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Increasing the surface porosity of a support membrane has been proposed as an effective way to improve the water permeability of thin-film composite (TFC) reverse osmosis (RO) membranes by reducing the diffusion pathway in the active layer. In this work, we prepared a highly porous microstructured (HPμS) support membrane with a suitable mechanical strength to enhance the water permeability of an RO membrane. The HPμS support membrane was prepared by increasing the thermodynamic instability of a 10 wt% polymer solution and thereby facilitating rapid desolvation. The rapid desolvation formed the narrow and regularly arranged pore structure in the sublayer, and we proposed the mechanism for the sublayer structure formation based on analyses of the thermodynamic properties of such a binary system. Owing to the narrow and regular structure, the HPμS support membranes showed the exceptional mechanical strength, which was comparable to the strength of support membranes used for conventional RO membranes. Also, the HPμS support membranes successfully endowed an in-house RO membrane with the performance (water permeability of 4.68 L m −2  h −1  bar −1 and NaCl rejection of 98.3%) surpassing commercial RO membranes and thin-film nanocomposite membranes recently reported in the literature. [ABSTRACT FROM AUTHOR]

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 direct contact membrane distillation system (DCMD) was simulated by using Aspen Plus for the purpose of energy efficiency and economic analyses. A cross-flow membrane module was firstly modeled and then incorporated into the flowsheet for system simulation. Detailed investigations have been conducted to understand the relationships of the water flux/production, the gain output ratio (GOR) and the water production cost (WPC) with respect to various design and operation parameters of the DCMD system. Simulation results revealed that in the DCMD studied here, a critical membrane area existed, below which, significant increases of water production and the GOR were observed with increasing membrane area, leading to a significant drop in the WPC. Increasing feed temperature imposes positive impacts on water flux and the GOR. For the higher feed and permeate velocities, there were increases in water flux, water production and the GOR. However for the WPC there were optimum fluid velocities beyond which the penalty of more energy input in the form of electricity consumption for pumping was significant. It was also found that when the temperature difference in the heat exchanger was increased to 6°C, the WPC can be reduced considerably by cutting down the heat exchanger cost. [Copyright &y& Elsevier]

Membrane distillation (MD) is a promising thermally-driven desalination process for various applications in food, pharmaceutical, textile, and chemical industries. However, membrane fouling and wetting are still major challenges, which limit the stability of MD membranes over long-term use. From 2005, researchers have developed many strategies to enhance membrane fouling resistance by simultaneously engaging reactions, but these works have not been systematically reviewed and categorized. Therefore, this review aims to identify research gaps and provide an overview of the state-of-the-art reactive MD processes, which are categorized broadly based on two configurations: 1 – " hybrid" involving coupling MD with an oxidation or biological process as a pre-treatment step and 2 – " integrated" involving immobilizing reactive materials on the membrane. The reactive MD processes were sub-classified into five categories based on reaction technology then analysed in terms of working mechanisms, advantages, limitations, and their application potentials. It shows that minimizing fouling in both hybrid and integrated processes can be attributed to the interaction of the organics/degraded by-products with the membrane surface/immobilized reactive layer, and the capability of the pollutants to be oxidized. In addition, depending on the types of the coupled process, oxidation can be accompanied by other mechanisms, such as electrostatic repulsion and electro flotation which is the most promising mechanism. Overall, despite the current developments in hybrid and integrated MD processes, many challenges exist including flux decline in the case of the complex feed solutions, a trade-off between oxidation and other accompanied mechanisms (e., electrostatic repulsion), and the possibility of membrane alteration. Future opportunities can be explored in terms of dedicated fouling studies, energy efficiency, removing/converting waste streams to valuable by-products, durability of the process equipment against oxidation, and targeting unique applications such as the treatment of concentrated organic waste streams. [Display omitted] • Reactive MD categorized into "hybrid" and "integrated" configurations. • Oxidation processes are a major focus in reactive MD. • Challenges include membrane fouling and material degradation. • Reactive MD demonstrates highly efficient treatment simultaneous with desalination. • Future studies should focus on fouling, reaction efficiency and targeted applications. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is emerging as a promising technology for treating the reverse osmosis brines. However, limited cases were reported on the design of a large-scale direct contact MD (DCMD) system. The practical scale-up options for modular matrix design in a multi-element MD system and a multi-subsystem MD train were explored by commercial flowsheet simulator Aspen Plus. Compared to the benchmark single module system, which showed drastically deteriorating membrane performance with increasing membrane area, the multi-element DCMD system with modules in parallel matrix was found to perform better with water production improved slightly but specific power consumption ( SPC ) greatly reduced down to 0.5% of the single module system. The optimal matrix was obtained at module number of eight for a 20 m 2 module due to trade-off relationship between module specifications and effective process driving force in MD. Supported by theoretical analysis, it was found that the matrix array pattern had no influence on the performance of the multi-subsystem DCMD train. Further investigation showed that an 18-subsystem MD train with a membrane area of 200 m 2 achieved a 16 times water production rate with only 10% of the SPC , as compared to that of single system with the same membrane area. [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]

Pressure retarded osmosis (PRO) has been identified as a promising technology to harvest the salinity gradient energy. For practical applications of PRO process, membrane fouling is a challenging issue as it leads to severe decline of PRO performance in terms of water flux and power density. It is imperative to develop anti-fouling membranes for PRO process. The current study demonstrated the unique roles and the great potential of aminosilane in developing anti-fouling thin film composite (TFC) PRO membranes. Experimental results revealed that aminosilane as a grafting agent can modify both the support layer (interior) and the selective layer of PRO membranes with remarkably enhanced hydrophilicity via a very simple grafting procedure. In the grafting, aminosilane was able to minimize the pore-blocking issue with almost no increase in the membrane structural parameter ( S ). Meanwhile, the membrane mechanical strength was well maintained with the grafting due to the capability of aminosilane as a cross-linker. With enhanced hydrophilicity, it was interestingly found that the water permeability ( A ) was doubled, while the salt rejection was maintained nearly unchanged. The combination of these effects brought in remarkably enhanced water flux, power density and anti-fouling property to the resultant membrane. [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]

Aiming to optimize the system-level heat utilization, a pilot-scale direct contact membrane distillation desalination system integrated with heat recovery (DCMD–HX) was studied using Aspen Plus. An implicit expression of gain output ratio (GOR) was derived to reveal the interplay of heat utilization and process parameters including operating conditions, module specifications as well as membrane properties in the DCMD–HX desalination system. Compared to operating temperatures, the feed/permeate recirculating flowrates were identified as the most influential operational factors affecting the GOR. In the current settings, the maximal GOR of 6.0 was observed at low and equivalent feed- and permeate-side flowrates regardless of module specifications. Low flowrates, however, resulted in undesirable low water productivity, which was consistent with the trade-off relationship observed between the heat utilization efficiency and water recovery rate in MD. Employing membranes with high heat-transfer resistance (low conductivity and thicker membrane wall) helped to improve the GOR up to 32%. Simulated results also showed that the GOR value increased by 1.3-fold with the preheater parameter Δ T HX varying from 5 to 0 °C. The non-linear scale-up relationship existed between the membrane area and heat utilization (i.e., GOR) was also observed, indicating the possible uncertainty in accurately predicting the GOR value for industrial-scale desalination systems based on lab-scale module testing. [ABSTRACT FROM AUTHOR]

Abstract: A two-dimensional numerical model, involving energy conservation, momentum transport and continuity equations, was developed to provide the profiles of temperature, velocity and pressure of vacuum membrane distillation (VMD) process using hollow fiber module. The theoretical prediction was in good agreement with the experimental results from literature. Four design and operation variables, including feed temperature, hollow fiber length, feed volume flow rate and vacuum pressure, were optimized to minimize water production cost (WPC) using genetic algorithm (GA). A case study shows that the WPC can be decreased by 38.1% in comparison with the non-optimized VMD process. Meanwhile, a general guidance for reducing the WPC was also provided. The feed temperature should be adopted as high as possible, while the hollow fiber length cannot be too long to result in a decrease in water flux and an increase in pressure drop. The flow rate is recommended to take a lower bound value and the moderate degree of vacuum is preferable. This study indicates the importance of VMD system optimization to minimize water production cost. [Copyright &y& Elsevier]

Abstract: This study incorporates gas bubbling into direct contact membrane distillation (DCMD) and examines its effect on the MD performance especially at elevated salt concentrations in the feed steam. Process optimization in the bubbling assisted DCMD process was carried out which involved varying operating conditions and module configurations. Also, observations were performed for the scaling status on the membrane surface with operating time in different modules to further understand the role of gas bubbling in affecting the behavior of crystal deposition when the salt concentration has reached super-saturation. Due to intensified local mixing and physical flow disturbance in the liquid boundary layer on the feed side, a higher flux enhancement could be achieved in a bubbling system with either a higher feed operating temperature, lower feed and permeate flow velocities, inclined module orientation, shorter fiber length or lower packing density. It was also found that gas bubbling not only enhanced the permeation flux by average 26% when concentrating feed solution from 18% salt concentration to saturation, but also delayed the occurrence of major flux decline due to crystal deposition when compared to the module with spacers. These results were confirmed by membrane surface autopsy at different operating stages using SEM. [Copyright &y& Elsevier]

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: There has been a resurgence of interest in forward osmosis (FO) as a potential means of desalination, dewatering and in pressure retarded osmosis, which Sidney Loeb was advocating over 3decades ago. This paper describes the characteristics and potential applications of a newly developed FO hollow fiber membrane, which was fabricated by interfacial polymerization on the inner surface of a polyethersulfone (PES) hollow fiber. This FO membrane presents excellent intrinsic separation properties, with a water flux of 42.6L/m2 h using 0.5M NaCl as the draw solution and DI water as the feed with the active layer facing the draw solution orientation at 23°C. The corresponding ratio of salt flux to water flux was only 0.094g/L, which is superior to all other FO membranes reported in the open literature. To evaluate different application scenarios, various NaCl solutions (500ppm (8.6mM), 1wt.% (0.17M) and 3.5wt.% (0.59M)) were used as the feed water to test the performance of the FO membrane. The membrane can achieve a water flux of 12.4L/m2 h with 3.5wt.% NaCl solution as the feed and 2M NaCl as the draw solution, suggesting it has good potential for seawater desalination. [ABSTRACT FROM AUTHOR]

This study focused on the effect of sodium alginate on the performance of direct contact membrane distillation (DCMD). The feed solution contained various combinations of sodium chloride, sodium sulfate and calcium chloride along with bovine serum albumin, xanthan gum and sodium alginate. Unlike findings from the majority of prior studies that suggested the presence of alginate in feed solution caused the deterioration of membrane process performance, our results indicated that sodium alginate exhibited anti-scaling properties and water flux enhancing effect. However, this interesting phenomenon was exhibited by sodium alginate under particular conditions only. Experiments performed with other organic foulants such as xanthan gum did not display the same trend. It is believed that the presence of a hydrophilic layer (calcium alginate gel), which is much less thermal conductive as compared to the PTFE membrane, on the top of the membrane could reduce the amount of heat dissipated due to evaporative cooling or reduce conductive heat loss in the membrane, thus enhancing the thermal efficiency of the system. • Sodium alginate exhibited anti-scaling properties and water flux enhancing effect • Reduction of conductive heat loss with the presence of hydrophilic layer • The degree of improvement was governed by the consistency of the gel layer formed [ABSTRACT FROM AUTHOR]

This study focuses on enhancing the mechanical strength of aquaporin (AQP)-based biomimetic membranes for seawater desalination. AQP incorporated vesicles were embedded into the selective layer of an optimized thin film composite (TFC) membrane. The resultant membrane, denoted as ASW, exhibited a stable water flux around 20 L·m−2·h−1 and 99% NaCl rejection at a constant pressure of 55 bar using 32,000 mg·L−1 NaCl solution as feed in reverse osmosis (RO) measurement. The robustness of the ASW membranes were evaluated. The water flux of ASW membrane was almost 100% enhanced compared with that of AQP-free control TFC membranes. The filtration performance of the ASW membrane was further evaluated by a seven-day desalination test using a real seawater secondary effluent collected from a desalination plant in Singapore as feed. To our best knowledge, our study is the first report on the AQP-incorporated RO membrane applied for seawater desalination. A commercial SW30HR membrane was tested in parallel for comparison. The robust ASW membrane exhibited a nearly 80% higher water flux in comparison to the SW30HR membrane with a comparable overall solute rejection, suggesting the advantage and feasibility of Aquaporin based biomimetic membranes for seawater desalination. • The mechanical strength of aquaporin incorporated polyamide layer was characterized with AFM. • The effects of high pressure compaction and salinity on aquaporin incorporated polyamide layer were investigated. • The aquaporin based biomimetic membranes were optimized for seawater desalination (SWRO) application. • A seven-day SWRO measurement of the ASW was conducted using a real seawater secondary effluent. [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]

Polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) hollow fiber membranes were developed via thermally induced phase separation (TIPS) method for direct contact membrane distillation (DCMD). The effects of PTFE addition on the thermal behavior of the dope mixtures and membrane formation were investigated. It was found that the crystallization of PVDF was significantly enhanced with increased nucleation sites provided by PTFE particles, leading to promoted formation of smaller spherulites in a greater density. Furthermore, the improved uniformity and increased amount of cavity between the spherical crystallites coherently facilitated the formation of smaller pores ranging from 0.08 to 0.12 μm. With certain PTFE loading, the membranes exhibited improved porosity, water permeability and hydrophobicity as well as enhanced tensile strength of 9.4 ± 0.3 MPa. To examine the DCMD performance, the membranes were tested under various conditions using 3.5 wt% NaCl solution. A stable permeation flux of 28.3 kg m − 2 h − 1 at the feed temperature of 60 °C with 99.99% NaCl rejection for over 50 h of operation was achieved, which is comparable with similar type of PVDF membranes while the newly developed membrane exhibited better mechanical strength. This study suggests that the as-spun PVDF/PTFE hollow fiber membranes have potential for DCMD applications. [ABSTRACT FROM AUTHOR]

The emerging technology of pressure retarded osmosis (PRO) has been intensely studied over the past decades due to its potential in harvesting salinity gradient energy, but membrane fouling can deteriorate the PRO performance. To mitigate membrane fouling, the outer surface of the inner-selective thin-film composite (TFC) polyetherimide (PEI) hollow fiber membrane was modified by depositing poly-(allylamine hydrochloride) (PAH) and poly acrylic acid (PAA) polyelectrolytes. The results show that the outer surface of the modified membrane had less pores exposed and was more negatively charged, which was beneficial for preventing the entrance and adsorption of the negatively charged foulants into the membrane substrate. It was further proved that the modified membrane was effective in reducing PRO fouling by organic macromolecules such as alginate and bovine serum albumin, while maintaining the mechanical properties and intrinsic separation properties well. Interestingly, after 200 ppm alginate was introduced to the feed water, the power density of the modified membrane could be maintained constant at 16.2 W·m − 2 at 15 bar while that of the non-modified membrane reduced around 17% at the end of a 300-min testing period. The results suggest that the polyelectrolytes deposition is a feasible strategy for adding anti-fouling property to PRO membranes. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is an attractive technology for seawater reverse osmosis (SWRO) brine treatment. Submerged MD (S-MD) offers an additional advantage of a compact system compared to cross-flow MD. This study evaluated the performances of three different S-MD configurations; submerged direct contact membrane distillation (S-DCMD), submerged vacuum direct contact membrane distillation (S-VDCMD) and submerged vacuum membrane distillation (S-VMD) for SWRO brine treatment. A 13–77% higher water flux was obtained by S-MDs with vacuum incorporation (S-VMD and S-VDCMD) compared to S-DCMD, attributed to higher driving force. Evaluation on the influence of feed concentration and permeate temperature revealed that S-MD with high vacuum was significantly affected by feed concentration. Meanwhile S-DCMD was more severely affected by feed temperature losses, based on the tendency of membrane pore crystallization formation. The crystallization tendency on the membrane surface was influenced by the presence of vacuum pressure. A repeated cycle of S-DCMD with membrane air-backwashing was effective for flux recovery and to reduce membrane crystallization, enabling to concentrate SWRO brine by 2.8 times of volume concentration factor. [ABSTRACT FROM AUTHOR]

This study investigated the fouling behavior and chemical cleaning of forward osmosis (FO) membranes for treating produced/process water (PPW) from a real gas field using thin-film composite FO hollow fiber membranes. Experiments revealed that membrane fouling occurred during the PPW treatment, which hindered the water and solute transport through the membrane. The water permeability and FO reference water flux of the membrane decreased by 22.9% and 24.8%, respectively, after fouling. Membrane surface characterization was carried out, and the results indicated the deposition and entrapment of organic species on the membrane after the PPW treatment. The efficiencies of various cleaning agents, including sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic (EDTA) and NaOH, were evaluated. It was found that cleaning with SDS for 15 min is the most effective method for restoring water flux, and very stable FO performance can be obtained during batch treatment of PPW. The FO membrane can reduce the PPW volume by 50% at a relatively high average water flux of 15.6 L·m − 2 ·h − 1 in the active layer facing feed solution orientation using 1 M NaCl as draw solution (equivalent to the draw solution available in the field). This study demonstrates the great potential of FO technology for produced/process water treatment. [ABSTRACT FROM AUTHOR]

Micellar draw solutions containing either sodium dodecyl sulphate (SDS), tetraethyl ammonium bromide (TEAB), 1-Octane sulphonic acid sodium salt (1-OSA) or trimethyloctyl ammonium bromide (TMOAB) were tested in the FOMBR system. After 48 h, reverse transported draw solute concentrations with 1 M draw solution concentrations for NaCl, SDS, TEAB, TMOAB and 1-OSA reached 3.22 mg/l (55 μM), 0.012 mg/l (0.04 μM), 0.067 mg/l (0.32 μM), 0.057 mg/l (0.23 μM) and 0.062 mg/l (0.29 μM), respectively. Thus, reverse transport of surfactant solute was minimal. The toxicity of each draw solution was tested using Pseudomonas aeruginosa specie and mixed (activated) sludge. The percentage growth for P. aeruginosa at the highest tested draw solute concentration of 0.05 M was 60% for SDS and 49% for TEAB, while the other surfactants proved to be more toxic. Similar to bacterial growth, the TOC reduction was higher for P. aeruginosa when compared to the mixed sludge consortium. For membrane cleaning, 0.0005 M EDTA with 0.125 g/l NaOH (a pH of 11.6) for 0.5 h was found to be an effective cleaning strategy, along with prior- and post-cleaning of the membrane using DI water. Reuse of the regenerated draw solutes indicated that the SDS flux returned close to the original flux, while the TEAB flux reached 50% of the original. Overall, SDS and TEAB are recommended for future investigation, because of minimal reverse solute transport, low in-situ microbial toxicity, good flux recovery after membrane cleaning, and effective draw solute regeneration. [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]

The emerging thin film composite (TFC) forward osmosis (FO) and pressure retarded osmosis (PRO) membranes generally have better separation properties compared with their cellulose triacetate (CTA) counterparts. Nevertheless, their scaling performance has been rarely reported. In the current study, the phenomenon of membrane integrity loss as a result of scaling is reported for the first time for osmotically driven membrane processes (ODMPs). The results show that the TFC membrane suffered marked flux reduction during the scaling in the active-layer-facing-feed-solution (AL-FS) orientation, accompanied with the severe damage of the membrane active layer. The membrane integrity loss is attributed to the scale formation and growth in the confined space between the membrane and the feed spacer. Compared with the CTA membrane, the TFC was more prone to scaling and membrane damage due to its unfavorable physiochemical properties (presence of Ca 2 + binding sites and ridge-and-valley roughness). Although antiscalant addition was shown to be effective for scaling control in AL-FS, it was ineffective in the active-layer-facing-draw-solution orientation. The current study reveals the critical need for scaling control in ODMP processes with respect to the membrane integrity and flux stability. The results also have far-reaching implications for FO and PRO membrane design and process operation. [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]

The ultra-permeable membranes (UPMs) are expected to reduce the specific energy consumption (SEC) of desalination, but the potential of UPMs in hollow fiber configuration has not been well quantified. Herein, we analyse the SEC and footprints of UPM modules in three feed salinities: seawater reverse osmosis (SWRO), brackish water RO (BWRO) and low-pressure RO (LPRO). Through the modelling the fluid dynamics and mass transport of RO systems, we find that a tripling in spiral-wound SWRO membrane permeability (based on the current value of 1 L m−2 h−1 bar−1; LMH/bar) could result in 16% decrease in SEC. Contrastingly, the quadrupling of hollow fiber SWRO membrane permeability (based on the current value of 0.25 LMH/bar) could reduce the SEC by 23%. According to our analysis, hollow fiber and spiral-wound SWRO membranes with permeabilities up to 1 LMH/bar and 3 LMH/bar, respectively, can reduce the SEC of seawater desalination. On the other hand, membranes with permeabilities up to 9 LMH/bar and 12 LMH/bar can lead to SEC savings in BWRO and LPRO desalination, respectively. This study provides a general guidance to RO membrane researchers on the permeability upper-limit of which UPMs could bring about SEC and footprint savings at a system level. [Display omitted] • Energy savings achievable by high permeability RO membranes were quantified. • Modelling was performed by simulating fluid dynamics in various RO configurations. • Hollow fiber SWRO membranes (up to 1 LMH/bar) could reduce energy consumption. • Spiral-wound SWRO membranes (up to 3 LMH/bar) could reduce energy consumption. • High permeability RO membranes could bring about greater benefits in BWRO/LPRO. [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]

Abstract: The layer-by-layer (LBL) polyelectrolyte deposition was applied on polyethersulfone (PES) hollow fiber ultrafiltration membrane to prepare nanofiltration (NF) membrane for low pressure water softening application for the first time. The effects of polyelectrolyte type and molecular weight (MW), deposited bilayer number, polyelectrolyte solution pH and supporting electrolyte concentration on the performance of resultant membranes were studied thoroughly. Experiments revealed that the pH of the polyelectrolyte solution and supporting electrolyte concentration presented the most notable effects. For weak poly-cations, Poly(ethylenimine) (PEI) and Poly(allylamine hydrochloride) (PAH), the solution pH affected the membrane performance significantly, and high water permeability and divalent cation rejection were obtained at optimum pH values. Using a low concentration of supporting electrolyte at underneath layers was proved to be an effective way to increase water permeability while maintaining high salt rejection. A salt water flux (SWP) of 12LMH/bar and 94% Mg2+ rejection was obtained by depositing only two bilayers of PSS/PAH polyelectrolytes on the PES substrate, while for the 3000ppm mixed salt solution, the water permeability was 11LMH/bar with Mg2+ and Ca2+ rejection as high as 90%. These promising results demonstrate that LBL technique is potentially applicable for preparing low-pressure water softening hollow fiber membranes. [Copyright &y& Elsevier]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

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: Forward osmosis (FO) has attracted wide interest for its many potential applications. Recent developments suggest that double-skinned FO membranes may perform superiorly over conventional single-skinned ones. In this design, a dense rejection skin facing the draw solution is responsible for the separation, while a second skin facing the feed solution is designed to prevent foulants entering into the porous support layer sandwiched between the two skins. For the first time, an analytical model is developed for double-skinned FO membranes and is verified experimentally. Model simulations suggest that an optimal double-skinned membrane shall have a feed skin similar to that of a low rejection nanofiltration membrane to minimize the overall hydraulic resistant and to reduce internal concentration polarization. On the other hand, the optimization of the draw skin calls for a compromise between its water permeability and solute rejection. FO water flux is greater for support layers with higher mass transfer coefficients. In addition, it decreases with decreasing draw solution concentration and increasing feed solution concentration. While membrane orientation plays an important role for applications with low feed solution concentrations (with the denser skin preferentially facing the draw solution), this effect becomes negligible at high feed solution concentrations. [Copyright &y& Elsevier]

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]

In this study, a prototype microgranular adsorptive filtration (μGAF) system was constructed employing a 7-bore ceramic membrane as the primary membrane and either heated aluminum oxide particles (HAOPs) or powdered activated carbon (PAC) as the pre-deposited dynamic membrane (DM). The system was used to pre-treat membrane bioreactor (MBR) effluent from a full-scale MBR-reverse osmosis (RO) water reclamation plant. The downstream RO performance and membrane fouling potential of the treated effluent were then assessed. The results indicated that: (i) although PAC removed more overall EfOM than HAOPs did, HAOPs were more effective in removing biopolymers such as polysaccharides and proteins, (ii) HAOPs virtually eliminated fouling of the primary ceramic membrane, whereas considerable fouling (much of it irreversible) occurred when the feed was pretreated with PAC, (iii) HAOPs removed more than 90% of the phosphorus and fluoride from the feed, but PAC removed negligible amounts of these contaminants, and (iv) HAOPs-treated effluent resulted in only a 43% decline in RO permeate water flux over 5 d of continuous filtration, as opposed to 62% flux decline for untreated or PAC-treated effluent. This study thus demonstrates the effectiveness of the HAOPs-based μGAF process as a pre-treatment for improving downstream RO recovery. • A prototype μGAF system was used to treat an MBR effluent from a full-scale MBR-RO plant. • μGAF using HAOPs demonstrated an efficient removal of biopolymer, phosphorus, silica and fluoride. • HAOPs was more effective at mitigating downstream RO fouling compared to PAC. • HAOPs demonstrated the potential to enhance the overall performance of a water recovery process. [ABSTRACT FROM AUTHOR]

Membrane fouling occurs in all membrane processes. Surface modifications have gained popularity for enhancing membrane antifouling capability via introducing a hydrophilic component or reducing membrane surface roughness. In this work, we proposed to develop a green antimicrobial lysozyme nanofilm on the polyamide membrane surface with remarkable antibacterial and antifouling properties to effectively reduce membrane fouling. The nanofilm is rooted in the molecular assembly of a protein which is an extraction of food and natural products. The nanofilm exhibits the combination of various functions including antimicrobial, antifouling and antibiofilm. This protein-based nanofilm is robustly transferred and self-adhered on the membrane surface by a simple one-step aqueous coating. The modified RO membrane exhibited good performance in bacterial reduction of ~50% in comparison to the control membrane and experienced almost zero loss in water flux and salt rejection under SWRO testing condition. The membrane is further evaluated with real seawater for 14 days and the modified membrane showed its superiority in flux and fouling control which were verified by the confocal laser scanning microscopy (CLSM) and quantified by inductively coupled plasma optical emission spectrometer (ICP-OES). This work demonstrates that the protein-based biomaterials offer a safe and environmentally friendly way of antimicrobials, which can reduce membrane fouling significantly in membrane filtration. Unlabelled Image • A protein-based antimicrobial nanofilm was in-situ fabricated on a commercial SWRO membrane surface. • The modification did not change the SWRO membrane's selectivity and water permeability. • The modified membrane demonstrated ~50% bacterial reduction compared to the control membrane. • The modified membrane had good anti-fouling property applied in SWRO. [ABSTRACT FROM AUTHOR]

Membrane compaction is commonly observed in polymeric membranes when subjected to elevated hydraulic pressure, but was rarely discussed in forward osmosis (FO) processes, since there was usually little hydraulic pressure difference across the membrane. In the current study, three TFC membranes were fabricated using hollow fiber substrates with varied water permeability to study the effect of the osmotic pressure on the TFC membranes. The TFC membranes were continuously tested in FO experiments for 24 h by using DI water as feed and NaCl solutions of different concentrations as draw solution, and their performances were checked again using fresh feed solutions. At the end of FO experiments, all TFC membranes experienced water flux and salt flux decline to different extents. The TFC membranes were characterized using SEM, TEM and AFM. Visible changes in the cross-section morphology and surface topography of the TFC membranes were observed after FO experiments. The observation suggested that the occurrence of membrane compaction could be associated with "negative pressure" build-up within the support layer of the TFC membranes. The current study could shed light on the important factors that should be considered during membrane fabrication and when establishing the testing protocols for the characterization of FO membrane. Unlabelled Image • The effect of the osmotic pressure on the TFC membrane structure during FO process was studied. • Three hollow fiber substrates with substantially different water permeability values were fabricated for the investigation. • FO tests with AL-DS configuration for 24 h continuously were conducted and membrane autopsy was performed. • All TFC membranes experienced irreversible water flux and salt flux decline in different extents. • The deformation in the polyamide layer and the support layer implied substantial internal stress build-up in the FO tests. [ABSTRACT FROM AUTHOR]