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Abstract Several fouling indexes, such as silt density index (SDI), have been applied in the reverse osmosis (RO) process to predict the fouling tendency, design the pretreatment process, and optimize the cleaning cycles. However, the forward osmosis (FO) process has no reliable method, as yet, that relates fouling with its performance. This study utilized the concept of fouling reversibility to develop a fouling index for the FO process simulation. The osmotically driven reversibility index (ORI) was determined by measuring the flux recovery after the physical cleaning or flushing cycle. The protocols of ORI measurement were developed systematically by determining the proper operation mode, cross-flow velocity for physical cleaning, and draw solution type and concentration. The applicability of ORI was examined by investigating the FO process in treating secondary effluents from various full-scale wastewater treatment plants. The results demonstrated that the normalized final flux by fouling in FO was closely correlated to the ORI measurements with high statistical reliability (R2 = 0.84). After conducting a long-term stable FO operation, it is deduced that the ORI is a useful evaluation parameter for continuous FO and its cleaning cycles in which periodic flushing is normally utilized to exploit and enhance the fouling reversibility of FO. Graphical abstract fx1 Highlights • An osmotically-driven reversibility index (ORI) was developed for FO process. • ORI simulates FO fouling reversibility and its operational protocol was constructed. • High correlation of ORI and FO fouling was obtained using various real wastewaters. • ORI is a useful evaluation parameter for continuous FO and its cleaning cycles. [ABSTRACT FROM AUTHOR]

Although pristine graphene oxide (GO)-based membranes have previously demonstrated promising molecular separation due to their well-defined interlayer spacing, their applications in water processing operations remain limited due to the natural swelling tendency of GO in the aqueous phase which decreases separation ability. In this work, pristine GO laminate has been successfully integrated into a highly crosslinked network to produce membranes with anti-swelling behaviour and excellent desalination capability. The process of free-radical polymerisation in aqueous conditions of a GO suspension enables the formation of a GO-polymer network without covalent bonding between GO and polymer, leading to a combination of mechanical robustness, remarkable water transport properties, and an anti-swelling tendency suitable for the high-pressure operation required for reverse osmosis (RO) membrane process. The resulting GO-polymer membrane was not swollen during RO operation while it was stable under a harsh oxidising environment. It also demonstrated water flux of 33.5 L m −2 h −1 with 98.5% NaCl rejection at 10 bar when prepared by high-vacuum filtration and subsequent polymerisation of the precursor solution on to a mesoporous substrate. This methodology makes large-scalable membrane fabrication very feasible. [ABSTRACT FROM AUTHOR]

Artificial neural network (ANN) models were developed from a six-year process database to quantify causes of membrane fouling in the first stage of a full-scale, three-stage reverse osmosis (RO) system. The data comprised 59 hydraulic and water quality parameters, representing 190 runs between membrane cleanings. The runs were segmented into a Phase 1 period of initial particle deposition followed by a Phase 2 period of gradual biofilm and scale growth. The phases were modeled separately. Rather than specific flux, a fouling indicator P foul ′ was calculated from RO system pressures which are normally modulated in part to compensate for fouling. The ANN modeling found that the best predictors of Phase 1 fouling were total chlorine, electrical conductance, TDS, ammonia, and the cartridge filter pressure drop. The best predictors of Phase 2 fouling were turbidity, nitrate, organic nitrogen, nitrite, and total chlorine. These results are consistent with known Phase 1 and 2 fouling mechanisms. The predictive electrical conductance, TDS, and turbidity are “bulk” water quality parameters which were found significantly correlated to sparsely measured cations, sulfates, chlorides, and alkalinity. Simulations with different chlorine concentrations demonstrate how the model could be used to reduce fouling rates. [ABSTRACT FROM AUTHOR]

In this study, the anti-fouling ability of coating ultrafiltration (UF) and reverse-osmosis (RO) membranes with a block copolymer of polystyrene (PS) bound to an alternating lysine–glutamic acid peptide PS-b-(KE) 15 ) was analyzed. The PS-b-(KE) 15 coating had no effect on membrane permeability. Membrane fouling experiments were conducted with extracellular polymeric substances (EPS) extracted from the biological sludge of a membrane bioreactor, which treats municipal wastewater. The mechanism responsible for the anti-fouling behavior, of the modified membranes was found to be the hydration of the coating – attributed to the adsorption of electrolytes – as detected by quartz crystal microbalance with dissipation monitoring (QCM-D). The hydration of the coating was observed in the presence and absence of calcium. However, fouling of the modified membranes with EPS was mediated and enhanced by calcium, and the presence of calcium abolished the anti-fouling effects of the PS-b-(KE) 15 layer on both UF and RO membranes. The interaction between EPS and the bare, uncoated membrane area in the presence of calcium likely eliminated the anti-fouling capabilities of the PS-b-(KE) 15 layer. Membrane coating may be further improved by designing a continuous, denser layer of PS-b-(KE) 15 . [ABSTRACT FROM AUTHOR]

Triple antifouling strategies with fouling release, fouling resistance and contact killing attributes have been utilized for the control of reverse osmosis membrane biofouling. The membrane surface modification procedure is simple and time-efficient. After the interfacial polymerization process, the membrane was rinsed by n-hexane with addition of 2,2,3,4,4,4-hexauorobutyl methacrylate (HFBM), then exposed to UV irradiation for 20 s, and finally immersed into a tobramycin (TOB) aqueous solution for 30 s. The resultant membrane maintains the high permselectivity of the virgin membrane. Because of the synergistic effects of low-surface-energy brushes (fouling release) and hydrophilic TOB segments (fouling resistance) on the modified membrane surface, the membrane demonstrates superior antifouling property. Further, owing to the bactericidal attribute of TOB, the membrane exhibits strong antimicrobial activity. The membrane shows high antibiofouling property due to the triple antifouling strategies. The fouling results of combined foulants also highlight the membrane antifouling and antibiofouling properties. Moreover, the membrane shows excellent performance stability during the long-term cross-flow test and chemical cleaning process. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) and reverse osmosis (RO) hybrid process is taking center stage under the international spotlight in water treatment and desalination industries. Nevertheless, most existing researches are on the lab-scale and only few researches have been done on the element-scale. Currently, two types of elements are available, spiral wound FO (SWFO) and flat sheet FO (FSFO). However their performances have not yet been clearly addressed or compared. In addition, there is no research of which type of FO element is suitable for FO-RO hybrid process for wastewater treatment and desalination. Therefore, this paper investigated to find the main factors that need to be considered for scale-up with lab-scale and element-scale experiments under different operational conditions (draw solution (DS) concentration, and flow rates of feed and draw side). For SWFO, it is limited in the changing operating conditions due to its structural characteristic. However, FSFO is relatively free to change operating conditions and the flow rate difference also show a positive effect on the FO performance (water fluxes at 20 and 30 L/min with 0.5 M of DS were around 6.0 and 13.7 L/m 2 h, respectively). Through the scenario of serial stage for scale-up, the volume of DS, it was found that the final concentration of DS, and the inlet pressure are the important factors for determining the suitability of FO element. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) demonstrates great potential in energy harvesting when combining with seawater reverse osmosis. However, the lack of suitable membrane modules and the issue caused by the membrane fouling greatly impede the practical application of PRO to a larger scale. In this study, two-inch thin film composite hollow fiber modules were fabricated by using in-house developed PRO membranes. The produced PRO modules have a maximum effective area of 0.5 m 2 . By assessing the PRO performances of the modules with different sizes, external concentration polarization (ECP) was found to have significant impact on the flux reduction during module scale-up. Different module designs, including fiber bundles, distribution baffles and distribution tubes, were thus adopted as an attempt to boost the membrane performance. A power density of 8.9 W/m 2 at 15 bar was obtained using tap water as feed and 1 M NaCl solution as draw solution. PRO performance tests were also carried out using the developed two-inch modules on a pilot-scale setup with actual wastewater retentate as feed solution. Low pressure nanofiltration was selected as the pretreatment of the wastewater retentate to mitigate fouling. A power density of larger than 8 W/m 2 was obtained when pretreated wastewater retentate was used as the feed solution, implying high potential of PRO in the pilot scale. Nevertheless, full potential of PRO can only be realized by mitigating ECP, which could be achieved by improving the module design in the further endeavor. [ABSTRACT FROM AUTHOR]

Biofilm occurrence in reverse osmosis (RO) membranes constitutes a key problem in water plants, leading to a loss of performance and a decrease in treatment efficiency. Knowledge on the microbial community composition and the links to operational conditions is therefore crucial to understand biofilm formation and develop proper biofouling management strategies. The advent of molecular methodologies in the last years has evidenced the failure of culture-dependent techniques to assess the great level of diversity present in RO membranes. More recently, the application of – omics has unveiled a new horizon to study microbial diversity and function in wastewater treatment. This manuscript focuses on the latest discoveries in prokaryotic diversity in RO membranes, highlighting the importance of operating conditions and cleaning strategies in community structure. The current knowledge of biofilm dynamics in these systems is also reviewed. However, despite the enormous possibilities that metagenomics and metatranscriptomics can offer, studies using these methodologies in RO membranes are still scarce, and further efforts to uncover a core microbial composition and expression patterns of relevant genes are still needed. [ABSTRACT FROM AUTHOR]

This work reports the repairing of partially degraded polyamide TFC RO membrane for restored salt rejection and simultaneously enhanced resistance to both chlorine and fouling through adopting an in-situ, simple and upscalable approach of cross-flow filtration of sericin aqueous solution followed by flushing with de-ionized water. The attachment of sericin molecule on membrane surface was confirmed by XPS analysis and was found to be effective in recovering membrane reverse osmosis performance. The membrane with a degraded salt rejection higher than 94.0% exhibited a restored salt rejection the same as or a little higher than that of the new membrane (before chlorination). The deposition of sericin was also found to make membrane surface smoother and more hydrophilic and negatively charged under neutral condition, and thus endow the restored membrane with enhanced fouling resistance to bovine serum albumin compared with the new membrane. Furthermore, the chlorine exposure experiments demonstrated that the restored membrane with the coating of sericin exhibited better resistance to chlorine compared to the new membrane. The simplicity and good reproducibility of the restoration treatment procedure and the satisfactory performance stability of the restored membrane reveal that the in-situ restoration approach of present work is attractive for practical applications. [ABSTRACT FROM AUTHOR]

Seawater and brackish water constitute ~ 97% of the water on Earth. Therefore, future water shortages could be alleviated if we develop more efficient and cost-effective desalination technologies. Reverse osmosis (RO) has been established as the best available technology for commercial seawater (SW) desalination during the last two decades. Because the standard SWRO membrane element is designed to achieve a very high salt (NaCl) rejection (> 99%) with a low water recovery (~ 15%), current SWRO desalination plant design is based on the staging of arrays of RO membrane elements to achieve an overall water recovery of ~ 50% with an energy consumption of 3–4 kWh per m 3 of water treated. Moreover, SWRO desalination plants generate substantial amounts of brines that must be disposed of. In addition, SWRO desalination plants require post-treatment including remineralization. Here, we report an energy-efficient hybrid desalination process for high salinity brackish water. This new desalination process couples flow capacitive deionization (FCDI) with nanofiltration (NF). Our experiments and energy calculations using a 10000 ppm NaCl solution as model brackish water show that the energy consumption of the new FCDI-NF unit (0.460 kWh_total m −3 ) is lower by 16–20% than the best reported energy consumption (0.571 kWh m −3 ) and the 1-stage practical minimum energy consumption (0.550 kWh m −3 ) of a brackish water reverse osmosis (BWRO) unit treating the same feed at 70% water recovery, while final total dissolved solids (TDS) are in the drinking water range. [ABSTRACT FROM AUTHOR]

Aromatic polyamide has emerged as the most prominent material for thin film composite (TFC) reverse osmosis and nanofiltration membranes. However, these membranes are susceptible to free chlorine attack, and lose their performance after about 1000 ppm h of chlorine exposure. This necessitates removal of chlorine from the feed water before desalination, leading to an increase in the cost of water treatment in desalination plants, especially for drinking water. Chlorine and chloramine being widely used disinfectants of drinking water the world over, a chlorine resistant membrane (CRM) is highly desirable to extend the membrane's life and bring down costs. This paper reviews the mechanisms of TFC membrane degradation by chlorine and strategies for its mitigation. Induced physiochemical changes by N-chlorination and concomitant ring chlorination reaction in presence of chlorinating agent are seen to be the major degradation mechanisms. Induced changes in physiochemical structure by chlorine attack can be assessed from the membrane characteristics and performance evaluation. The different approaches reported to develop CRMs have been reviewed extensively. These include: surface protection, coating with hydrophilic materials, use of chlorine scavengers, reducing chlorine sensitive sites, use of novel monomers and polymers for selective layer etc. Finally, the water permeability and salt rejection trade-off for native and modified membranes is discussed. [ABSTRACT FROM AUTHOR]

Thin-film composite membranes comprising modified polyamide layers were cast on an ultrafiltration polysulfone support using sequential interfacial polymerization, thus obtaining bilayer membranes with a final layer of polyols at the surface. A traditional polyamide layer made by interfacial polymerization of trimesoyl chloride and m-phenylene diamine, as well as a reference bilayer membrane with a topmost layer of m-phenylenediamine, were compared with novel bilayer membranes containing N-Methyl-D-glucamine, (±) 3-amino-1,2-propanediol, or serinol functionalizations. Filtration experiments performed with pure water, or with solutions containing 2000 mg/L NaCl and 5 mg/L boric acid, indicated that the water permeance of the modified membranes was improved with no associated loss of salt rejection compared to reference membranes. In particular, functionalization using (±)-3-amino-1,2-propanediol allowed achievement of the highest water flux and the best rejection (NaCl permeance, B , of 0.18 L m −2 h −1 ) with 40% reduction in salt passage compared to the reference membranes ( B of 0.26 L m −2 h −1 ). Bilayer membranes also showed enhancement in boron removal, performing about 90% observed boron rejection at pH 5.2, condition under which boron is mostly present as neutral boric acid. The strategy employed in the present work allows for robust design of TFC membrane consisting of active layers with improved water permeance and boron rejection performances. [ABSTRACT FROM AUTHOR]

Polyvinylpyrrolidone (PVP) modified graphene oxide (GO), hereinafter referred to as PVP-GO, was synthesized as a novel modifier to fabricate thin film nanocomposite forward osmosis membranes. The results indicated that by coating PVP on the surface of GO nanosheets, the dispersibility of GO was increased and the aggregation of GO was reduced. Compared with the pristine and GO modified FO membranes, the PVP-GO modified membranes enhanced the desalination performance giving both a higher water flux and lower reverse solute flux. When using 2 mol L −1 of NaCl as the draw solution and 10 mmol L −1 NaCl as the feed solution, the water flux of the FO membrane modified with 0.0175 wt% of PVP-GO reached 33.2 LMH in the ALDS mode (the active layer facing the draw solution), which was 3.3 times higher compared with the water flux of the pristine FO membranes. Improved desalination performances of PVP-GO modified FO membranes were attributed to the better dispersibility of the PVP-GO nanosheets and increased surface hydrophilicity of the modified FO membranes. This study indicated that PVP-GO is an effective modifier to enhance the performance of FO membranes. [ABSTRACT FROM AUTHOR]

An osmotic dilution process of forward osmosis (FO) and reverse osmosis (RO) was applied at pilot-scale to integrate wastewater treatment with seawater desalination in a coal-fired power plant. FO was osmotically driven by seawater used as cooling water. FO-treated wastewater was diluted with seawater and then further processed by RO. Seasonal variation in water flux, fouling behavior and reversibility, and energy consumption in both FO and RO were systematically evaluated during 5 months of pilot operation. The FO water flux, which declined due to the organic fouling induced by the wastewater from the coal-fired power plant, was readily recovered by physical cleaning. The integrated FO-RO dilution process was able to reduce the RO fouling potential through FO treatment of wastewater, significantly decreasing SDI value to 1.5 ± 0.1. This study also reported energy consumption data, to our knowledge for the first time, at pilot scale operation of FO-RO dilution process, and showed that total energy consumption for desalinating the diluted feed, including wastewater reclamation by FO, was 15% less than that of typical seawater desalination by RO. The results of this FO-RO pilot study demonstrated that sustainable FO-RO operation can be achieved in the treatment of power plant wastewater owing to easy fouling control, low energy consumption, and superior final water quality. [ABSTRACT FROM AUTHOR]

Thin film composite (TFC) polyamide reverse osmosis (RO) membranes are naturally prone to fouling, especially the biofouling, due to their inherent physicochemical surface properties. In the current study, highly efficient anti-biofouling membrane was fabricated by assembly of poly acrylic acid and potent anti-microbial agent tobramycin on a commercial TFC RO membrane surface using the layer-by-layer technique. The successful modification was verified by XPS, and the membrane surface hydrophilicity was substantially improved as detected by contact angle measurement. Membrane prepared under optimized condition shows 18% increased water flux and slightly enhanced (0.4%) salt rejection properties. The antifouling performance is significantly improved, as the modified membrane demonstrates 37% and 26% higher flux than the virgin membrane after three-cycling fouling of bovine serum albumin and sodium alginate solution, respectively. In addition, modified membrane possesses dramatically efficient anti-microbial property, which can achieve more than 99.6% killing ratio for both the Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. The modified membrane well maintains its high permselectivity after 7-d severe biofouling test. Moreover, the membrane shows excellent performance stability. [ABSTRACT FROM AUTHOR]

This study compared the performance of the asymmetric cellulose triacetate (CTA) and polyamide thin film composite (TFC) forward osmosis (FO) membranes in an osmotic membrane bioreactor (OMBR). A reverse osmosis (RO) system was integrated with OMBR to regenerate the draw solution and produce clean water. Results show that the TFC membrane exhibited a higher initial water flux but more dramatic flux decline compared to the CTA membrane when they were used for OMBR. The CTA and TFC membranes also resulted in discernible difference in salinity build-up in the bioreactor and thus biomass characteristics during OMBR operation. All 30 trace organic contaminants (TrOCs) selected in this study were effectively removed by the OMBR-RO hybrid system regardless of the FO membrane type. Compared to the CTA membrane, the TFC membrane contributed more significantly toward the removal of hydrophilic and biologically persistent compounds and thus reduced their accumulation in the draw solution during OMBR-RO operation. In addition, CTA and TFC FO membranes also resulted in considerable differences in TrOC residuals in the sludge during OMBR operation. [ABSTRACT FROM AUTHOR]

Membrane biofouling is regarded as a Gordian knot in applying reverse osmosis and nanofiltration for water treatment. It occurs in the feed spacer channels of spiral wound membrane elements. The influence of feed spacer structure on hydrodynamic condition and biofouling development remains yet to be fully understood. This study aims to quantify the dynamic evolution and spatial distribution of biomass in feed spacer channels, and reveal the great importance of spacer–membrane clearance in the biofouling development. Four kinds of feed spacers with the same thickness (28 mil) but different clearance width, by varying filament diameter (0.4, 0.45, 0.55 and 0.6 mm), were used. A relatively long-term (20 d) biofouling experiment was conducted by using a feed solution of lower bacterial load and nutrient dosage. Results showed that the "shear stress effect" dominated the early stage of biofouling as biofilm was first attached to the low-shear regions, regardless of the spacer–membrane clearance width. In the middle and late stage, the "blocking effect" emerged with the continuous accumulation of biomass, as was especially the case in the feed channel with narrow spacer–membrane clearance. In this period, biofilm was prone to deposit and block the narrow flow passage between the spacer filaments and membrane surface, which decreased the uniformity of flow field, expanded the flow "dead zone" area, boosted the feed channel pressure (FCP) drop, and resultantly accelerated the rate of membrane biofouling. Enhancement of the "shear stress effect" under an appropriate range of spacer–membrane clearance width and thus channel porosity, as well as customed design of feed spacer geometries according to specific fouling locations are suggested for the future optimization of feed spacer. [Display omitted] • Dynamic evolution of membrane biofouling in feed spacer channel was characterized. • Biomass distribution in the spacer mesh was carefully quantified in 5 sub-regions. • "Shear stress effect" played a vital role at early stage of membrane biofouling. • "Blocking effect" exacerbated biofouling at late stage in narrow-clearance channel. • Suggestions for feed spacer optimization are proposed for membrane fouling control. [ABSTRACT FROM AUTHOR]

Silica scaling of RO membranes was evaluated via real-time direct surface imaging demonstrating a capability for detecting the onset of silica scale formation and its evolution. Silica scaling was detected significantly earlier than by traditional flux decline measurements. The observed rate of silica particle nucleation followed classical nucleation theory while the growth of individual silica particles, at the early stages of silica scaling, was governed by diffusional growth. SEM and optical images of the membrane surface suggest that silica scaling occurs through the formation of both primary silica particles and their agglomerates (~1–30 µm), as well as a gel-like silica film embedded with silica particles both of which contribute to permeate flux decline. At low silica saturation index at the membrane surface (SI m ≤1.93) silica gel film formation resulted in a smoother and less porous film than at higher silica saturation (SI m ≥2.72). At the higher silica saturation levels (SI m =2.72–3.50), silica scaling resulted in larger observed particles as well as rapid permeate flux decline. The silica scale layer thickness was in the range of ~0.1–3.5 µm, with surface roughness being higher by a factor of 2.6–8.3 relative to the native membrane. Results of the present study suggest that there is merit in exploring the application of the present approach for early detection and monitoring of silica scaling in RO plants in support of strategies for silica scale mitigation. [ABSTRACT FROM AUTHOR]

Desalination and water reuse are rapidly evolving technologies that have become mainstays of a broad portfolio of water management practices around the globe. Osmotically-driven molecular partitioning processes mediated by functional permselective membranes lay at the heart of each of these technologies. Despite a strong theoretical and empirical framework of knowledge discovered over the past half century that allows engineering of modern reverse osmosis (RO) systems at unprecedented scales, our understanding of water transport and solute rejection at the atomic and molecular scales by the semipermeable membranes is incomplete. One reason for this is a dearth of analytical techniques capable of non-invasively accessing (and visualizing) in real time the exceedingly small spatial and temporal dimensions of atomic interactions underlying membrane transport phenomena. This knowledge gap has been increasingly eroded, however, since the first use of molecular simulations to explore RO membrane structure and dynamics in the late 1990s. Over the last decade, molecular dynamics (MD) and related simulations techniques have been aggressively pursued to advance understanding of membrane architecture and transport at the atomistic scale. Results emerging from sophisticated computational approaches, especially when coupled with today's powerful new imaging technologies, reveal a rich landscape of physicochemical interactions not only inside the polymer membranes, but also at the water-membrane interface. For example, it is now clear that the discriminating polyamide (PA) layer of modern RO membranes consists of an inhomogeneous tangled polymer network pervaded by tortuous water-filled transmembrane “tunnels” and nanopores whose shapes fluctuate at ambient temperatures over femtosecond to picosecond time scales. Recent modeling efforts indicate that the nanoscale roughness of PA membranes, evident in electron micrographs, is also reflected at the atomic scale, with an ill-defined diffuse interfacial region shared with the bulk water phase. Simulations are also yielding a clearer picture of water and solute (ions and small organics) behaviors inside the membrane matrix resulting from complex intermolecular hydrogen bonding and atomistic solvation processes. The thermodynamic (enthalpy and free-energy) barriers to water and solute entrance into nanopores located at membrane surfaces have been recently elucidated by means of specialized non-equilibrium simulations protocols. Notwithstanding these recent successes, questions nonetheless remain concerning membrane molecular organization and performance, especially with respect to their ability to reject certain small organic compounds and not others. Other questions concern the dynamic interplay between membrane surfaces and foulant molecules as they undergo adsorption. Because of its unique ability to translate atomic-scale interactions and processes into a dynamic visual experience, it is anticipated that computational chemistry will play an ever greater role in the coming years in helping to answer these and related questions about membrane structure and function. It is expected that fundamental advancements in these areas will lead to a new generation of membrane materials with improved durability and reduced energy demands. [ABSTRACT FROM AUTHOR]

A life cycle assessment tool and methodology were used to study two potable reuse treatment schemes: a full-advanced treatment (FAT) approach and a hybrid ultrafiltration osmotic membrane bioreactor (UFO-MBR). FAT combines conventional wastewater treatment followed by low-pressure membrane filtration, reverse osmosis (RO), and ultraviolet advanced oxidation processes (UV–AOP). The UFO-MBR couples biological treatment processes with forward osmosis (FO) membranes and ultrafiltration (UF) membranes in one integrated system. RO is coupled with FO in the UFO-MBR process to produce ultra-pure water and a reconcentrated draw solution (DS) for reuse in the FO process. Construction material, energy demand, and chemical use data were collected and calculated to determine the energy use and a subset of environmental impacts of each system. Results from the LCA illustrate that the energy use and environmental impacts of FAT are lower than those of UFO-MBR treatment. The higher impacts of UFO-MBR treatment were associated with the required large area of the FO membrane and high RO energy use. UFO-MBR treatment was further assessed using higher permeability FO membranes and RO energy recovery. Following simulation of process optimization, the environmental impacts of UFO-MBR were brought much closer to those of FAT. [ABSTRACT FROM AUTHOR]

Biofouling is a major operational problem in reverse osmosis (RO) processes. Although direct dosing of non-oxidizing biocides (e.g. DBNPA) in RO vessels is an effective method for reducing biofouling, the application of non-oxidizing biocides to the production of potable water is strictly banned due to their human toxicity. In this regard, while food preservatives (i.e. non-toxic to human ingestion) can be used for this purpose, a systematic evaluation has not been conducted. Here, we explored the applicability of a food preservative, lauroyl arginate ethyl (LAE), to RO processes for potable water production. The compatibility of LAE with the RO membrane was tested by exposing the membrane to high concentrations of LAE. The membrane showed no significant morphological or chemical damage up to 100,000 mg/L. LAE demonstrated high and fast antimicrobial activities, which was verified by measuring the minimum concentrations needed to inactivate and kill bacteria, measuring the inhibition zones, and analyzing the rates of bacterial killing. LAE was also effective in inhibiting biofilm formation and removing biofilm formed on the RO membrane. Furthermore, LAE did not negatively affect the RO performance factors such as water flux and salt rejection. Taken together, this study clearly demonstrated that LAE can be used to reduce biofouling in RO processes without risk of human toxicity. [ABSTRACT FROM AUTHOR]

The Ångström-scale transport characteristics of water and six different solutes, methanol, ethanol, 2-propanol, urea, Na + , and Cl - , were studied for a polyamide reverse osmosis (RO) membrane, FT-30, using non-equilibrium molecular dynamics (NEMD) simulations. Results indicate that water transport increases with an increasing fraction of connected percolated free volume, or water-accessible open space, in the membrane polymer structure. This free volume is enhanced by the dynamic structure of the membrane at the molecular level as it swells when hydrated and vibrates due to molecular collisions allowing a continuous path connecting the opposite membrane surfaces. The tortuous paths available for transport of solutes result in Brownian motion of solute molecules and hopping from pore to pore as they pass through the polymer network structure of the membrane. The transport of alcohol solutes decreases for solutes with larger Van der Waals volume, which corresponds to less available percolated free volume, or solute-accessible space, within the membrane polymer structure. However, the Van der Waals size of the dehydrated solutes is generally not a good measure to predict solute transport or rejection. Urea has reduced transport compared to ethanol, most likely due to more complex chemistry, even though urea has a smaller Van der Waals volume than ethanol. Na + and Cl - experience the lowest transport, likely due to strong ion-water and ion-ion electrostatic interactions. [ABSTRACT FROM AUTHOR]

With a total capacity of 70 million cubic meters per day, seawater desalination industry represents the most affordable source of drinking water for many people living in arid areas of the world. Seawater Reverse Osmosis (SWRO) technology, driven by the impressive development in membrane materials, modules and process design, currently shows an overall energy consumption of 3–4 kW h per m 3 of desalted water, substantially lower than thermal systems; however, the theoretical energy demand to produce 1 m 3 of potable water from 2 m 3 of seawater (50% recovery factor) is 1.1 kW h. In order to move towards this goal, the possibility to recover the energy content of discharged concentrates assumes a strategic relevance. In this work, an innovative approach combining Direct Contact Membrane Distillation (DCMD) and Reverse Electrodialysis (RE) is tested for simultaneous water and energy production from SWRO brine, thus implementing the concept of low energy and Near-Zero Liquid Discharge in seawater desalination. DCMD operated on 1 M NaCl RO retentate fed at 40–50 °C resulted in a Volume Reduction Factor (VRF) up to 83.6% with transmembrane flux in the range of 1.2–2.4 kg/m 2 h. The performance of RE stack fed with DCMD brine (4–5.4 M) and seawater (0.5 M) was investigated at different temperatures (10–45 °C) and flow velocities (0.7–1.1 cm/s). Experimental data show the possibility to obtain an Open Circuit Voltage (OCV) in the range of 1.5–2.3 V and a gross power density of 0.9–2.4 W / m MP 2 (membrane pair). In general, optimization is required to find best operating conditions for the proposed system. [ABSTRACT FROM AUTHOR]

Novel composite forward osmosis (FO) hollow fiber membranes with two selective skin layers were developed in the present work. The polyethersulfone (PES) hollow fiber substrate was firstly fabricated by a phase inversion method. The RO-like polyamide skin layer was then prepared on the inner surface of the hollow fiber substrate via interfacial polymerization (IP), while the NF-like outer skin layer was prepared via polyelectrolyte layer-by-layer (LBL) assembly. Three double-skinned membranes with negative (DS#1.5), positive (DS#2.0) and minimal (DS#2.5) outer surface charges under neutral pH environment were evaluated for their capabilities against organic fouling in the FO process. The newly developed double-skinned membranes possess water permeability greater than 2 l/m 2 h bar and NaCl rejection higher than 95% under 2 bar pressure, and have superior water flux and less salt leakage than the commercial HTI FO membranes as well as all the reported double-skinned FO membranes with RO-like selective layers. Most importantly, the double-skinned DS#2.5 hollow fiber membrane exhibits exciting organic fouling resistance because of its highly hydrophilic NF-like secondary layer with minimal surface charge and tightened surface structure to mitigate possible substrate pore clogging and fouling layer formation. A stable water flux of around 25 l/m 2 h was attained for DS#2.5 membrane using <0.5 M NaCl as the draw solution and a water containing 200 ppm dextran (DEX) or Aldrich humic acid (AHA), or lysozyme (LYS) and 10 mM NaCl as the model feed in the active layer against the draw solution (AL-DS) configuration, suggesting its great potential for practical FO applications. [ABSTRACT FROM AUTHOR]

In this study, high scaling potential brackish water was used as feed water. To avoid rapid and severe scaling on the RO membrane, a forward osmosis stage was used as a pre-treatment of RO stage to remove scaling ions and organic matter. First, a modelling approach has been developed to optimise the operational conditions of FO–RO train. Both water flux and energy consumption have been considered. Then, experiments were conducted using spiral wound TFC FO membranes. Then, results confirmed that FO was a very efficient pre-treatment for RO process where FO demonstrated much lower scaling tendency than RO. Bench scale observation of scaling on FO membrane has confirmed that loosely packed visible scaling was formed on the surface of FO membrane; however, the water flux of FO was almost not affected by scaling. By carrying out FO–RO pilot plant experiments, the energy consumptions of FO–RO process were compared with that of the RO process only; the results indicated that, when treating the high scaling potential brackish water, FO–RO hybrid was more sustainable and feasible in terms of energy consumption and operations. FO appeared to be the ultimate pre-treatment solution that removes both scaling and fouling agents. Nevertheless, the application of this combined FO and RO process can only be justified for treating the brackish water with high scaling potential, when using RO directly is not feasible due to the rapid scaling beyond the control of antiscalent and frequent chemical cleaning. [ABSTRACT FROM AUTHOR]

During hydrolysis of lignocellulosic materials for ethanol production, compounds toxic for fermentation are formed. Ten nanofiltration (NF) and reverse osmosis (RO) membranes with low molecular weight cut-off (150–400 g mol −1 ) were screened on a flat-sheet plant for their ability to separate C5 and C6 sugars from acetic acid, furfural, 5-hydroxymethyl furfural and vanillin in a model solution. RO led to the highest sugars rejection (>97%) but inhibitors transmission was low. NF membranes, especially NF270, NF- and NF245 (Dow) and DK (GE Osmonics) were found suitable for detoxification with glucose rejection >94% and inhibitors transmission >80%. At high Volume Reduction Ratio, VRR , transmission of inhibitors was still enhanced (>96% at VRR =8 and 10 bars). In these conditions, NF270 gave the highest permeate flux (20 L h −1 m −2 ) followed by DK, NF- and NF245. However, DK and NF- could be preferred because of lower sugar loss. [ABSTRACT FROM AUTHOR]

Fouling of membrane surfaces by organic, inorganic and biological materials is a significant cause of increased operational costs and power consumption for membrane separation processes including reverse osmosis, nanofiltration, membrane bioreactors and membrane distillation. Novel polymeric membrane surfaces are being developed by numerous research groups to counter foulant attachment and build up. One such type of membranes under development are ones which contain an active surface created using polymeric bicontinuous microemulsions (PBM) [1] . In this work we use humic acid functionalised colloidal probes to simulate organic foulants to investigate the adhesion forces between polymer membranes modified with a PBM coating, both in high purity water and model textile dye wastewater (MTDW). Membrane performance varied considerably when comparing different preparations and with the commercial PES membrane which was used as the base-layer. When making measurements in the two liquid media it was found that the behaviour was very different, with some membranes showing low adhesion in water showing high adhesion in the textile dye wastewater and vice versa. Water contact angle measurements of clean membranes showed good correlation with measured adhesion forces. Conversely, contact angle measurements made with membranes after prolonged exposure to MTDW showed a strong inverse correlation with the measured adhesion forces in MTDW, with more hydrophilic surfaces showing greater adhesion with the functionalised probe. Measurements of contact angle of humic acid before and after exposure to MTDW showed a change from a hydrophobic substance (129°) to a moderately hydrophilic substance (29°). These measurements suggest that the modification of both membranes and probe by components in the MTDW changed the adhesion forces experienced by the HA probe from favouring hydrophobic interactions to hydrophilic ones. [ABSTRACT FROM AUTHOR]

We present here an experimental method of dialysate production by forward osmosis (FO) using an inexpensive reverse osmosis (RO) membrane element. This method was developed in response to the increasing need for dialysis treatment in remote and desert regions of Australia where water is precious and electricity supplies are generally unreliable. A 4040 RO membrane element was oriented for FO, using dialysate concentrate as a draw-solution and pre-treated tap-water as a feed-solution. Diluted draw-side output was collected and mixed over a range of target flow-rates. After each test the element was osmotically backwashed. Measurements were made of production time, volume and equivalent flow rates. The benefits of FO were diminished by the process׳ need for osmotic backwashing. Our system had an equivalent water recovery ranging from 65 to 75%. Its energy efficiency was 66% of its RO equivalent. Its operation was almost silent. Two 4040-size RO membrane elements would be necessary to complete a dialysis treatment. Dialysate production may be possible by this method, but its economic and conservation benefits appear to be modest. [ABSTRACT FROM AUTHOR]

Electrical Impedance Spectroscopy (EIS) was explored as an in situ tool for the detection of fouling of reverse osmosis membranes, during filtration of industrial (molasses) wastewater and model feeds containing silica and BSA foulants. The electrical capacitance measured at low frequencies (<100 Hz) was found to be the most sensitive electrical parameter for detecting fouling, during the early stage of flux decline. The effective gain (the percentage of change in capacitance divided by the percentage change in the flux) was ~3 for molasses waste water, 1.4 for silica and 2.5 for BSA. The formation of the reversible fouling layer occurred in conjunction with concentration polarization during this period and EIS was more sensitive than flux decline in monitoring this process. Hence EIS has potential in industrial application for fouling detection. Further the impedance spectra after cleaning were consistent with the flux recovery. The impedance spectra obtained following macromolecular (BSA and molasses wastewater) fouling was found to be significantly different from those obtained with colloidal (silica) fouling. The decrease in capacitance observed for BSA and molasses wastewater, suggests the formation of a gel like layer on the membrane surface, while the increase in capacitance of the silica suggests a loose cake which enhances concentration polarization. Hence EIS may also be capable of indicating the type of fouling which is occurring at the membrane surface. [ABSTRACT FROM AUTHOR]

We demonstrated that a thin-film composite (TFC) membrane with graphene oxide (GO) embedded in its polyamide (PA) layer exhibited high water permeability, anti-biofouling property, and chlorine resistance without loss of salt rejection. The GO fabricated by chemical exfoliation was fractionated for size control, and then the fractionated GO was dispersed in an aqueous solution of m-phenylenediamine (MPD) before interfacial polymerization. The water permeability and anti-biofouling property of the GO-embedded TFC (GO-TFC) membrane were enhanced by approximately 80% and 98% (based on the biovolume), respectively, and high salt rejection was retained even at 48,000 ppm h chlorination. Compared with the TFC membrane, the enhanced performances of the GO-TFC membrane were attributed to the change of hydrophilicity, surface charge, surface roughness, and thickness of the PA layer through the incorporation of GO. Both the size and the concentration of GO were the key factors in improving the performance of the GO-TFC membrane. [ABSTRACT FROM AUTHOR]

This study aims to investigate the impact of irradiation on the behavior of Polyamide (PA) composite reverse osmosis (RO) membranes. Irradiations were performed for two doses (0.1 and 1 MGy) in wet conditions under an oxygen atmosphere, with a gamma 60 Co source. Irradiation effect on RO membranes performances (NaCl rejection, permeability) was studied before and after irradiation. ATR-FTIR, XPS, AFM, FESEM microscopy, ion chromatography were also used to characterize structural modifications. Results show that NaCl rejection of RO membranes irradiated at 1 MGy decreased until 64% and permeability increased by a factor of three. Nevertheless, membranes irradiated at 0.1 MGy did not exhibit any change in theirs permselectivity properties. Advanced analysis techniques confirmed that the firsts effects of gamma rays on RO membranes occurred between 0.1 and 1 MGy. Results emphasize that gamma rays effects on the RO membranes led to the breaking of amide and ester bonds at 1 MGy. These breakings resulted in loss of hydrogen bonds between polyamide chains, and consequently to a relaxation of the polyamide network. Finally, modifications of the polysulfone layer underneath were highlighted. Both relaxation of the polyamide network and modifications of the polysulfone layer could be involved in the drop of the permselectivity properties. [ABSTRACT FROM AUTHOR]

In the textile industry, high salinity waste streams are a challenge urging for the recovery and purification of dyes and salts (e.g., NaCl), requiring a treatment going beyond the classical filtration by e.g., reverse osmosis to produce pure water. In this work, two commercial loose nanofiltration (NF) membranes (Sepro NF 6 and NF 2A, Ultura) are proposed to fractionate dye/salt aqueous mixtures. It was observed that both NF membranes have a salt rejection <33.3% in solutions with 0.1–40.0 g L −1 of NaCl at 6 bar. Furthermore, both membranes have >99.6% retention of direct dyes (direct red 80, direct red 23, and congo red), even though 40.0 g L −1 NaCl is present, indicating salt addition has no obvious impact on the dye retention. The combination of a low salt rejection and a high dye rejection indicates the feasibility for the reuse of salt from fractionation in forward osmosis and bipolar membrane electrodialysis. Application of diafiltration for an aqueous mixture containing direct red 80 (1000 ppm) and NaCl (~20 g L −1 ) by both membranes demonstrates that above 95% of NaCl is removed from aqueous mixture, and <0.9 g L −1 NaCl remains after the addition of pure water with a volume factor of 4.0 in the feed solution. At the premise of excellent diafiltration performance, concentration as the post-treatment for dye recovery expectedly indicates direct red 80 is concentrated by a factor of 4.0 for both membranes while keeping the salt concentration with a very slight increase. Over 99.9% dye retention in both diafiltration and concentration procedures yields a very high recovery since <0.045% of dye is permeated. These results indicate that loose nanofiltration membranes have potential for dye/salt fractionation. [ABSTRACT FROM AUTHOR]

Zeolites are potentially a more robust desalination alternative as they are chemically stable and possess the essential properties needed to reject ions. This work proposes to use zeolite membranes for desalination of saline recycled wastewater for the possibility of avoiding the costly pre-treatment needed for polymeric reverse osmosis membranes. The MFI-type zeolite membrane was developed on a tubular α-alumina substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N 2 ) permeation, and underwent desalination tests with saline wastewater under different conditions. When saline wastewater was fed at 7 MPa to the zeolite membrane it showed a salt rejection of 80% based on electrical conductivity (EC) and a flux of 4 L m −2 h −1 . A 254 (organics absorption at the wavelength of 254 nm measured by a HACH DR5000 spectrophotometer) removal exceeded 90%. Slightly lower salt removal and A 254 results were observed when operating at a lower pressure of 3 MPa. During batch concentration runs on the saline wastewater, the EC of the feed water increased from the initial value of 1770 µS cm −1 to 3100 µS cm −1 over the 48 h test time which indicates that a 43% water recovery was achieved. EC reduction remained >70% and flux was maintained at around 2 L m −2 h −1 throughout the test period, indicating that the membrane resisted organic fouling. Chlorine stability studies showed that a long-term (7 days) strong hypochlorite clean did not significantly alter the flux or rejection confirming the chemical stability of zeolite membranes. Overall, the zeolite membrane showed excellent chemical resilience and produced a desalinated product suitable for reuse applications (e.g. irrigation, residential or industrial). Fluxes, however, need to be improved to be competitive with current polymeric membranes as do rejections for higher purity water applications. [ABSTRACT FROM AUTHOR]

In this study, the porous structures of two commercial fully-aromatic polyamide (FAPA) reverse osmosis (RO) membranes as well as homemade RO membranes were thoroughly characterized and revealed by using SEM and TEM. With a designed “inverse” interfacial polymerization experiment, it was confirmed that pores always form on the surface of the FAPA film facing the aqueous phase. Based on the SEM observation on the cross-section of FAPA film and the TEM results, a new structure model of FAPA film in RO membrane was proposed. The dense layer of the flat area and the dense layer near the top surface of the protuberances and ridges connect together to form a complete dense discriminating layer as the key barrier layer of the RO membrane. Protuberances and ridges have irregular interconnecting cavities and tunnels, through which the dense layer and the pores on the back surface of the FAPA film are connected. All these findings proved the correctness of Cadotte׳s assumption about the pores׳ forming mechanism during interfacial polymerization process. [ABSTRACT FROM AUTHOR]

Due to water scarcity, development of innovative processes for wastewater reuse has become a priority. Hence, hybrid processes coupling membrane separation with advanced oxidation processes could play a decisive role in the production of safe water. However, membrane fouling is still one of the main limitations to process widespread application. Thus, the present study investigates the impact of e-beam irradiation on the fouling ability of a secondary effluent (SE) filtered on MF and subsequently on RO membranes. For this, two electron beam radiation doses (1 and 5 kGy) were investigated. Results demonstrate that whatever the radiation dose investigated, no change in terms of TOC in SE was observed (prior to filtration). However, a strong decrease in UV254 and fluorescence signal was observed for organic matter (OM) exhibiting a MW ranging from 135 to 10 kDa. Pre-oxidation was found to efficiently optimize MF filtration permeate flux whereas no improvement could be observed regarding RO separation. Moreover it was demonstrated that MF efficiently removed the high-MW compounds and was barely efficient in low-MW compounds removal. Energetic balance based on experimental results demonstrates that 1 kGy was a sufficient dose to operate the hybrid e-beam irradiation and MF process. [ABSTRACT FROM AUTHOR]

To better understand full-scale fouling of nanofiltration and reverse osmosis membranes, it is common to autopsy a membrane element from a specific location in the full-scale system of interest, or conduct fouling tests at bench and pilot scale. However, several factors that may impact fouling at full scale vary along full-scale membrane systems and are difficult to recreate at bench and pilot scale. Thus, we performed an in-depth comparison of fouling in membranes at the lead and tail ends of a full-scale nanofiltration system treating a groundwater containing silica, as well as in a membrane fouled at bench scale with concentrate water from the full-scale system. We characterized the elemental composition, chemistry and structure of the foulant layers, and water permeability recovery upon chemical cleaning. Results showed that while there were apparent physico-chemical differences between the foulant layers of membranes fouled at the lead and tail ends of the full-scale system, water permeability recovery upon cleaning was similar for the two membranes. Bench-scale fouling tests produced foulant layers that were different in composition from those generated at full scale and led to the incorrect conclusion in terms of which was the optimum cleaning solution at full-scale. The dissimilarities between bench and full scale results were likely caused by the various challenges in reproducing full-scale conditions at bench-scale, particularly the inability to maintain anoxic conditions and use a one-pass filtration scheme. Thus, to determine the optimum cleaning solutions for the full-scale system, it was preferable to conduct bench-scale cleaning tests on a membrane fouled at full scale than to attempt recreating fouling at bench scale; this finding may hold true for other anoxic waters. In this study, we also introduce Rutherford backscattering spectrometry (RBS) for elemental and structural characterization of foulant layers. Our results showed that RBS is able to depth profile the elemental composition of the first few microns from the surface of foulant layers, which is information that the more commonly used X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy analyses cannot provide. [ABSTRACT FROM AUTHOR]

Commercial polyamide (PA) reverse osmosis (RO) membranes were surface modified in a sequential two-step polymerization process to impart anti-biofouling properties to the membrane surface. In the first step, a 2-bromoisobutyryl bromide initiator-polydopamine (BiBBr-initiator-PDA) layer was deposited onto the membrane surface from a Tris(hydroxymethyl)aminomethane buffered solution of dopamine hydrochloride and 2-bromoisobutyryl bromide at ambient conditions. In the second step, polymer chains of [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC) were grafted-from the BiBBr-initiator-PDA surface using activators regeneration by electron transfer-atom transfer radical polymerization for between 1 and 24 h. The modified surfaces were characterized using attenuated reflectance-Fourier transform infrared spectroscopy and water contact angle and their pure water flux, saline water flux and ability to reject salt were determined. Results showed that the water flux and salt rejection properties of the PDA-g-PMTAC modified membranes were similar to the unmodified PA RO membranes. Chlorine resistance tests showed the coating had enhanced stability in regards to salt rejection properties. Significantly, after six days of incubation in nutrient solution there was 93.2% less bacteria on the PDA-g-MTAC modified PA RO membranes, compared to the unmodified membranes. [ABSTRACT FROM AUTHOR]

Long-term performance and fouling behavior of four full-scale nanofiltration (NF) plants, treating anoxic groundwater at 80% recovery for drinking water production, were characterized and compared with oxic NF and reverse osmosis systems. Plant operating times varied between 6 and 10 years and pretreatment was limited to 10 µm pore size cartridge filtration and antiscalant dosage (2-2.5 mg L-1) only. Membrane performance parameters normalized pressure drop (NPD), normalized specific water permeability (Kw) and salt retention generally were found stable over extended periods of operation (>6 months). Standard acid-base cleanings (once per year or less) were found to be sufficient to maintain satisfying operation during direct NF of the described iron rich (≤8.4 mg L-1) anoxic groundwaters. Extensive autopsies of eight NF membrane elements, which had been in service since the plant startup (6-10 years), were performed to characterize and quantify the material accumulated in the membrane elements. Investigations using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), total organic carbon (TOC) and adenosine triphosphate (ATP) measurements revealed a complex mixture of organic, biological and inorganic materials. The fouling layers that developed during half to one year of operation without chemical cleaning were very thin (<2 µm). Most bio(organic) accumulates were found in the lead elements of the installations while inorganic precipitates/deposits (aluminosilicates and iron(II)sulfides) were found in all autopsied membrane elements. The high solubility of reduced metal ions and the very slow biofilm development under anoxic conditions prevented rapid fouling during direct NF of the studied groundwaters. When compared to oxic NF and RO systems in general (e.g. aerated ground waters or surface waters), the operation and performance of the described anoxic installations (with minimal pretreatment) can be described as very stable. [ABSTRACT FROM AUTHOR]

The performance of a wind-powered membrane filtration system using a brackish water reverse osmosis (BW30) module and synthetic brackish (5500 mg/L NaCl) feed water was determined. When tested with real wind speed data (average wind speed 6.1 m/s; interval of 1 s) over one day of realistic fluctuation levels, the wind-membrane system produced 0.78 m³ of water with a final concentration of 191 mg/L NaCl at an average specific energy consumption (SEC) of 7.2 kWh/m³. When a single bank of supercapacitor (SC) energy buffers were added to the system, performance increased to 0.93 m³ of permeate produced and a final concentration of 173 mg/L NaCl at average SEC of 4.2 kWh/m³. Tripling the size of the SC bank further increased productivity to 1.15 m³ (47% increase) at a final concentration 172 mg/L NaCl and average SEC of 3.1 kWh/m³ (57% reduction). The time spent within the safe operating window (SOW) per day, increased from 8 h12 m under the poorest operating conditions up to 19 h56 m with the triple SC bank. Importantly, the results indicate that steady-state system performance at an average wind speed can be used as a very good indicator of the expected performance under fluctuating wind conditions. The results described can assist with the design of autonomous, decentralised, off-grid renewable energy powered water treatment systems and help decide whether to include energy buffering components. [ABSTRACT FROM AUTHOR]

Abstract: Novel thin-film-composite reverse osmosis membranes were synthesized successfully for seawater desalination by incorporating the hydrophilic additive, o-aminobenzoic acid–triethylamine (o-ABA–TEA) salt, into the aqueous m-phenylenediamine (MPD) solution to react with trimesoyl chloride (TMC) in the organic solution during the interfacial polymerization on a nanoporous polysulfone support. The membrane synthesis conditions, including o-ABA–TEA salt concentration, isopropanol (IPA) concentration, additional amine drying time, and hydrocarbon removal time, were optimized by characterizing membrane performances using synthetic 3.28wt% NaCl solution under seawater desalination conditions at 800psi (5.52MPa) and 25°C. The synthesized membranes showed a very high flux of 1.81m3/m2/day (44.4gallons/ft2/day (gfd)) and a salt rejection of 99.41%. The improvement of membrane hydrophilicity was confirmed by comparing the contact angles of the membranes synthesized with and without the hydrophilic additive. The high-flux membrane was further tested using seawater from Port Hueneme, CA and exhibited a very good and stable desalination performance for 30 days. The fouling-resistant properties of the membranes synthesized with and without the hydrophilic additive were evaluated by using sodium alginate, a common contaminant derived from seaweed, as the model foulant. The membrane synthesized with hydrophilic additive showed significantly smaller water flux decline. The surface morphologies of the membranes were analyzed using atomic force microscopy (AFM). The results showed a smoother membrane surface for the membrane incorporated with the hydrophilic additive. [Copyright &y& Elsevier]

Abstract: The purification performance of tannic acid and dissolved organic matter (DOM) contained real surface water by forward osmosis (FO) was investigated systematically. Since representing the main characteristics of natural DOM fractions, tannic acid was first used as a surrogate for natural DOM analysis. The FO could reject tannic acid effectively with removal efficiencies of approximately 99.0%, as well as for natural DOM removal. The more severe fouling flux decline accompanied with lower tannic acid retention was found at greater draw solution concentrations and in the active-layer-facing-the-draw-solution (AL-facing-DS) orientation, which was ascribed mainly to the more severe fouling resulting from greater tannic acid adsorption in the porous support layer of the FO membrane under these conditions. In the AL-facing-DS mode, it was revealed that the higher the concentrations of initial substances (i.e., tannic acid and calcium ion) in the feed water, the more notable fouling flux decline and tannic acid retention occurred. In natural DOM purification experiments, the main factors investigated had the similar influences on FO performance as those mentioned above. Further, the membrane orientation has a minor impact on the natural DOM removal by FO membrane. The permeation drag influenced by the water flux probably played a critical role in the retention of tannic acid and natural DOM contained surface water by the FO membrane in AL-facing-DS mode. [Copyright &y& Elsevier]

In this study, three different brackish surface water qualities, which represented the water quality in the Iraqi marshes, were simulated and used as feed waters to run a flat sheet reverse osmosis (RO) membrane system. The performance of three different types of the RO membrane (Thin-Film Composite (SE), Cellulose Acetate (CE), and Polyamide (AD)), under these water qualities, was investigated. The effect of the high and low feed water temperature (37°C and 11°C) on the operation efficiency of the three RO membranes was also investigated. In addition, using the Microfiltration (MF) membrane to pretreat the feed water and its effect on the performance of the RO membrane was examined. The results revealed that the SE membrane produced the highest permeate flux, while the AD membrane produced the lowest permeate flux in all three feed waters. Also, the elemental analyses showed that the CE membrane had the least rejection percentage (from 91.1% to 99.2%), but the AD membrane had the highest rejection percentage (from 97.6% to 99.5%) for all the existing feed water ions. Moreover, using the MF membrane increased the permeate flux, particularly of the runs conducted with a high temperature, and slightly improved salt ions rejection ratios by the RO membranes. Additionally, all membranes at the temperature of 37°C exhibited higher permeate fluxes than those of corresponding membranes at a lower temperature (11°C). [ABSTRACT FROM AUTHOR]

Abstract: A key to maximizing flux and decreasing fouling in reverse osmosis (RO) is to decrease concentration polarization. This is currently partially accomplished by mesh feed spacers, but mesh spacers increase the longitudinal pressure drop and form dead zones where foulants accumulate. Alternative spacer geometry is presented here where sinusoidal flow patterns are created. Several models of RO spacer channels with varying amplitude and wavelength in their sinusoids were created for evaluation by three-dimensional computational fluid dynamics (CFD) simulations (COMSOL Multiphysics software) that included predictions of concentration polarization and flux. Results over a range of pressures and salt concentrations indicated that the more tortuous geometries (higher amplitude and shorter wavelength) induced greater local fluid velocity and decreased concentration polarization, which led to greater flux. Taylor–Goertler vortices generated in the peaks and valleys of the channels aided in mass transfer. The drawback to the sinusoidal geometry was an increased pressure drop, but one of the sinusoidal geometries tested had both a lower pressure drop and higher flux than a conventional mesh spacer. A subset of the spacer geometries was built and tested experimentally in a bench-scale RO unit. Experimental and modeling data were in good agreement, confirming the benefits of the sinusoidal spacer geometries and suggesting that CFD is an effective tool for predicting performance. [Copyright &y& Elsevier]

Abstract: Reverse osmosis (RO) process is the most popular seawater desalination technology to solve global water crisis. However, the effluent of concentrated brine from RO plant could induce severe damage to marine ecosystems, especially for closed continental areas. Electrodialysis (ED) as an excellent technology has been used to treat RO effluent. An electrodialyzer which consisted of five pieces of cation-exchange membranes (CEMs) and four pieces of anion-exchange membranes (AEMs) was used to treat concentrated brine of RO plant. The effect of operation parameters such as current density, operating mode, type of membranes and initial brine concentration was investigated to measure a Lab-scale device. The results indicate that water transportation phenomenon through ED process are mainly induced by electro-osmotic rather than osmotic water transfer due to concentration difference. The ED process of RO concentrated brine can produce both refresh water and highly concentrated brine (ca. 27.13% (m/v)) for producing coarse salt via further crystallization. [Copyright &y& Elsevier]

Abstract: Despite significant advances in forward osmosis (FO) membrane development, organic fouling, due to adsorption of organic molecules prevalent in natural waters and wastewater effluents, remains a major technical problem, decreasing process performance and membrane life. We report the fabrication, characterization, and testing of thin film composite (TFC) FO membranes functionalized with poly(ethylene glycol) (PEG) for improved fouling resistance. The membranes comprise a microporous polysulfone support over which a polyamide selective layer is synthesized by interfacial polymerization. To facilitate PEG grafting, a second interfacial reaction is carried out between ethylenediamine and acyl chloride groups on the nascent polyamide layer, yielding a selective layer rich in primary amine groups. The resulting amine-rich active layer is functionalized with PEG diglycidyl ether, whose epoxide groups readily react with primary amines. Surface characterization by ATR-FTIR spectroscopy and zeta-potential measurements shows the presence of PEG and amine groups on the membrane surface, and contact angle measurements demonstrate that the PEG-functionalized active layer is more hydrophilic than that of control polyamide membrane surfaces (whose active layer does not contain a grafted PEG layer). We report the results of dynamic fouling experiments using alginate as model organic foulant, showing that membrane fouling is significantly reduced in the case of PEGylated membranes, due to the presence of a PEG barrier that hinders foulant adsorption. Finally, we use AFM adhesion force measurements to demonstrate that the interaction energy between a carboxylated colloidal probe and the PEGylated membrane is significantly weakened as compared to the control polyamide surface. The approach of amine enrichment of the membrane active layer that is reported in this work holds promise as a versatile platform on which to study different anti-fouling modifications. [Copyright &y& Elsevier]

Abstract: Polyamide reverse osmosis membranes incorporating carboxy-functionalized multi-walled carbon nanotubes (MWNTs) were prepared by interfacial polymerization of metaphenylene diamine and trimesoyl chloride. The pristine MWNTs were pre-treated with mixed acids before being modified with diisobutyryl peroxide to enhance their dispersity and chemical activity. The prepared nanocomposite membranes had a 100–300nm skin layer and the modified MWNTs were embedded within the skin layer, which was confirmed by scanning electron microscopy and transmission electron microscopy. The surface of the nanocomposite membrane was shown to be more negatively charged than bare polyamide membrane. It was shown that with an increase in the carbon nanotube loading in the membrane, the membrane morphology changed distinctly, leading to a significantly improved flux without sacrificing the solute rejection. Meanwhile, the nanocomposite membranes showed better antifouling and antioxidative properties than MWNT-free polyamide membranes, suggesting that the incorporation of modified MWNTs in membranes is effective for improving the membrane performance. [Copyright &y& Elsevier]

We present surface modification of thin-film-composite (TFC) polyamide (PA) reverse osmosis (RO) membrane by atomic layer deposition (ALD) process using trimethylaluminium (AlMe3). The aim of the inorganic ALD coating is to improve the anti-fouling performance of TFC PA membranes. The ALD processing parameters were systematically studied because of the lack of previous investigations of the ALD coated RO membranes. Two different processing temperatures (70°C and 100°C) and three different ALD cycles (10, 50 and 100) were used to deposit the Al2O3 ALD coatings on TFC PA membranes. The ALD process parameters affected on the hydrophilicity and the surface polarity as well as on the surface roughness of the coated membranes. The bacteria attachment test results indicated that the lowest number of Pseudomonas aeruginosa cells was adhered on the most hydrophilic and polar surface, among the ALD coated membranes. RO tests showed the effect of ALD coating on the water and salt permeability as well as on the salt rejection of the membranes. [ABSTRACT FROM AUTHOR]

Abstract: A Computational Fluid Dynamics (CFD) model is used to compare the reliability and accuracy of the Helmholtz–Smoluchowski (HS) approximation against a one-dimensional charge density distribution (CD) solution of an electro-osmotic perturbation in a 2D membrane channel for reverse osmosis (RO). Electro-osmotic flow within the boundary layer is induced via the placement of a pair of electrodes parallel to the membrane surface and perpendicular to the bulk flow. Although this electrode configuration results in a two-dimensional electric field, the HS approximation considers only the electric field in the direction tangential to the membrane and not the normal component. The effect of the normal component of the electric field (E y) on the flow field in the CD solution is compared against the solution using the HS approximation and it is found that the effect of E y is minimal. Greater agreement between the CD solution and the HS approximation is found at higher bulk solute mass fractions, such as typically found on the membrane surface in RO systems. The relationships between cross-flow velocity, perturbation velocity and mixing are explored. [Copyright &y& Elsevier]

Abstract: The concentrated salt solution from reverse osmosis (RO) or other desalination plants is a critical environmental problem that can impact water quality and thereby have economic and social consequences. An integration of a membrane distillation (MD) with a crystallization unit could serve as a potential way to mitigate this problem by having an almost complete water recovery and eliminating the secondary disposal problem. Hence, the continuous membrane distillation crystallization (CMDC) process was studied for a high concentration (close to saturation) feed solution. In addition, the operating conditions were optimized using an orthogonal fractional factorial (OFF) experiment design in order to realize a near zero discharge by varying the flow rates and operating temperatures on both the feed and permeate sides. The results from an L9(34) OFF experiment design indicated that the flow rates on the feed and permeate sides are the principal factors controlling CMDC performance, whereas the temperatures either on the feed or permeate sides are not main factors. The optimal operating parameter values based on four factors and three levels are a flow rate and temperature on the feed side of 0.64Lmin−1 and 338K, respectively, and on the permeate side of 0.35Lmin−1 and 303K, respectively. These operating conditions not only affect the pure water and NaCl solid production, but also the quality of the crystals obtained from the crystallizer. Factors affecting the crystal size distribution were investigated and indicated that the sodium chloride crystals had a narrow size distribution. The feed flow rate and inlet temperature had more influence on the mean crystal size and crystal size distribution, whereas the permeate flow rate and inlet temperature had relatively less effect. Therefore, CMDC operation was found not only to produce a high quality water product but also sodium chloride crystals with a relatively narrow size distribution. These results are beneficial to a better understanding of the CMDC process and improving its performance to realize zero salty water discharge to the environment. [Copyright &y& Elsevier]

Abstract: The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin film composite (TFC) spiral wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and ζ-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor to higher water permeability as the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an indirect comparison showed that the flux for the virgin TFN would be about 1.4 times that for the virgin TFC. [Copyright &y& Elsevier]