An efficient approach in water desalination using high flux induced magnetic-field hydroxyl-functionalized MgFe2O4 /CA RO membranes with organic/inorganic fouling control capability

Freshwater scarcity is a critical challenge that human society has to face in the 21st century. Desalination of seawater by reverse osmosis (RO) membranes was regarded as the most promising technology to overcome the challenge given that plenty of potential fresh water resources in oceans. However, the requirements for high desalination efficiency in terms of permeation flux and rejection rate become the bottle-neck which needs to be broken down by developing novel RO membranes with new structure and composition. Cellulose acetate RO membranes exhibited long durability, chlorine resistance, and outstanding desalination efficiency that are worthy of being recalled to address the current shortcomings brought by polyamide RO membranes. In terms of performance enhancement, it is also important to use new ideas and to develop new strategies to modify cellulose acetate RO membranes in response to those complex challenges. Therefore, we focused on the state of the art cellulose acetate RO membranes and discussed the strategies on membrane structural manipulation adjusted by either phase separation or additives, which offered anti-fouling, anti-bacterial, anti-chlorine, durability, and thermo-mechanical properties to the modified membranes associated with the desalination performance, i.e., permeation flux and rejection rate. The relationship between membrane structure and desalination efficiency was investigated and established to guide the development of cellulose acetate RO membranes for desalination.

A series of 23 neutral, anionic, and zwitterionic surfactants were tested at a concentration of 0.1% wt/vol for their influence on attachment of a Mycobacterium sp. to cellulose acetate (CA) and polyamide (PA) reverse osmosis (RO) membranes. Four cell attachment bioassays were used: (1) semiconcurrent addition of surfactant and bacteria to RO coupons (standard assay); (2) surfactant pretreatment of RO membranes (membrane pretreatment assay); (3) surfactant treatment of adsorbed cells (detachment assay); and (4) surfactant pretreatment of mycobacteria (cell pretreatment assay). Seventeen surfactants inhibited attachment to PA membranes, whereas 15 inhibited attachment to CA in standard assays and, in 13 cases, the same surfactant inhibited attachment to both PA and CA. Despite greater cell attachment to PA than CA, surfactants were typically more effective in the former membrane system. More surfactants were effective in impairing cell attachment than in promoting detachment and a number enhanced attachment in membrane pretreatment assays, suggesting surface modification of RO membranes. Cell pretreatment inhibited attachment to CA membranes, suggesting the bacterial surface was also a target for detergent activity. Multivariate regression and cluster analyses indicated that critical micellar concentration (CMC) was positively correlated with Mycobacterium attachment in CA and PA standard assays. Surfactant dipole moment and octanol/water partitioning (LogP) also contributed to detergent activity in the PA system, whereas dipole moment, molecular topology (i.e., connectivity indices), and charge properties influenced activity in the CA system. Influential variables in membrane pretreatment assays included the LogP, topology indices, and charge properties, whereas CMC played a diminished role. Surfactant dipole moment was most influential in CA membrane detachment assays. Increasing system ionic strength by LiBr addition strengthened inhibition of cell attachment to CA membranes by dodecylbenzene sulfonic acid (DBSA) and promoted DBSA adsorption to CA surfaces as indicated by attenuated total reflection Fourier-transform infrared spectrometry. Results indicate that inhibition of bacterial attachment to RO membranes may be maximized by manipulating surfactant molecular structure to optimize surface adsorption behavior.

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.

Membrane Filtration technique is being accepted worldwide as an environment friendly and energy efficient technique in Desalination Industry as compared to Thermal Desalination techniques. However, the performance of membranes which include permeate flux and rejection is affected by the membrane fouling. The properties of membrane and surface features such as porous structure, hydrophilicity/hydrophobicity charge, polymer characteristics, surface roughness determine the fouling potential of the membrane. The hydrophilic and smooth membrane surface is usually considered desirable in tackling membrane fouling issues. Therefore, many studies have focused on to enhance surface characteristics of membranes by surface coating with polymers and nanomaterials. Since, membrane coating is not done during fabrication of the most commercially available membranes, therefore, it is also important to determine the surface features of the commercially available membranes to investigate their membrane fouling potential. Thus, the objectives of this study were (1) to perform membrane surface characterization of commercial Reverse Osmosis (RO) and Nanofiltration (NF) membranes using techniques such as SEM, AFM, FTIR and XPS; (2) to measure hydrophilicity/hydrophobicity of commercial RO and NF membranes through water contact angle measurement using sessile drop method and (3) to measure the flux and percentage rejection of NF and RO membranes using Dead end filtration technique. Here, the characterization of membrane surface in terms of surface roughness, using SEM and AFM, showed that the commercial RO membrane had more ridge and valley structures and higher average surface roughness i.e. 71.24 nm as compared to NF membranes (6.63 nm). In addition, water contact angle measurements showed that the NF membrane was more hydrophilic as compared to RO membrane. The average contact angle found for RO membrane was 59.94°. On the other hand, it was observed that NF membrane is extremely hydrophilic in nature. Due to which, contact angle value was not obtained for most of the runs. The droplet could diffuse in less than 5 seconds. In addition, the dead-end filtration experiments showed that the RO membrane had much lower flux as compared to NF membrane. This can be associated with the pore structure of these membranes. Since, the NF membrane has porous structure, in oppose to RO membrane, the flux of the NF membrane is usually higher than the RO membranes. As the membrane surface roughness and hydrophobicity makes it more susceptible to the fouling leading to reduction in membrane flux and performance, it can be concluded from this study that there is a need for surface coating of RO membrane with suitable nanomaterials such as graphene oxide to improve its hydrophilicity and surface smoothness. This will eventually make the membrane more resistant to membrane fouling and will establish the use of membrane filtration technique in desalination industry in Qatar in the future. Microorganisms have been isolated from Gulf sea water, identified and differentiated and are being used to study the biofouling of RO and NF membranes, that would be coated to limit the fouling problems. Acknowledgement: This research was made possible by NPRP grant # [9-318-1-064] from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the author[s].

Development of reverse osmosis desalination membranes composition and configuration: Future prospects

Cellulose diacetate (CDA) and triacetate (CTA) were derived from Egyptian cotton to fabricate reverse osmosis (RO) membranes. The Pphase inversion method was utilized for the production of CDA‐based membranes. Comprehensive characterization of these membranes involved structural, morphologial, and hydrophilic property analyses through techniques such as nuclear magnetic resonance (NMR), infrared spectroscopy, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. NMR spectra indicated a degree of substitution of 2.9 for CTA and 2 for CDA. The resulting RO membrane demonstrated a water flux of 6.1 L/m 2 ·h and a salt rejection of 90.3%. Annealing led to an enhanced top layer with reduced defects and macrovoids in the support layer. Moreover, grafting the RO membranes with 15 wt% of 2‐acrylamidopropane‐2‐methyl sulphonic acid improved salt rejection to 96.2% and water flux to 8.7 L/m 2 .h. These findings underscore the significant performance enhancements achieved through both annealing and grafting processes in RO membranes.

Polyamide thin-film composite reverse osmosis (RO) membranes face poor chlorine resistance and antifouling properties, which greatly limit the wide application of RO technology. To evidently enhance chlorine stability, antifouling properties, and the permeability of the RO membrane, in this research, L-arginine (Arg) had been grafted on polyvinyl alcohol (PVA) first, and the functionalized PVA (denoted as PVA–Arg) had been grafted on the RO membrane surface subsequently. Results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicated the successful synthesis of PVA–Arg as well as the successful grafting of PVA or PVA–Arg on the RO membrane surface. The permeability, chlorine resistance property, and antifouling properties of all RO membranes were tested. The PVA- or PVA–Arg-grafted RO membranes showed obvious enhancements in permeability, chlorine resistance property, and antifouling properties. For PVA-modified RO membranes, the bonus PVA layer deteriorated its water flux while filtrating. However surprisingly, the PVA–Arg-grafted RO membranes exhibited excellent enhancement in water flux and antifouling properties. For the optimized sample, the pure water flux of the PVA–Arg-grafted RO membrane is 8.3% higher than the nascent RO membrane (57.2 L/m2 h compared with 52.8 L/m2 h); the salt rejection of membranes is promoted to around 99.50% from the original 95.58%. Meanwhile, the antifouling properties of PVA–Arg-grafted RO membranes are further enhanced than that of PVA-grafted RO membranes.

Styrene-grafted cellulose acetate reverse osmosis membrane for ethanol separation

The present work is focused on three main aims. The first one is the comparison of commercial polyamide (BE from Woongjin Chemical) and cellulose acetate (CE from GE Osmonics) reverse osmosis membranes when applied to the ultrapurification of aqueous hydrogen peroxide solutions. The second one is the search for possible advantages of combination of both types of membranes, which show quite different characteristics, under a hybrid cascade configuration. The results demonstrated that the employment of only polyamide membrane cascades is more competitive than hybrid systems for this application. The third one is the analysis of the influence of the product quality over the optimal economic cascades. The polyamide membrane systems were then formulated adding product quality metrics to economic criteria to afford a bicriteria nonlinear programming (NLP) problem. The Pareto solutions to the multiobjective problem were generated via the epsilon constraint method. On the one hand, maximum economic profit solutions corresponded with the configurations applying bypass. On the other hand, maximum quality solutions were obtained by low recovery rates (specifically in the last stages of the cascade).

Storage, disinfection, and life of cellulose acetate reverse osmosis membranes

Novel thin nanocomposite RO membranes for chlorine resistance

Engineering chlorine-resistant and boron selective reverse osmosis membrane: Strategies and challenges

Thermal annealing effect on cellulose acetate reverse osmosis membrane structure

The performance of cellulose acetate reverse osmosis membranes for desalination or purification is greatly affected by the microstructure of the membrane. It is, therefore, highly desirable to characterize the microstructure and its dependence on preparation conditions and past history. In this study, various types of cellulose acetate powders, flakes, and solvent cast films have been characterized by differential scanning calorimetry and thermo‐optical analysis. It is shown that ordered microstructures exist in many of these samples and that this ordering can be intensified or diminished by suitable treatments. It is conjectured that a similar microordering occurs in the dense layer of asymmetric cast membranes as a result of solvent evaporation, gelation and annealing and that the extent of orientation and chain packing in the ordered regions greatly affects the performance of reverse osmosis membranes.

Microbiological damage of cellulose acetate RO membranes