Enhanced Water Flux Research Articles

Decreasing ICP of forward osmosis (TFN-FO) membrane through modifying PES-Fe3O4 nanocomposite substrate

This film nanocomposite forward osmosis (TFN-FO) membrane was developed using polyethersulfone-ferrous ferric oxide (PES-Fe3O4) nanocomposite substrate. The results revealed that the porosity and the hydrophilicity of the PES substrate were improved after addition of Fe3O4 nanoparticles (NPs), leading to reducing in structural parameter (S value or S) and water flux enhancement. To fabricate TFN membranes for FO application, a thin polyamide layer was fabricated by interfacial polymerization of m-Phenylenediamine (MPD) and 1, 3, 5-trimesoylchloride (TMC) on the top surface of PES-Fe3O4 nanocomposite substrates. The TFN membrane prepared with 0.2 wt% Fe3O4 NPs showing the most reliable results by exhibiting high water flux and low reverse solute flux. Furthermore, TFN0.2 membrane exhibited significantly higher pure water flux than that of control thin film composite (TFC) membrane in both AL-FS and AL-DS orientation when 10 mM NaCl and Caspian seawater was used as feed solution and 0.5 or 2M NaCl was used as draw solution. This improvement can be attributed to the fact that the S value of TFN0.2 is much lower in comparison to control TFC membrane (0.42 vs 0.78 mm), leading to reduced internal concentration polarization (ICP) effect.

Effect of process parameters on flux for whey concentration with NH3/CO2 in forward osmosis

Increasing flow rate from 150 to 450L/h did not change water flux but further increase to 600L/h decreased it, which were between 2.74 and 4.1L/m2h. Rising flow rate from 150 to 450L/h enhanced final salt flux but rising flow rate to 600L/h caused opposite effect on salt flux and maximized solute resistivity. As temperature of feed was elevated from 20 to 30°C, water flux increased to 7.2L/m2h but changing temperature to 35 and 40°C reduced it. Salt flux was affected from process temperature in similar way as water flux was affected. Higher solute resistivity was obtained at 35 and 40°C. Ascending draw solution concentration from 1 to 2M enhanced water flux to 12L/m2h but its further increase to 4M reduced it. Salt flux did not change linearly and rose to the highest level at 2M draw salt concentration. The highest value of solute resistivity was obtained at 3 and 4M salt concentration. Effect of flow rate, feed temperature and salt concentration on water flux being expressed above was found similar to their effect on effective osmotic pressure difference and solute resistivity. This results show relation of water flux with effective osmotic pressure difference and solute resistivity.Carbohydrates passage from whey to draw solution was not detected but there was passage of other solubles from whey to draw solution. Flow rate of 450L/h, process temperature of 30°C and 2M salt concentration were optimum process conditions for water flux.

Ion exchange resin blended membrane: Enhanced water transfer and retained salt rejection for forward osmosis

To improve the efficiency of forward osmosis (FO) process, Na type ion exchange resin (IER-Na) powders were successfully blended into the support layer of FO membrane, which could introduce extra charged passageway. Consequently, the water flux of 5wt%IER-Na (with 5wt% IER-Na loading) was 1.75 times as large as that of 0wt%IER-Na (with 0wt% IER-Na loading), under the condition for evaluating FO performance (1.5mol/L NaCl as draw solution and de-ionized water as feed solution in AL-DS mode). Notably, the salt rejection was retained above 95.0%. By multi-techniques such as SEM, EDS, ATR-FTIR and the analysis of diffusion coefficients in both polysulfone and IER-Na, it was proved that the enhanced water flux was mainly attributed to the extra charged passageway introduced by IER-Na. Meanwhile, the retained salt rejection was ascribed to the considerable salt rejection of extra charged passageway in IER-Na. This work sheds light on a new perspective in promoting the mass transfer in FO membranes.

Molecular dynamics simulations of water flow enhancement in carbon nanochannels

Fluidic flow in carbon nanochannels or nanopores has shown great application prospects in nanofiltration. Therefore, enhancing water flux while maintaining their filtration property is crucial to further extend their applications. In this work, inspired by the hourglass-shaped aquaporin water channel, we proposed a method to optimize water flux in carbon nanochannels using conical carbon nanochannels. Adopting nonequilibrium molecular dynamics simulations, water flow in a series of conical carbon nanochannels was simulated. The results showed that the conical channel with apex angle of 19.2° (38.9°) had the optimum water flux when water flowed from the base (tip) side to the tip (base) side of the conical channel, and the water flux was nearly twice as the recently developed MoS2 desalination membrane. Then, the physical mechanism for the conical channel optimizing water permeation was revealed through detailed analyses of potential of mean forces, average number of hydrogen bonds and pressure distributions of the simulation systems. Finally, the microscopic water structures in these channels were also analyzed to further rationalize the optimizing mechanism. This work indicates that other than decreasing the membrane thickness, regulating the channel configuration is a more effective method to enhance water permeation rate in channels with limited channel sizes.

Analysis of enhancing water flux and reducing reverse solute flux in pressure assisted forward osmosis process

Pressure assisted osmosis (PAO) has been recently suggested as a way to overcome the current limitations of forward osmosis (FO), since water flux can be increased by additional hydraulic driving force. To validate its feasibility more fundamentally, the effect of hydraulic pressure combined with osmotically driven FO process was evaluated experimentally, and compared with theoretical modeling. Four different FO and NF membranes were selected and their performance characteristics were determined by both RO- and FO-based methods, since PAO is a simultaneous osmotic- and pressure-driven membrane process. The degree of enhancing water flux and reducing reverse solute flux (RSF) in the PAO process clearly differed according to the membrane type and their performance parameters. Modeling PAO performance, using the values of A, B, and S determined from both RO- and FO-based methods, often failed to exactly match experimental observations, particularly for thin film composite (TFC) FO membranes, suggesting that PAO membrane performance parameters are apparently pressure-dependent. Discernible compaction in the support layer of TFC FO membranes was identified and confirmed by FO tests at different operating modes and SEM analysis, partially explaining large variations in S values under pressurized PAO operation and thus resulting large deviation from theoretical predictions.

Fabrication and water desalination performance of piperazine–polyamide nanocomposite nanofiltration membranes embedded with raw and oxidized MWCNTs

Abstract Multiwalled carbon nanotubes (MWCNTs) were exposed to acid solution containing HNO 3 and H 2 SO 4 to synthesis of oxidized MWCNTs and used for preparation of piperazine-based polyamide thin film nanocomposite nanofiltration membrane. Both raw and oxidized MWCNTs were applied in the fabrication of the membranes with four different concentrations of 0.001, 0.002, 0.005, and 0.01 wt. % in the piperazine solution. Salt rejection, permeation, and antifouling properties of unfilled, raw and oxidized MWCNTs embedded membranes were investigated. Water flux for 0.005 wt. % oxidized MWCNTs significantly increased due to this fact that membrane hydrophilicity improved as a result of functionalization of MWCNTs. Contact angle measurements confirmed the improvement of hydrophilicity by adding oxidized MWCNTs to the membranes. Surface SEM and AFM images illustrated that the MWCNTs made surface of the membranes smoother and macro-voids enlargement leads to water flux enhancement. The antifouling properties were investigated using bovine serum albumin (BSA)/salt solution. The results showed that the membranes with a smoother surface had a better resistance against the fouling. The salt rejection performance exhibited that by embedding of the raw MWCNTs and oxidized MWCNTs, improvement in rejecting of Na 2 SO 4 salt can be observed. It could conclude that the addition of both raw and oxidized MWCNTs could improve the desalination performance of the piperazine–polyamide NF membranes.

Performance enhancement of TFC FO membranes with polyethyleneimine modification and post-treatment

In this work, simple and effective second interfacial polymerization (SIP) of thin-film composite (TFC) membranes is performed with polyethyleneimine (PEI) of various molecular weights, in order to improve the separation performance for forward osmosis (FO) applications. Various characterization techniques are employed to examine the modification mechanism. Compared to the control TFC membrane, PEI-modified membranes exhibit higher water permeabilities, acceptable salt rejection and lower fouling propensity. The effects of PEI molecular weight on the membrane morphology and separation performance are investigated systematically with various characterizations. Post-treatment of PEI-modified membranes in alkaline and acidic aqueous solutions is further investigated, and its effects on the FO performance, intrinsic separation properties and antifouling properties of these post-treated membranes are studied. In comparison with pristine PEI-modified TFC membranes, the post-treated TFC membranes show further enhanced water flux and improved anti-fouling properties.

Pressure assisted osmosis using nanofiltration membranes (PAO-NF): Towards higher efficiency osmotic processes

The pressure assisted osmosis (PAO) process has been recently considered as a new strategy to enhance water flux and to limit reverse salt transport (RST), hereby overcoming two critical limitations of forward osmosis (FO) operation through the use of additional pressure on the feed side. With the aim to achieve higher (economically sustainable) fluxes, the use of commercially available nanofiltration (NF) membranes under PAO operating conditions is considered for the first time in this study. When operated under PAO mode, the tested commercial NF membranes clearly outperform the state of the art FO membrane with fluxes up to 36Lm−2h−1 and RST below 0.01gL−1, demonstrating the relative potential of PAO-NF. For flat sheet NF membrane osmotic contribution was minimal due to intense internal concentration polarisation. However, the tested hollow fiber NF membrane allowed for low internal concentration polarisation and exhibited significant flux even in FO operation. However, transmission of salts from feed to draw solutions (forward salt transport, FST) also occurred and was observed to be linearly proportional with the NF top layer rejection. Therefore, it is an important parameter to consider in the membrane selection in addition to the trade-off between large flux and low RST. The PAO-NF concept also proved to be more efficient in terms of water flux than direct NF operation, owing to a small but significant contribution of osmotic pressure. A modelling study demonstrated that further flux enhancement could be obtained through modification of NF membranes support layer to improve the osmotic contribution. These encouraging initial results warrant the need for a more detailed assessment of the long-term operation and energy requirement of the PAO-NF concept for a range of industrial applications.

Improved separation and antifouling properties of thin-film composite nanofiltration membrane by the incorporation of cGO

Poly(piperazine amide) composite nanofiltration (NF) membranes were modified through the incorporation of carboxylated graphene oxide (cGO) in the polyamide layer during the interfacial polymerization (IP) process on the polysulfone (PSF)/nonwoven fabric (NWF) ultrafiltration (UF) substrate membrane surface. The composition and morphology of the prepared NF membrane surface were determined by means of ATR-FTIR, SEM-EDX and AFM. The effects of cGO contents on membrane hydrophilicity, separation performance and antifouling properties were investigated through Water Contact Angle (WCA) analysis, the permeance and three-cycle fouling measurements. The growth model of cGO-incorporated polyamide thin-film was proposed. Compared to the original NF membranes, the surface hydrophilicity, water permeability, salt rejection and antifouling properties of the cGO-incorporated NF membrane had all improved. When cGO content was 100ppm, the MgSO4 rejection of composite NF membrane reached a maximum value of 99.2% meanwhile membrane obtained an obvious enhanced water flux (81.6Lm−2h−1, at 0.7MPa) which was nearly three times compared to the virginal NF membrane. The cGO-incorporated NF membrane showed an excellent selectivity of MgSO4 and NaCl with the rejection ratio of MgSO4/NaCl of approximately 8.0.

Thin-Film Nanocomposite (TFN) Membranes Incorporated with Super-Hydrophilic Metal-Organic Framework (MOF) UiO-66: Toward Enhancement of Water Flux and Salt Rejection.

Zirconiumv (IV)-carboxylate metal-organic framework (MOF) UiO-66 nanoparticles were successfully synthesized and incorporated in the polyamide (PA) selective layer to fabricate novel thin-film nanocomposite (TFN) membranes. Compared to unmodified pure polyamide thin-film composite (TFC) membranes, the incorporation of UiO-66 nanoparticles significantly changes the membrane morphology and chemistry, leading to an improvement of intrinsic separation properties due to the molecular sieving and superhydrophilic nature of UiO-66 particles. The best performing TFN-U2 (0.1 wt % particle loading) membrane not only shows a 52% increase of water permeability but also maintains salt rejection levels (∼95%) similar to the benchmark. The effects of UiO-66 loading on the forward osmosis (FO) performance were also investigated. Incorporation of 0.1 wt % UiO-66 produced a maximum water flux increase of 40% and 25% over the TFC control under PRO and FO modes, when 1 M NaCl was used as the draw solution against deionized water feed. Meanwhile, solute reverse flux was maintained at a relatively low level. In addition, TFN-U2 membrane displayed a relatively linear increase in FO water flux with increasing NaCl concentration up to 2.0 M, suggesting a slightly reduced internal concentration polarization effect. To our best knowledge, the current study is the first to consider implementation of Zr-MOFs (UiO-66) onto TFN-FO membranes.

Fe2O3 nanocomposite PVC membrane with enhanced properties and separation performance

Organic and inorganic mixed matrix membranes are one of the most promising new membrane materials for ultrafiltration (UF) separation applications. In this study, PVC/Fe2O3-mixed UF membranes were fabricated at different nano-Fe2O3 loading levels (0–2wt%) using the phase inversion method. Surface chemical compositions, surface and cross-section morphologies and characteristics, hydrophilicity and mechanical strength of the membranes were characterized using several analytical techniques and instruments such as scanning electron microscopy (SEM), atomic force microscopy (AFM), a contact angle goniometer, dynamic mechanical analyzer (DMA) and a nanoindenter. Membrane performance was also tested in terms of water flux, solute rejection, and anti-fouling characteristics. The experimental results demonstrated that the overall membrane structure was remarkably enhanced with the addition of Fe2O3 nanoparticles up to a loading of 1%. This was due to the membrane's more hydrophilic and smoother surface and a more elongated finger-like structure as well as higher porosity and pore size. The nanoindentation experiments indicated that Fe2O3 incorporation greatly enhanced the hardness of the membranes providing a higher pore integrity degree. However, higher Fe2O3 content caused a nanoparticle aggregation resulting in a decline in the performance of the composite membranes. Compared with the pristine PVC membrane, the membrane containing 1% Fe2O3 exhibited better capabilities such as the enhanced water flux (782L/m2h), higher sodium alginate (SA) rejection rate (91.9%) and better antifouling properties. The PVC/Fe2O3 nanocomposite membranes may have applicable potential in water and wastewater treatment applications based on their low price, enhanced mechanical strength, high permeability, high removal efficiency, and good antifouling performance.

Enhancing the performance of thin-film nanocomposite nanofiltration membranes using MAH-modified GO nanosheets

In this work, novel thin-film nanocompostie NF membranes were developed through modification with maleic anhydride functionalized graphene oxideviainterfacial polymerization, which showed the enhanced water flux with retaining high salt rejection.

Liquid desiccant lithium chloride regeneration by membrane distillation for air conditioning

Abstract Liquid desiccant air conditioning (LDAC) has emerged as an attractive technology for improving indoor air quality and thermal comfort. Regeneration of liquid desiccants is critical to sustain the process efficiency of LDAC. This study explores membrane distillation (MD) for regeneration of lithium chloride (LiCl) desiccant solution commonly used in LDAC. The results demonstrate the viability of MD for LiCl regeneration. The MD process at the feed temperature of 65 °C could increase the LiCl concentration up to 29 wt.% without any observable LiCl loss. Given the high concentration of the LiCl solution feed, unlike traditional desalination applications, the impact of concentration polarisation on the process water flux was significant. Indeed, the calculated water flux obtained by excluding the concentration polarisation effect was more than twice the experimentally measured water flux from a concentrated LiCl solution (>20 wt.%). The regeneration process can be optimised in terms of regeneration capacity (ΔC) and specific thermal energy consumption (α) by regulating several operating conditions, including LiCl concentration, feed temperature, and circulation cross flow velocity. Increasing feed temperature and circulation cross flow velocity was beneficial to the process efficiency, enhancing water flux and ΔC while reducing α. On the other hand, increasing LiCl concentration resulted in a linear decrease in both water flux and ΔC, but an increase in α following a hyperbolic function.

Sulfonated multiwall carbon nanotubes assisted thin-film nanocomposite membrane with enhanced water flux and anti-fouling property

Sulfonated multiwall carbon nanotube (SMWCNT) with pendant alkyl sulfonic acid groups was synthesized from hydroxyl-functionalized multiwall carbon nanotube (MWCNT-OH). Small changes in microstructure, due to nucleophilic substitution reaction, were confirmed by X-ray photoelectron spectroscopy, transmission electron microscopy, and N2 adsorption-desorption measurements. Prepared SMWCNT exhibited excellent water dispersity, which facilitated interfacial polymerization to prepare novel poly(piperazine amide) thin-film nanocomposite (TFN) membranes. Water flux and salt rejections of the TFN membranes were readily adjusted by optimizing the SMWCNT content, to get most optimum separation performance. TFN-0.01% showed high water flux of 13.2Lm−2h−1bar−1, 1.6 times more than the pristine thin-film composite (TFC) membrane, maintaining reasonably high rejection of 96.8% to Na2SO4. TFN-0.01% membrane, with enhanced surface hydrophilicity exhibited better anti-fouling ability to bovine serum albumin with water flux recovery ratio as high as 91.2%, even after two “fouling-washing” cycles, compared to 82.0% for TFC membrane.

Novel Thin Film Composite Forward Osmosis Membranes of Highly Enhanced Water Flux with Interlayer Polysiloxane Between Polysulfone and Polyamide

Novel Thin Film Composite Forward Osmosis Membranes of Highly Enhanced Water Flux with Interlayer Polysiloxane Between Polysulfone and Polyamide

Novel thin film composite forward osmosis membrane of enhanced water flux and anti-fouling property with N-[3-(trimethoxysilyl) propyl] ethylenediamine incorporated

In this work, novel thin film composite (TFC) forward osmosis (FO) membranes are developed via interfacial polymerization on the polyacrylonitrile (PAN) substrate, using an organic-inorganic hybrid compound – N-[3-(trimethoxysilyl) propyl] ethylenediamine (NPED) as the amine monomer to mix with m-phenylenediamine (MPD). The PAN substrate was modified with sodium hydroxide and optimized by varying the hydrolyzation time. With the incorporation of NPED in the selective layer, the formed TFC membrane exhibits better hydrophilicity, improved water flux and fouling resistance, and therefore superior membrane performance. By varying the NPED content in the aqueous phase, the surface properties and performance of TFC membranes are investigated with various characterizations. In addition, the anti-fouling properties of the TFC membranes with different NPED content in the aqueous monomer are also studied.

Performance enhancement of polyvinyl chloride ultrafiltration membrane modified with graphene oxide

A novel polyvinyl chloride (PVC) membrane was modified with graphene oxide (GO) via phase inversion method to improve its hydrophilicity and mechanical properties. The GO presented a large amount of hydrophilic groups after the modification through the modified Hummers method. It was observed that with the addition of low fraction of GO powder, the GO/PVC hybrid membranes exhibited a significant enhancement in hydrophilicity, water flux, and mechanical properties. With optimal dosage (0.1wt%), the pure water flux of GO/PVC membrane increased from 232.6L/(m2hbar) to 430.0L/(m2hbar) and the tensile strength increased from 231.3cN to 305.3cN. The improved properties of the PVC/GO hybrid membranes are mainly attributed to the strong hydrophilicity of functional groups on the GO surface, indicating that GO has a promising candidate for modification of PVC ultrafiltration membranes in wastewater treatment.

Evolution of micro-deformation in inner-selective thin film composite hollow fiber membranes and its implications for osmotic power generation

Since thin film composite (TFC) hollow fiber (HF) membranes may experience micro-deformation under high hydraulic pressures in the pressure retarded osmosis (PRO) process due to their polymeric nature and self-supported configuration, this paper aims to elucidate (1) the micro-deformation of polyethersulfone (PES) TFC HF membranes within the pressure range from 0 to 20bar and (2) its effects on water and salt permeability of the polyamide layer, and structure parameter and tortuosity of the substrate layer for osmotic power generation. It is found that pre-stabilization of the TFC HF membranes at a high pressure close to their burst pressures for a certain period of time is a powerful way to maximize their PRO performance. After stabilization at 20bar for 30min, the power density of the PES TFC HF membranes increase from 15.37 to 22.05W/m2 due to the increased membrane surface area, stretched polyamide selective layer (i.e., decreased water transport length and resistance) and decreased membrane structure parameter (i.e., lower tortuosity and internal concentration polarization (ICP)). The intermittent cycle tests have confirmed the sustainability of the enhanced water flux and power density after stabilization of the TFC HF membranes at 20bar without compromising their selectivity.

Thin-film composite membrane on a compacted woven backing fabric for pressure assisted osmosis

The water flux in forward osmosis (FO) process declines substantially when the draw solution (DS) concentration reaches closer to the point of osmotic equilibrium with the feed solution (FS). Using external hydraulic pressure alongside the osmotic driving force in the pressure assisted osmosis (PAO) has been found effective in terms of enhancing water flux and even potentially diluting the DS beyond osmotic equilibrium. The net gain in water flux due to the applied pressure in the PAO process closely depends on the permeability of the FO membrane. The commercial flat sheet cellulose triacetate (CTA) FO membrane has low water permeability and hence the effective gain in water flux in the PAO process is low. In this study, a high performance thin film composite membrane was developed especially for the PAO process through casting polyethersulfone (PES) polymer solution on a compacted woven fabric mesh support followed by interfacial polymerisation for polyamide active layer. This PAO membrane possesses a water flux of 37Lm2h−1 using 0.5M NaCl as DS and deionised water as the feed at an applied hydraulic pressure of 10bar. Besides, the membrane was able to endure the external hydraulic pressure required for the PAO process owing to the embedded backing fabric support. While the membranes with low structural parameters are essential for higher water flux, this study shows that for PAO process, polymeric membranes with larger structural parameters may not be suitable for PAO. They generally resulted in compaction and poor mechanical strength to withstand hydraulic pressure.

Direct incorporation of silver nanoparticles onto thin-film composite membranes via arc plasma deposition for enhanced antibacterial and permeation performance

We report on a new technique that incorporates silver nanoparticles (AgNPs) onto polyamide (PA) thin film composite (TFC) reverse osmosis membranes via arc plasma deposition (APD) to impart antibacterial properties and simultaneously improve membrane performance. APD allows the direct deposition of AgNPs under vacuum dry condition, overcoming the drawbacks of the conventional wet-chemical methods. AgNPs (~7.6nm in diameter) were uniformly distributed without aggregation throughout the PA selective layer with some partially implanted into the PA matrix. Ag loading could be tuned by simply adjusting the number of APD purse shots. The deposited AgNPs exhibited good leaching stability, presumably due to the strong Ag-PA chemical interaction and partially buried AgNP morphology. The resulting Ag-incorporated TFC (Ag-TFC) membrane showed the strong and long-lasting antibacterial properties for both gram-negative and -positive bacteria. Simultaneously, the Ag-TFC membrane exhibited an enhancement in water flux of approximately 40% without deterioration in NaCl rejection. These performance changes were tentatively attributed to the partial destruction of the PA layer under the high energetic APD condition along with the increased membrane hydrophilicity. Hence, the APD process provides a simple and effective route to modify membranes with functional NPs.