Reverse Osmosis Membrane Desalination Research Articles

High performance polyester reverse osmosis desalination membrane with chlorine resistance

Chlorination is a common practice to prevent biofouling in municipal water supplies, wastewater reuse and seawater desalination. However, polyamide thin-film composite reverse osmosis membranes—the premier technology for desalination and clean-water production—structurally deteriorate when continually exposed to chlorine species. Here, we use layer-by-layer interfacial polymerization of 3,5-dihydroxybenzoic acid with trimesoyl chloride to fabricate a polyester thin-film composite reverse osmosis membrane that is chlorine-resistant in neutral and acidic conditions. Strong steric hindrance and an electron-withdrawing group effectively prevent direct aromatic chlorination, and residual OH groups capped with isophthaloyl dichloride preclude reaction with active chlorine. The poly(isophthalester) membrane exhibits high salt rejection (99.1 ± 0.2%) and water permeability (2.97 ± 0.13 l m−2 h−1 bar−1), even after demonstrating biofouling prevention with chlorine (50 mg l−1 of NaOCl for 15 min). We anticipate that our chlorine-resistant membrane will greatly advance reverse osmosis desalination as a sustainable technology to meet the global challenge of water supply. Reverse osmosis membranes are the primary technology used for desalination and wastewater recycling, but they are prone to biofouling and subsequent performance deterioration due to poor tolerance to disinfecting agents such as chlorine. Here a chlorine-resistant polyester reverse osmosis membrane is developed to prevent biofouling and increase the sustainability of desalination and wastewater reuse.

Exploiting interior surface functionalization in reverse osmosis desalination membranes to mitigate permeability–selectivity trade-off: Molecular simulations of nanotube-based membranes

Increasing demand for affordable desalinating water has stimulated the vigorous development of reverse osmosis (RO) membranes. To date, the performance of polymeric membranes is limited by the permeability–selectivity trade-off: more permeable membranes lead to a less ideal selectivity and vice versa. Significant efforts have been made to identify new classes of ultra-permeable nanoporous membranes, but such trade-off can still be commonly observed. In this study, we identify the key role of the surface uniformity and chemistry of permeation channels inside nanoporous membranes in mitigating the trade-off. By using highly tunable aluminosilicate nanotubes (AlSiNTs) as a model system, this study demonstrates that, by properly designing the interior surface of AlSiNTs, the materials can offer not only higher water permeability but also a better ability to reject salts. Detailed investigations on the capacity, dynamics, energetics, and distribution of water as well as the free energy landscapes for water molecules and ions are also carried out to understand the permeation mechanisms of species at an atomic level. The outcomes obtained herein can provide guidelines for the rational design of nanotube-based membranes, or porous materials in general, to achieve more efficient and effective desalination processes.

Novel functionalized graphitic carbon nitride incorporated thin film nanocomposite membranes for high-performance reverse osmosis desalination

In this study, a series of hydrophilic graphitic carbon nitride (g-C3N4) nanosheets was synthesized with various oxygen donor compounds to produce OH, COOH and SO3H groups on the surface of g-C3N4 and incorporated in polyamide layer (PA) of thin film nanocomposite (TFN) membrane to fabricate reverse osmosis (RO) membranes with excellent antifouling and desalination properties. The results of FTIR and EDX analysis indicated the successful introduction of functional groups on the g-C3N4 nanosheets surface. The average surface roughness of the modified membranes with COOH functionalized g-C3N4 nanosheets decreased to 3.2 nm with 82% decrease compared with g-C3N4 modified membranes. The effect of incorporated g-C3N4 nanosheets on the performance of the membranes was studied using pure water flux, NaCl and BSA solution filtration. The outcomes showed that introducing of the functionalized g-C3N4 nanosheets in the PA active layer of the membranes improved considerably the membrane permeation without decrease in rejection performance. The modified membrane with COOH functionalized g-C3N4 nanosheets showed maximum pure water flux of 91.8 L/m2 h with 54% increase compared with g-C3N4 modified membranes.

Quantitative Characterization of a Desalination Membrane Model System by X-ray Photoelectron Spectroscopy.

Aromatic polyamide films form the active layer in reverse osmosis desalination membranes. Despite widespread use of this technology, it suffers from low rejection rates for certain water contaminants and from membrane fouling. Through a better understanding of the fundamental surface chemical processes during reverse osmosis desalination, advances in membrane and material design are expected. The recent invention of a molecular layer-by-layer (mLbL) preparation technique [ Johnson , P. M. ; Molecular Layer-by-Layer Deposition of Highly Crosslinked Polyamide Films . J. Polym. Sci., Part B: Polym. Phys. 2012 , 50 ( 3 ), 168 - 173 ] yields films that are sufficiently smooth to warrant investigation with high-resolution microscopy and spectroscopy methods. We present high-resolution, quantitative X-ray photoelectron spectroscopy (XPS) data on the surface chemistry of ultrathin polyamide films that can serve as a model system for desalination membranes. We show that a quantitative analysis of the XPS spectra gives information about the functional groups of the film as well as other compounds present due to the synthesis under ambient conditions. Unpolymerized functional groups are identified and aid in understanding the degree of cross-linking. Investigation of polymers with synchrotron-based XPS requires taking beam-induced changes into account. We quantify X-ray beam damage and show that beam damage to the polyamide is limited, allowing long-term investigation of thin polyamide films. Characterizing mLbL-grown films via high-resolution XPS is the basis for a better understanding of the chemical interplay of polyamide surface functional groups with the major components of desalination systems.

Exploring the Potential of Defective UiO-66 as Reverse Osmosis Membranes for Desalination

Defects in metal–organic frameworks (MOFs) can play an important role in the development of MOFs as promising reverse osmosis (RO) membranes for water desalination. By employing molecular dynamics ...

Evaluation of biofouling behavior of zwitterionic silane coated reverse osmosis membranes fouled by marine bacteria

Zwitterionic modification of membrane surfaces is a promising approach to decrease membrane biofouling. In this study, biofouling properties of two commercial polyamide (PA) reverse osmosis (RO) desalination membranes coated with zwitterionic sulfobetaine silane compounds including4-(diethyl(3-(trimethoxysilyl)propyl)ammonia)butane-1-sulfonate (EPBS) and 3-(dimethyl(3-(trimethoxysilyl)propyl)ammonia)propane-1-sulfonate (MPPS) were investigated using five different marine bacteria isolated from Bosphorus, Turkey. To mimic the real environment, new marine strains were isolated for the biofouling assay. The biofouling behavior was monitored at different maturation stages of biofouling bacteria on the surfaces of the membranes. In addition, the permeability variation of the coated membranes was analyzed by measuring the flux values before and after the biofouling process compared to the uncoated, control membrane. According to the results, while commercial control RO membranes were highly prone to biofouling, zwitterionic sulfobetaine silane coated membranes showed a strong anti-bacterial effect against the isolated marine biofouling bacteria with significant bio-film adhesion resistance. When the flux value of commercial uncoated control membrane decreased by 38% after biofouling, the flux reduction was 16% and 20% in the EPBS and MPPS coated membranes, respectively.

Defect-free highly selective polyamide thin-film composite membranes for desalination and boron removal

Removal of boron from saline water sources has presented a major challenge for commercially available reverse osmosis desalination membranes. In this work, we report the boron and sodium chloride separation properties of truly defect-free, highly selective, interfacially polymerized aromatic polyamide thin-film composite membranes. The fabricated membranes show potential for separating sodium chloride with a maximum rejection of 99.6% obtained for the optimized film-forming protocol under lab-scale brackish water desalination conditions. This translated into promising boron rejection performance with rejections of up to 99% at pH 10, higher than a number of commercially available reverse osmosis membranes tested in-house. Comprehensive characterization including X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, ellipsometry, and surface charge measurements revealed intimate insights on interfacially polymerized polyamide membrane structure-property relationships. Increased membrane crosslinking was shown to be the primary determining factor for membrane permselectivity performance. Furthermore, relationships were established between microstructural properties such as crosslinking and morphological characteristics like surface roughness, highlighting an intricate and complex structure formation mechanism.

Composition and Molecular Identification of Bacterial Community in Seawater Desalination Plants

Biofouling is an important problem for reverse osmosis (RO) membrane manufacturers. Bacteria are mainly involved in generating fouling and obturating RO membranes. Insights into biofilm bacteria composition could help prevent biofouling, reduce the cost of using RO-fouling membranes and guarantee safe water. Culture-dependent and independent techniques were then performed in order to identify bacteria associated with RO membranes. Bacteria cultures described the presence of six pure colonies, four of which were identified through API testing. Based on 16s rRNA gene analysis, a predominant bacterium was identified and annotated as Sphingomonas sp. The 16s rRNA gene clone library, on the other hand, showed that the bacterium, Pseudomonas marincola, accounted for nearly 30% of the clone library, while the rest of bacteria were chimeras (62%) and non-representative species (3%). In conclusion, culture-dependent and independent approaches showed that two dominant bacteria were commonly observed in RO desalination membranes.

Permeate flux increase by colloidal fouling control in a vibration enhanced reverse osmosis membrane desalination system

Experiments and Computational Fluid Dynamics (CFD) simulations were performed to investigate the colloidal fouling control of a vibration enhanced reverse osmosis (VERO) membrane system for up to 12 h of operation time. A porous cake mass transfer model for the reverse osmosis (RO) colloidal fouling analysis was derived by combining the cake filtration model, cake enhanced osmotic pressure (CEOP) effect, the critical flux theory, and the solute convection-diffusion model. The process of colloidal particle deposition and fouling formation on the membrane surface were visualized using this model. The permeate flux variation and cake layer distribution along the membrane were depicted. Systematic studies including different initial permeate fluxes, Reynolds numbers, particle concentrations, and vibration frequencies were carried out to investigate the system performance under different operation conditions. The results suggest that colloidal fouling induced permeate flux decline could be improved by the high-frequency vibration in the VERO module. Both simulations and experiments demonstrated that, with a fixed vibration amplitude, membrane module with higher vibration frequencies will have less NaCl accumulation and higher permeate flux under the influence of colloidal fouling.

Investigating the prospects of water desalination using a thermal water pump coupled with reverse osmosis membrane

This paper presents the design and experimental analysis of a thermal water pump coupled with a reverse osmosis desalination membrane. The operation, thermodynamic cycle and design of the proposed system are explained with the aid of system schematics and thermodynamic process diagrams, while the experimental performance of the thermal water pump in combination with a reverse osmosis membrane is presented and discussed. It is shown that for feed water at a salt concentration of 1184 ppm and a heat source temperature of 86 °C, the proposed system is shown to be able to produce fresh water at a rate of 1.27 L/h with a specific energy consumption of 165 MJ/m3. The recovery ratio obtained under these conditions is shown to be 26%. The performance and characteristics of the proposed system are contrasted with data for existing multi-stage thermal desalination systems as well as Rankine cycle–reverse osmosis desalination systems and it is shown to compare favourably to both for low salinity applications.

Polymersomes-based high-performance reverse osmosis membrane for desalination

Polymersomes-based reverse osmosis (RO) membrane (PBM) for desalination was reported for the first time. An amphiphilic tri-block copolymer, PMOXA6-PDMS35-PMOXA6 (ABA), was self-assembled to form polymersomes with spherical nanostructure. The polymersomes were then immobilized into a polyamide network via an interfacial polymerization reaction on top of polysulfone membrane substrate. Under a moderate salinity condition, the PBM presented almost doubled water permeability and higher salt rejection than the control membrane without polymersomes in the polyamide network. Based on the results of a series of characterization the better water permeation of the PBM is believed to result from larger globular features containing highly water permeable polymersomes, which created a higher void fraction in the selective layer, whereas the highly cross-linked polyamide selective layer as well as the polymersome bilayer’s impermeability to NaCl may led to the enhanced salt rejection. Surprisingly, at an elevated NaCl concentration up to 32,000 ppm, the PBM exhibited ~ 60% water flux enhancement and even better NaCl rejection as compared with commercial seawater RO membranes. In general, the PBM presented a water flux similar to the RO membranes with loose polyamide matrix (BW30), but a rejection behavior close to the dense RO membranes (SW30). This study provides a paradigm shift in developing new-generation RO membranes for energy and cost-effective desalination process.

A novel pathway for high performance RO membrane: Preparing active layer with decreased thickness and enhanced compactness by incorporating tannic acid into the support

We report a novel pathway for preparing polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane with high permselectivity by incorporating tannic acid (TA) into the polysulfone (PSf) support. The support and RO membrane were characterized systematically. The results showed that (1) the support surface was enriched with TA due to the high hydrophilcity of TA and (2) TA endowed the RO membrane with a thinner and more compact PA active layer. The influencing mechanism of TA on the PA layer formation was discussed. TA affected the formation of PA layer through changing the m-phenylenediamine (MPD) molecules absorption behavior and the formation of the nascent film. The RO membrane desalination performances for both brackish water and seawater were evaluated. Due to the thinner and more compact PA active layer, PSf/TA-RO (the membrane prepared on PSf/TA support) possessed a higher rejection and a comparative flux compared to PSf-RO (the membrane prepared on PSf support). This work provides an effective way for preparing high performance RO membranes via utilizing support to tailor the aqueous phase monomer absorption and the formation of the nascent film.

High fouling-resistance of polyamide desalination-membrane modified with PEI/PAH polyelectrolyte multilayers

Membrane fouling is a persistent problem in reverse osmosis (RO) process which leads to higher operating pressure, quality deterioration, and frequent chemical cleaning of the membranes. The objective of this paper is to prepare a fouling-resistant RO desalination membrane while keeping high salt rejection and permeate flux. Polyamide (PA) membranes were prepared and modified using spin assisted Layer-by-Layer assembly of polyelectrolytes (PEI/PAH), characterized and tested in a cross-flow desalination setup. The effect of preparation conditions (number of coating layers, concentration and pH of the polyelectrolyte solutions) on the performance of the membrane was also investigated. SEM micrographs showed that the surface of the PA membrane is rough and has typical ridge and valley structure. However, images of the modified membranes showed smoother surfaces as the number of polyelectrolyte bilayers was increased which was verified using the AFM analysis. In addition, contact angle measurements suggested that the surfaces of the modified membranes became more hydrophilic due to the presence of hydrophilic hydroxyl and amine groups. Permeation results showed comparable salt rejection under saline feed water of 2000ppm. 50 bilayer modified membrane having 110mg/L of polyelectrolyte solution, possess permeability of 0.83L/m2hbar with 95% salt rejection. However, 27 bilayer modified membrane having 200mg/L of polyelectrolyte solution, possess greater permeability of 1.78L/m2hbar with 96% salt rejection. Fouling experiments showed that after three hours of filtration, functionalized membranes retained more than 88% of water flux compared to pristine polyamide membrane which suffered from more than 42% flux drop.

Treatment of cleaning waters from seawater desalination reverse osmosis membranes for reutilization purposes. Part II: Application of photo-Fenton and photocatalysis processes

This is the second part of the study of cleaning waters from seawater desalination reverse osmosis membranes treatment, with the aim of reclaiming them for reuse. In the first part, Fenton process was applied in these wastewaters and a TOC removal of 67% and a final BOD5 value of 14.8mgL−1 O2 were achieved by using 4000mgL−1 of H2O2 and 200mgL−1 of Fe2+. In this part, photo-Fenton and photocatalysis processes were explored in order to enhance mineralization degree. The highest elimination was achieved with the photo-Fenton process at pH 3, where 79% of TOC removal was obtained with 1400mgL−1H2O2 and 70mgL−1 Fe2+ (3 times lower than in the Fenton process) under solar radiation after 60min, and 85.6% after 157min, with the total removal of sodium dodecyl sulfate and obtaining a suitable water for irrigation. This photo-Fenton reaction could also be performed at pH 7, as after 157min, the same elimination is reached. The addition of P25 accelerates the photo-Fenton process, although after one hour of treatment, similar elimination was reached for both conditions. 77% of TOC removal after 180min was obtained under solar radiation at pH 3 by adding 1200mgL−1 of H2O2 with 250mgL−1 of P25 instead of Fe.

Treatment of cleaning waters from seawater desalination reverse osmosis membranes for reutilization purposes. Part I: Application of Fenton process

The scope of the present work is the study of the Fenton process applied to the removal of the organic load of cleaning waters from seawater desalination reverse osmosis membranes in order to be reused for irrigation or in other stages of the process and contribute to the concept of zero discharge in a reverse osmosis desalination plant. Fenton experiments were performed at pH 3 after selecting ratios of H2O2/COD (wt.) between 1.9 and 20, and H2O2/Fe2+ (wt.) between 0.13 and 82.80. For the studied conditions, it was observed that the optimal reaction time was 157min and the optimal reagents doses were above 4000mgL−1 of H2O2 and 200mgL−1 of Fe2+. This combination achieved a maximum TOC removal of 67% and a final BOD5 value of 14.8mgL−1 O2.

Theoretical performance prediction of a reverse osmosis desalination membrane element under variable operating conditions

Sea Water Reverse Osmosis (SWRO) desalination systems powered by Renewable Energy (RE) can reduce drastically costs, specific energy consumption and CO2 emissions. A direct connection of a SWRO desalination system with RE technologies such as photovoltaics, can result in lowering the specific energy consumption due to the part-load operation of the desalination unit. However, due to the variable nature of solar energy, the membranes could operate outside of their nominal operating ranges. Therefore, research is needed to investigate the effect of the variable operation (non-stable pressure and flow rate) on the membranes. This paper presents the development of a dynamic mathematical model of a spiral wound reverse osmosis membrane module aiming to investigate the mass transfer in the membrane under non-constant operating conditions. The main pursue of the model is to investigate the physical compaction, as well as the raise of the concentration polarization in order to predict the performance of the membrane under variable operating conditions. The results show a water flux drop of 0.2×10−3kg/m2·s due to the sudden increase in the applied pressure, when the impact of physical membrane compaction was taken into consideration under non-constant operating conditions.

Fouling characteristics and fouling control of reverse osmosis membranes for desalination of dyeing wastewater with high chemical oxygen demand

Fouling of reverse osmosis (RO) membranes is a severe problem for desalination of dyeing wastewater with high chemical oxygen demand (COD). In this paper, fouled RO membranes in a pilot-scale desalination system of biologically treated dyeing wastewater containing high COD (143–228mg/L) with or without injection of non-oxidizing biocides were analyzed. The two non-oxidizing biocides used are K5030 (a kind of isothiazoline biocide) and FR110 (an inorganic base type of combined chlorine agent), respectively. For the RO membrane from the system without non-oxidizing biocide injection to the influent, a typical biofilm occurred on the RO membrane in a short operation time of 19days. The injection of non-oxidizing biocides caused a decline of nearly 99.0% in active biomass on the RO membrane. Burkholderiales ruled mature biofilm on the RO membrane without injection of non-oxidizing biocide. Pseudoxanthomonas exhibited a certain resistance to non-oxidizing biocides and ruled the bacterial community on the RO membrane with injection of non-oxidizing biocides. Fe, P and Al were major inorganic elements on RO membranes, decreasing with injection of non-oxidizing biocides. Hydrophobic neutral (HON) fraction was the most major organic component of dissolved organic matter (DOM) on RO membranes, decreasing notably with injection of non-oxidizing biocides.

Permeability of uncharged organic molecules in reverse osmosis desalination membranes

Reverse osmosis (RO) membranes are primarily designed for removal of salts i.e. for desalination of brackish and seawater, but they have also found applications in removal of organic molecules. While it is clear that steric exclusion is the dominant removal mechanism, the fundamental explanation for how and why the separation occurs remains elusive. Until recently there was no strong microscopic evidences elucidating the structure of the active polyamide layers of RO membranes, and thus they have been conceived as “black boxes”; or as an array of straight capillaries with a distribution of radii; or as polymers with a small amount of polymer free domains. The knowledge of diffusion and sorption coefficients is a prerequisite for understanding the intrinsic permeability of any organic solute in any polymer. At the same time, it is technically challenging to accurately measure these two fundamental parameters in very thin (20–300 nm) water-swollen active layers. In this work we have measured partition and diffusion coefficients and RO permeabilities of ten organic solutes in water-swollen active layers of two types of RO membranes, low (SWC4+) and high flux (XLE). We deduced from our results and recent microscopic studies that the solute flux of organic molecules in polyamide layer of RO membranes occurs in two domains, dense polymer (the key barrier layer) and the water filled domains.

Performances of nanofiltration and low pressure reverse osmosis membranes for desalination: characterization and modelling

The nanofiltration and the reverse osmosis processes are the most common techniques for the desalination of water contaminated by an excess of salts. In this present study, we were interested in the characterization of commercial, composite and asymmetric membranes of nanofiltration (NF90, NF270) and low pressure reverse osmosis (BW30LE). The two types of characterization that we opted for our study: (i) characterization of electrical proprieties, in terms of the surface charge of various membranes studied by the measurement of the streaming potential, (ii) hydrodynamic characterization in terms of hydraulic permeability with pure water, mass transfer and phenomenological parameters for each system membrane/salt using hydrodynamic approaches. The irreversible thermodynamics allowed us to model the observed retention Robs of salts (NaCl and Na2SO4) for the different membranes studied, to understand and to predict a good filtration with a membrane. A study was conducted on the type of mass transfer for each system membrane/salt: convection and diffusion. The results showed that all tested membranes are negatively charged for the solutions at neutral pH, this is explained by their material composition. The results also showed competitiveness between the different types of membranes. In view of that the NF remains effective in terms of selective retention with less energy consumption than LPRO.

Interactions of Organics within Hydrated Selective Layer of Reverse Osmosis Desalination Membrane: A Combined Experimental and Computational Study.

In this work we have examined a computational approach in predicting the interactions between uncharged organic solutes and polyamide membranes. We used three model organic molecules with identical molecular weights (100.1 g/mol), 4-aminopiperidine, 3,3-dimethyl-2-butanone (pinacolone) and methylisobutyl ketone for which we obtained experimental data on partitioning, diffusion and separation on a typical seawater reverse osmosis (RO) membrane. The interaction energy between the solutes and the membrane phase (fully aromatic polyamide) was computed from molecular dynamics (MD) simulations and the resulting sequence was found to correlate well with the experimental rejections and sorption data. Sorption of the different organic solutes within the membrane skin layer determined from attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) nicely agreed with interaction energies computed from molecular simulations. Qualitative information about solute diffusivity inside the membrane was also extracted from MD simulations while ATR-FTIR experiments indicated strongly hindered diffusion with diffusion coefficients in the membrane about 10-15 m2/s. The computational approach presented here could be a first step toward predicting rejections trends of, for example, hormones and pharmaceuticals by RO dense membranes.