Enhanced Water Flux Research Articles

Molecular Layer‐by‐Layer Assembled Thin‐Film Composite Membranes for Water Desalination

Molecular layer-by-layer (mLbL) assembled thin-film composite membranes fabricated by alternating deposition of reactive monomers on porous supports exhibit both improved salt rejection and enhanced water flux compared to traditional reverse osmosis membranes prepared by interfacial polymerization. Additionally, the well-controlled structures achieved by mLbL deposition further lead to improved antifouling performance.

A novel membrane showing both hydrophilic and oleophobic surface properties and its non-fouling performances for potential water treatment applications

Membrane organic and biological fouling has been one of the major problems for membrane technology applications in water and wastewater treatment. In this study, a novel membrane showing both hydrophilic and oleophobic surface properties was developed and evaluated for its resistance against organic and biological fouling. The membranes in flat sheet configuration were prepared from PVDF as the base matrix polymer, blended with an additive polymer that was synthesized to contain both hydrophilic and oleophobic segments. The prepared novel membranes displayed high affinity to water but low affinity to oil. Experimental results from the filtration of protein solution, humic acid solution and oil/water emulsion confirmed that the developed membranes had greatly enhanced water flux and reduced organic fouling performance (shown as slow flux decay and high flux recovery after membrane cleaning). In the biofouling tests with the developed membranes being immersed in bacteria suspension or used for the filtration of bacteria suspension, it was found that the novel membranes effectively prevented bacteria adhesion on the membrane and the flux decay incurred during the filtration can be fully recovered after a simple cleaning with water under the experimental conditions. This study also demonstrated that a membrane surface showing both hydrophilic and oleophobic surface properties provided an effective and better way to reduce the effect of membrane fouling by organic as well as biological foulants than a membrane surface showing the hydrophilic property only. The developed membrane has a great potential for water and wastewater treatment applications.

Hydrophilic Nanofibers as New Supports for Thin Film Composite Membranes for Engineered Osmosis

Engineered osmosis (e.g., forward osmosis, pressure-retarded osmosis, direct osmosis) has emerged as a new platform for applications to water production, sustainable energy, and resource recovery. The lack of an adequately designed membrane has been the major challenge that hinders engineered osmosis (EO) development. In this study, nanotechnology has been integrated with membrane science to build a next generation membrane for engineered osmosis. Specifically, hydrophilic nanofiber, fabricated from different blends of polyacrylonitrile and cellulose acetate via electrospinning, was found to be an effective support for EO thin film composite membranes due to its intrinsically wetted open pore structure with superior interconnectivity. The resulting composite membrane exhibits excellent permselectivity while also showing a reduced resistance to mass transfer that commonly impacts EO processes due to its thin, highly porous nanofiber support layer. Our best membrane exhibited a two to three times enhanced water flux and 90% reduction in salt passage when compared to a standard commercial FO membrane. Furthermore, our membrane exhibited one of the lowest structural parameters reported in the open literature. These results indicate that hydrophilic nanofiber supported thin film composite membranes have the potential to be a next generation membrane for engineered osmosis.

Significantly enhanced water flux in forward osmosis desalination with polymer-graphene composite hydrogels as a draw agent

We report here a new strategy to dramatically increase water flux in a forward osmosis (FO) process using reduced graphene oxide (rGO)-composite hydrogels as draw agents as well as increasing the rate of the subsequent regain of pure water from the hydrogel particles. The composite hydrogels were prepared by incorporating 0.3 wt%–3 wt% rGO into two different hydrogels: poly(sodium acrylate) (PSA) and poly(sodium acrylate)-poly(N-isopropylacrylamide) (PSA-NIPAM). The amount of incorporated rGO sheets had a significant effect on the swelling pressure of the composite hydrogels and the composite hydrogels with contained small amounts of rGO sheets (0.3–1.2 wt%) showed significantly enhanced swelling ratios while those with more rGO (e.g., 3 wt%) exhibited decreased swelling ratios. Consequently, significant enhancements in water flux in the FO process were achieved for composite hydrogels with small amounts of rGO. When compared with the pure hydrogels, the composite hydrogels PSA-1.2 wt% rGO and PSA-NIPAM-1.2 wt% rGO showed increased water fluxes of some 310% and 227%, respectively, when 2000 ppm of a NaCl aqueous solution was used as the feed. When deionized water was used, even higher water fluxes were attained, i.e., 8.2 L m−2 h−1 for PSA-1.2 wt% rGO and 6.8 L m−2 h−1 for PSA-NIPAM-1.2 wt% rGO. The swelling process of the particles was investigated using optical microscopy where it was found that the addition of small amounts of rGO greatly increased the softness of the composite hydrogels and improved the inter-particle and particle-membrane contact, leading to dramatically improved water fluxes. In addition, the light-absorbing property of rGO produced much better outcomes in terms of dewatering of the composite hydrogels in the second stage of the FO process, in which the pure water from the hydrogels is harvested, with dewatering stimulated by heating induced from absorbed solar energy. The water recovery rate for composites with 1.2 wt% rGO was found to be twice as fast as that for pure hydrogels.

Accelerating water transport through a charged SWCNT: a molecular dynamics simulation

The properties of a nanotube, such as the hydrophobicity and charge of the surface, can significantly affect water transport behavior. However, our knowledge of the effects of charge density, dipole orientation, frequency of flipping, and movement behavior on water flow through carbon nanotubes (CNTs) is far from adequate. This study is aimed at gaining insight into the transport of single-file water molecules in a charged carbon nanotube. It was shown that the water chains inside the charged nanotube exhibit bipolar properties. The water dipoles are parallel to the z-axis, and point toward (D-defect) and away from (L-defect) the center of the nanotube for a negatively charged nanotube and a positively charged one, respectively. Compared with a pristine single-wall carbon nanotube (SWCNT), the charged nanotubes, including both positively charged and negatively charged, favor the water-filling process due to electrostatic interactions. According to the dipole distribution in the nanotube, the water dipole only flips in the middle region because of the bipolar nature of water chains. Additionally, flipping of the entire water chain is inhibited, which allows for the enhanced water flux. A negatively charged single-walled carbon nanotube (N-SWCNT) accelerated water transport by tuning the single-file flow from a "hopping" to a "continuous" mode, thus decreasing the energy barrier. The hydrogen bonds between water molecules inside the nanotube are also strengthened in the negatively charged nanotube, favoring water transport. Any distortion of uniformity will lead to additional energy barriers to water flux. Our results provide a comprehensive view of molecular events underpinning the water transport inside a SWCNT, which may be of assistance in creating innovative designs for water nanochannels.

Highly water‐selective mixed matrix membranes from natural rubber‐blend‐poly(acrylic acid) (NR‐blend‐PAA) incorporated with zeolite 4A for the dehydration of water–ethanol mixtures through pervaporation

AbstractThe mixed matrix membranes (MMMs) were developed from a composite of hydrophobic‐hydrophilic NR‐blend‐PAA with zeolite 4A. A separation performance of the MMMs was investigated by performing the pervaporation dehydration of water–ethanol mixtures. The results showed a dramatically greater flux of water than the ethanol flux indicating that the developed membranes were highly water‐selective. Upon incorporating of zeolite 4A, the flux and separation factor were significantly improved. Increasing the water content in the water–ethanol feed mixtures resulted in an increase in both water and ethanol fluxes leading to a decrease in water separation factor. Similarly a flux‐separation factor trade‐off was observed as raising feed temperature. The water permeance, however, declined when either the feed water concentration or the feed temperature increased. This suggests that the driving force, i.e. the partial pressure difference, has a pronounced effect on the water flux enhancement. Conversely, the driving force was less influential on the ethanol permeance. The activation energies of the permeations obtained from the Arrhenius plots, showed the lower activation energies of water permeation than those of ethanol permeation; this is because water molecules experiences less restrictive passage through the membranes compared with ethanol molecules. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effect of modified TiO2 nanoparticles on the polyethersulfone ultrafiltration hollow fiber membranes

Addition of nanoparticles to polymer solution in membrane fabrication process has the potential to improve membrane separation performance. Recently, the mechanical and chemical modifications of TiO2 nanoparticles have shown to provide improvements in reducing the nanoparticles agglomeration and fouling in flat sheet membranes. In this study, hollow fiber PES membranes with 2wt.% mechanically and chemically modified TiO2 were fabricated. The effect of chemical and mechanical modifications on the titania nanoparticles was compared with the effect of mechanical modification only and membranes without nanoparticles additives. The results showed that the migration of nanoparticles toward outer layer only occurred after mechanical modifications, whereas the migration and size of agglomerations reduced significantly after both the chemical and mechanical modifications of particles. Higher thermal resistance, stiffness and lower elasticity were observed in fibers made with chemically and mechanically modified particles. Enhancement in initial pure water flux due to lower intrinsic membrane resistance and bigger pore size was also observed. While the rejection of BSA remained similar and lower overall ultrafiltration resistance was observed, the benefits of particles modifications on flux recovery after cleaning of hollow fiber membranes was not observed, possibly due to a significant change in pore structure and initial permeabilities.

Amphiphilic poly(acrylonitrile‐co‐acrylic acid)/silver nanocomposite additives for the preparation of antibiofouling membranes with improved properties

AbstractThis work focuses the preparation of polymer‐silver nanocomposite (Ag‐Nc) dense free standing films and nonwoven fabric supported porous ultrafiltration membranes with improved membrane performance and long‐term antibiofouling properties. New polyacrylonitrle‐based Ag‐Ncs, poly(acrylonitrle‐co‐acrylic acid)‐silver (PAN‐co‐PAA‐Ag) containing 35 wt% of PAA and 0.35–0.65 wt% of Ag‐nanoparticles (Nps) were synthesized and used as additives for the fabrication of PAN‐based (PAN/PAN‐co‐PAA‐Ag) Ag‐Nc porous membranes and dense‐free standing films. The Ag‐Nps were homogeneously dispersed into the PAN‐co‐PAA random copolymer matrix. The prepared membranes (PAN/PAN‐co‐PAA‐Ag) showed combination of properties such as excellent antimicrobial activity towards both Gram Negative and Gram Positive bacteria (prevent biofilm formation), improved protein antifouling properties, and enhanced water flux when compared to neat PAN‐based membrane. The antimicrobial properties, hydrophilicity, and the water flux of various membranes follow the following order for the membranes PAN < PAN/PAN‐co‐PAA < PAN/PAN‐co‐PAA‐Ag. Extraneous addition of small amount of polyethylene glycol (PEG) during preparation of additive i.e. [PEG + PAN‐co‐PAA]‐Ag further improved the protein antifouling properties of the PAN‐based membranes (PAN/[PEG+PAN‐co‐PAA‐Ag]). The dispersed Ag‐Nps were stable on the surface of phase inverted membranes for long period of time and PAN/PAN‐co‐PAA‐Ag membranes are therefore suitable for long‐term water treatment under bacterial environment. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Bioengineering and subjective approaches to the clinical evaluation of dry skin

Dry skin (also known as xerosis) is a cutaneous reaction pattern indicative of abnormal desquamation, which has not only cosmetic considerations, but can also lead to the penetration of irritants and allergens through the stratum corneum (SC). Over the last few decades, our understanding of the structure, composition, formation and function of the SC has advanced tremendously; however, despite these advancements, the occurrence of dry skin remains prevalent in the adult population. The clinical evaluation of dry skin is therefore of significant importance to the cosmetic industry not only for understanding the condition but also for measuring the effects of treatment. Traditionally, dry skin has been evaluated by visual inspection, however, recently a variety of bioengineering techniques have emerged enabling the investigator to objectively assess the extent of xerotic conditions. The most frequently employed methods for the evaluation of dry skin are discussed in this review, including regression testing, squametry, measurement of transepidermal water loss, epidermal hydration, profilometry, confocal Raman spectroscopy, optical coherence tomography, in vivo confocal microscopy and magnetic resonance imaging.

Theoretical studies on structural and electrical properties of PES/SPEEK blend nanofiltration membrane

AbstractPolyethersulfone (PES) nanofiltration membranes were prepared using a simple dry‐jet wet spinning technique with different contents of sulfonated poly(ether ether ketone) (SPEEK) ranging from 0 to 4 wt %. The structural parameters (rp and Ak/Δx) and electrostatic properties (ξ and X) of the blend membranes were deduced by employing the combination of irreversible thermodynamic model, steric hindrance pore (SHP) model, and Teorell‐Meyer‐Sievers (TMS) model. The modeling results obtained have been analyzed and discussed. The mean pore radius and pore size distribution of the blends were also determined based on the theoretical models. The results showed that pore radius increased with increasing the concentration of SPEEK from 0 to 2 wt % but decreased with a further increase in SPEEK content. The water flux, however, showed a systematically increase with increasing SPEEK content. The SPEEK also showed significant effect on membrane electrical properties. Both effective charge density and ratio of effective charge density to electrolyte solution increased with increasing concentration of SPEEK in the dope solution, reaching a value of −21.02 and −2.29, respectively. The pore radius which was determined by using different transport models has also been analyzed and discussed. It is found that the addition of SPEEK into dope solution is one of the paramount parameters in developing the negatively charged nanofiltration membrane with enhanced water flux while retaining the pore radius in the nanometer range. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Formation of appropriate sites on nanofiltration membrane surface for binding TiO 2 photo-catalyst: Performance, characterization and fouling-resistant capability

Titanium dioxide (TiO 2) nanoparticles were assembled on the surface of nanofiltration blend membrane. For settling TiO 2 on the membrane surface, two membrane categories were used: (i) unmodified polyethersulfone (PES)/polyimide (PI) blend membrane, and (ii) –OH functionalized PES/PI blend membrane with different concentrations of diethanolamine (DEA). These membranes were radiated by UV light after TiO 2 depositing with different concentrations. 15 min immersion in colloidal suspension and 15 min UV irradiation with 160 W lamps were used for modification. The modification resulted in the formation of a photo-catalytic property with enhanced membrane hydrophilicity. The self-assembly of TiO 2 nanoparticles was established through coordinance bonds with –OH functional groups on the membrane surface. A comparison between the UV irradiated TiO 2 deposited blend membrane and deposited-functionalized blend membranes showed that –OH groups originate excellent adhesion of TiO 2 nanoparticles on the membrane surface, increase reversible deposition, and diminish irreversible fouling. The membranes were characterized using SEM, FTIR, EDX, contact angle, cross flow filtration, and antifouling measurements. SEM images show that the presence of –OH groups on the DEA-modified membrane surface is the main parameter for extra uniformly settlement of TiO 2 nanoparticles on the membrane surface. This procedure is a superior technique for modification of PES/PI nanofiltration membranes to enhance water flux and minimization membrane fouling.

Enhanced Water Permeation of Reverse Osmosis through MFI-Type Zeolite Membranes with High Aluminum Contents

MFI-type zeolite membranes with different Si/Al ratios were synthesized by seeding and secondary growth. Several factors including alkalinity, synthesis time, and Si/Al ratio were varied to optimize the synthesis conditions. Ion separation of 0.10 M NaCl solution by zeolite membranes was investigated through a cross-flow reverse osmosis system. The aluminum content was found to play an important role in zeolite growth and reverse osmosis separation performance afterward. Membrane hydrophilicity and surface charge measured by the contact angle and particle ζ-potential were found to be strongly dependent on the aluminum composition of the membranes. Both water flux and ion rejection increased considerably as aluminum ions were incorporated into the zeolite framework with a water flux increase from 0.112 to 1.129 kg/m2·h and ion rejection improvement from 90.6% to 92.9%. The enhancement in ion separation and water flux for high aluminum ZSM-5 membranes was further analyzed by enhanced water affinity on the membrane surface and restricted ion permeation in confined spaces.

Characterization of membrane distillation modules and analysis of mass flux enhancement by channel spacers

The first aim of this work is to present a method in order to characterize a direct contact membrane distillation (DCMD) module, namely a method to determine the value of the parameters included in a commonly accepted transport model. The model includes membrane and module design characteristic parameters which have the same values regardless of feed used. The characterization method proposed here, includes DCMD measurements (both, water flux and evaporation efficiency measurements) using pure water as feed, and air–liquid displacement measurements. The latter are used to extract previous structural information about the membrane used. The method is applied to characterize two DCMD modules with different designs. The first module has open flow channels while the second one includes a spacer within the flow channels. The transport model together along with the obtained characteristic parameter values adequately predicts the water flux measured with both modules when different operating conditions were imposed and aqueous solutions of different solutes were used as feed. The results given here are for NaCl and sucrose feed solutions. They show that the membrane distillation performance is highly dependent on the design of membrane module, the specific separation being performed and the operating conditions (besides membrane characteristics). The second aim of this work is to study the water flux enhancement induced by the improvement of the fluid-dynamic conditions within the module with spacer in relation to the module with open channels. The dependence of flux enhancement on operating conditions (average temperature, temperature difference between feed and permeate solutions, type of solute, and feed concentration) is analysed. In the range of operating variables studied, the systems with high vapour pressure polarization have water fluxes especially sensitive to the fluid-dynamic changes induced by the spacer.

Coupled membrane process applied to fruit juice concentration

AbstractA coupled membrane process of membrane distillation and osmotic evaporation, where the solutions were thermostated separately at different temperatures, was developed. Enhanced water flux was obtained since the total driving force of the coupled process was higher than the sum of the driving forces of single processes. Apple, raspberry, sour cherry, red, and black currant juices were concentrated by the novel, mild technique.

Enhanced water flux in fruit juice concentration: Coupled operation of osmotic evaporation and membrane distillation

The coupled operation of osmotic evaporation (OE) and membrane distillation (MD) for concentration of fruit juices was studied. Both membrane processes were applied in a way where both solutions in the membrane contactor were thermostated separately at different temperatures: the osmotic solution was the cold side, while the aqueous solution to be concentrated was the warm side (heated). The experiments have proven that the driving forces were added, which resulted in enhanced water flux during the operation, thus the coupled process is more effective.

001 Stabilité du rythme nycthéméral de la pression intra-oculaire chez l’homme

A thin-film composite (TFC) membrane with a functionalized carbon nanotubes (fCNT) blended support layer (fTFC) was successfully synthesized by phase inversion method and interfacial polymerization. fTFC membrane was characterized and compared with TFC bare membrane to investigate the effect of fCNT on membrane performance. The fTFC membrane showed enhanced water permeability due to its increased hydrophilicity, enhanced pore properties of the support layer without sacrificing NaCl rejection compared to that of the TFC bare membrane. The fTFC membrane showed a 10–20% enhanced water flux in the seawater reverse osmosis (SWRO) at pressures over 50 bar, and a 90% enhanced water flux in the brackish water reverse osmosis (BWRO) operating pressure at 30–40 bar. Moreover, the fTFC membrane exhibits higher organic fouling resistance compared to the TFC bare membrane due to the 50% higher initial water flux and more negative surface charged surface.

Positron Annihilation Spectroscopic Evidence to Demonstrate the Flux-Enhancement Mechanism in Morphology-Controlled Thin-Film-Composite (TFC) Membrane

In this study, positron annihilation lifetime spectroscopy (PALS) is applied to explain the flux-enhancement mechanism in thin-film-composite (TFC) membranes prepared by using dimethyl sulfoxide (DMSO) as an additive in the interfacial polymerization. The TFC membranes show a large increase in water flux, up to 5-fold, compared to nonadditive membrane. Atomic force microscopy (AFM) shows that surface roughness and surface area increase when DMSO in the aqueous phase solution phase works to increase miscibility of the aqueous and the organic phase by reducing the solubility difference of two immiscible solutions. X-ray photoelectron spectroscopy (XPS) reveals the variation of the chemical compositions to the extent that there is a considerable increase in the cross-linked amide linkages of the flux-enhanced TFC membranes. The effects of these structural changes on the molecular-size free volume properties are evaluated by PALS studies. The PALS results are the first to experimentally show that the thin films of cross-linked aromatic polyamide RO membranes are composed of two types of pores having radii of about 2.1-2.4 A from tau3, network pore, and 3.5-4.5 A from tau4, aggregate pore. The increase in the size and number of network pores by means of DMSO addition during interfacial polymerization enhances the water flux notably. The size of aggregate pores also increases and may contribute to enhance water flux, although their number inevitably decreases as the number of network pores becomes increased. Details on the correlations between RO performances and o-Ps lifetime parameters are clearly described based on the pore-flow model of reverse osmosis developed by Sourirajan et al.

Effects of bioturbation by the lugworm Arenicola marina on cadmium uptake and distribution in sandy sediments

The effect of bloturbation by the lugworni Arenicola marina on uptake and distribution of cadnxum in sediment was assessed using laboratory sediment cores. Carner-free was added to the water phase each day. Bioturbation (irrigation) was measured using bromide (Br-) as a tracer for water movement. In cores without lugworms all Cd was found in the surface sediment where it continued to build up over 16 d of exposure. In cores containing lugworms a distinct peak of Cd was found both at the sediment surface and, after a few days, at the feeding pocket of the worm (10 to 15 cm depth). During the 16 d of exposure this subsurface: peak broadened and eventually Cd was found in all depths from top to feeding depth of the indiv~dual worm. Compared to sediment cores without worms, the presence of lugxeorms more than doubled the rate of removal of Cd from water to sediment. Thls was attributed to an ~ncreased turnover of sediment (due to feeding activity), an increased sediment surface area (due to fecal casts, head shaft, tube and irrigation of the whole burrow) and an increased contact of Cd-labelled water with potential binding sites in the sediment due to irrigation Exposure to 1 ppm Cd reduced the fract~onal ratcl at which lugworms removed Cd from the water (as 'F of Cd in the water). The total Cd flux to the sediment, however, was much greater due to the h g h e r Cd concentrations in the water Water fluxes estimated using Bras a solute tracer revealed a 10to 20fold increase in water exchange of the sediments when lugworms were present. This enhanced water flux was not affected by exposure of lugworms to 1 ppm Cd. The results indicate that the presence of bioturbating infauna influences both the uptake rates of trace metals in near-shore sediments and the distribution of those metals.

New techniques for extreme conditions: high temperature reverse osmosis and nanofiltration

New techniques for operating spiral-wound membranes at temperatures as high as 90°C have been welcomed by users in the pharmaceutical, biotech, electronics, power plant, food production, and similar industries. The performance characteristics of Duratherm® reverse osmosis, nanofiltration, and ultrafiltration elements at high temperature are described. The advantages include hot water sanitizing, flux enhancement, and heat recovery. Process economics are reviewed.

Temperature-Dependent Water and Ion Transport Properties of Barley and Sorghum Roots : II. Effects of Abscisic Acid

Water flux through excised roots (J(v)) is determined by root hydraulic conductance (L(p)) and the ion flux to the xylem (J(i)) that generates an osmotic gradient to drive water movement. These properties of roots are strongly temperature dependent. Abscisic acid (ABA) can influence J(v) by altering L(p), J(i), or both. The effects of root temperature on responses to ABA were determined in two species differing in their temperature tolerances. In excised barley (Hordeum vulgare L.) roots, J(v) was maximum at 25 degrees C; 10 micromolar ABA enhanced J(v), primarily by increasing L(p), at all temperatures tested (15-40 degrees C). In sorghum (Sorghum bicolor L.) roots, J(v) peaked at 35 degrees C; ABA reduced this optimum temperature for J(v) to 25 degrees C by increasing L(p) at low temperatures and severely inhibiting J(i) (dominated by fluxes of K(+) and NO(3) (-)) at warm temperatures. The inhibition of K(+) flux by ABA at high temperature was mostly independent of external K(+) availability, implying an effect of ABA on ion release into the xylem. In sorghum, ABA enhanced water flux through roots at nonchilling low temperatures but at the expense of tolerance of warm temperatures. These effects imply that ABA may shift the thermal tolerance range of roots of this heat-tolerant species toward cooler temperatures.