Transformation of brackish water Reverse Osmosis membranes to nanofiltration & ultrafiltration membranes by NaOCl treatment: Kinetic and characterization studies (original) (raw)

Degradation of Polyamide Nanofiltration and Reverse Osmosis Membranes by Hypochlorite

Environmental Science & Technology, 2012

The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)−N). FTIR data indicated the disappearance of the amide II band (1541 cm −1 ) and aromatic amide peak (1609 cm −1 ) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that Nchlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.

Controlled chlorination of polyamide reverse osmosis membranes at real scale for enhanced desalination performance

Journal of Membrane Science, 2020

State-of-the-art desalination and water purification processes use reverse osmosis and nanofiltration membranes. Their thin polyamide (PA) top-layers ensure concurrent high water permeances and salt rejections, but are also intrinsically sensitive to chlorine, originating from disinfectant added upstream. The chlorine resistance of PA-based membranes has been thoroughly studied at lab-scale, as opposed to industrial-scale membrane modules, where fundamental studies are lacking. Therefore, to better understand chlorine-induced changes in membrane performance and physicochemical properties at industrial scale, chlorination of commercial 8" elements was conducted at different pH (4-7-10) in pressurized modules with low chlorine concentrations (0, 1, 20, 50 ppm NaOCl) during 2.5 h. After 50 ppm acidic chlorination, water permeability decreased (-40%) but salt rejection increased significantly (+0.4%, i.e., salt passage decreased with-78.8%). Boron (+27%) and isopropanol (+8%) rejection also increased. Chlorination with 20 ppm NaOCl at pH 7 and with 50 ppm NaOCl at pH 10 caused boron rejection to drop with-17% and-33%, respectively, but had negligible influence on isopropanol rejection. However, neutral and alkaline chlorination drastically improved water permeability with +40% and salt rejection with +0.6% (i.e., salt passage decreased with-66.9%), approaching and in some cases even slightly exceeding the salt/water permselectivity limit. It can thus be concluded that, under controlled conditions, chlorination can boost the performance of membrane modules. Significant changes in the membrane physicochemical properties were observed at pH 4. At pH 7 and pH 10, a low chlorine-uptake in the PA network was observed, although no significant PA deterioration was observed with XPS and ATR-FTIR. This study is the first to fundamentally investigate chlorination of PA-based realscale membrane modules as a function of feed pH. Furthermore, it provides a promising strategy to boost membrane performance at real scale and highlights the importance of chlorination conditions. 2. Table Of Contents 2 3. Introduction Water treatment and desalination allow access to unconventional water sources and the (re-)use of contaminated waters for domestic and industrial consumption [1]. Water purification is hence an energy-efficient solution to overcome water scarcity, one of the major sustainable development goals of the United Nations [2]. State-of-the-art nanofiltration (NF) and reverse osmosis (RO) membranes have a polyamide (PA) top-layer, synthesized through the interfacial reaction of m-phenylene diamine (MPD) and trimesoyl chloride (TMC), that ensures excellent salt rejection and water permeance [3]. However, some micro-pollutants, such as endocrine disruptive compounds (EDCs), perfluoroalkyl substances (PFAs) and pharmaceutically active compounds (PhACs) are only poorly rejected and may cause health threats [4-7]. Another poorly rejected species is boron, typically found as boric acid at 4.5 mg L-1 in sea water [8]. As boron can also have adverse effects on human, animal and plant health, the World Health Organization (WHO) recommends a boron concentration of 2.4 mg/L for drinking water [9]. For agricultural irrigation, boron concentration should ideally be lower than 0.3 mg L-1 [10]. However, as current commercially available RO membranes exhibit boron rejections below 90%, a single-pass RO process does not meet the regulatory guidelines for water sources with high boron content [11]. The low boron rejection of PA-based RO membranes is mainly caused by the small and uncharged nature of boric acid (pKa ~ 8.6-9.2) under operating conditions (< pH 8), impairing rejection mechanisms based on ion exclusion [12]. Additionally, hydrogen bonding between water and boric acid can possibly drag boric acid through the membrane [13]. To achieve low enough boron concentrations in permeates, membranes with improved rejection of small and uncharged species, as well as innovative desalination process designs are actively investigated [7,12,14-17]. Another drawback of PA-based membranes is their sensitivity to chlorine, originating from disinfectant added upstream of the membrane filtration unit to minimize bio-fouling [18]. To avoid PA chlorination, chlorine removal is executed by dosing sodium metabisulfite or sodium bisulfite to the feed water in the so-called dechlorination step. However, complete continuous chlorine removal sometimes fails because of various practical factors, such as imperfect mixing of the chlorine-quencher, dechlorination system upsets and indirect monitoring of chlorine residuals. When this happens, accidental chlorination of the PA membrane takes place [18-21]. Chlorine, often dosed as sodium hypochlorite (NaOCl), will attack the PA network in various ways, depending on, amongst others, the pH of the feed solution and the presence of other ions [18]. Under acidic conditions, chlorine reacts through N-chlorination of the amide bond, and direct or indirect ring-chlorination of the aromatic MPD moieties inside the PA network. In alkaline environments, chlorination-promoted hydrolysis takes place, causing cleavage of the amide

Testing of water treatment copolymers for compatibility with polyamide reverse osmosis membranes

Environmental Progress, 2005

Cationic polymers used in traditional water and wastewater treatment, in theory, will bind to the partially negatively charged polyamide membrane during reverse osmosis (RO) treatment. This study tested a variety of cationic, anionic, and nonionic polymers in terms of (1) aiding in turbidity removal when used in conjunction with alum coagulation [10 mg/L as Al 2 (SO 4) 3 ⅐14H 2 O], sedimentation, and dual-media filtration; and (2) their binding affinity toward a polyamide membrane. Binding affinity was tested by exposing polyamide RO membranes to 50 mg/L of each polymer for 48 h and then conducting attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy on the membrane samples and principal-component analysis (PCA) of the FTIR spectra. Results from the turbidity removal tests showed that cationic polymers provided the lowest median effluent turbidity (0.03-0.11 NTU), followed by anionic polymers (0.06-0.08 NTU), and finally nonionic polymers (0.11-0.17 NTU). Although PCA of the FTIR spectra did detect differences in polymer-exposed membranes vs. a control, no discernable difference in RO membrane performance was observed. Therefore, under the conditions studied, the issue of "membrane poisoning " caused by organic polymer absorption onto polyamide membranes was minimal.

Membrane technologies for water treatment and agroindustrial sectors

Comptes Rendus Chimie, 2009

Although water is essential for human survival and progress, it is distributed very unevenly and with a different purity over the surface of the earth. A variety of contaminants can be present in raw water, depending on its origin. The size of these contaminants ranges from the micrometer (e.g. bacteria) to the tenths of a nanometer order (ions). Membrane processes like microfiltration, ultrafiltration, nanofiltration and reverse osmosis could be a solution for an advanced physical treatment of water for drinking purposes as well as for agroindustrial sectors. Many applications are well assessed and are expanding very quickly; however, to obtain an ever-growing performance, it is necessary to prepare membranes with tailored structure and transport properties. Characterisation methods play also a role of paramount importance for the selection of the more appropriate membrane for the above-mentioned applications. In this work the main membrane preparation techniques and characterisation methods will be reviewed and discussed. To cite this article: A.

End-of-life reverse osmosis membranes: Recycle procedure and its applications for the treatment of brackish and surface water

Journal of Applied Research in Water and Wastewater, 2021

As a result of population growth and potable water scarcity, an increasing number of reverse osmosis desalination plants are being installed and operated (more than 15,000 in the world). Reverse osmosis membranes tend to reach the end of the life cycle in around two to five years, becoming a solid waste. Recycling/repurposing these aged membranes could be a sustainable and profitable solution. This project aimed to transform end-of-life reverse osmosis membranes through the oxidation of their active layer using chlorine into nanoporous/microporous membranes, while searching possible applications for the resulting membranes. The results show that membranes oxidized at 10,000 ppm.h had a significant increase in permeability (3.1x), reaching NF-like capacity. On the other hand it was observed a decrease in the rejection of salt (4.35x) and acetaminophen (1.5x). Scanning Electron Microscopy (SEM) shows the positive effect of chlorine in the complete removal of particles deposited over the membrane. This oxidation condition also increased the average roughness (2.42x) of the membrane, as shown by Atomic Force Microscopy (AFM). Analysis by Fourier Transform Reflectance Spectroscopy (FTIR) suggests that chlorine oxidation replaced the hydrogen in the amide nitrogen. Both FTIR and SEM suggests the polyamide layer was not fully degraded. Application tests suggests that the recycled membrane can be used for the treatment of brackish and surface waters. The recycling of reverse osmosis membranes can be an alternative to simple landfill disposal, allowing owners to shift from disposal cost to revenue, as well as being a sustainable solution. The high permeability achieved on these oxidized membranes suggest many other NF/UF functions could potentially use recycled RO membranes.

Oxidative degradation of polyamide reverse osmosis membranes: Studies of molecular model compounds and selected membranes

Journal of Applied Polymer Science, 2003

Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin-film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH-history dependent. An alternative strategy is presented for the design of chlorine-resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003

ORIGINAL ARTICLES The Effect of Nano-Materials on The Characteristics and Performance of Aromatic Polyamide Membranes and Its Use in Groundwater Desalination in the Area Between Safaga and El-Quseir – Egypt

The thin film zeolite nanocomposite (TFNC) membranes were coated via interfacial polymerization of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers over porous polysulfone support. Different types of nanocomposite membranes were synthesized depending zeolite loading into the polyamide film. X-ray diffraction (XRD), FT-IR, transmission electron microscopy (TEM) and scanning electron microscopy techniques were employed to study the morphology of the pure zeolite and nanocomposite membranes. The calculated grain size of zeolite nanoparticles was 5.32 to 11.57 nm. The nanocomposite membranes had higher water permeability than the pure polyamide membranes. The results showed that addition of zeolite to the polyamide membrane led to improvement of surface properties such as an increase in pore size and water flux. The nanocomposite membranes with high concentration of monomers in interfacial polymerization exhibited a high water flux and low salt rejection. Excellent membrane performance was observed for the nanocomposite membrane containing about 0.05 % (w/v) zeolite, 0.15 % (w/v) TMC and 2 % (w/v) MPD which its flux was higher by 1.45 times than the flux value of the polyamide membrane with slightly decreasing in salt rejection. The obtained results show that TFZNC membranes are suitable for groundwater desalination.

Polyamide Thin Film Composite Membranes Using Interfacial Polymerization:Synthesis, Characterization and Reverse Osmosis Performance for Water Desalination

A variety of polyamide thin film composite (PA-TFC) membranes was synthesized via interfacial polymerization (IP) technique. IP was carried out between aqueous solution of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) in dodecane as organic solvent onto polysulfone (PSf) supporting membrane. The characterization of synthesized membranes was conducted using attenuated total reflection Fouier transform infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM) and contact angle measurement. Reverse osmosis performance included permeate flux (L/m2.hr) and salt rejection (%) was evaluated as a function of the synthesis conditions to investigate the optimum conditions that give the best performance membrane. The optimum conditions of synthesized membranes included MPD (1.5 wt.%) for 5 min. soaking time, TMC (0.05 wt. %) in dodecane for 30 sec. reaction time. The best synthesized membrane exhibited high salt rejection (99.81%) with high permeate flux (36.15 L/m2.h). Also, the concentration polarization modulus (M) and the true salt rejection (%) were measured using pure water with different salinities up to ≈ 10000 ppm NaCl feed solution. The obtained results showed that the concentration polarization modulus (M) ranged from 1.06 to 1.29 according to the salinity range.

Permeability and chemical analysis of aromatic polyamide based membranes exposed to sodium hypochlorite

Journal of Membrane Science, 2011

In this study, a cross-linked aromatic polyamide based reverse osmosis membrane was exposed to variable sodium hypochlorite ageing conditions (free chlorine concentration, solution pH) and the resulting evolutions of membrane surface chemical and structural properties were monitored. Elemental and surface chemical analysis performed using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), showed that chlorine is essentially incorporated on the polyamide layer of a commercially available composite RO membrane, when soaked in chlorine baths, presumably through a two step electrophilic substitution reaction governed by the concentration of hypochlorous acid (HOCl), at pH values above 5. Deconvolution of the FTIR vibrational amide I band experimentally confirmed previous assumptions stated in the literature regarding the weakening of polyamide intermolecular hydrogen bond interactions with the incorporation of chlorine. An increase in the fraction of non associated C O groups (1680 cm −1 ) and a decrease of hydrogen bonded C O groups (1660 cm −1 ) were observed with an increase in the concentration of the free chlorine active specie. The relative evolution of pure water permeability was assessed during lab-scale filtration of MilliQ water of a membrane before and after exposure to chlorine. Filtration results indicate polyamide conformational order changes, associated with the weakening of polyamide intermolecular H bonds, as observed with the increase in the packing propensity of the membrane, dominant for HOCl doses above 400 ppm h. In addition, water-sodium chloride selectivity capabilities permanently decreased above this HOCl concentration threshold, further suggesting polyamide chain mobility. However, under controlled exposure conditions, i.e., HOCl concentration, operating conditions (applied pressure or permeation flux) can be improved while maintaining similar RO membrane separation performance.

On the influence of salt concentration on the transport properties of reverse osmosis membranes in high pressure and high recovery desalination

2019

In this work, we investigate the effect of varying the concentration of sodium chloride up to 70 g.L-1-equivalent to a recovery of approximately 50% in seawater desalination-on the transport properties of different reverse osmosis membranes. The study was performed using five commercial thin film composite (TFC) membranes and an analogue TFC membrane fabricated via the interfacial reaction of m-phenylenediamine and trimesoyl chloride. The surface properties of the membranes as measured by atomic force microscopy (AFM), zeta potential, and X-ray photoelectron spectroscopy (XPS) are presented. The solution diffusion model coupled with film theory was used to calculate the permeance of water and salt through the membranes, to account for the effect of concentration polarisation. The mass transfer coefficient in the test cells was estimated independently using the dissolution rate of benzoic acid; and was found to be approximately 1 × 10 −4 í µí±š. í µí± −1. A linear reduction in salt permeance was observed in some of the RO membranes, while it remained constant for other membranes, including the analogue membrane. All the tested membranes maintained constant water permeance below 45 g.L-1 NaCl. However, when the salt concentration at the membrane surface exceeded 45 g.L-1 , water permeance either increased, remained constant or decreased. The results demonstrate the dependence of water and salt transport on the concentration of sodium chloride at the membrane surface. 1. Introduction Thin film composite (TFC) membranes formed via the interfacial polymerisation of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a polysulfone or polyethersulfone ultrafiltration support are the most widely used membranes in water treatment and desalination. This is due to the reliability and relatively low-cost of the interfacial polymerisation technique in producing membranes with excellent separation properties and a wide variety of surface properties [1]. This enables the utilisation of TFCs in reverse osmosis water desalination systems with feed solutions ranging from low-salinity fresh and brackish water (~2-10 g.L-1 NaCl) to high-salinity seawater (~35 g.L-1 NaCl). Since, it is common to operate RO plants with overall recoveries around 50% [2], the membrane elements in a seawater reverse osmosis (SWRO) plant are subjected to salt concentrations in the feed between 35 to 70 g.L-1 from the entry point until the solution exits the RO spiral wound elements.