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Membrane desalination has become an important solution to global water problems. Graphene-based materials have excellent advantages in the desalination process due to their intriguing features, including single atomic layer structure, large specific surface area, hydrophobic property, rich modification approaches, etc. After an introduction of membrane, graphene and graphene oxide (GO), this review systematically summarizes the current progress and gives an insight into the graphene-based separation membranes (GBSMs). The applications of the pressure-driven graphene-based membranes are introduced and their performances are listed and analyzed. By molecular dynamics simulation (MDS), the researchers predict the excellent performances of GBSMs, including high water flux, good salt rejection, etc. which have been verified in subsequent experiments. We believe that the application of graphene-based materials in pressure-driven membrane is worthy of further exploration. Several researchers have prepared electric-driven membranes with graphene-based materials, since their good stabilities and water-retention. However, graphene is not efficient in forward osmosis membrane area for now. In spite of the shortcomings like weak mechanical strength of single layer graphene, difficult to prepare nanopores on graphene film and hard to integrate with polymer, we hold the opinion that graphene-based films still have great research value especially in the membrane separation technology. [ABSTRACT FROM AUTHOR]

Membrane fouling is the main problem during the nanofiltration (NF) process of brackish water desalination due to the existence of natural organic matter, especially humic acid (HA). Moreover, the conventional membrane cleaning method would do great harm to the environment because large amount of chemicals were employed. In order to control organic fouling, a novel cleaning method via direct osmosis backwash (DOBW) by injecting high salinity (HS) solution was developed. Different operating conditions for HS-DOBW technology in the actual process were systematically investigated. The results demonstrated that there was a strong driving force to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal conditions in terms of HS (150 kg/m 3 NaCl solution) flow rate of 0.121 L/min were selected for the subsequent experiments. The results showed that the fouling could be almost fully reversible (more than 99.78% permeate water flux recovery), and the membrane needed to be cleaned for about 10 min because of the appearance of HA on membrane surface at the fouling time of 24 h. Most importantly, the HS-DOBW technology is very effective in keeping the membrane continuously clean and ensuring stable permeate production. [ABSTRACT FROM AUTHOR]

Abstract: Pilot-scale tests were carried out on a nanofiltration (NF)–seawater reverse osmosis (SWRO) integrated membrane system (IMS) using a kind of ultra-low pressure and high selectivity NF membrane (ESNA3, Hydranautics). Three different schemes were investigated for the NF seawater softening processes. The effect of increasing NF permeate recovery rate (R NF) on the potential of scaling in the NF and RO modules was investigated in term of concentration polarization modulus (CP) of scalant ions, Stiff and Davis Stability Index (S&DSI), and Supersaturation Index (SI) of CaCO3 and CaSO4. The results show that within the test range, high R NF, large permeate flux and low specific energy consumption (Es) could be achieved simultaneously for the loosen NF membrane. The Es for ESNA3 membrane could be lower than 0.95kWh·m−3. CP SO4 2− was larger than CP CO3 2− in the NF module under the NF retentate recycling operating conditions. The SI data indicated that at R NF of higher than 65% and with antiscalant addition and pH adjustment, CaSO4 would preferentially precipitate on NF membrane surface. However, with pH adjustment, the S&DSI values on the NF and SWRO membrane surface remained negative, which indicated that CaCO3 scaling could not form in the pilot test operating range. [Copyright &y& Elsevier]

Abstract: In this study, several anti-fouling approaches including coagulation conditions (FeCl3 dosage and feed pH), air-enhanced backwash (AEB) conditions (backwash interval and AEB duration) and chemical cleaning conditions (reagents, soak time and temperature) were evaluated to enhance the feasibility of a commercial ultrafiltration (UF) membrane as a pretreatment of RO seawater desalination. A tubular commercial ceramic UF membrane with a surface layer of zirconium dioxide (ZrO2) and a supporting layer of α-alumina oxide (α-Al2O3) was employed in this study. The results showed that ferric coagulation was functional to enhance the performance of ceramic UF for seawater treatment, especially on COD removal. The trial of cleaning demonstrated that the performance of NaClO was much better than that of HNO3 under various evaluated pH values. The relevant additional experiments showed that the cleaning efficiency increased with NaClO concentration, soak time and soak temperature but decreases when soak temperature was up to 60°C. An important finding of this study is that the fouled membrane from coagulation-filtration trial can be easily and quickly recovered by acid cleaning regents followed by NaClO solution. Furthermore, short backwash interval performed more efficiently. However, it is certain that both backwash interval and AEB duration enhanced less than other approaches on the permeate quality. This study finally summarized the operating condition of each anti-fouling approach for the further potential application of UF ceramic membrane as a pretreatment of RO seawater desalination. [Copyright &y& Elsevier]

Abstract: A novel thin-film composite (TFC) seawater reverse osmosis membrane was developed by the interfacial polymerization of 5-chloroformyloxyisophthaloyl chloride (CFIC) and metaphenylenediamine (MPD) on the polysulphone supporting membrane. The performance of the TFC membrane was optimized by studying the preparation parameters, which included the reaction time, pH of the aqueous-MPD solution, monomer CFIC concentration, additive isopropyl alcohol content in aqueous solution, curing temperature and time. The reverse osmosis performance of the resulting membrane was evaluated through permeation experiment with synthetic seawater, and the structure of the novel membrane was characterized by using SEM, AFM and XPS. Furthermore, the separation properties of the TFC membrane were tested by examining the reverse osmosis performances of various conditions, the boron rejection performance and the long-term stability. The results show that the desired TFC seawater reverse osmosis membrane has a typical salt rejection of 99.4% and a flux of about 35L/m2 h for a feed aqueous solution containing 3.5wt.% NaCl at 5.5MPa, and an attractive boron rejection of more than 92% at natural pH of 7–8; that the novel seawater reverse osmosis membrane appears to comprise a thicker, smoother and less cross-linking film structure. Additionally, the TFC membrane exhibits good long-term stability. [Copyright &y& Elsevier]

High performance membrane is crucial for energy-efficient desalination of salty water and reclamation of wastewater. Commercially available reverse osmosis membranes manufactured by interfacial polymerization or phase inversion techniques usually face the obstacle of "trade-off" effect between water permeation ability and salt rejection capability. In this work, a novel approach of constructing selective separation layer of double-layer structure was proposed to break through the difficulty of fabrication of reverse osmosis membrane with both high water permeation and salt rejection capabilities. Selective separation layer comprising loose polyamide (PA) sub bulk and dense hydroxypropyl methylcellulose (HPMC)-modified polyvinyl alcohol (PVA) top skin was constructed by the technique of interfacial polymerization followed with surface coating and cross-linking. The double-layer selective separation layer was found to possess an enhanced balance in water and salt permeations and endow the composite membrane with both high water flux and salt rejection. The desired membrane with an optimized selective layer of PA2/PVA + HPMC0.2 achieved 99.4% salt rejection and 37.9 kg/m2 h MPa water permeance to brackish water, which were higher than those of commercial membrane BW30. Furthermore, the desired membrane also exhibited better separation and antifouling performances in reclamation of secondary industry effluent when compared with the state-of-the-art antifouling membrane BW30FR. Unlabelled Image • Selective separation layer of double-layer structure was successfully constructed. • 99.4% rejection and 37.9 kg/m2 h MPa water permeance to brackish water were achieved. • Desalination performance of desired membrane was better than BW30 and BW30FR. • Performance of desired membrane in treating textile effluent was better than BW30FR. • Durability of desired membrane was also better than commercial membrane BW30FR. [ABSTRACT FROM AUTHOR]