Composite Polyamide Reverse Osmosis Membranes Research Articles

Antibacterial and Antifouling Properties of Ag‐ and Cu‐Decorated Thin Film Composite Polyamide Reverse Osmosis Membranes

AbstractIn this work, silver and copper particles of different nanoparticle precursor concentrations were decorated on the surface of thin film composite polyamide (TFC‐PA) reverse osmosis (RO) membranes by in situ method. The modified membranes were characterized by different techniques including Field emission scanning electron microscopy (FE‐SEM), X‐ray Absorption Spectroscopy (XAS), and attenuated total reflection – Fourier transforms infrared spectroscopy (ATR‐FTIR), water contact angle (WCA), and antibacterial capacity. After that, the membrane performance was compared through normalized flux and the possibility of the removal of bovine serum albumin (BSA) protein; the anti‐fouling and anti‐biofouling properties were also compared through the maintained flux ratios (%) after 5‐hour filtration. The used organic foulants were BSA protein and humic acid (HA) solutions. The results showed that, compared to the flux of the base, the flux of AgNPs‐decorated membrane can improve the separation ability up to 24% while that of CuNPs‐decorated membrane was 14%. The anti‐fouling property of decorated membranes was significantly increased compared to that of the base (from 64% for the base to over 77% for decorated membranes). Especially, the anti‐biofouling property of nanoparticles decorated membranes was also increased because of the higher maintained flux ratios (from 50% for the base to over 75% for decorated membranes). It indicates that this method can be applied to produce reverse osmosis (RO) membranes for reclamation wastewater with a high content of organic matter.

Corrigendum to “Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel” [Colloids Surf. A: Physicochem. Eng. Asp. 654 (2022) 130140

Corrigendum to “Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel” [Colloids Surf. A: Physicochem. Eng. Asp. 654 (2022) 130140

Does Surface Roughness Necessarily Increase the Fouling Propensity of Polyamide Reverse Osmosis Membranes by Humic Acid?

Surface roughness has crucial influence on the fouling propensity of thin film composite (TFC) polyamide reverse osmosis (RO) membranes. A common wisdom is that rougher membranes tend to experience more severe fouling. In this study, we compared the fouling behaviors of a smooth polyamide membrane (RO-s) and a nanovoid-containing rough polyamide membrane (RO-r). Contrary to the traditional belief, we observed more severe fouling for RO-s, which can be ascribed to its uneven flux distribution caused by the "funnel effect". Additional tracer filtration tests using gold nanoparticles revealed a more patchlike particle deposition pattern, confirming the adverse impact of "funnel effect" on membrane water transport. In contrast, the experimentally observed lower fouling propensity of the nanovoid-containing rough membrane can be explained by: (1) the weakened "funnel effect" thanks to the presence of nanovoids, which can regulate the water transport pathway through the membrane and (2) the decreased average localized flux over the membrane surface due to the increased effective filtration area for the nanovoid-induced roughness features. The current study provides fundamental insights into the critical role of surface roughness in membrane fouling, which may have important implications for the future development of high-performance antifouling membranes.

Calcium Sulfate and Calcium Carbonate Scaling of Thin-Film Composite Polyamide Reverse Osmosis Membranes with Surface-Tethered Polyacrylic Acid Chains.

The gypsum and calcite scaling propensities of the thin-film composite polyamide (PA-TFC) reverse osmosis (RO) membrane, modified with a tethered surface layer of polyacrylic acid (PAA) chains, was evaluated and compared to the scaling of selected commercial RO membranes. The tethered PAA layer was synthesized onto a commercial polyamide membrane (i.e., base-PA) via atmospheric pressure plasma-induced graft polymerization (APPIGP). The PAA nano-structured (SNS) base-PA membrane (SNS-PAA-PA) was scaled to a lesser degree, as quantified by a lower permeate flux decline and surface imaging, relative to the tested commercial membranes (Dow SW30, Toray SWRO, and BWRO). The cleaning of gypsum-scaled membranes with D.I. water flushing achieved 100% water permeability recovery for both the SNS-PAA-PA and Dow SW30 membranes, relative to 92-98% permeability restoration for the Toray membranes. The calcium carbonate scaling of SNS-PAA-PA membranes was also lower relative to the commercial membranes, but permeability recovery after D.I. water cleaning was somewhat lower (94%) but consistent with the level of surface scale coverage. In contrast, the calcite and gypsum-scaled membrane areas of the commercial membranes post-cleaning were significantly higher than for the SNS-PAA-PA membrane but with 100% permeability recovery, suggesting the potential for membrane damage when mineral scaling is severe.

Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel

In order to optimize antifouling performance to organic foulants, a commercial polyamide reverse osmosis membrane of composite polyamide material was modified by surface gelation using sodium alginate (NaAlg) as surface coating agent, which was widely known as a natural polymer and environmentally friendly materials. NaAlg-GA hydrogel layer was successfully deposited on commercial membrane surface by combining immersion coating with in-situ crosslinking method and the chemical structure was verified by FT-IR spectroscopy. SEM and AFM was adopted to analyze the changes of morphology and roughness. Zeta potentiometer, and contact Angle analyzer were all used to analyze the hydrophilicity and charge property of relevant NaAlg modified membranes in detail. Specific separation performance was also evaluated by cross-flow filtration tests. Results from above experiments confirmed that NaAlg modified membranes exhibited a surface with more hydrophilic, smoother and more regular, denser negative charge, slightly improved selectivity and lower permeability. Long-term monitored the performance of 100 ppm NaAlg modified membrane, it was found that the rejection rate fluctuated between 98.96% and 99.17%, and the flux ranged from 25.15 ∼ 26.06 L/m2 h during the whole test period, which fully proved that modified membrane had good durability. BSA pollution experiment results showed that the flux attenuation rate of 100 ppm NaAlg modified membrane decreased from 40.87% to 25.01%, and flux recovery rate of contaminated membrane after washing was as high as 90.8%. In addition, the flux of 100 ppm NaAlg modified membrane exceeded that of unmodified membrane after filtrating 20 h. Moreover, with the extension of time, the cumulative flux loss of modified membrane caused by additional resistance at the initial filtration stage would soon be compensated, and it completely exceeded that of unmodified membrane after 40 h. All above results showed that NaAlg-GA hydrogel layer can effectively improve the antifouling performance.

Thin Film Composite Polyamide Reverse Osmosis Membrane Technology towards a Circular Economy.

It is estimated that Reverse Osmosis (RO) desalination will produce, by 2025, more than 2,000,000 end-of-life membranes annually worldwide. This review examines the implementation of circular economy principles in RO technology through a comprehensive analysis of the RO membrane life cycle (manufacturing, usage, and end-of-life management). Future RO design should incorporate a biobased composition (biopolymers, recycled materials, and green solvents), improve the durability of the membranes (fouling and chlorine resistance), and facilitate the recyclability of the modules. Moreover, proper membrane maintenance at the usage phase, attained through the implementation of feed pre-treatment, early fouling detection, and membrane cleaning methods can help extend the service time of RO elements. Currently, end-of-life membranes are dumped in landfills, which is contrary to the waste hierarchy. This review analyses up to now developed alternative valorisation routes of end-of-life RO membranes, including reuse, direct and indirect recycling, and energy recovery, placing a special focus on emerging indirect recycling strategies. Lastly, Life Cycle Assessment is presented as a holistic methodology to evaluate the environmental and economic burdens of membrane recycling strategies. According to the European Commission’s objectives set through the Green Deal, future perspectives indicate that end-of-life membrane valorisation strategies will keep gaining increasing interest in the upcoming years.

Deciphering the Role of Amine Concentration on Polyamide Formation toward Enhanced RO Performance

Polyamide surface morphology and its underneath nanosized voids have crucial influence on the separation performance of thin film composite (TFC) polyamide reverse osmosis membranes. Although there have been numerous studies reporting the impact of amine monomer concentration on polyamide formation and membrane performance, the observations and interpretations in the existing literature remain controversial. In this study, we performed interfacial polymerization (IP) of polyamide films over a wide range of m-phenylenediamine (MPD) concentration (0.05–8.0 w/w %). For the first time, we demonstrate that the water permeance of the resultant TFC membranes is governed by the competing effects of (1) promoted polyamide film growth for forming thicker polyamide films and (2) improved nanofoaming effect that results in more extensive nanovoids at higher MPD concentrations. To dissect these competing mechanisms, we further adopted a free-interface IP strategy to suppress the nanofoaming effect. The corresponding polyamide nanofilms had negligible nanovoids and monotonously increased film thickness, leading to decreased water permeance at high MPD concentrations. In contrast, the conventional TFC membranes exhibited optimal water permeance at the intermediate MPD concentration of 2.0 w/w %, which results from the trade-off between improved nanovoid formation (which promotes higher permeance) and increased film growth (which limits permeance). On the other hand, the better film growth at greater MPD concentration was generally beneficial for achieving better membrane rejection. The current study unveils the fundamental chemistry–morphology–performance relationship of TFC polyamide membranes and provides important implications on their synthesis and environmental applications.

Facile polyamide microstructure adjustment of the composite reverse osmosis membrane assisted by PF127/SDS mixed micelles for improving seawater desalination performance

The integrity and uniformity of polyamide (PA) layer have a great influence on the separation performance of thin-film composite (TFC) polyamide reverse osmosis (RO) membrane. In this work, three kinds of micelles including the neutral macromolecule Pluronic F127 (PF127), anionic surfactant sodium dodecyl sulfate (SDS) and the PF127/SDS mixed micelles (PSMM), were proposed to be introduced in the aqueous phase to regulate the interfacial polymerization (IP) process with the purpose of constructing a more integrated and uniform PA separation layer of the RO membrane for seawater desalination. Compared to the single PF127 and SDS, the PSMM-1 (0.05 wt% PF127/0.05 wt% SDS) in the aqueous solution exhibited special advantages including unique three-dimensional (3D) spherical structure, lower solution viscosity and water-Isopar G interface tension (IFT), which sped up m-phenylenediamine (MPD) to homogeneously diffuse to the water-Isopar G interface and further regulated the interfacial polymerization reaction between MPD and trimesoyl chloride (TMC). Ultimately, the regulated RO membrane via PSMM-1 had more uniform PA layer and thus exhibited better comprehensive separation performances including higher salt rejection (more than 99.5%) and ideal water flux (about 35 L·m−2·h−1). This study provides a facile method of PA microstructure adjustment via micelles to fabricate higher-performance TFC RO membrane for seawater desalination.

Antifouling and Flux Enhancement of Reverse Osmosis Membrane by Grafting Poly (3-Sulfopropyl Methacrylate) Brushes.

A commercial thin film composite (TFC) polyamide (PA) reverse osmosis membrane was grafted with 3-sulfopropyl methacrylate potassium (SPMK) to produce PA-g-SPMK by atom transfer radical polymerization (ATRP). The grafting of PA was done at varied concentrations of SPMK, and its effect on the surface composition and morphology was studied by Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), optical profilometry, and contact angle analysis. The grafting of hydrophilic ionically charged PSPMK polymer brushes having acrylate and sulfonate groups resulted in enhanced hydrophilicity rendering a reduction of contact angle from 58° of pristine membrane sample labeled as MH0 to 10° for a modified membrane sample labeled as MH3. Due to the increased hydrophilicity, the flux rate rises from 57.1 L m−2 h−1 to 71.2 L m−2 h−1, and 99% resistance against microbial adhesion (Escherichia coli and Staphylococcus aureus) was obtained for MH3 after modification

Improved antifouling performance of a polyamide composite reverse osmosis membrane by surface grafting of dialdehyde carboxymethyl cellulose (DACMC)

Antifouling properties are considered to be essential to polyamide (PA) composite reverse osmosis (RO) membranes for their industrial applications. In this work, an antifouling material, dialdehyde carboxymethyl cellulose (DACMC), was prepared by the oxidation of carboxymethyl cellulose (CMC) and then grafted onto the surface of a nascent PA RO membrane to improve its antifouling properties. The results showed that DACMC grafting could endow the membrane with improved hydrophilicity, surface smoothness and NaCl retention, while the permeability was decreased slightly after DACMC grafting. The zeta potentials of the membrane could be adjusted by changing the DACMC concentration. In addition, three typical surfactants with various charge properties, including sodium dodecyl sulfate (SDS), polyoxyethylene octylphenol ether (OP-10) and cetyltrimethylammonium bromide (CTAB), were used as feed foulants to evaluate the antifouling property of membranes. The results showed that, for the anionic SDS and nonionic OP-10 surfactants, the modified membranes with more DACMC had better antifouling performance because the membrane hydrophilicity dominated the interaction between foulants and the membrane surface. For the cationic CTAB, however, the pristine membrane showed better antifouling performance than the modified membrane with low DACMC grafting concentrations (5 and 10 g/L). This difference was attributed to the stronger electrostatic adsorption between the cationic CTAB and the modified membranes with more negative charges. The modified membrane with high DACMC grafting concentrations (20 g/L) exhibited the best antifouling performance for all the surfactants thanks to its high hydrophilicity and low negative charge. Therefore, the charge and hydrophilic properties of the RO membrane must be designed rationally to enhance the antifouling performance of the RO membrane when treating surfactant-containing wastewater.

Surface Grafting of Reverse Osmosis Membrane with Chlorhexidine Using Biopolymer Alginate Dialdehyde as a Facile Green Platform for In Situ Biofouling Control.

We report a new robust and green facile platform for nonoxidizing chemical grafting to simultaneously improve antifouling and antibacterial properties of thin film composite (TFC) polyamide (PA) reverse osmosis (RO) membranes. In this work, alginate dialdehyde (ADA) was used as a green platform to graft chlorhexidine (CH), a nonoxidizing chemical, on TFC-RO membrane surface. A synergistic effect due to ADA and CH grafting was revealed. The modified membrane surfaces were characterized using XPS, FT-IR, AFM, SEM-EDS, contact angle, and zeta potential analysis. A simple two-step Schiff base reaction was performed. Improved salt rejection performances were observed for the grafted PA membranes at the expense of negligible flux drop for the CH-ADA-PA membranes (38 to 42 L m-2 h-1) compared with the pristine PA membrane (45 L m-2 h-1). All the CH-ADA-PA membranes had excellent antibacterial activity against E. coli along with a highly superior resistance to the formation of biofilms. Organic fouling behaviors with a protein (bovine serum albumin, BSA) and a surfactant (dodecyl trimethylammonium bromide, DTAB) were investigated as typical foulants for the grafted PA membranes. The results indicated that the CH-ADA-PA membranes showed the best antifouling performance followed by the ADA-PA membranes, the pristine membrane being the most inferior. Hence, these results pave the way for a new robust and green bioinspired route for practical application in RO membrane fouling control.

Tailoring Polyamide Rejection Layer with Aqueous Carbonate Chemistry for Enhanced Membrane Separation: Mechanistic Insights, Chemistry-Structure-Property Relationship, and Environmental Implications.

Surface roughness and the associated nanosized voids inside the roughness structures have great influence on the separation performance of thin film composite polyamide reverse osmosis (RO) membranes. Inspired by the recent findings that these voids are formed due to the degassing of CO2 nanobubbles during interfacial polymerization, we systematically investigated the role of carbonate chemistry, particularly the solubility of CO2, in the aqueous m-phenylenediamine (MPD) solution for the first time. "Ridge-and-valley" roughness features were obtained when the pH of the MPD solution was between the two acidity constants of the carbonate system (i.e., 6.3 ≤ pH ≤ 10.3), under which condition HCO3- dominates over the other carbonate species. Increasing pH over this range led to both increased water permeability and better rejection of various solutes, thanks to the simultaneously enhanced effective filtration area and cross-linking degree of the polyamide layer. Further increase of pH to 12.5 resulted in more disparate rejection results due to membrane hydrolysis: rejection of neural solutes (B and As(III)) was compromised whereas that of charged solutes (NaCl and As(V)) was maintained. The mechanistic insights gained in the current study reveal the critical need to design RO membranes directly for end applications based on first principles.

Scaling prevention of thin film composite polyamide Reverse Osmosis membranes by Zn ions

On the West Coast of South Africa, there is an abundance of brackish groundwater. Reverse Osmosis membrane systems are used to make the borehole water fresh. Unfortunately, the salts that are removed from the water, precipitates on the membrane surface, thus, decreasing the overall process efficiency. In this study, the use of Zn2+ ions as an anti-scalant was investigated in terms of feasibility in the treatment of brackish water influent. Experimental tests were conducted on a bench scale unit, followed with a pilot plant thereafter. Three commercial membranes were exposed to natural groundwater scaling. The first, commercial anti-scalant treatment, second, anti-scalant treatment with Zn2+ ions and the third, untreated. The results, after a period of close to 5 months, showed that the flux of the membranes treated with commercial (32.78 L·m−2·h−1) and zinc (30.80 L·m−2·h−1) ions anti-scalant was higher than the untreated membrane flux (25.56 L·m−2·h−1), which decreased continuously.

Coupling reverse osmosis and osmotic distillation for clarified pomegranate juice concentration: Use of plasma modified reverse osmosis membranes for improved performance

Abstract In this study, a low pressure nitrogen plasma (LPNP) activation was implemented to modify the surface characteristics of a commercial thin film composite (TFC) polyamide reverse osmosis (RO) membrane. The free energy of interaction (ΔGiwi) results showed that the hydrophobic nature of untreated TFC RO membrane became considerably hydrophilic with the effect of LPNP treatment. Among various plasma powers and exposure times tested, a general decreasing trend was observed for the water contact angle with increasing plasma duration, reaching a minimum of 13.2 ± 0.8° for 90 W at 15 min. A remarkable increase in water flux of the LPNP modified RO membrane was observed throughout the RO process, which promoted higher soluble solids content (SSC) values in the concentrated juice at the same period of time with the plain one. The higher SSC values achieved by the modified RO membrane enabled 30% time-saving during further osmotic distillation process.

Surface modification of composite polyamide reverse osmosis membrane by irradiated chitosan and TiO2 nanoparticles

Surface modification of composite polyamide reverse osmosis membrane by irradiated chitosan and TiO2 nanoparticles

Study of Mass Transfer during Reverse-Osmosis Demineralization of Dilute Solutions of Strong Electrolytes

The results of studies of mass transfer through a polyamide composite reverse-osmosis membrane in the demineralization of dilute solutions of six strong electrolytes are summarized. The relation of the electrolyte concentration at the surface of the reverse-osmosis membrane, at which its true selectivity tends to zero, to the specific water flux and the sum of the hydration numbers of the cations and anions of this electrolyte has been revealed. It has been shown that at a low salinity of the feed solution, the product of the molar electrolyte flux and the sum of the hydration numbers of its cations and anions for the test membrane is almost independent of the electrolyte type. An analysis of the dependence of the solute flux on the transmembrane pressure, concentration, and temperature in the electrolyte concentration range of 0.2 to 20 mol/m3 in the feed solution, as well as the experimentally determined activation energy of the NaCl flux, has led to the conclusion that there is an additive component of the electrolyte flux, whose contribution to the total flux is insignificant at high concentrations and becomes determining at concentrations below 2–5 mol/m3.

Performance of Reverse Osmosis Membranes in the Treatment of Flue-Gas Desulfurization (FGD) Wastewaters

Reverse osmosis (RO) was studied to reduce salinity of flue gas desulfurization (FGD) wastewaters after softening with Na2CO3·H2O and ultrafiltration (UF). Two commercial thin film composite polyamide RO membranes (SWC-2540 and ESPA-2540, from Hydranautics) in spiral-wound configuration were tested and their performance in terms of salinity reduction as well as permeate flux, fouling index and water recovery was evaluated. Experimental runs were performed according to the feed and bleed configuration in selected operating conditions. For the SWC-2540 membrane experiments were also performed in total recycle configuration in order to evaluate the effect of operating pressure on permeate flux and quality. Experimental results indicated that the SWC-2540 membrane showed a better performance in the rejection of ions: Mg2+ ions were completely rejected, while the rejection towards monovalent ions such as Na+ was of about 95.5%. The ESPA-2540 membrane showed rejections towards Ca2+ and Mg2+ higher than 86.5% whilst the observed rejection towards Na+ was of 80%. For the SWC-2540 membrane an increased rejection for Ca2+ and Na+ ions was observed by increasing the operating pressure in the range 16-50 bar. Mg2+ ions were totally rejected independently by the operating pressure.

Performance benchmarking of polyamide composite Sea water reverse osmosis membranes

Abstract Standardization of reverse osmosis (RO) membrane system allows transparency and accountability in performance benchmarking of different membrane elements, especially when a new product is introduced to the market. In the current study, we compared performance of three polyamide composite RO membranes (one from new entrant in the market, the other two are established manufacturers) for seawater desalination. Experimental work was conducted at a desalination plant in Egypt. The new membrane had higher permeate conductivity and lower salt rejection values than the two established products. Similar trend was observed as far as permeate flow was concerned.

Multilayer thin-film composite membranes for helium enrichment

This paper describes a novel approach to fabricate a multilayer composite membrane for recovering and enriching helium from natural gas processing using commercially available thin-film composite polyamide reverse osmosis (RO) membranes. The RO membranes, which are defective in a dry state, were caulked with different polymeric materials to seal the defects; then, the permeation and separation properties were characterized using pure and mixed gases. A benchmark (Nafion®−117) membrane was selected for its superior selectivity towards helium over carbon dioxide, and the performances of the caulked RO membranes were compared. The experimental results show that the ideal selectivity of He/CO2 in the pure gas tests is in the range 20–55, while the permeance of helium is in the range 8–40 GPU depending on the caulking material. A quaternary mixture of CH4, N2, CO2, and He was used to evaluate the separation performance of the novel membrane, which was compared with that of the benchmark membrane. This study confirms that the proposed novel approach for membrane fabrication is technically practical to recover and enrich helium from CO2-containing natural gas streams.

Catalytic effect of iron on the tolerance of thin-film composite polyamide reverse osmosis membranes to hydrogen peroxide

Hydrogen peroxide (H2O2) is potentially an attractive alternative to chlorine-based (hypochlorous acid and monochloramine) antifouling agents in reverse osmosis (RO) because H2O2 does not form toxic disinfection byproducts and is tolerated by polyamide (PA) membranes up to high concentrations. However, aqueous H2O2 solutions are corrosive and iron corrosion products activate H2O2 to reactive oxygen species (ROS) that can degrade the PA separation layer. The impact of iron oxides on membrane stability was studied in the presence of H2O2 in two different systems: a corrosion-resistant system (constructed with plastic components) and an all-steel system. Tests in the all-steel system were conducted under enhanced corroding conditions and in deoionized (DI) water. H2O2 concentrations were 2.0mM (68mg/L) or 10mM (340mg/L). Corrosion was enhanced by adding 10mM Cl- or suppressed by adding phosphate buffer. Membrane performance was evaluated by determining salt rejection and the water flux. Under corrosion-suppressed conditions, membranes were stable during the 8-d test. In the all-steel testing system containing 10mM Cl- ion as corrosion promoter, the membrane tolerance was significantly diminished. In DI water, corrosion was relatively slow but degradation of the membranes was noticeable. Kinetic data of pCBA degradation indicated that membrane damage was caused by ·OH radicals. Quenching of the ·OH radical by methanol, and X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM) data are consistent with the hypothesis that Fenton reactions caused cleavage of the polyamide cross-linkages.