Composite RO Membranes Research Articles

Piezoelectric reverse osmosis (RO) membrane: Fabrication and anti-fouling effect

In this study, a novel piezoelectric RO membrane with vibrating mechanism when exposed to an electric field was developed. The vibration due to the piezoelectric effect can disturb the concentration polarization layer on the membrane surface and minimize membrane fouling. Polyvinylidene fluoride (PVDF) which has piezoelectric properties was selected as the porous substrate for a thin film composite (TFC) polyamide RO membrane in this study. Electrical poling was performed to enhance the piezoelectric properties of the PVDF substrate. RO membranes fabricated via interfacial polymerization using different PVDF substrates (i.e., with and without pre-wetting the PVDF substrate, with and without polyethylene terephthalate (PET) non-woven fabric support (denoted as NWF and no-NWF, respectively), with and without electrical poling) were systematically investigated. The results indicated that RO membrane fabricated on poled PVDF-NWF substrate shows reasonable pure water permeability of ∼2 LMH/bar and sodium chloride (NaCl, 2000 ppm) rejection of ∼98.9 % when tested at 15 bar. In the accelerated fouling study using colloidal silica particles (∼20 nm in diameter, 200 ppm with background of 2000 mg/L NaCl), when the RO membrane fabricated using both unpoled and poled PVDF-NWF substrates were excited with AC signal, membrane fouling was significantly reduced. These findings suggested that electrical poling may not be necessary for such piezoelectric RO membrane.

Comprehensive treatment of aroma chemicals industrial effluent with substantial COD content by a novel PVP/polyamide composite hydrophilized RO membrane

A hydrophilized polyvinyl pyrrolidone/polyamide composite high rejection reverse osmosis (HPA-HR RO) membrane was used for the treatment of aroma chemicals containing effluent coming as multiple effect evaporators (MEE) condensate at UK Aromatics Pvt. Ltd., Boisar, Maharashtra. The unique membrane has an active composite layer of polyamide prepared by interfacial polymerization of high diamine (3%) and acid chloride (0.2%) monomer concentrations, which is further coated with polyvinyl pyrrolidone (PVP) to enhance hydrophilicity and chemical inertness. The plant provides removal of total dissolved solids (TDS) from 2500 to 3500 ppm in the feed to a value of 50–100 ppm in the permeate water indicating a rejection of more than 95% of the dissolved solids, with a high water recovery of 80% in permeate. Similarly, complete rejection of color was observed from dark brown to colorless (transparent), whereas the COD content was brought down from 3000 to 5000 mg/L in the MEE condensate to around 1000 mg/L indicating removal of 60 % to 80% depending upon the pressure applied to overcome the high osmotic pressure of the effluent. Physicochemical interactions between the PVP and polyamide skin layers of the composite membrane make the separating barrier durable and highly hydrophilic. Water would have greater sorption due to high affinity with the membrane and higher diffusion coefficient from its smaller size, while the less polar esters that constitute most of the COD would have low interaction and their larger molecular sizes make them less diffusive. The recovered permeate water has been reused in various internal industrial applications like cooling towers, cleaning, etc. at UK Aromatics.

Effect of Vacuum UV Irradiation and PVA grafting on thin-film composite RO Membranes

Effect of Vacuum UV Irradiation and PVA grafting on thin-film composite RO Membranes

Ionic Liquid-Mediated Interfacial Polymerization for Fabrication of Reverse Osmosis Membranes.

This study revealed the effects of incorporating ionic liquid (IL) molecules: 1-ethyl, 1-butyl, and 1-octyl-3-methyl-imidazolium chlorides with different alkyl chain lengths, in interfacial polymerization (IP) on the structure and property (i.e., permeate-flux and salt rejection ratio) relationships of resulting RO membranes. The IL additive was added in the aqueous meta-phenylene diamine (MPD; 0.1% w/v) phase, which was subsequently reacted with trimesoyl chloride (TMC; 0.004% w/v) in the hexane phase to produce polyamide (PA) barrier layer. The structure of resulting free-standing PA thin films was characterized by grazing incidence wide-angle X-rays scattering (GIWAXS), which results were correlated with the performance of thin-film composite RO membranes having PA barrier layers prepared under the same IP conditions. Additionally, the membrane surface properties were characterized by zeta potential and water contact angle measurements. It was found that the membrane prepared by the longer chain IL molecule generally showed lower salt rejection ratio and higher permeation flux, possibly due to the inclusion of IL molecules in the PA scaffold. This hypothesis was supported by the GIWAXS results, where a self-assembled surfactant-like structure formed by IL with the longest aliphatic chain length was detected.

On the importance of selectivity and support layer compaction in pressure retarded osmosis

In this work, we use a modified thin film composite RO membrane to examine the impacts of selectivity and compaction on the performance of pressure retarded osmosis. RO membranes are promising platforms to study PRO because they are tolerant to typical PRO pressures and are well characterized for permeance and selectivity. Their availability across a range of selectivity (from nanofiltration to seawater RO) also allows us to systematically investigate the impact of selectivity on PRO power density under real PRO conditions. Parallel modeling efforts found that experimentally measured power densities for these membranes were less than 50% of predicted ideal values due to compaction. Interestingly, the highest selectivity membranes, which corresponded to the least permeable, exhibited the highest power densities.

A Novel Approach To Optimize the Fabrication Conditions of Thin Film Composite RO Membranes Using Multi-Objective Genetic Algorithm II.

This work focuses on developing a novel method to optimize the fabrication conditions of polyamide (PA) thin film composite (TFC) membranes using the multi-objective genetic algorithm II (MOGA-II) method. We used different fabrication conditions for formation of polyamide layer—trimesoyl chloride (TMC) concentration, reaction time (t), and curing temperature (Tc)—at different levels, and designed the experiment using the factorial design method. Three functions (polynomial, neural network, and radial basis) were used to generate the response surface model (RSM). The results showed that the radial basis predicted good results (R2 = 1) and was selected to generate the RSM that was used as the solver for MOGA-II. The experimental results indicate that TMC concentration and t have the highest influence on water flux, while NaCl rejection is mainly affected by the TMC concentration, t, and Tc. Moreover, the TMC concentration controls the density of the PA, whereas t confers the PA layer thickness. In the optimization run, MOGA-II was used to determine optimal parametric conditions for maximizing water flux and NaCl rejection with constraints on the maximum acceptable levels of Na2SO4, MgSO4, and MgCl2 rejections. The optimized solutions were obtained for longer t, higher Tc, and different TMC concentration levels.

TREATMENT OF PRODUCED WATER FROM CRUDE OIL DESALTER BY COMPOSITE POLYAMIDE RO MEMBRANE

Produced water generated from oil refinery desalting unit requires proper treatment to adhere to stringent regulations before discharging or recycling into the processing area. In this research, desalter’s produced water from PP(M)SB (PETRONAS Penapisan (Melaka) Sdn. Bhd.) was treated via AFC99 tubular thin film composite polyamide RO membrane and were investigated concerning TMP, feed pH and feed-solution concentration. The experimental results indicated that AFC99 membrane removed 100% of TSS and salinity, and more than 95% of COD, salts ions and TDS. This work shows that the RO membrane was feasible and technically viable to be used for optimum salts and contaminants removal from produced water of the desalting unit. Besides, the treated water (permeate) fulfills the watering standards and can be used for recycling and other purposes.
 Keywords: produced water, reverse osmosis, polyamide membrane, operating conditions, watering standards

Surface coating of polyamide reverse osmosis membranes with zwitterionic 3‐(3,4‐dihydroxyphenyl)‐l‐alanine (l‐DOPA) for forward osmosis

AbstractTo overcome low permeability and fouling problems of membranes used in FO processes, modification is needed to improve the hydrophilicity, permeability and selectivity of membranes. In this work, thin film composite (TFC) commercial polyamide RO membranes (BW30‐LE, SW30‐HR, AG and AC) were functionalized with zwitterionic l‐DOPA. The effect of l‐DOPA on the morphology of membranes was determined via SEM, FT‐IR, AFM and contact angle analysis. The l‐DOPA modified BW30‐LE membrane showed excellent properties with 46° contact angle and 3.8 L/m2hbar water permeability and 0.83 L/m2h salt permeability. Although, l‐DOPA modified BW30‐LE membrane had the highest water flux and hydrophilicity, l‐DOPA modified SW30‐HR membrane showed higher FO flux with 9.38 L/m2h than BW 30 membrane with 3.5 L/m2h at 50 g/L NaCl draw solution. Introducing hydroxyl and carboxyl ionic groups on the membrane surface with l‐DOPA coating enhanced the FO performance and water permeability which provide a new insight in FO applications.

Performance of Acacia Gum as a Novel Additive in Thin Film Composite Polyamide RO Membranes.

Novel thin film composite (TFC) polyamide (PA) membranes blended with 0.01–0.2 wt.% of Acacia gum (AG) have been prepared using the interfacial polymerization technique. The properties of the prepared membranes were evaluated using contact angle, zeta potential measurements, Raman spectroscopy, scanning electron microscopy, and surface profilometer. It was found that the use of AG as an additive to TFC PA membranes increased the membrane’s hydrophilicity (by 45%), surface charge (by 16%) as well as water flux (by 1.2-fold) compared with plain PA membrane. In addition, the prepared PA/AG membranes possessed reduced surface roughness (by 63%) and improved antifouling behavior while maintaining NaCl rejection above 96%. The TFC PA/AG membranes were tested with seawater collected from the Arabian Gulf and showed higher salt rejection and lower flux decline during filtration when compared to commercial membranes (GE Osmonics and Dow SW30HR). These findings indicate that AG can be used as an efficient additive to enhance the properties of TFC PA membranes.

Polyamide–surfactant interaction: Exploration of new avenues for reverse osmosis separation applications

AbstractThin‐film composite (TFC) RO membrane has got widespread acceptability for desalination and water reuse applications. A novel approach toward modification of surface of TFC RO membrane using surfactant (anionic, cationic, and nonionic) has been presented. Anionic surfactant, sodium dodecyl sulfate, increased the water flux of TFC RO membrane up to 142% when TFC RO membrane was exposed to sodium hypochlorite solution of 2,000 mg/L for 2 hr followed by sodium dodecyl sulfate for 1 hr at pH 11. However, surface modification by cationic surfactant, that is, cetrimonium bromide resulted in decreased water flux. Boron rejection decreased to 87.31% when cetrimonium bromide of 500 mg/L was exposed after 2,000 mg/L sodium hypochlorite at pH 11 because of positive charge on the membrane surface. Nonionic surfactant Triton X‐100 exposure lower than critical micelle concentration, that is, 100 mg/L for 1 hr after sodium hypochlorite exposure of 2,000 mg/L for 2 hr, resulted in increased water flux of about 22%, however, on increasing surfactant concentration more than critical micelle concentration, that is, 4% with the same sodium hypochlorite pre‐exposure, resulted in 47.5% decline in water flux. Thus, surfactant can bind the top barrier layer of polyamide membrane to alter its performance.

A novel approach to bind graphene oxide to polyamide for making high performance Reverse Osmosis membrane

We report the novel thin film composite RO membrane modified by graphene oxide. The thin film composite RO membrane was exposed to 2000 mg/l sodium hypochloride; thereafter it was subjected to different graphene oxide concentration ranging from 50 mg/l to 1000 mg/l in water. The resultant membrane was crosslinked with 5000 mg/l N-hydroxysuccinimide. The performance of different membranes were analysed by solute rejection and water-flux measurement. It was found that 100 mg/l graphene oxide exposure followed by 5000 mg/l N-hydroxysuccinimide treatment resulted in the membrane with the highest solute rejection of 97.78% and water-flux of 4.64 Liter per sqm per hour per bar g. The membranes were characterized by contact angle for hydrophilicity, scanning electron micrographs for surface morphology, energy dispersive X-Ray for chemical composition of the surface, Atomic force microscope for surface roughness, ATR-FTIR for chemical structure identification. It was found that the graphene oxide modified membrane increases the salt rejection performance after exposure to high-fouling water containing albumin. Highly hydrophilic, antifouling surface formation with the nanomaterial led to the improved membrane performance. Moreover, the protocol of incorporating nanomaterial by this post-treatment is simple and can be applied to any RO membrane after it is manufactured.

Surface modification of thin film composite reverse osmosis membrane by glycerol assisted oxidation with sodium hypochlorite

Need for improvement in water flux of thin film composite (TFC) RO membrane has been appreciated by researchers world over and surface modification approach is found promising to achieve higher water flux and solute rejection. Thin film composite RO membrane was exposed to 2000mg/l sodium hypochlorite solution with varying concentrations of glycerol ranging from 1 to 10%. It was found that there was a drop in concentration of sodium hypochlorite after the addition of glycerol because of a new compound resulted from the oxidation of glycerol with sodium hypochlorite. The water flux of the membrane treated with 1% glycerol with 2000mg/l sodium hypochlorite for 1h was about 22% more and salt rejection was 1.36% greater than that of only sodium hypochlorite treated membrane for the same concentration and time. There was an increase in salt rejection of membrane with increase in concentration of glycerol from 1% to 5%, however, increasing glycerol concentration further up to 10%, the salt rejection declined. The water flux was found declining from 1% glycerol solution to 10% glycerol solution. The membrane samples were characterized to understand the change in chemical structure and morphology of the membrane.

Preparation of spherical mesoporous aminopropyl-functionalized MCM-41 and its application in polyamide thin film nanocomposite reverse osmosis membranes

Aminopropyl-functionalized MCM-41 (NH2-MCM-41) was synthesized by the one-pot hydrothermal method using tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES) as silica sources, cetyltrimethylammonium bromide as template, ethanol as a cosolvent, and sodium hydroxide as the alkali source. The synthesized nanoparticles were noticeably monodisperse with standard deviation of under 10% for the mean particle size. The specific surface area, pore size, pore volume and amino group density of the NH2-MCM-41 varied with the content of APTES in the initial solution. The NH2-MCM-41-polyamide thin film nanocomposite reverse osmosis (TFN RO) membranes were obtained by interfacial polymerization of trimesoyl chloride (TMC) and m-phenylene-diamine (MPD). The hydrophilicity of the TFN RO membranes was improved by the incorporation of NH2-MCM-41 nanoparticles. The water flux of 54 L m−2 h−1 at 1.6 MPa for NH2-MCM-41-polyamide TFN RO membrane was nearly 2.8 times that of the pure polyamide thin film composite (TFC) RO membrane and the solute rejection was 96.5% with a 0.1% w/v NH2-MCM-41 loading.

Efficacy of synthesis conditions on functionalized carbon nanotube blended cellulose acetate membrane for desalination

Cellulose acetate membrane has been applied to reverse osmosis for desalination due to chlorine tolerance and biofouling resistance. Since it requires optimized synthesis condition for application, we investigated the effect of different conditions on membrane performances. It was found that polymer concentration, solvent ratio, and evaporation time were critical to determine membrane selectivity and permeability. Based on the study, optimized conditions were obtained, which were 14 wt% of polymer concentration, 1:2.9 of ratio of 1,4-dioxane to acetone, and 30 s of evaporation time. Further, functionalized multi-walled carbon nanotubes (MWCNTs) were applied to the optimized bare membrane in order to enhance the performances. The composite membranes were characterized by fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle measurement. It was found that the MWCNTs influenced the morphology and surface chemistry of the membrane. This study could contribute to develop a commercial composite RO membrane with nanomaterial for desalination application.

Improving fouling resistance and chlorine stability of aromatic polyamide thin-film composite RO membrane by surface grafting of polyvinyl alcohol (PVA)

Improving fouling resistance and chlorine stability of aromatic polyamide (PA) thin-film composite (TFC) reverse osmosis membrane is still of considerable need in desalination membrane technology. Here, we reported the chemical linkage of neutral hydrophilic polymer polyvinyl alcohol (PVA) on the surface of a commercial PA TFC membrane through a single step of grafting with potassium persulfate as thermal dissociation initiator and its role on the improvement of membrane resistance to both chlorine and fouling. Membrane characterization was conducted through ATR-FTIR spectroscopy, SEM, AFM, measurements of streaming potential and contact angle and cross-flow permeation tests. It was found that membrane surface became smoother, more hydrophilic and less charged after modification and the modified membrane exhibited an increased slat rejection, a slightly declined water flux and improved fouling resistances to the model foulants of bovine serum albumin (BSA), sodium dodecyl sulfate (SDS) and dodecyltrimethyl ammonium bromide (DTAB). The chlorine exposure tests under accelerated conditions also indicated that the membrane chlorine stability has been enhanced effectively. The PVA molecules on the membrane surface could effectively enhance membrane anti-adsorption capability and prevent the underlying polyamide backbones from chlorine attack, and thereby improving membrane resistance to both fouling and chlorine.

A novel high-flux, thin-film composite reverse osmosis membrane modified by chitosan for advanced water treatment

This work demonstrates a novel method for improving the performance of thin-film composite RO membrane by making a polyamide–chitosan composite.

Relating fouling behavior and cake layer formation of alginic acid to the physiochemical properties of thin film composite and nanocomposite seawater RO membranes

In this study, fouling behavior of alginic acid onto four types of hand-cast and one commercially-available seawater reverse osmosis membranes was investigated. Hand-cast membranes included a polyamide thin film composite and a zeolite-polyamide thin film nanocomposite, as well as poly(vinyl alcohol) coated versions of both. Flux decline due to fouling and the structural features of the fouling layers formed during seawater desalination experiments were analyzed using classic Kozeny–Carman cake filtration theory along with a more recently developed crossflow model. Initial rates of flux decline correlated strongly with membrane permeability and root-mean-squared roughness and moderately with alginate–membrane interfacial free energy. The porosity (i.e., hydraulic resistance) of the fouling layers correlated strongly with deionized water contact angle and moderately with surface area difference of the membranes. The contact angle of the membranes also heavily impacted the fouling layer mass and thickness. Membranes with high permeability, strong alginate–membrane interfacial energy of adhesion, and hydrophobic surfaces had the highest propensity for fouling by low porosity, high specific resistance cake layers. Results indicate that reverse osmosis membranes should be produced with hydrophilic, smooth, and large peak-to-peak surfaces in order to reduce flux decline due to cake layer formation.

Surface modification of thin film composite RO membrane for enhanced anti-biofouling performance

Anti-adhesion and antimicrobial coatings were prepared and applied on commercial thin-film-composite (TFC) polyamide (PA) membrane to enhance anti-biofouling performance. Polyvinyl alcohol (PVA) coating was modified with cationic polyhexamethylene guanidine hydrochloride (PHMG) polymer to obtain antimicrobial performance. ATR-FTIR, SEM and AFM investigated the surface chemistry and morphology of the coated membranes. The contact angle measurement was used to determine hydrophilicity and surface energy. All coated membranes revealed more hydrophilic and lower surface roughness compared to uncoated membrane. Lower number of adhered Pseudomonas aeruginosa (P. aeruginosa) bacteria was detected on coated membranes, indicating anti-adhesion performance. The colony forming unit (CFU) and diffusion inhibition zone (DIZ) tests determined antimicrobial activity of the coated membranes against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), showing the antimicrobial performance of PHMG. The results suggested that an optimal anti-fouling surface could be obtained applying a coating, which combines anti-adhesion and antimicrobial performance.

Interfacially synthesized chlorine-resistant polyimide thin film composite (TFC) reverse osmosis (RO) membranes

Chlorine-resistant polyimide thin film composite (TFC) RO membranes were prepared via interfacial polymerization of m-phenylene diamine (MPD) and 1,2,4,5-benzene tetracarbonyl chloride (BTC) and subsequent thermal imidization. Thermogravimetric analysis, differential scanning calorimetry and attenuated total reflection-Fourier transform infrared spectroscopy confirmed that the use of a tertiary amine catalyst allowed the preparation of the polyimide films at below the glass transition temperature of the polysulfone support sublayer, thus preventing its degradation. The effects of annealing on the membranes performance were investigated. Increasing temperature and duration during the thermal treatment accelerated the imidization of the poly(amic acid) membranes and converted their amorphous structures to semi-crystalline structures, deteriorating their performance. The addition of a cross-linking agent, trimesoyl chloride (TMC), during the interfacial polymerization improved the membrane's performance. The polyimide thin film composite, reverse osmosis membranes prepared from MPD, BTC and TMC showed significantly enhanced chlorine resistance due to the elimination of chlorine-sensitive sites by the replacement of amide linkage with imide linkage.

Rejuvenation of discarded RO membrane for new applications

Abstract The sensitivity of thin film composite RO membrane (TFCs) with chlorine has been widely reported. In the present paper, attempt has been made to modify the chemical structure of thin film composite RO membrane by exposing the membrane to free chlorine in order to evaluate potential of utilizing the discarded membrane after its useful life. The different variants of thin film composite RO membrane in terms of flux and rejection could be prepared by altering the exposure time and concentration of sodium hypochlorite solution. Tailoring the membrane for solute rejection offers advantages over the conventional process for instance: (1) It avoids re-mineralization and directly produces the water of required quality; (2) It enhances flux of membrane and thereby improves the productivity of the membrane; (3) Improved recovery leads to lower capacity pre-treatment and thereby improves the operational efficiency; (4) Number of membrane required for the given capacity will be less and the associated unit cost, e.g. pumping cost will also decrease. Successful attempt has been made to enhance permeability seven times that of the terminally fouled membrane by sequential hypochlorite treatment in controlled fashion, i.e. fouled seawater RO membrane with flow 3.36 l/min and solute rejection of 97.21% has been converted to the membrane with flow 24 l/min and solute rejection 82.37%.Moreover, the thin film composite RO membrane has been degraded totally till its solute rejection efficiency falls to approximately zero in order to convert it to microfiltration/ultra-filtration membrane, i.e. the membrane with pure water permeability 257 gfd @50 psig pressure has been made by exposing 3286 mg/l free chlorine for 96 h to TFC RO membrane. The characterization of this membrane was performed by measuring molecular weight cut off of the membrane and pure water permeability of the membrane to evaluate its performance as an ultra-filtration membrane. These membranes were also tested for micro-organism removal and found that their performance resembles the new ultra-filtration membrane. The hypochlorite treated membranes were also evaluated for their permeability after bio-film formation with different micro-organisms where it manifested higher permeability as compared to untreated membrane.