PVA/TEOS crosslinked membranes incorporating zinc oxide nanoparticles and sodium alginate to improve reverse osmosis performance for desalination

Pure water is becoming less available with increases in world population, so seawater desalination is becoming more important. For efficient seawater desalination, this paper proposes a novel mixed matrix membrane (MMM) based on the deposition of a poly(vinyl alcohol) (PVA) nanofibrous active layer on a 3-triethoxysilylpropylamine-functionalized cellulose acetate substrate. The active layer is fabricated by utilizing a tetraethyl orthosilicate–crosslinked PVA incorporating zinc oxide nanoparticles (ZnO-NPs) and sodium alginate (NaAlg). The overall reverse osmosis performance of the MMMs is enhanced by the infusion of ZnO-NPs and NaAlg in PVA; we find the optimum concentration for the best performance to be ZnO-NPs at 0.1 wt % and NaAlg at 0.01 wt %. In terms of permeation flux, salt rejection, salt passage, stability, long-term rejection, membrane antifouling, reusability, and chlorine resistance, the proposed MMMs are examined using a dead-end reverse osmosis filtration setup. The results show that the active layer achieves an optimal permeation flux of 34.6 L/m² h, a natural sea salt rejection of 97%, and a chlorine resistance of 93%, suggesting that the proposed MMMs can be useful for seawater desalination. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47559.     

A new thin-film composite seawater reverse osmosis membrane

During the past year a new thin-film composite reverse osmosis membrane that shows excellent potential for single-pass seawater operation has been developed. This membrane, designated FT-30, is formed by depositing a proprietary thin polymer coating on a microporous polysulfone support layer.Membrane samples, tested at an operating pressure of 1000 psi with synthetic seawater, yielded fluxes of about 30 gallons per square foot per day (gfd) and salt rejections as high as 99.6 percent. At 800 psi the flux dropped to 23 gfd with little decrease in salt rejection. Membrane tested with other raw waters, including tapwater at a pressure of 50 psi and brackish waters at 200-600 psi, also provided excellent results. The membrane appears to be suitable for a variety of applications, ranging from water conditioning to single-pass seawater operation.Other important performance characteristics of the new membrane are that it appears to be chlorine-resistant (not damaged by chlorine concentrations of 100 ppm in three-day immersion tests), can be operated over a wide range of pH (3–11), is resistant to compaction, and can operate at tempreatures as high as 60°C without damage.     

Performance of Nanofiltration Membranes in the Treatment of Synthetic and Real Seawater

Abstract

Nanofiltration membranes (NF) are being employed in pretreatment unit operations in both thermal and membrane seawater desalination processes and as partial demineralization to seawater. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against seawater is presented in this paper. Two commercial nanofiltration membranes (NF90 and NF270) have been investigated in details to study their performance in filtering the salt mixture, synthetic and real seawater in a cross‐flow NF membrane process at a pressure range from 4 to 9 bars. The Spiegler‐Kedem model was used to fit the experimental data of rejection with the permeate flux in order to determine the fitting parameters of the reflection coefficient (σ) and the solute permeability (P_s). The results showed that the rejection increases with pressure for NF90 and slightly increases with pressure for NF270. Also, the NF90 membrane has shown to be able to reject both monovalent and divalent of all investigated mixtures and seawater with very reasonable values but at a relatively low flux. Moreover, it reduced the salinity of investigated seawater from 38 to 25.5 g/L using one stage of the NF membrane at 9 bars. This makes NF90 more suitable for the application in the pretreatment of desalination processes. On the other hand, NF270 can reject monovalent ions at relatively low values and divalent ions at reasonable values. It has also reduced the seawater salinity to 33.6 g/L, but at a very high permeate flux. The SKM model fitted the experimental data of divalent ions in salt mixture and seawater.     

纳滤膜脱盐性能及其在海水软化中应用的研究

选择了ESNA1型纳滤膜对NaCl、MgCl2、Na2SO4、MgSO4等4种无机单盐水溶液体系进行分离实验;考察操作压力和料液浓度等的变化对纳滤膜分离性能的影响及纳滤膜脱盐的稳定性,得到一些纳滤膜脱盐的规律;并对ESNA1膜在人工海水和海水软化脱盐中的应用作了初步探索.无机盐体系脱盐实验结果显示:随操作压力升高和料液浓度增大,ESNA1膜对4种盐溶液中的离子的截留率分别增大和减小,操作压力和料液浓度的变化对一价盐溶液的截留率影响较大,对二价盐溶液的截留率影响较小.人工海水和海水软化脱盐试验结果显示:ESNA1纳滤膜在实验过程中稳定性好,在较低的操作压力下膜通量也较高,且ESNA1纳滤膜对Ca2 、Mg2 、SO42-离子的截留率均＞90%,初步判断此种纳滤膜可用于海水软化预处理.     

Rejection of salt mixtures from high saline by nanofiltration membranes

Nanofiltration (NF) membranes have recently been employed as pretreatment unit operations in seawater desalination processes and as partial demineralization to seawater. The present paper investigates the performance of selected commercial NF membranes to reject salts of high concentrations at salinity levels representative of brackish and sea water. Two commercial nanofiltration membranes (NF90 and NF270) have been investigated in detail to study their performance in filtering aqueous solutions containing different salt mixtures in a cross-flow NF membrane process within the pressure range from 4 to 9 bar. Spiegler-Kedem model (SKM) was used to fit the experimental data of rejection with the permeate flux. The results showed that NF90 membrane was shown to have a distinct ability to reject both monovalent and divalent ions of all investigated mixtures with very reasonable values but with relatively low flux. This will make NF90 more suitable for the application in the pretreatment of desalination processes. On the other hand, NF270 can reject monovalent ions at relatively low values and divalent ions at reasonable values, but at very high permeate flux. The SKM model only fitted well the experimental data of divalent ions in salt mixture. Based on the evaluation of the overall performance of NF90 and NF270 membranes, their distinct ability to reject salts at high salinity from seawater is considered an advantage in the field of pretreatment of seawater feed to desalination units.     

Flux enhancement of thin film composite RO membrane by controlled chlorine treatment

A major stumbling block in polyamide thin film composite RO membrane performance is its incompatibility with chlorine and oxidizing agents. The amide bond of the membrane is highly vulnerable to chlorine attack. Two reactions are possible with chlorine exposure i.e. N-H bond chlorination and/or aromatic ring chlorination. In this way, chlorine may cause degradation/modification in the membrane leading to deterioration in performance.However, low concentration of chlorine up to a certain time may give synergistic effect on membrane and improve its performance. Chlorine solution, if exposed to membrane for certain time gives enhancement in trans-membrane flux of the membrane.The same solution if exposed for more time deteriorates ultra-thin polyamide layer of TFC membrane. Conspicuously, the membrane with poor salt rejection and flux benefited more as compared to the membrane with better performance. In the present study, membranes with different salt rejection and flux were taken and exposed to the inorganic chlorine solution. The inorganic chlorine solutions were made by dissolving sodium hypochlorite in pH buffer. The different solutions were made by varying pH to investigate the pH dependence. The membrane samples were kept in solution for different time durations. The exposure time was monitored and the exposure level was taken in terms of ppm h (ppm chlorine solution exposed to membrane for a fixed time in h). With the same chlorine concentration, effect of varying pH was studied. Spiral wound TFC membrane modules were also subjected to chlorine solution to study its effect.     

Effects of aluminum sulfate and ferric chloride coagulant residuals on polyamide membrane performance

Pretreatment may constitute up to one-fourth of the total costs of a membrane desalting facility. By using preexisting conventional filtration plants for pretreatment, significant cost savings may be realized. However, coagulant residuals from the pretreatment process may negatively affect reverse osmosis (RO) membrane performance. Various RO membranes were tested at three different treatment plants in southern California, using either aluminum sulfate (alum) or ferric chloride coagulants and chloramines. Repeated testing using alum with multiple RO elements revealed rapid deterioration in specific flux (up to 60% over 100 h of operation), as well as progressive reductions in salt rejection (typically 3-4% over 500 h of operation). Microscopic analysis of the fouled membranes revealed that the foulants were primarily aluminum hydroxide and aluminum silicate materials. In contrast to the RO data for alum coagulation, which showed declining membrane flux, the specific flux data using ferric chloride and chloramines increased over time for all membranes. Salt rejection decreased significantly during testing of each membrane. These data suggest that the RO membranes were physically degrading over time. The RO membranes may have been degraded by residual iron catalyzing a chlorine-amide reaction on the membrane surface, despite the fact that chlorine was present as chloramines.     

Nanofiltration of Magnesium Chloride,Sodium Carbonate,and Calcium Sulphate in Salt Solutions

Abstract

Nanofiltration (NF) membranes have been employed in pre‐treatment unit operations in both thermal and membrane seawater desalination processes. This has resulted in reduction of chemicals used in pretreatment processes as well as lowering the energy consumption and water production cost and, therefore, has led to a more environmentally friendly processes. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against brackish water and seawater is required. In this study, three commercial nanofiltration membranes (NF90, NF270, N30F) have been used to treat highly concentrated different salts solutions (MgCl₂, Na₂CO₃, and CaSO₄) at salinity level similar to that of brackish water and seawater. The main parameters studied in this paper are salt concentration and feed pressure. The experimental data were correlated and analysed using the Spiegler‐Kedem model. In particular, the reflection coefficient (σ) of all studied membranes and the solute permeability (P_s) have been determined for all membranes and at different salinity levels of studied salts. All the studied membranes fitted the model well for all investigated salts except the experimental data of MgCl₂ using N30F membrane, which did not fit well at low rejection. The results showed that NF90 produced a high rejection around 97% for all salts with medium permeate flux while NF270 gave a high flux with medium rejection and N30F gave low rejection and flux.     

Change of membrane performance due to chlorination of crosslinked polyamide membranes

A systematic investigation of the relationship between chlorine exposure of a thin film composite crosslinked polyamide membrane (LE membrane, FilmTec©) and changes in membrane performance (water flux and salt rejection) is discussed here. Performance change of crosslinked polyamide membranes due to chlorination depended on pH and concentration of chlorine in the soaking bath. Membranes chlorinated at low pH and high chlorine concentration showed flux decreases at an early stage of filtration and then increases with filtration time. On the other hand, membranes chlorinated at high pH and low chlorine concentration showed flux increases at an early stage and then decreases with filtration time. Performance of chlorinated polyamide membranes was determined by the balance between rearrangement of polymer chains and the distortion of the chains due to chlorination. A conceptual model of performance change was proposed consistent with the chlorination of polyamide membranes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5895–5902, 2006     

Spiral-wound new thin film composite membrane for a single-stage seawater desalination by reverse osmosis

New thin film composite membrane system, designated PEC-1000, formed by the acid catalyzed polymerization on the surface of a reinforced-porous supporting membrane, make it possible to produce potable water from seawater by reverse osmosis in a single-stage with a high recovery operation. TDS rejection over 99.9% and stable water fluxes of 0.20–0.30 m³/m²-day (5.0–7.4 gal/ft²-day) have been attained with 3.5% synthetic seawater at an applied pressure of 56Kg/cm²(800psi). For brackish water, sodium chloride rejections of 99.6–99.9% and fluxes of 0.61–0.81m³/m²-day(15.0-20.0 gal/ft²-day) have been attained with 5000 ppm sodium chloride feed at an applied pressure of 40Kg/cm² (571psi). TDS rejection of 99.8% and water flux of 0.30 m³/m²-day (7.4 gal/ft²-day) have been attained with two- or four-inch diameter PEC-1000 composite membrane elements at an applied pressure of 56Kg/cm²(800psi) in a single-stage synthetic seawater desalination test. This performance is kept for more than 1500 hours in PEC-1000 thin film composite membrane and two-inch diameter element. 280 ppm in TDS and water flux of 0.11 m³/m² day (2.7 gal/ft²-day) are observed at an applied pressure of 56Kg/cm²-40% water recovery with one four-inch diameter spiral-wound PEC-1000 composite membrane element in a single-stage seawater desalination. This membrane shows high selectivity for low molecular weight valuable organic materials such as ?-caprolactam, dimethylsulfoxide, dimethylformamide. The thickness of ultrathin salt barrier of the composite membrane is found to be 300Å by the Electron Microscopy with special ultrathin section techniques.     

Desalination of non-chlorinated surface seawater using TFC membrane elements

The Umm Lujj II reverse osmosis (RO) desalination plant in Saudi Arabia has produced high quality potable water [< 200 mg/L total dissolved solids (TDS) concentration] at better than design capacity [4,400 m³/d (1.16 MGD)] from non-chlorinated Red Sea surface seawater (42 g/L TDS concentration) since May 1986. The plant employs thin-film composite (TFC^R) spiral-wound membrane elements manufactured by UOP Fluid Systems. During the two years of operation, there have been no element additions or replacements and no element cleaning has been required. The only meaningful biological concern for surface seawater RO plants containing TFC^R membrane is algae growth, which is effectively controlled by a low concentration of copper sulfate. The seawater is not pretreated with a general disinfectant such as chlorine because other live microorganisms in the surface seawater do not attack or excessively foul UOP's TFC^R membrane. There has been no evidence of fouling by microorganisms or other foulants at Umm Lujj. This is reflected in the normalized membrane water flux after the two-year period being at the predicted value for a non-fouling feedwater. It is proposed that the long-term stability of TFC^R membrane with non-chlorinated surface seawater is due to its surface properties.     

Hydrophobic mullite ceramic hollow fibre membrane (Hy-MHFM) for seawater desalination via direct contact membrane distillation (DCMD)

A low-cost hydrophobic mullite hollow fibre membrane (Hy-MHFM) fabricated via phase inversion/sintering technique followed by fluoroalkyl silane (FAS) grafting is presented in this study. The prepared CHFMs were characterized before and after the grafting step using different characterization techniques. The pore size of the CHFM surface was also determined using ImageJ software. The desalination performance of the grafted membrane was evaluated in direct contact membrane distillation (DCMD) using synthetic seawater of varying salt concentrations for 2 h at various feedwater temperatures. The outcome of the evaluations showed declines in the permeate flux of the membrane at increasing feed concentration, as well as increased flux with increased feed temperature. The long-term stability of the membrane was achieved at time 20 h, feed temperature 60 °C, and permeate temperature 10 °C, the membrane achieved a salt rejection performance of about 99.99 % and a water flux value of 22.51 kg/ m² h.     

氧化石墨烯掺杂反渗透混合基质膜制备及性能

由于芳香族聚酰胺反渗透膜在抗污染性以及耐氯性方面存在不足,限制了其在海水淡化等方面的应用。采用往油相中添加氧化石墨烯（GO）的二次界面聚合法改性了商业反渗透膜,评价了GO掺杂反渗透混合基质膜的分离性能和耐氯性能,并用接触角仪、Zeta电位仪、扫描电镜和原子力显微镜等仪器表征了膜的亲水性能、荷电性能以及膜表面形貌。结果表明,GO的添加提高了膜的分离性能、耐氯性能和亲水性能;当GO添加量为30 mg·L^-1时,膜的通量为（77.7±0.9） L·m^-2·h^-1,膜的截留率为97.6%±0.5%,相比商业膜分别提高了38.4%和4.5%。当氯化强度低于4800 mg·L^-1·h时,膜的水通量和盐截留率变化不明显。     

Preparation of graphene oxide/polyamide composite nanofiltration membranes for enhancing stability and separation efficiency

Polyamide (PA) NF membranes are synthesized on a hollow fiber support by the interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). Then, GO is coated on the PA layer to decorate the NF membrane surface (denoted GO/PA-NF). This strategy aims to improve the hydrophilicity, chlorine resistance and separation stability of the membrane. The optimization, chemical composition, morphology, and hydrophilicity of the synthesized GO/PA-NF membrane are characterized. Results indicate that the optimized GO/PA-NF in terms of rejection rate and flux are with 0.05 wt% GO. The rejection of GO/PA-NF for Na2SO₄ and MgSO₄ is 99.4% and 96.9%, respectively. Even if the GO/PA-NF is immersed in 1000 ppm NaClO solution for 48 h, the NF membrane still maintains stable salt rejection. The developed NF membranes exhibit excellent treatment performance on dying wastewater. The permeate flux and rejection of GO/PA-NF toward Congo red solution are determined to be 44.2 L/m²h and 100%, respectively. Compared with the PA membrane, GO/PA-NF presents a higher rejection for Na₂SO₄ (99.4%) and a lower rejection for NaCl (less than 20%), which shows that the NF membranes have a better divalent/monovalent salt separation performance. This study highlights the superior performance of GO/PA-NF and shows its high potential for application in wastewater treatment.     

沸石/聚酰胺反渗透复合膜的制备

为了提高反渗透膜的通量,通过在界面聚合反应过程中添加NaA型纳米沸石分子筛制备了沸石/聚酰胺反渗透复合膜,采用SEM及复合膜性能测试的方法比较了沸石分子筛添加在水相或者油相中时对膜结构及分离性能的影响.SEM图谱结果表明:沸石分子筛添加在油相中时,沸石在聚酰胺基质中分散均匀,膜结构比较均一;但当沸石分子筛添加在水相中时...     

Cellulose triacetate membranes for seawater desalination

Experimental data on reverse osmosis using a sodium chloride solution by cellulose triacetate membranes are presented. The investigation involved studies on the composition of membrane casting solutions and their effects on the performance. A higher polymer concentration (11–13%) is found suitable for production of a uniform and highly salt rejecting membrane. Salt rejection of 99.0% and 4–5 GFD product water flux were obtained at 1000 psi operating pressure using 30,000 ppm TDS seawater in the initial experiments.     

Impact of halogen based disinfectants in seawater on polyamide RO membranes

The effect of halogen based disinfectants including monochloramines (NH₂Cl), free chlorine (HOCl/OCl⁻), and free oxidants (mixture of HOCl/OCl⁻ and HOBr/OBr) on polyamide membrane was studied in synthetic Ocean seawater. Formation and stability of these oxidants were also examined. Permeability and salt rejection of flat sheet polyamide RO membranes following exposure to the halogen based oxidants were compared to the baseline performance of unexposed membranes. The ratio between free chlorine and free bromine was found to depend on the ratio between the bromides, naturally found in seawater, and the added chlorine. Bromide enhanced the degradation of monochloramines but did not affect the stability of free chlorine. All the oxidants damaged the polyamide membranes studied while the free oxidants appeared to be the most aggressive.     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Self-doped sulfonated polyaniline ultrafiltration membranes with enhanced chlorine resistance and antifouling properties

Membranes heavily rely on chlorination to diminish (bio)fouling, but chlorination can also lead to membrane degradation. We developed sulfonated polyaniline (S-PANI) ultrafiltration (UF) membranes with improved chlorine resistance and intrinsic antifouling properties. The S-PANI membranes were synthesized through Non-solvent Induced Phase Separation (NIPS). Membrane performance was evaluated under harsh chlorine conditions (250 ppm sodium hypochlorite for 3 days under different pH conditions). The S-PANI membranes showed improved chlorine resistance including a stable performance without changes in model foulant BSA rejection. In contrast, PANI membranes suffered critical structural damage with complete leakage and commercial PES membranes showed a 76% increase in pure water flux and a noticeable change in BSA rejection. Small changes in S-PANI membrane performance could be linked to membrane structural changes with pH, as confirmed by SEM, IR spectroscopy, and contact angle measurements. Additionally, the S-PANI membranes showed better antifouling properties with a high flux recovery ratio in comparison to PANI membranes using alginic acid, humic acid, and BSA model foulants. Chemical cleaning by sodium hypochlorite re-instated the transport properties to its initial condition. Overall, the developed S-PANI membranes have a high chlorine tolerance and enhanced antifouling properties making them promising for a range of UF membrane applications.     

High‐performance composite nanofiltration membranes fabricated via ternary mixture: Complementary preponderance of the fluorine‐containing monomer 2,2′‐bis(1‐hydroxyl‐1‐trifluoromethyl‐2,2,2‐triflutoethyl)‐4,4′‐methylene dianiline and the rigid monomer bisphenol F

In a previous study, we proved that tailoring the polyamide backbone stiffness is an effective way to fabricate high‐performance polyamide nanofiltration (NF) membranes. However, in the previous study, we mainly focused on the flat membrane and did not consider its chlorine tolerance. In this study, by regulating the aqueous‐phase compositions in the interfacial polymerization process, chlorine tolerance on NF hollow‐fiber membranes was endowed while the membrane performance stayed high. The experimental results show that when the ratio of Piperazine (PIP)–bisphenol F (BPF)/2,2′‐bis(1‐hydroxyl‐1‐trifluoromethyl‐2,2,2‐triflutoethyl)‐4,4′‐methylene dianiline (BHTTM) was 5:1:4, the NF membrane possessed a permeate flux of 21.0 L m^?2 h^?1 bar^?1 and an Na₂SO₄ rejection up to 90.0%. X‐ray photoelectron spectroscopy analysis also confirmed that the polymerization degree of the PIP–BPF–BHTTM NF membrane was the highest. Moreover, the NF membrane could tolerate active chlorine to over 10,000 ppm h Cl. After the active chlorine treatment, the permeate flux increased over 30.0 L m^?2 h^?1 bar^?1, and the Na₂SO₄ rejection was about 90.0%. Although the PIP–BHTTM NF membrane also possessed good chlorine tolerance, its permeate flux (after active chlorine treatment) was only 60% of that of the PIP–BPF–BHTTM NF membrane. Therefore, the PIP–BPF–BHTTM NF membrane possessed a combination of high flux and high chlorine tolerance and showed good potential in water treatment in rigorous environments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46482.