (FO) process declines substantially when the draw solution (DS) concentration reaches closer to the point of osmotic equilibrium with the feed solution (FS). Using external hydraulic pressure alongside the osmotic driving force in the pressure assisted osmosis (PAO) has been found effective in terms of enhancing water flux and even potentially diluting the DS beyond osmotic equilibrium. The net gain in water flux due to the applied pressure in the PAO process closely depends on the permeability of the FO membrane. The commercial flat sheet cellulose triacetate (CTA) FO membrane has low water permeability and hence the effective gain in water flux in the PAO process is low. In this study, a high performance thin film composite membrane was developed especially for the PAO process through casting polyethersulfone (PES) polymer solution on a compacted woven fabric mesh support followed by interfacial polymerisation for polyamide active layer. This PAO membrane possesses a water flux of 37 L m 2 h −1 using 0.5 M NaCl as DS and deionised water as the feed at an applied hydraulic pressure of 10 bar. Besides, the membrane was able to endure the external hydraulic pressure required for the PAO process owing to the embedded backing fabric support. While the membranes with low structural parameters are essential for higher water flux, this study shows that for PAO process, polymeric