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The focus of whey processing has been changed from waste treatment to the production of valuable products owing to the advancement of membrane technology. Producing high quality whey products at low energy consumption entails novel techniques for whey concentration. This study proposes forward osmosis (FO) as a potential approach to concentrate whey protein solutions, which is superior to the concentration via reverse osmosis (RO), mainly owing to the low hydraulic pressure during FO process. In particular, this work validated the feasibility of FO-based whey concentration using high-performance hollow fiber membranes that were fabricated in-house. The investigation focused on the effects of various operating conditions on the concentration performance. The experimental results reveal that optimal concentration efficiency would be achieved by appropriately choosing the cross-flow velocity, draw solution concentration and the maximum attainable concentration of whey protein solution. Especially, the flux decline behaviour as a function of the whey protein concentration in the feed solution indicated rapid formation of a polarized or gel foulant layer at the membrane surface. The proposed mechanism was supported by the investigation of physical cleaning with water, showing that the post-process cleaning after the concentration cycle was able to recover the membrane performance, whereas the intermediate cleaning during one concentration cycle had little impact on the concentration efficiency enhancement. This study has practical significance for the application of FO in the concentration of dairy streams and other liquid foods. [ABSTRACT FROM AUTHOR]

The fabrication of new membrane that is able to produce stable high power density is essential for the development of pressure retarded osmosis (PRO) technology. In this work, thin film composite (TFC) polyetherimide membranes with three different substrate structures were fabricated and characterized. The PRO performance of the resultant membrane was evaluated through two pressure cycle experiments and stability tests. The primary objective of this work is to systematically study PRO membrane’s mechanical stability and mass transfer properties under high operating pressures, which determine the power density of the membrane in the PRO process. Experiments revealed that water permeability ( A p ) and salt permeability ( B p ) under different pressures varied. The A p and B p are better indicators for examining the variation of PRO membrane structure under pressure. Within the operating pressure range of 17.2 bar, the top polyamide layer of TFC PEI-2# membrane mainly experienced a reversible deformation. In the two pressure cycle tests, the water flux, specific salt flux and power density obtained in the upward and downward measurements in each cycle are close to each other. The first cycle and the second cycle also show excellent reproducibility. The membrane was able to maintain almost unchanged water flux and power density of 12.8 W/m 2 at 17.2 bar over the 10 h testing time, suggesting the membrane’s great potential to be used in practical application in the future. [ABSTRACT FROM AUTHOR]

Abstract: Pressure retarded osmosis (PRO) is a promising membrane process to harvest the vast amount of free energy from the mixing of fresh and salty waters without adverse environmental impacts. A competent membrane for PRO should possess the features of high water permeability to allow water permeation, excellent salt rejection to maintain the osmotic driving force, low structure parameter to minimize the internal concentration polarization (ICP), and robust strength to withstand the required hydraulic pressure. In this work, we have developed a novel hollow fiber membrane by balancing these competing factors based on our prior experience in the thin-film composite (TFC) membranes. The newly developed TFC hollow fiber membrane can achieve a power density of 20.9W/m2 at a pressure of 15bar, using synthetic seawater brine (1.0M NaCl) as the draw solution and synthetic river water (1mM NaCl) as the feed water, respectively. The simultaneous specific reverse salt flux was found to be 0.03mol/L, which is much lower than reported flat-sheet membranes, as the self-supported hollow fiber membrane can eliminate the deformation-enhanced reverse salt diffusion that is typical for flat-sheet membranes. However it was observed that the water permeability and structure parameter of the TFC hollow fiber membrane varied noticeably corresponding to the change in the hydraulic pressure imposed in the fiber lumen. Over a certain range (ΔP<15bar), such variations of increasing A value and decreasing S value proved to have positive impacts, as they facilitate the water permeation and reduce the ICP in the PRO process. [Copyright &y& Elsevier]

Abstract: One of the major barriers that hinder the application of forward osmosis (FO) processes is the lack of optimized membranes that possess high water flux, low salt leakage and good anti-internal concentration polarization (ICP) and anti-fouling/anti-scaling properties during practical FO operations. In this study, novel composite FO hollow fiber membranes with an RO-like selective skin and an NF-like secondary selective skin were successfully developed for the first time. The fabrication procedures involved making ultrafiltration hollow fiber substrate using poly(amide–imide) (PAI) polymer material via phase inversion method, followed by interfacial polymerization (IP) and chemical modification to yield a polyamide RO-like inner skin and a positively charged NF-like outer skin, respectively. It was found that the sequence of conducting IP on the substrate inner surface prior to the chemical modification of the outer skin was preferred in order to achieve better performance for the resultant double-skinned hollow fibers. The newly developed FO hollow fibers exhibited high water permeability of 2.05L/m2 hbar and 85% rejection to NaCl at 1bar pressure as well as superior FO water flux of 41.3L/m2 h and low ratio of salt flux over water flux of 0.126g/L when using DI water and 2.0M NaCl as feed and draw solutions, respectively, in the active layer facing draw solution (AL-DS) orientation. Furthermore, the experimental results showed that the composite FO hollow fiber membrane was able to outperform single-skinned membrane when the feed contains divalent ions or the feed exhibits high scaling tendency to membrane. This suggested that the integration of RO- and NF-like two selective skins in FO membrane is an effective way to minimize the ICP effect, mitigate the membrane scaling and thus enhance the feasibility of FO processes for practical applications. [Copyright &y& Elsevier]

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: For the first time, a specially designed pressure retarded osmosis (PRO) hollow fiber membrane has been successfully developed and applied in the PRO process to demonstrate its potential for power generation. The membrane fabrication method is similar to that used for making thin-film composite (TFC) forward osmosis hollow fiber membranes, but further optimization and improvement have led to a new type of TFC hollow fiber membranes with much greater mechanical strength in addition to its excellent separation property and high water flux. The TFC PRO hollow fiber membranes have a water permeability (A) of 9.22×10−12 m/(sPa), salt permeability (B) of 3.86×10−8 m/s and structural parameter (S) of 4.6×10−4 m. It can withstand hydrostatic pressure as high as 9bar with its relatively large dimension of 0.98mm lumen diameter. This PRO hollow fiber membrane is superior to all other PRO membranes reported in the open literature in terms of power density. A power density as high as 10.6W/m2 can be achieved using seawater brine (1.0M NaCl) and wastewater brine (40mM NaCl), which suggests that the newly developed PRO hollow fiber membrane has great potential to be applied in PRO processes to harvest salinity gradient energy. A higher pressure is preferred as it allows generation of higher power density (pressures of 12bar may be optimal for seawater as the high salinity stream), and this can be realized by reduced fiber dimension. Further optimization of the membrane structure will be performed. [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]

Abstract: 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 RO membranes. Two types of thin-film composite FO hollow fibers with an ultra-thin polyamide-based RO-like skin layer (300–600nm) on either the outer surface (#A-FO) or inner surface (#B-FO) of a porous hollow fiber substrate have been successfully fabricated. These novel composite FO hollow fibers have been characterized by a series of standard protocols and benchmarked against commercially available FO flat sheet membranes and reported NF hollow fibers used for the FO process. The characterization reveals that the FO hollow fiber membranes possess a large lumen. The substrates are highly porous with a narrow pore size distribution. The active layers present excellent intrinsic separation properties with a hydrophilic rejection layer and good mechanical strength. The #B-FO hollow fiber membrane can achieve a high FO water flux of 32.2L/m2 h using a 0.5M NaCl draw solution in the active rejection layer facing draw solution (AL-facing-DS) configuration at 23°C. The corresponding salt flux is only 3.7g/m2 h. To the best of our knowledge, the performance of the #B-FO hollow fiber is superior to all FO membranes reported in the open literature. The current study suggests that the optimal FO membrane structure would possess a very small portion of sponge-like layer in a thin and highly porous substrate, which suggests a way for further improvement. [Copyright &y& Elsevier]

Pressure-retarded osmosis (PRO) has attracted worldwide attention for its potential applications in renewable osmotic energy harvesting, low energy seawater desalination, and industrial waste brine disposal. However, membrane fouling is one of the major issues limiting PRO performance with the use of a high-salinity draw solution and a low-value impaired feedwater. This study systematically investigated membrane fouling in the PRO process using a real wastewater retentate (a waste byproduct from wastewater reclamation plants) as the PRO feed. Organic fouling (e.g., by humic substances) and inorganic fouling (e.g., by calcium phosphate) were identified to be the major types of fouling, where the latter dominated the overall water-flux decline. The internal PRO membrane fouling was exacerbated by internal concentration polarization (ICP) and intermolecular interactions between the organic macromolecules and the scaling precursor ions (e.g., Ca 2+ ). A limiting flux that was independent of the initial flux (i.e., applied pressure) was observed during the PRO fouling and was explained by a novel PRO limiting flux model. A membrane with a smaller structural parameter could achieve a higher limiting flux in PRO. A simple and effective pressure-assisted osmotic backwashing protocol was developed to clean the internally fouled membrane that could restore over 92% of the water flux within a short cleaning period (15 mins). The PRO performance could also be significantly improved by decreasing the feedwater pH that mitigated alkaline scaling. Finally, performing the PRO membrane fouling test in the active-layer-facing-feed-solution (AL-FS) orientation revealed that the integral cellulose triacetate (CTA) membrane exhibited strong mechanical stability and anti-fouling tendency whereas the thin-film composite (TFC) membrane was not mechanically stable in this orientation. This study for the first time identified that an integral membrane instead of a TFC membrane is an excellent candidate for PRO operation in the AL-FS mode for fouling control. [ABSTRACT FROM AUTHOR]

The performance of pressure retarded osmosis (PRO) processes is significantly limited by membrane fouling. This study systematically investigated PRO scaling by silica, which is one of the most common salts causing membrane scaling. In particular, the effect of silica concentration, the initial water flux, the chemistry of feed solution (FS) /draw solution (DS), and the type of membrane were studied in the PRO mode of operation. It has been observed that a low silica concentration (e.g., 10 mg/L SiO 2 ) could even cause membrane scaling during a PRO process. The rate and extent of the scaling was mainly governed by the internal concentration of silica in the membrane support layer and the solution chemistry of the FS/DS. The results suggested that the scaling could be mitigated by decreasing the internal concentration through the reduction of bulk silica concentration, the optimization of operating water flux, and the decrease in membrane structural parameter. The structural parameter seems to play a dominant role in PRO scaling by silica than the membrane materials and other physico-chemical properties. In addition, silica scaling can be controlled by lowering the pH of the FS and/or DS. For the first time, it has been demonstrated that utilizing an acidic DS was highly effective in controlling PRO scaling, which can be attributed to the low local pH in the membrane support layer as a result of the internal concentration polarization (ICP) of the reversely diffused H + . This method opens a new dimension for PRO scaling/fouling control. [ABSTRACT FROM AUTHOR]

In present study, we explored the fabrication of a high performance thin-film composite (TFC) forward osmosis (FO) membrane by minimizing the structural parameter of hollow fiber substrates and enhancing the water permeability of selective layer. A theoretical analysis specified that a minimized structural parameter of substrate combined with an enhanced water permeability of selective layer could generate a significantly high water flux in FO process. The experimental results showed that the addition of LiCl into polyetherimide (PEI) polymer dope made the membrane less tortuous and thereby significantly reduced the structural parameter. The elevated take-up speed reduced the substrate thickness but also made the substrate more tortuous. Further study showed that a robust hollow fiber with low structural parameter can be obtained by reducing the substrate wall thickness and dimension simultaneously. After optimization, the structural parameter of the substrate declined from 308 µm to 172 µm. After interfacial polymerization, the thin-film composite membrane constructed on the optimized substrate showed an improved water permeability (from 2.85 L m −2 h −1 bar −1 to 3.66 L m −2 h −1 bar −1 ) and a comparably low salt permeability (0.36 L m −2 h −1 versus 0.31 L m −2 h −1) . The low structural parameter, in combination with the high water permeability and low salt permeability, contributed to significantly increased water flux ( J v ) from 25.4 L m −2 h −1 to 38.5 L m −2 h −1 when 1 M NaCl was used as draw and deionised water as feed in a configuration of active layer facing feed solution (AL-FS). Furthermore, aquaporins were incorporated into the polyamide selective layer to enhance the water permeability, which remarkably reached up to 7.6 L m −2 h −1 bar −1 . The aquaporin-incorporated FO membrane demonstrated a J v of 49.1 L m −2 h −1 and a J s /J v ( J s indicates the salt flux) of 0.10 g/L with 1 M NaCl as draw and deionised water as feed in the AL-FS configuration, which is favourable to mitigate membrane fouling in practical application. The AQP-FO membrane reported in this study outperforms most of other reported FO membranes. [ABSTRACT FROM AUTHOR]

The use of porous membranes for forward osmosis (FO) applications has been recently reported in the literature. In the current study, a series of porous-FO membranes were fabricated to systematically study the role of membrane separation properties on the FO performance of porous membranes. In addition, two types of draw solutes, a polyelectrolye poly(sodium 4-styrene-sulfonate) (PSS) and a neutral linear polymer polyethylene glycols (PEGs), were evaluated as the draw solutes. The effect of draw solution properties (type of draw solutes, their molecular weight, and concentration) on the FO performance was investigated. Membrane post-treatment at higher annealing temperature was found to increase solute rejection and decrease water permeability. As a result, reverse solute diffusion (RDS) became less severe at higher annealing temperature. The FO water flux of the porous membranes was affected by RDS in addition to the water permeability of the porous FO membranes, both of which had a strong dependence on the annealing temperature. Compared to neutral PEG, the polyelectrolyte PSS was a much better choice for draw solutes with higher FO water flux and lower RDS. The better performance of PSS can be attributed to its higher rejection by the porous FO membranes and its high osmotic pressure compared to PEG at same weight concentration. Implications for the design of porous FO membranes and draw solution are discussed. [ABSTRACT FROM AUTHOR]

Abstract Forward osmosis (FO) membranes have received attention as an energy-efficient and low-cost technique in stream concentrating processes. In this work, a novel double-skinned hollow fiber thin film composite (TFC) FO membrane has been successfully fabricated, which consists of a one-step prepared dual layer substrate and a thin inner selective layer formed via interfacial polymerization. The substrate consists of a relatively dense ultrafiltration (UF) outer layer and a porous UF inner layer, both of which were constructed from polyethersulfone (PES) as the substrate material by using dual-layer co-extrusion technique. Compared to the commercial and reported double-skinned FO membranes, the FO membrane developed in this work exhibited a higher permeate flux with humic acid solution as feed. Furthermore, the double-skinned FO membrane was applied in concentrating activated sludge using 0.5 M NaCl as draw solution, and a permeate flux at 5.4 L/m2h was achieved after 5 h operation, which was higher than or comparable to those of the reported FO membranes. Membrane autopsies and foulant analysis suggested that the dense UF skin layer helped to reject greater-sized organic foulants (> 300 Da). This study shed light on the important fabrication features and promising application of the double-skinned hollow fiber TFC FO membrane in sludge concentration. Graphical abstract fx1 Highlights • A dual-layer UF substrate was prepared via a single-step fabrication process. • TFC FO membrane was fabricated via interfacial polymerization in the lumen of the substrate. • FO performance in sludge thickening process was investigated. • Tight UF layer helped rejecting greater-sized organics in sludge. • A permeate flux of 5.4 L/m2h was achieved after 5 h operation using 0.5 M NaCl as draw solution. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is an innovative technique to yield osmotic energy. Nevertheless, the PRO performance is exacerbated by the severe membrane fouling occurring within the porous support. It is a potential alternative for sustainable power harvesting to change the membrane orientation from active layer facing draw solution (AL−DS) or PRO mode to active layer facing feed solution (AL−FS) or FO mode for a low-fouling propensity. A novel integral PRO hollow fiber membrane was developed in this work by phase inversion and followed with a facile cross-linking post-treatment. The structure and properties of the resultant membrane were systematically investigated using a series of characterization protocols. The PRO performance of the membrane was studied under various hydraulic pressures at the AL−FS orientation. The results reveal that the substrate with sponge-like structure and relatively dense inner surface can better withstand high pressure in PRO process. Two steps of cross-linking endowed the membrane with a smaller pore size on the outer surface that exhibits high rejection against various inorganic salts. The novel integral membrane can achieve a stable power density output around 4.3 W m −2 at 12 ~ 13 bar hydraulic pressure, using a real wastewater reverse osmosis (RO) retentate and 1.0 M sodium chloride as the feed and draw stream, correspondingly. This result demonstrates that the PRO operation in the AL−FS orientation (FO mode) offers a significant advantage over the AL−DS orientation (PRO mode) by eliminating the pretreatment of the feed water or/and other measures associated with membrane fouling control in the PRO mode. To implement the PRO operation with the AL−FS orientation, developing a robust membrane with an integral structure is critical. The newly developed integral hollow fiber membrane via chemical cross-linking presents the potential for PRO operation in the AL−FS orientation. [ABSTRACT FROM AUTHOR]

The salinity gradient is a renewable and sustainable energy source that can be utilized by a pressure-retarded osmosis (PRO) process. Development of the PRO technology was impeded by shortage of efficient membranes until recent surge on PRO research. In this work, flat-sheet thin film composite (TFC) PRO membranes with reinforced support layer were developed. The membrane properties were optimized by blending high molecular weight polyvinylpyrrolidone (PVP) into the polysulfone (PSf) casting solution. Influences of PVP addition on the kinetic and thermodynamic properties of the casting solution, resultant membrane properties as well as PRO performance were systematically investigated. It is showed that PVP can effectively improve the membrane morphology and pore structure. By adjusting the PSf/PVP composition in the substrate recipe, the reinforced TFC membrane is able to achieve a power density of 12.9 W/m 2 at 22 bar using 1 M NaCl draw solution and pure water feed. Long-term PRO test at the peak power density and multi-pressure cycle tests were performed on the membranes. Consistent power density and low salt flux/water flux ratio were observed in the whole tests. The results demonstrated that the reinforced TFC membrane in this study had excellent mechanical strength and stability. It would be promising for future engineering application. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is a promising energy harvesting technique. However, when polymeric hollow fiber membrane is used for the PRO process, the mechanical strength of the membrane is a big concern. As hollow fiber membrane is self-supported and due to its polymeric nature, it may gradually deform over time under high pressure loading, or membrane “creeping” will occur. Current work is the first attempt to analyze the membrane creeping phenomenon of a novel thin film composite (TFC) hollow fiber. The membrane creeping was evaluated via nanoindentation by using atomic force microscope (AFM). A non-stop 200-hour PRO test and integrity check, which have not been reported previously, were carried out to investigate the membrane performance under various operating pressures. The results show that the membrane is able to produce a stable power density output of 19.2 W/m 2 at 15.0 bar, using 1.0 M NaCl as the draw solution and DI water as the feed water. Membrane creeping was observed when the applied pressure exceeded the safe operation limit (or the flux turning point, where the membrane flux started to increase with increasing applied pressure in the PRO mode), which caused an irreversible damage to the membranes. This study identified safe and optimum operation conditions of the laboratory-made PRO hollow fiber membrane to achieve the most favorable PRO performance. It provides guidance for practical applications of polymeric hollow fiber membranes in PRO process. [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

Abstract: A novel functionalized multi-walled carbon nanotube (MWCNT) immobilized polyethyleneimine–poly(amide–imide) (PEI–PAI) hollow fiber membrane was designed and fabricated using an easily scalable method. PAI hollow fiber was spun via phase inversion, followed by functionalized MWCNTs immobilization via vacuum filtration before a chemical post-treatment using PEI was applied to obtain a positively charged selective layer. The resulting membranes were evaluated in the forward osmosis (FO) process. The membrane prepared using a 0.62mg/L of MWCNTs solution shows a pure water permeability of 4.48L/m2hbar with a MgCl2 rejection of 87.8% at 1bar. This is a 44% enhancement in water permeability without significant compromise on the salt permeability when compared to membranes without MWCNTs. In addition, FO water flux of membranes prepared using 0.31 and 1.25mg/L of MWCNTs solutions have also been enhanced up to 29% without compromising the solute flux in the active layer facing feed water orientation using 0.5M MgCl2 solution as the draw solution and deionized water as the feed water. These encouraging results suggest that hollow fiber membranes immobilized with commercial MWCNTs exhibit good potential to be further developed for applications in the FO process. [Copyright &y& Elsevier]

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]

Abstract: Polyamide thin film composite (TFC) membranes with tailored porous substrate and rejection layer are promising for forward osmosis (FO) applications. The current study investigates the effect of rejection layer synthesis conditions on the performance of the resulting TFC polyamide FO membranes. The influence of monomer concentrations (i.e., m-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentrations) on the membrane separation properties as well as FO performance was systematically studied. A strong trade-off between the water permeability and salt rejection was observed, where increasing the TMC concentration or reducing the MPD concentration resulted in higher membrane permeability but lower salt rejection. In FO tests, membranes with poor salt rejection had severe solute reverse diffusion, which enhanced the internal concentration polarization (ICP). It was found that the FO water flux was governed by both the membrane water permeability and its solute rejection. For a membrane with higher water permeability but lower solute rejection, the reduced membrane frictional resistance was compensated by the simultaneously more severe solute-reverse-diffusion-induced ICP. The net effect on the FO water flux depends on the competition of these two opposing mechanisms. Under conditions where solute reverse diffusion may cause severe ICP (e.g., high draw solution concentration and high water flux level), membranes need be optimized to achieve a high salt rejection even if this is at the expense of lower water permeability. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) technology has become increasingly attractive in the past decades for water related applications and will likely continue to develop rapidly in the future. This calls for the development of high performance FO membranes. Thin film composite (TFC) polyamide FO membranes with tailored support structure were prepared in the current study. The porous polysulfone substrates with finger-like pore structures were prepared via phase inversion, and the polyamide rejection layers were synthesized by interfacial polymerization. The resulting TFC FO membranes had small structural parameters (s =0.67–0.71mm) due to the thin cross-section, low tortuosity, and high porosity of the membrane substrates. Meanwhile, their rejection layers exhibited superior separation properties (higher water permeability and better selectivity) over commercial FO membranes. When the rejection layer is oriented towards the draw solution, FO water flux as high as 54L/m2 h can be achieved with a 2M NaCl draw solution while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and RO membranes reveals the critical importance of the substrate structure, with straight finger-like pore structure preferred over spongy pore structure to minimize internal concentration polarization. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux. [Copyright &y& Elsevier]

Abstract: Novel osmotic membrane bioreactors (OMBRs) have been recently reported in the literature. An OMBR uses a dense salt-rejecting forward osmosis (FO) membrane, which exhibits high retention of organic matter and various other contaminants. Meanwhile, the high rejection nature also leads to the accumulation of salts in the bioreactor, which can adversely affect the biological activities as well as the FO water flux. A salt accumulation model is developed in the current study. Our model suggests that both the bioreactor salt concentration and the FO water flux are controlled by membrane properties (water permeability A, salt permeability B, mass transfer coefficient K m, and membrane orientation relative to the draw solution) and the OMBR operational conditions (salt concentration of the influent wastewater, draw solution concentration, hydraulic retention time (HRT), and sludge retention time (SRT)). The salt accumulation is contributed by both the influent wastewater and the reverse diffusion of solutes from the draw solution, and is directly proportional to the volumetric concentration factor (i.e., the SRT/HRT ratio). The relative importance of reverse diffusion over contribution from influent solutes is governed by the membrane selectivity. For a relatively selective membrane (B/A ≪the osmotic pressure of the influent water), solute reverse diffusion has negligible effect on OMBR performance. In contrast, the salt accumulation and FO water flux reduction are governed by reverse diffusion for B/A greater than the osmotic pressure of the influent water. The current study reveals the critical importance of the B/A ratio and HRT/SRT ratio for optimized OMBR operation. [ABSTRACT FROM AUTHOR]

Abstract: Forward osmosis (FO) is attracting increasing interest for its potential applications in water and wastewater treatment and desalination. One of the major drawbacks of FO is internal concentration polarization (ICP), which significantly limits the FO flux efficiency. In addition, FO membrane flux can be adversely affected by membrane fouling. The effects of ICP and fouling on FO flux behavior were systematically investigated in the current study. Both theoretical model and experimental results demonstrated that the FO flux was highly non-linear with respect to the apparent driving force (the concentration difference between the draw solution and the feed water) as a result of ICP. ICP played a dominant role on FO flux behavior at greater draw solution concentrations and/or greater membrane fluxes due to the exponential dependence of ICP on flux level. Compared to the active layer facing draw solution (AL-facing-DS) configuration, more severe ICP was observed when the membrane active layer faced the feed water (AL-facing-FW) as a result of dilutive ICP in the FO support layer. Interestingly, the AL-facing-FW configuration showed remarkable flux stability against both dilution of the bulk draw solution and membrane fouling. In this configuration, any attempt to reduce membrane flux was compensated by a reduced level of ICP. The net result was only a marginal flux reduction. In addition, foulant deposition was insignificant in this configuration. Thus, the AL-facing-FW configuration enjoyed inherently stable flux, however, at the expense of severer initial ICP. In contrast, the AL-facing-DS configuration suffered severe flux reduction as porous membrane support faced the humic acid containing feed water. The flux loss in this configuration was likely due to the combined effects of (1) the internal clogging of the FO support structure as well as (2) the resulting enhanced ICP in the support layer. The latter was caused by reduced porosity and reduced mass transfer coefficient of the support. The pore clogging enhanced ICP mechanism probably played a dominant role in FO flux reduction at higher flux levels. To the authors’ best knowledge, this is the first study to systematically demonstrate the coupled effects of ICP and fouling on the FO flux behavior. [Copyright &y& Elsevier]

External concentration polarization (ECP) remains a pervasive challenge for submerged forward osmosis (FO) systems, as it critically reduces the water flux of membranes. In this study, we propose to use transverse vibration on hollow fiber membranes to effectively reduce the ECP and increase the FO water flux performance. The effects of different vibrating amplitude and frequency were investigated. Also, the vibration effect was evaluated under different draw solution concentrations, membrane orientations and draw solute types. Our results show increased water flux with increasing vibrating intensity (i.e., amplitude and frequency) while maintaining a constant specific reverse solute flux (J s /J w). At the highest amplitude (1.2 cm) and frequency (3 Hz) used, the mass transfer coefficient is increased from 0.7 × 10−5 m s−1 (at no vibration) to 1.8 × 10−5 m s−1, which falls within the optimal flux range as determined from our FO modelling results. The increment in mass transfer coefficient is found to be closely related to the improved hydrodynamic conditions due to vibration, and less dependent on the membrane orientation and draw solution concentration. In addition, both modelling and experimental results show that maintaining a reasonably high mass transfer coefficient is especially important for FO process with severe ECP conditions, such as when dilutive ECP is present (i.e., active-layer-facing-feed-solution orientation) or when a high water flux is applied (usually in the active-layer-facing-draw-solution orientation). However, the severe ECP arising from large draw solutes (e.g., larger sized polymer with low diffusivity and high viscosity) might not gain greater benefits from the vibration or improved hydrodynamic conditions. Image 1 • Transverse vibration can mitigate ECP and improve flux in submerged FO processes. • Increasing vibration intensity increases mass transfer coefficient at membrane surface. • Maintaining a high mass transfer coefficient is important for severe ECP conditions. • Severe ECP resulting from large draw solutes cannot gain more benefits from vibration. [ABSTRACT FROM AUTHOR]