Search

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

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

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

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

This study provides a novel method to enhance boron removal in a forward osmosis (FO) process. It utilizes the reverse solute diffusion (RSD) of ions from alkaline draw solutions (DSs) and the concentration polarization of the hydroxyl ions to create a highly alkaline environment near the membrane active surface. The results show that boron rejection can be significantly enhanced by increasing the pH of NaCl DS to 12.5 in the active-layer-facing-feed-solution (AL-FS) orientation. The effect of RSD enhanced boron rejection was further promoted in the presence of concentration polarization (e.g., in the active-layer-facing-draw-solution (AL-DS) orientation). The current study opens a new dimension for controlling contaminant removal by FO using tailored DS chemistry, where the RSD-induced localized water chemistry change is taken advantage in contrast to the conventional method of chemical dosing to the bulk feed water. [ABSTRACT FROM AUTHOR]

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

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

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 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]

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

The 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]

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]

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

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]

• Thermo-responsive amphiphilic copolymers show high feasibility as FO draw solute. • Key properties of the copolymers used as draw solute strongly depend on their PEO segments. • The copolymers demonstrate a great stability after multiple cycles of regeneration. • Pluronic® L35 DS at 65% can concentrate a SWRO brine at a FO flux of 1.22 L m‒2 h‒1. • Copolymer induced fouling shows insignificant effect on FO with high-salinity feeds. Recently, thermo-responsive nonionic amphiphilic copolymers have shown a great potential as forward osmosis (FO) draw solutes for high-salinity water desalination and zero-liquid discharge (ZLD). However, the relationship between the copolymer structural properties and key characteristics as draw solutes, as well as copolymer's chemical stability after regeneration have not been much studied. In this work, we systematically investigated poly (ethylene oxide)- block -poly (propylene oxide)- block -poly (ethylene oxide) (PEO-PPO-PEO) copolymers as draw solute. The results showed that the PEO segments significantly influenced the viscosity, osmotic pressure and lowest phase separation temperature of the copolymer aqueous solutions. Among four commercial copolymers studied, Pluronic® L35 with moderate molecular weight (Mn 1,900 Da), 50% PEO, and relatively high hydrophilic-lipophilic balance (HLB) showed the best draw solution (DS) performance. It also showed great stability in physiochemical properties and draw capacity after more than ten cycles of regeneration. On the other hand, despite the fact that membrane fouling was observed due to the use of copolymer DS, the FO flux (∼1.2 L m‒2 h‒1, as similar with the virgin membrane) was not affected when high-salinity feedwater such as seawater RO brine was applied. Overall, our study has provided a more comprehensive understanding on the characteristics of nonionic amphiphilic copolymer DS and showcased the promise of copolymer-driven FO process in high-salinity water desalination and ZLD. [Display omitted]. [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]

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

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]

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]

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

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

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]

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

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]