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A major limiting factor of forward osmosis (FO) membrane, particularly in pressure retarded osmosis (PRO) mode, is fouling by natural organic matters. In this work, we investigated the effect of the nanocomposite substrate on the fouling of a thin film nanocomposite (TFN) membrane due to organic foulants in PRO mode. The TFN membrane was synthesized by coating a polyamide film over the surface of substrate made of polysulfone-titanium dioxide. The TFN membrane always showed much higher FO water flux than the typical thin film composite TFC membrane prepared from the pristine polysulfone substrate. Reduced internal concentration polarization following a significant decrease of the structural parameter in the nanocomposite substrate causes the mass transfer coefficient of the substrate to increase. In the PRO mode, BSA removal in the presence of Ca2+ confirmed that the TFN FO membrane could significantly mitigate fouling tendency compared to a typical TFC membrane. Results also showed that fouling in TFN FO is highly reversible, recovering >92% permeate flux after a simple water rinse process. A complete study of the membrane fouling was reported with detailed scientific discussion. To the best of our knowledge, this is the first report on the effect of the nanocomposite membrane on membrane fouling in PRO mode. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modifications on PSf substrate of TFC membrane using TiO2 nanoparticles. [•] Performances of PSf substrate were improved upon addition of TiO2 nanoparticles. [•] TFN FO membrane with small S value and minimum ICP was able to produce. [ABSTRACT FROM AUTHOR]

Abstract: Realizing that one of the most important challenges in the forward osmosis (FO) membrane is internal concentration polarization (ICP), thin film nanocomposite (TFN) membranes were prepared by incorporating different loadings of titanium dioxide (TiO2) nanoparticles (ranging from 0 to 0.90wt%) into the polysulfone (PSf) substrate in order to reduce ICP. The nanocomposite substrates prepared were characterized with respect to hydrophilicity, overall porosity, surface roughness and cross-sectional morphology by different methods. Results revealed that both hydrophilicity and porosity of the substrate were increased upon addition of TiO2 nanoparticles. Moreover, a large number of finger-like macrovoids were developed by increasing the loading of TiO2 nanoparticles, leading to enhancement in water permeability. As for the FO performance tested at AL-FS orientation and with DI water as feed and 0.5M NaCl as draw solution, the TFN membrane prepared using PSf substrate embedded with 0.60wt% TiO2 nanoparticles (designated as TFN0.60) exhibited the most promising result by showing water flux of 18.81L/m2 h, i.e. 97% higher than the control TFC membrane prepared by substrate without TiO2 incorporation (designated as TFC), with no significant change in reverse solute flux. Compared to the control TFC membrane, the FO water flux of TFN0.60 was also reported to increase significantly from 4.2 to 8.1L/m2 h (AL-FS orientation) and from 6.9 to 13.8L/m2 h (AL-DS orientation) when seawater was used as feed solution and 2M NaCl was used as draw solution. The increase in water flux can be attributed to the decrease in structural parameter (S value=0.39mm), mainly due to the formation of finger-liked macrovoids that connect the top and bottom layer of the substrate and reduce the tortuosity, resulting in decreased ICP. Although further increasing TiO2 nanoparticles loading to 0.90wt% could increase membrane water permeability, the FO performance was compromised by a significant increase in reverse solute flux. To the best knowledge of the authors, this is the first report on TFN membrane using PSf-TiO2 nanocomposite substrate for FO applications. [Copyright &y& Elsevier]

Abstract: In this study, thin film nanocomposite (TFN) membrane was developed using novel polysulfone–titanium dioxide (PSf–TiO2) nanocomposite substrate. The effects of TiO2 on the PSf substrate morphologies, hydrophilicity and water permeability were investigated and discussed. The results revealed that the hydrophilicity and the porosity of the substrate were improved upon the TiO2 addition, leading to significant enhancement in water flux. TFN membrane was then fabricated by establishing a polyamide layer made of 1,3-phenylendiamine and 1,3,5-benzenetricarbonyl trichloride monomers over the surface of the modified substrate. Compared with the typical TFC and commercial CTA membranes, the TFN membrane prepared always demonstrated much higher FO water flux without showing a significant increase in reverse solute flux when tested under same conditions. When tested in AL–FS orientation using 0.5M NaCl as a draw solution and 10mM NaCl as feed solution, the water flux of the TFN membrane was ∼120% and ∼87% higher than that of the commercial membrane and typical TFC membrane, respectively. The water flux of the TFN membrane was also reported to be much higher under prolonged filtration time, mainly due to the improved properties of substrate upon addition of TiO2. [Copyright &y& Elsevier]

• CFD simulation of FO and PRO processes with loading TiO 2 nanoparticles conducted. • Addition of TiO 2 NPs to the polymers produced a cross-linking membrane. • Loading of TiO 2 NPs to the membranes caused to increase the water flux. • Hydrophilic properties of TiO 2 NPs improved the water permeation. • Good coincidence of the results obtained with 0.3% error in a PRO process. Forward osmosis (FO) has made significant progress in recent years as an emerging membrane technology for the treatment of water and wastewater. Differential osmotic pressure is used to extract pure water across a semi-permeable membrane in this process. CFD simulations were used to investigate the performance of flux changes in membrane systems in this study. This paper simulates the performance of a thin film composite (TFC) membrane with a titanium dioxide (TiO 2) modified substrate in terms of FO and pressure retarded osmosis (PRO). The results showed how the simulation results (CFD) can be used to detect flux changes with additive particles. It was discovered that even a small amount of TiO 2 nanoparticles can alter water flux. In the FO and PRO systems, adding 1 wt% TiO 2 to the membrane matrix increased water flux by about 15% and 14%, respectively. Nevertheless, the increased solute flux was insignificant in simulation, which indicates the positive effect of adding TiO 2 nanoparticles. Finally, a comparison of the results for different membranes indicated the best correlation between the simulation and experimental results, when 0.75 wt% TiO 2 was used, and a relative error of 0.3% has been recorded in PRO process. Also, the maximum pure water flux rate (8 · 974 × 10 − 4 m o l m 2 · s) obtained in the simulation of thin film nanocomposite (TFN) 1 and PRO process. [Display omitted] [ABSTRACT FROM AUTHOR]