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Abstract: Delamination-free ultrafiltration (UF) dual layer hollow fibers have been successfully fabricated by dry jet-wet spinning technique. Two different polymers of poly(amide-imide) (PAI) and polyethersulfone (PES) were utilized as the selective layer on the outer side and the porous support layer on the inner side, respectively. The dual layer substrates were subsequently modified to develop a nanofiltration (NF)-like skin on the outer layer by polyethyleneimine (PEI) cross-linking followed by multilayer polyelectrolyte depositions. These membranes were characterized by a series of standard protocols in terms of membrane structure, permeability and salt rejection, and were applied in FO process. Experiments reveal that the dual-layer NF hollow fiber modified by polyelectrolyte cross-linking and depositions can achieve pure water permeability of 4.1l/m2.h.bar and a high rejection to MgCl2 up to 97%. In FO process, the dual-layer hollow fibers exhibited a water flux of 39 and 21lm−2 h−1 in the orientations of active layer facing draw solution and feed water, respectively, by using 0.5M MgCl2 as draw solution and de-ionized (DI) water as feed at room temperature. It suggests that the combined treatment of polyelectrolyte cross-linking and deposition is an effective way to form a NF-like selective layer for FO dual-layer hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: A novel dual-layer forward osmosis (FO) hollow fiber membrane has been designed and successfully fabricated by using a triple orifice spinneret. The fiber consists of two layers made from polyamide-imide (PAI) polymer for the outer layer and polyethersulfone (PES) polymer for the porous inner layer. Specifically, after obtaining asymmetric microporous PAI/PES dual-layer hollow fibers via non-solvent induced phase inversion, polyethyleneimine (PEI) polyelectrolyte modification on the outer PAI layer was applied to produce a nanofiltration (NF)-like thin layer, while the PES porous inner layer remained intact as PES is inert to PEI. The membrane morphology, structure and surface property were carefully tailored by adjusting polymer dope composition and spinning conditions. These membranes were subsequently characterized by a series of standard protocols in terms of membrane structure, permeability and salt rejection, and were utilized in FO process. It was found that the resultant dual-layer NF hollow fiber membrane can achieve pure water permeability of 15.9lm−2 h−1 bar−1 and a high rejection to divalent cations up to 89%. In FO process, the dual-layer hollow fiber exhibited a water flux of 27.5lm−2 h−1 in the orientation of active layer facing feed water by using 0.5MMgCl2 as draw solution and de-ionized (DI) water as feed at room temperature. The newly developed dual layer hollow fibers outperform all the single layer and dual-layer NF hollow fibers reported in the literature for FO applications. [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: 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]

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]

One of the critical challenges faced by forward osmosis (FO) is the internal concentration polarization (ICP) during FO process, which can drastically reduce the effective osmotic driving force. In this work, silica nanoparticles were embedded in polyetherimide (PEI) nanofibrous support for making thin film nanocomposite (TFN) polyamide FO membranes to mitigate undesired ICP. The experimental results show that the pore size and porosity of the FO membrane substrate was significantly increased due to silica incorporation; the reason could be mainly attributed to the better heat-press resistance of the silica based nanofibrous substrates, leading to less substrate compaction and porosity reduction during the heat-press treatment. The FO membranes supported with such substrates demonstrated higher osmotic water flux, likely arising from the reduced structural parameter of the support layer. The current work showed that the FO membrane with the highest silica loading of 1.6 wt% in dope solution had the maximum substrate porosity (83%), the smallest structural parameter (~ 174 μm), and the most promising water flux, i.e., 42 L/m 2 h in the active layer facing the feed water orientation and 72 L/m 2 h in the active layer facing the draw solution orientation when 1.0 M NaCl draw solution and deionised feed water were applied. [ABSTRACT FROM AUTHOR]

One of the big challenges for forward osmosis (FO) practical application is the lack of high performance FO membranes. In this research, we successfully fabricated a novel thin film nanocomposite (TFN) FO membrane consisting of a polyetherimide (PEI) nanofibrous substrate reinforced by functionalized multi-walled carbon nanotubes (f-CNTs) and an ultrathin polyamide rejection layer. In addition to the superior inter-connected porous structure of nanofibrous substrate, the well-distributed f-CNTs in the nanofibers increased the substrate porosity by 18% and reduced membrane's structural parameter ( S value) by 30%, and significantly improved the substrate tensile modulus by 53%. The high mechanical strength provided by the embedded f-CNTs enabled us to further increase the substrate pore size and porosity in order to mitigate the internal concentration polarization (ICP). This was demonstrated by the high performance TFN-2 FO membrane with a structural parameter of 310 μm. Its water flux at 1.0 M NaCl draw solution (DS) was as high as 61 and 33 L/m 2 h in the active layer facing draw solution (AL-DS) and active layer facing feed water (AL-FW) orientations, respectively, indicating the success of the design strategy, i.e., improved membrane mechanical strength enables a further improvement of the membrane structure to mitigate the ICP. [ABSTRACT FROM AUTHOR]

The layer-by-layer (LBL) polyelectrolyte deposited membranes have drawn increasing attention in various applications due to the ease of selective layer formation and their stability and versatility. In this study, the LBL deposition was performed at the inner surface of the polyethersulfone (PES) hollow fiber substrate to form composite nanofiltration (NF) membrane. The semi-dynamic deposition procedure was adopted with the aid of syringes. The newly developed inner deposited (id-LBL) membranes were then tested in NF and forward osmosis (FO) applications and the performance were compared with outer surface deposition as well as some literature data. The id-LBL membranes could not only withstand higher operating pressure but also possess superior hardness rejection especially in high concentration mixed salt solutions (more than 95% rejection to Mg 2+ and Ca 2+ in a 5000 ppm total dissolved salt (TDS) mixture under 4.8 bar). As for the FO process, with only two layer deposition, the id-LBL membranes also demonstrated significant performance improvement with increased water flux (up to 70 L/m 2 h using 0.5 M MgCl 2 as draw solution in active layer facing draw solution configuration) and reduced salt leakage (around 0.5 g/m 2 h using 1 M MgCl 2 draw solution in active layer facing feed water configuration). This study suggests that for hollow fiber substrate, the inner surface is more suitable for the formation of the selective layer via LBL deposition than the outer surface. [ABSTRACT FROM AUTHOR]

Abstract: High performance flat sheet forward osmosis (FO) membranes have been successfully fabricated using Torlon® polyamide-imide (PAI) materials via phase inversion followed by polyelectrolyte polyethyleneimine (PEI) post-treatment to form a nanofiltration (NF)-like rejection layer with positive charges. The structure and charge property of the FO membranes were carefully tailored by optimizing casting conditions and selecting different immersing methods for the post-treatment. Especially, when the PAI micro-porous substrate was embedded with a woven fabric, the enhanced mechanical strength of the membrane made it possible to reduce the thickness of the substrate to 55μm, which is in favor of high water flux. The resultant membranes can reach a water flux of 29.65Lm−2 h−1 with a ratio of salt flux to water flux (J s /J v ) of <0.8gL−1 in the active layer facing draw solution (AL-facing-DS) configuration, or the water flux of 19.2Lm−2 h−1 and the J s /J v of <0.5gL−1 in the active layer facing feed water (AL-facing-FW) configuration using 0.5M MgCl2 as the draw solution and de-ionized water as the feed water at room temperature. [Copyright &y& Elsevier]

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]

Forward osmosis (FO) is an increasingly important technology that has been deemed promising for addressing the global issue of water scarcity. Rapid progress over the past decade has been marked by significant innovations in the membrane development and process design. The key idea is to develop next-generation membranes through advanced membrane fabrication methods as well as hybrid systems where the FO process can really value-add. As such, this article provides an overview of the various FO membrane designs, in particular, the thin-film composite, surface-modified, and mixed matrix and biomimetic membranes. The pros and cons of each type of membranes are discussed together with the strategies used to optimize membrane properties such as structural parameter ( S ), water permeability ( A ) and salt permeability ( B ) to achieve enhanced FO performances. Furthermore, we also discuss the roles of FO in the various hybrid systems and evaluate the potential of these hybrid systems for desalination. Lastly, we provide our perspectives, especially in the area of membrane fabrications and FO hybrid systems, to shed light on the future research directions for harnessing the true potential of FO for desalination. [ABSTRACT FROM AUTHOR]

Internal concentration polarization (ICP) in a dense support layer is one of the main reasons holding back forward osmosis (FO) process. In this regard, a highly porous microstructured support (HPμS) featuring a quasi-sponge-free sublayer pore structure can be considered a suitable alternative to develop high-performance FO membranes. However, it has not been tested for its effects on FO. This study demonstrates that a TFC membrane prepared using the HPμS works out for FO by inducing 3.35 times higher water flux without compromising a reverse salt flux (J s) compared to a control TFC membrane prepared without support adjustment. The performance improvement could be achieved by HPμS's almost no sponge-like region and lateral walls, which were desirable to minimize ICP. Furthermore, we verified that it is possible to leverage co-solvent assisted interfacial polymerization (CAIP) to further improve FO membrane performances by creating a more permeable active layer. The in-house TFC membrane optimized by the HPμS and CAIP displayed 5.3 times higher FO water flux than the control membrane, while keeping comparable J s. We expect that this research could contribute to kicking the FO membrane performance up a notch by providing a practical example of simultaneous optimization of both support and active layers. [Display omitted] • A highly porous microstructured support (HPμS) successfully reduced ICP in FO. • Almost no sponge-like region and lateral walls of the HPμS were key in reducing ICP. • A sublayer structure of a support layer was examined by a non-destructive inspection. • Co-solvent assisted interfacial polymerization further improved FO performances. • The simultaneous optimizations of support and active layers maximized FO performances. [ABSTRACT FROM AUTHOR]

This paper presents studies on the interactions and effects of biomacromolecules compounds on forward osmosis (FO) membrane performance. Individual components and a combination of various organic substances such as bovine serum albumin (BSA), dextran, sodium alginate and xanthan gum were used as model feeds and tested for their influences on FO performance with the active layer of the FO hollow fiber membrane facing the feed solution (AL-FS). The interactions between foulants were examined by using fluorescence spectroscopy, rotational rheometry and laser doppler micro-electrophoresis techniques. For a system containing combined organic foulants, it was found that viscosity was not the dominant factor governing FO membrane fouling as the decrease in viscosity did not always result in less fouling. The effect of divalent cations on the FO fouling behavior was also studied by adding CaCl 2 . The presence of calcium ions has exacerbated the flux decline, this occurred particularly for any combined organic foulants containing alginate, due to intermolecular bridging among alginate molecules. It is interesting to note that combined BSA + alginate caused moderate flux decline, while BSA and alginate alone did not cause any observable water flux loss. The (BSA + alginate) fouling became more severe with the presence of calcium ions. [ABSTRACT FROM AUTHOR]

Produced water management is one of the key challenges faced by the oil and gas industry globally. Specifically, the gas industry in Qatar is challenged to minimize the produced/process water (PPW) volumes injected into disposal wells to ensure long term sustainability of the reservoirs. This research evaluated a novel application of forward osmosis (FO) to reduce the volumes of PPW disposed of by deep well injection using brine from thermal desalination plants or seawater as draw solutions. In the case of brines, this process also provides some environmentally beneficial dilution before discharge. In order to verify the PPW volume reduction concept, bench-scale FO experiments were carried out using commercial flat sheet membranes. FO performance was evaluated using PPW with and without pretreatment and results confirm that pretreatment is key to the successful implementation of FO for the treatment of PPW. Experimental results indicate that FO is effective in achieving 50% volume reduction of pretreated PPW with stable flux of 12 LMH. Lab analyses show that the TOC in the diluted draw solution was below the detection limit indicating that the TOC from the feed did not appear in the draw solution and hence would not be discharged to the environment. [ABSTRACT FROM AUTHOR]

In this paper, the viability of using micellar draw solutions (DS) for Forward Osmosis (FO) is presented for the first time. Above the critical micelle concentration (CMC) and the Krafft temperature (Tk), the monomers in a surfactant solution aggregate to form micelles, resulting in a relatively constant osmotic pressure above the CMC. These properties can be useful for a FO system in order to maintain a constant water flux and to enable draw solution regeneration at low energy. Three cationic and two anionic surfactants were studied at different concentrations as potential draw solutions for FO applications. Both flat sheet and hollow fiber FO membranes were used in the study. The study revealed that the micellar solutions generated more stable flux compared to other inorganic DS; the hypothesis of a constant flux above the CMC was valid only for concentrations slightly above the CMC, and micellar solutions behaved similar to inorganic solutes at concentrations significantly higher than the CMC. It was shown that external concentration polarization (ECP) does not have a significant effect in micellar solutions just above the CMC. Furthermore, all surfactants demonstrated between 3 and 300 times less reverse transport compared to NaCl at similar concentrations. Finally, the surfactant solute could be regenerated with recoveries as high as between 95% and 99%. It was thus verified that micellar solutions are an attractive DS for application to Forward Osmosis and potentially in the forward osmosis membrane bioreactor (FO-MBR). [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of intrinsic properties of foulants on FO membrane performance was studied. [•] Diffusivity governs hollow fiber membrane performance in FO mode. [•] Flat sheet membrane performance in PRO mode was controlled by combined mechanisms. [•] The mechanisms include diffusivity, size exclusion and electrostatic interactions. [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]

Highlights: [•] Using electrospun PVDF nanofibers as substrates to make FO membranes was explored. [•] Polyamide thin films were formed via interfacial polymerization (IP) on two different substrates. [•] 30.4L/m2 h water flux was achieved in AL–DS orientation using 1.0 M NaCl draw solution. [•] The ratio of reverse salt flux to water flux was able to be kept as low as 0.21g/L. [Copyright &y& Elsevier]

Abstract: We report a study to explore new materials and a new concept for temperature driven quasi-continuous desalination using hydrogels as draw agents in forward osmosis (FO). This concept is enabled by the design and preparation of thermally responsive hydrogels having a semi-interpenetrating network (semi-IPN) structure. Thermally responsive semi-IPN hydrogels were synthesized by polymerization of N-isopropylacrylamide (NIPAm) in the presence of polysodium acrylate (PSA) or polyvinyl alcohol (PVA). Their functions as draw agents in FO were systematically studied and compared with hydrogels prepared from the PNIPAm homopolymer or the NIPAM-SA copolymer. While the semi-IPN hydrogels displayed the desirable balanced thermally responsive swelling and dewatering behavior, the NIPAm-SA copolymer hydrogels were found to have poor dewatering behavior, making them unsuitable for a continuous temperature driven desalination process. At 40 °C, the semi-IPN hydrogels rapidly release nearly 100% of the water absorbed during the FO drawing process carried out at room temperature. Results clearly indicate the potential of semi-IPN hydrogels as semi-solid draw agents in the FO process, in which quasi-continuous desalination could be achieved by cyclic heating and cooling within a moderate temperature change. [Copyright &y& Elsevier]

Abstract: Exploitation of osmotically-driven membrane (OM) technologies and accompanying semi-permeable OM fabrication have become promising topics with numerous potential applications. This paper presents a systematic comparison study of nanofiltration (NF)-like and reverse osmosis (RO)-like thin film composite (TFC) OMs in terms of flux performance and fouling behavior. Major governing mechanisms of OM performance were elucidated and revealed to be related with properties of membrane, draw and feed solutions. Results showed the crucial influence of draw solute reverse diffusion (M ICP-Js ) on OM water flux. Thus the high-rejection RO-like OMs generally performed better than NF-like counterpart in sodium chloride based osmotic processes. On the other hand, the high permeability of NF-like OMs can achieve higher water flux when proper draw solutes were used to minimize M ICP-Js . Fouling tests also suggest that the NF-like TFC OMs tend to be more fouling resistant due to its smooth membrane surface. The current study led to a set of systematic criteria for the selection of osmotically-driven membranes, draw solution and other operational conditions, of which the practicability was further elucidated in potential OM applications. [Copyright &y& Elsevier]

Abstract: Great efforts from the membrane community have been devoted in developing suitable membranes for forward osmosis (FO) applications in recent years. In the current study, the layer-by-layer (LBL) polyelectrolyte assembly technique has been successfully applied onto a microporous polyethersulfone (PES) hollow fiber substrate to make novel LBL hollow fiber membranes suitable for FO process for the first time. The FO performance of the LBL hollow fibers with different numbers of deposited layers has been evaluated using deionized (DI) water as the feed and MgCl2 solution of various concentrations as the draw solution in both orientations. With 6 layers deposited and in the active layer facing draw solution (AL-facing-DS) orientation, the membrane showed high water fluxes of 14.6, 25.9 and 40.5L/m2 h with corresponding salt to water flux, J s /J v, ratio of 0.034, 0.066 and 0.201g/L using 0.05, 0.1 and 0.5M draw solution, respectively. These promising results demonstrate the potential application of the LBL hollow fibers in FO process using low concentration draw solutions, which can substantially reduce the draw solution replenishment, and the energy consumption for draw solution regeneration and separation. [Copyright &y& Elsevier]

Abstract: This research focused on combined organic–inorganic fouling and cleaning studies of forward osmosis (FO) membranes. Various organic/inorganic model foulants such as sodium alginate, bovine serum albumin (BSA) and silica nanoparticles were applied to polyamide-polyethersulfone FO hollow fiber membranes fabricated in our laboratory. In order to understand all possible interactions, experiments were performed with a single foulant as well as combinations of foulants. Experimental results suggested that the degree of FO membrane fouling could be promoted by synergistic effect of organic foulants, the presence of divalent cations, low cross-flow velocity and high permeation drag force. The water flux of fouled FO hollow fibers could be fully restored by simple physical cleaning. It was also found that hydrodynamic regime played an important role in combined organic–inorganic fouling of FO membranes. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) process as an alternative to conventional desalination techniques has attracted much attention in recent years. Since mineral salt scaling is one of the major limitations for seawater desalination, the current study focused on the behaviors of thin film composite (TFC) FO hollow fibers, which were fabricated in our laboratory, under the circumstance of calcium sulfate (CaSO4) scaling with sodium chloride as draw solution. The performance of FO hollow fiber membranes was compared with commercially available FO flat sheet membranes. Several cleaning strategies were also explored. Depending on the membrane orientation, experimental results suggested that the scaling of the FO hollow fibers was dominated by cake layer formation along with pore blocking in the orientation of active layer facing draw solution (AL-DS). The pore blocking could be a result of the penetration of crystals from the feed solution into the support matrix of the membrane, or the formation of crystals inside the porous support layer. At the same driving force, the water flux of the FO hollow fibers in the orientation of active layer facing feed solution (AL-FS) was twice higher than the water flux of the flat sheet membrane in both orientations. The water flux of scaled FO hollow fibers and flat sheet membranes in the AL-DS orientation could be successfully restored by hydraulic backwash procedure. To the best of our knowledge, this is the first study to examine the inorganic scaling of FO membranes in the AL-DS orientation. [Copyright &y& Elsevier]

Abstract: The forward osmosis membrane bioreactor (FOMBR) has received much attention recently. Due to the high rejection nature of FO membranes, the biomass, dissolved organic and inorganic compounds retained in the bioreactor could cause membrane fouling by multiple mechanisms. In this study, a 45% permeate flux decrease was observed in a well controlled FOMBR equipped with a submerged hollow fiber FO membrane module with the active layer facing the draw solution (AL-DS) configuration. A series of characterizations were performed to explore membrane fouling mechanisms in the FOMBR. It was found that a biofouling layer covered the substrate surface of the FO membrane with a combined structure of bacterial clusters and extracellular polymeric substances (EPS), which contributed to 72% drop of the membrane mass transfer coefficient (K m ) and around 10% increase in the hydraulic resistance. The inorganic fouling was caused by Ca, Mg, Al, Si, Fe and P that contributed 60% of the total hydraulic resistance of the fouled membrane and decreased the K m by around 34%. These results suggest that in this application the FO fouling is governed by the coupled influences of biofilm formation and inorganic scaling. When the configuration was reversed with the active layer facing the feed solution (AL-FS), a negligible flux decline was obtained by applying intermittent tap water flushing to the membrane surface, which suggests that the AL-FS orientation is favorable for FOMBR operation. An effective strategy for fouling control is to prevent internal scaling and the over-growth of biofilm on the membrane surface. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) is an emerging osmotically driven membrane process, and its applications are becoming diversified. As one important membrane configuration, hollow fiber modules have been applied to some innovative FO processes, e.g., osmotic membrane bioreactor (OMBR). Aside from the inherent concentration polarization (CP) phenomena, new challenges are posed by the coupled concentrating and dilution effects in the design of FO hollow fiber modules. In this paper, a mathematical model is therefore developed to account for the evolution of the local performances within the FO hollow fiber module and to evaluate the global performances of interest. Then, this model is employed to theoretically investigate the filtration behaviors of the FO hollow fiber module by using the well-defined dimensionless groups, which indicates the complex interplay among a variety of design parameters. Particularly, the optimization objectives are focused on enhancing the module-averaged FO efficiency and avoiding the severe concentration variations in the module channels. In terms of the simulation results, some criteria are obtained for optimizing the operating conditions (flow configuration, inlet concentration level, inlet flow rate), the hollow fiber characteristics (fiber length), and the FO membrane properties (active layer selectivity, support layer transport resistance). This work provides deep insights into the design of the FO hollow fiber module, and could be readily modified to accommodate more complicated cases. [Copyright &y& Elsevier]

The integration of forward osmosis (FO) and biological process, known as the osmotic membrane bioreactor (OMBR), may be viewed as beyond the state of the art for used water treatment and water reclamation. While it is known that the OMBR is able to produce good product water quality in terms of total organic carbon (TOC) removal, limited information is available on the removal of organic micro-pollutants in relation to process performance under the concentrated environment. In this study, a novel OMBR system was continuously operated over 73 days, during which pharmaceuticals were dosed on two occasions into the system. It was found that while pharmaceutical removal was high (>96%), other process parameters in the form of TOC, mixed liquor suspended solids (MLSS) and extracellular polymeric substances (EPS) were unmistakably affected. The major portion of TOC that permeated the FO membrane was found to be low-molecular weight neutral compounds which were associated with the impaired biological process. Microbiological analysis confirmed shifts in microbial populations occurred due to the increased salinity and dosage of the pharmaceuticals. The study demonstrated the importance of the biological process for optimal OMBR system performance, and paves the way for further research in this direction. [ABSTRACT FROM PUBLISHER]

Abstract: There has been an increasing interest in the novel integration of forward osmosis (FO) and biological process known as the osmotic membrane bioreactor (OMBR). However, little operating experience is available to adequately assess the feasibility of the technology for larger scale application. The goal of this study is to provide fundamental information on the technology. In this study, an OMBR system was continuously operated for 73days. It was found that the high retention property of the FO membrane and salt transmission from the draw solution resulted in increasing mixed liquor salinity until a stable state was reached. In spite of the elevated salinity, the water flux was relatively stable at around 3Lm−2 h−1. Post-experiment analyses indicated mild membrane fouling, and its effect on water permeability was insignificant. An ion analysis check indicated that scaling did not occur. The SEM examination detected a thin gel-like secondary layer on the membrane surface. It was deduced that this secondary layer could have an influencing role on salt transmission during the experiment, and moderated salt concentration in the bioreactor. [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]