Commercial Thin Film Composite Polyamide Research Articles

Treatment of Chitosan Modified-composite Polyamide Membranes by Sodium Hypochlorite for Enhancing Antifouling Property

To enhance the antifouling resistance, this study modified commercial thin-film composite polyamide membranes with chitosan by redox-initiated graft polymerization process before treating the modified membrane’s surface using sodium hypochlorite. The surfaces of the modified membranes were characterized using field emission scanning electron microscopy, and attenuated total reflection - Fourier transform infrared spectroscopy. The membranes’ performance and fouling resistance were shown through flux, retention, and maintained flux ratios during the filtration of calcium chloride solution. In addition, the antibacterial ability of membranes was evaluated through the growth of bacteria on their surface, and the anti-biofouling resistance of these membranes was evaluated through the maintained flux ratios, irreversible antifouling factor, and flux after 90-minute filtration of actual river water. The results showed that the modified membrane had superior antibacterial ability compared to the original membrane. Additionally, although the flux was reduced slightly, the modified membrane treated with NaClO exhibited a remarkable improvement in the maintained flux ratios (up to 99%) and the irreversible antifouling factor (~ 100%). This is similar to the filtration of actual river water, the chitosan-grafted polyamide membrane after NaClO treatment was shown to be more effective than the unmodified membrane in reducing the fouling phenomenon.

Improved antifouling ability of thin film composite polyamide membrane modified by a pH-sensitive imidazole-based zwitterionic polyelectrolyte

In this work, poly[1-vinyl-3(2-carboxyethyl) imidazolium betaine] (PVCIB), as a zwitterionic polyelectrolyte, was tethered onto a commercial thin film composite polyamide (TFC PA) membrane. First, polyvinyl imidazole (PVI) was grafted onto the TFC PA membrane surface by free radical graft polymerization method at various grafting times. Afterwards, one of PVI-modified membranes was betainized using 3-bromopropionic acid to obtain PVCIB brushes on the membrane surface. Evaluation of membrane performance through desalination process indicated that despite decrease of salt rejection, water flux increased from 73.4 L/m2 h in the PA membrane to 91.6 L/m2 h in the PA-PVCIB membrane. Antimicrobial assessment using Escherichia coli showed that the PVCIB-modified membrane was able to inhibit bacterial growth by about 98.8%. Antifouling and cleaning abilities of membranes were investigated using BSA and lysozyme at various pH values. It was revealed that hydrophilic PVCIB brushes considerably improved protein-resistant property of the TFC PA membrane. However, by considering pH-dependent behavior of PVCIB (zwitterionic at alkaline pH or polyelectrolyte at acidic pH), it was found that hydration repulsion or electrostatic repulsive forces also made a major contribution to the fouling mitigation. Accordingly, the PA-PVCIB membrane exhibited remarkable antifouling ability to resist non-specific protein adsorption at neutral and alkaline pHs, whereas both PA-PVI and PA-PVCIB membranes exhibited high resistance to the positively charged lysozyme adhesion at acidic pH.

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.

REMOVAL OF HEAVY METAL IONS IN WATER USING MODIFIED POLYAMIDE THIN FILM COMPOSITE MEMBRANES

Heavy metals in the wastewater can pollute the water resources because they are durable, have a high toxicity in the environment and body tissues. Thus, the treatment of wastewaters containing heavy metal ions has attracted much attention, because they can economically provide water for industrial production, decrease the wastewater discharge amount, and minimize the effluent pollutant concentration. In some methods for treatment of heavy metal ions, membrane separation is considered as a great promise technique, because of their high efficiency, easy operation, and space saving. The commercial thin film composite polyamide (TFC-PA) membranes are used for the wastewater treatments, due to a high permeate flux, as well as a great rejection for relatively wide operation of temperature and pH range. However, TFC-PA membranes are sensitive to fouling. The improvement of the fouling resistance of TFCPA membrane can be achieved through the surface modification techniques. In this work, the surface of TFC-PA membrane has been successfully modified by the UV-photo-induced grafting of poly(ethylene glycol) (PEG) and acrylic acid (AA). The separation performance of the modified membranes has been investigated, through the possibility for removal of heavy metals such as Ni (II), Cu (II), Fe (III) and Cr (III) in water, and in electroplating wastewater. The experimental results indicated that the separation performance of the PEG-grafted and AAgrafted membranes is significantly improved, with an increased membrane flux at a great retention. The antifouling property of the modified membrane is also improved, with a higher maintained flux ratio, and a lower irreversible fouling factor in comparison with those of the unmodified one. Article DOI: https://dx.doi.org/10.20319/mijst.2017.31.91103 This work is licensed under the Creative Commons Attribution-Non-commercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Treatment of florfenicol of synthetic trout fish farm wastewater through nanofiltration and photocatalyst oxidation

ABSTRACT The aquaculture system is a potential significant source of antibacterial agents. The removal of florfenicol (Flo) antibiotic from synthetic aqueous wastewater is performed by applying a commercial thin film composite polyamide nanofilter (NF). For concentrated wastewater treatment, the advanced oxidation process (AOP) is applied. The effects of pH, pressure and Flo concentration on removal efficiency of NF and the effects of pH, Flo concentration and dosage of hydrogen peroxide and contact time on the AOP are assessed. In the nanofiltration system, it is found that an increase in pH enhances the removal efficiency up to 99%. In this membrane, an increase of pressure between 4 and 7 bar would increase the removal percentage, followed by a decrease from 7 to 10 bar. In AOP, it is observed that the degradation efficiency of Flo increases by both an increase in its initial concentration up to values above 50 ppm and contact time. The degradation efficiency of Flo is at its highest in the pH range of 7–10. With increasing H2O2 dosage, from 0 to 500 ppm, the removal efficiency increases. The results of this study indicate that a combination of a polyamide nanofilteration together with an AOP introduces an effective manner of removing Flo antibiotic from synthetic trout fish farm wastewater.

Surface mineralization of commercial thin-film composite polyamide membrane by depositing barium sulfate for improved reverse osmosis performance and antifouling property

In this study, a novel approach, namely surface mineralization, was adopted to modify the commercial thin-film composite (TFC) polyamide (PA) reverse osmosis (RO) membrane for improved membrane properties. BaSO4-based mineral coating was deposited on the surface of the PA-RO membrane by alternate soaking process (ASP) using aqueous solutions containing barium chloride (BaCl2) and sodium sulfate (Na2SO4), respectively. Membranes with different mineralization degrees were prepared by varying the number of ASP cycles. The mineralized TFC PA-RO membranes were characterized through FESEM microscopy, AFM analysis, EDX analysis, zeta-potential analysis, contact angle measurement and cross-flow permeation test. It was found that the mineral coating composed of BaSO4 particles distributed evenly on membrane surface. The surface of the membrane became more hydrophilic and negatively charged after mineralization and the membranes modified under certain conditions exhibited both increased water flux and salt rejection. Fouling experiments with bovine serum albumin (BSA) aqueous solution also demonstrated that the BaSO4-based surface coating layer could effectively alleviate the adsorption and deposition of foulant molecules on the membrane surface through enhancing electrostatic repulsion and lowing hydrophobic interaction between BSA molecules and membrane surface, and that the mineralized membrane possessed improved fouling resistance to BSA aqueous solution.

Elucidating the Rejection Mechanisms of PPCPs by Nanofiltration and Reverse Osmosis Membranes

In this study, the rejection mechanisms of six commonly detected pharmaceutical and personal care products (PPCPs) were systematically studied with three commercial thin film composite polyamide reverse osmosis (RO, XLE) and nanofiltration (NF, NF90, and NF270) membranes at pH 3–10. The amount of PPCP adsorption on membrane surfaces was also extracted and calculated so as to determine the contribution of adsorption mechanism on PPCP rejection using adsorption kinetics and adsorption isotherms. At low pHs, PPCP rejection was the highest for XLE followed by NF90 and NF270. As pH increased to 10, PPCP rejection increased significantly for NF90 and NF270, attributed to the enhanced electrostatic repulsion between the negatively charged membrane surface and ionized PPCPs, while being slightly increased for XLE due to the dominant mechanism of steric hindrance. The simplified charge concentration polarization model predicted well for most cases, which demonstrated the contribution of steric hindrance and electr...

Surface modification of a commercial thin-film composite polyamide reverse osmosis membrane through graft polymerization of N-isopropylacrylamide followed by acrylic acid

Surface modifications including physical and chemical treatments are effective approaches to improve the fouling and chlorine resistances of the commercial thin-film composite (TFC) aromatic polyamide reverse osmosis (RO) membranes. However, the major problem facing the modification is the influence on membrane performance. In this study, surface modification of a commercial TFC RO membrane was performed through redox initiated graft polymerization of N-isopropylacrylamide (NIPAm) followed by acrylic acid (AA) and the modified membrane showed improved membrane properties. Membrane characterization was conducted through ATR-FTIR analysis, zeta-potential analysis, contact angle measurement and cross-flow permeation test. Changes in surface characteristics confirmed the graft polymerizations of NIPAm and AA. The surface of the membrane became more hydrophilic and negatively charged after modification. The membrane modified under certain conditions showed both increased water flux and salt rejection. Fouling experiments with bovine serum albumin (BSA) aqueous solution demonstrated that the modification could mitigate the deposition of foulants on the membrane surface through enhancing electrostatic repulsion and lowering hydrophobic interaction between BSA molecules and membrane surface and thereby improving fouling resistance. Furthermore, chlorination tests also showed that surface modification through graft polymerization of NIPAm followed by AA could effectively enhance the chlorine stability of the polyamide membrane.

Sorption of phenolic compounds on NF/RO membrane surfaces: Influence on membrane performance

Two commercial thin film composite polyamide reverse osmosis (BW-30) and nanofiltration (NF-90) membranes were studied for sorption of 2-nitrophenol and 2-chlorophenol. Adsorption kinetics and equilibrium on the surface of both membranes were studied. The rate of adsorption was adequately modeled by a linearized form of the pseudosecond-order kinetics in all cases. Adsorption isotherms obtained from equilibrium experiments were quite similar, except for the 2-nitrophenol/BW-30 system, which showed a higher maximum adsorption capacity. Experimental adsorption isotherms were compared with Freundlich and Langmuir models; the Langmuir model yields the best fit in all cases, suggesting the formation of a fouling monolayer onto the membrane surface. Organic deposition onto the membrane surface systematically increased hydrophobicity and diminished roughness. A strong graphical correlation was found between the relative flux decline and the organic concentration decrease in the feed. As expected, solute rejection was higher for the RO membrane (BW-30) than for the NF membrane (NF-90); the lowest rejection values were found for 2-nitrophenol. This was attributed to the increase of the solute concentration on the membrane surface due to organic sorption, which enhanced the driving force for diffusion through the membrane.

Surface modification of a commercial thin film composite polyamide reverse osmosis membrane by carbodiimide-induced grafting with poly(ethylene glycol) derivatives

Based on the existing carboxylic acid groups on surface of used commercial thin film composite polyamide reverse osmosis membrane, two kinds of poly(ethylene glycol) derivatives with different chains were grafted by carbodiimide-induced method to improve the antifouling property. The membranes before and after modification were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and static contact angle measurement. Moreover, the water flux, NaCl rejection and fouling experiments were also conducted. The changes of chemical composition and morphology on membrane surfaces indicated the successful grafting of poly(ethylene glycol) derivatives. Compared to unmodified membrane, the modified membranes were more resistant to fouling in protein and cationic surfactant feeding solutions. The method in this study provided a new way for surface modification of commercial polyamide reverse osmosis membranes.

Thin-film composite polyamide reverse osmosis membranes with improved acid stability and chlorine resistance by coating N-isopropylacrylamide-co-acrylamide copolymers

This study focus on the surface modification and the improved acid stability and chlorine resistance of the commercial thin-film composite polyamide reverse osmosis membranes coated with hydrophilic copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) surface layer. The virgin flat-sheet polyamide membranes were modified in situ with dilute P(NIPAM-co-Am) aqueous solution, and the modified membranes were then tested for their acid stability and chlorine resistance through long-term cross-flow permeation tests with aqueous solution containing 0.5 mol/l HCl and 2000 ppm NaCl and chlorine exposure experiments with hypochlorite aqueous solutions of different concentrations, respectively. The membrane properties were characterized in terms of reverse osmosis performance and surface chemical structure. The membrane modification was found to improve the chlorine tolerance and acid stability significantly. The P(NIPAM-co-Am) surface coating layer would impede the hydrolysis and the replacement of hydrogen with chlorine on the amide groups of the aromatic polyamide thin-film through enhancing intermolecular hydrogen bonding, and prevent the attack of acid and chlorine on the underlying polyamide film as a protective and sacrificial layer. The P(NIPAM-co-Am)-coated membrane would offer a potential use as a new type of thin-film composite polyamide membrane with improved acid stability and chlorine resistance.

Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes: I. FTIR and XPS characterization of polyamide and coating layer chemistry

The physiochemical properties of reserve osmosis (RO) and nanofiltration (NF) polyamide (PA) membranes are largely determined by their PA chemistry and coatings, if any. Knowledge on such inherent relationship is critically needed in advancing membrane technology. This paper presents a consistent and in-depth characterization on diagnosing the chemistry of polyamide and the presence of any coating or modifying agent. Fourier-transform infrared (FTIR) and x-ray photoelectron spectra (XPS) of 17 commonly used commercial thin film composite polyamide RO and NF membranes are presented. The FTIR spectra for fully aromatic trimesoyl chloride and 1,3-benzenediamine based membranes had an amide II band (1541 cm −1) and an aromatic amide band (1609 cm −1) that were absent for the semi-aromatic membranes. Consistent with that, the XPS binding energy shift for carbon atoms in fully aromatic amide groups was higher than that for semi-aromatic ones likely due to the more electron withdrawing environment. An additional intermediate peak with a binding energy shift of 1.1–1.6 eV was present in the XPS spectra of C(1s) for some commercial RO and NF membranes. The additional peak, coupled with FITR analysis over the high wave number region and XPS elemental analysis, provided consistent evidence that these membranes were either coated with an additional coating layer or had a modified PA chemistry.

Sodium cyanide separation and parameter estimation for reverse osmosis thin film composite polyamide membrane

Sodium cyanide separation data are obtained from synthetic binary aqueous solutions using a commercial thin film composite polyamide reverse osmosis membrane. The separation data are analyzed with the help of two membrane transport models, i.e., combined film theory–solution–diffusion (CFSD) model and combined film theory–Spiegler–Kedem (CFSK) model. The membrane transport parameters and mass transfer coefficients are estimated, simultaneously, from both the models, using a graphical method in case of CFSD model, and a nonlinear parameter estimation method for CFSK model. The new phenomena that there exists a maximum in rejection when it is plotted against product flux, which was observed previously using the same membrane for the phenol–water system, is observed in the present case too. This behavior is explained using the above said models. Though both the models predict the membrane performance reasonably, the values of CFSK model are more accurate and the mass transfer coefficients estimated from the CFSK model are comparable with the literature values.

Thin Film Composite Polyamide Membrane Parameters Estimation for Phenol-Water System by Reverse Osmosis

ABSTRACT A commercial thin film composite polyamide reverse osmosis membrane is used to separate an aqueous phenol-water binary system. The separation data are analyzed using a combined film theory-solution-diffusion (CFSD) model and a combined film theory-Spiegler-Kedem (CFSK) model. In the present investigation a new phenomenon is observed: there exists a maximum in the rejection when it is plotted against the product flux through the membrane. This behavior is explained for both models. An equation for Jv,min, which is the value of the product flux Jv at which the rejection reaches a maximum, is derived from both models. Although the parameters for both models are consistent over the range of operating conditions, the CFSK model is more accurate for the phenol-water system.