Properties Of Reverse Osmosis Membranes Research Articles

Investigation of the main properties of reverse osmosis membranes and their influence on changes in the physico-chemical composition of aqueous solutions

The article discusses the relevance and features of the use of reverse osmosis when adjusting the physico-chemical composition of aqueous solutions and especially the composition of drinking water. The main element of any reverse osmosis plant is a semi-permeable membrane, which is a polymer composite material of uneven density. It has been shown that reverse osmosis membranes must meet certain requirements, the main of which are selectivity to the components that are removed at this functional stage, compliance with a high level of permeability, i.e. stable physical and chemical properties during their operation. The main physicochemical properties of membranes (selectivity, specific productivity, concentration reduction factor, separation factor) and methods for their calculation are described. The effect of temperature on the change in the selectivity and specific productivity of a semipermeable membrane for MgCl2 and CaCl2 salts has been experimentally studied. It has been proven that an increase in the temperature of the solution leads to an increase in the selectivity of the membrane and a linear decrease in the specific productivity. Experimental studies were carried out on model solutions to study the effect of pressure on the change in membrane selectivity. It is shown that the shrinkage of the membrane structure is especially noticeable in the first hours of its operation, which leads to a decrease in the selectivity of the membrane. A practically steady state in terms of selectivity usually occurs in 4–5 hours. It was studied that with an increase in the concentration of salts in the initial solution, a decrease in the specific productivity of the membrane and an increase in selectivity occur. It is shown that the selectivity of the studied membrane in the presented range of concentrations is higher for electrolytes of the 2:2 type than for electrolytes of the 2-1 type. The parametric dependences of the change in selectivity and the concentration reduction factor of the Filmtec TW30-1812-50 membrane over time for the components of a “model multicomponent solution” at a pressure of P = 18 atm are given.

A Novel Antifouling RO Polyamide/Myrrh Membrane for Waste Water Purification

In the present work, desalination of real samples from Dumat Al-Jandal Lake water (located in Jouf region) was carried out via reverse osmosis (RO) technique. The growth of bacteria on the surface of RO membrane is an essential issue of this method. It creates defects in membrane properties as salt rejection and preparation. Many approaches have been proposed to prevent the growth of bacteria on membrane. The addition of some materials such as natural products was one of those approaches. In this work, myrrh was chosen because it is well known as an antibacterial natural product. Unmodified RO membrane was prepared in the lab using interfacial polymerization between trimesoyl chloride (TMC, 0.1 M) and m-phenylenediamine (MPD, 0.3 M). The characterization was obtained by using infrared (IR) and scanning electron microscopy (SEM). The properties of RO membrane as water flux and salt rejection were determined using lake water. The obtained results were 25 and 65% for water flux and salt rejection, respectively. In respect of modified RO membrane, myrrh solution with different concentrations was prepared and mixed with membrane materials. The modified membrane was characterized with IR and SEM. Water flux and salt rejection were determined obtaining results of 42 and 41% for water flux and salt rejection, respectively. The resistance of bacterial growth was tested for both modified and unmodified membranes, showing that the modified membrane presented high resistance of bacterial growth in contrast to the unmodified one.

Reusing and Characterization of the Used Reverse Osmosis Membrane and its Application in Surface Water Purification

The current study concerns the recycling of the used reverse osmosis membrane named DOW FILMTEC™ SW30HR–380. The performance improvement includes the following steps:(1) Molecular characterization of the used membrane where it contributes to understanding the physicochemical properties of reverse osmosis membranes and their performance, using different analytical techniques like FTIR, SEM, and tensile strength. (2) reuse of the Polysulfone layer of the membrane as a filter for the turbidity removal of surface water.(3) Comparison between the turbidity removal % by the Polysulfone layers (arranged in a disc filter) and the conventional coagulants. From the results, we found that SEM photographs were evidence for the high fabrication of the membrane. The coating layer showed a high hydrophilic hydroxyl group appearing in FTIR spectra. Mechanically, the polyamide layer showed the best tensile properties. Raw water quality and the conditions leading to filter clogging were discussed. The removal percentage of turbidity and algae from surface water reached 60 and 80% respectively using five successive Polysulfone layers with a surface area of 12.5 cm2/layer. At the same turbidity, tested coagulants achieved higher removal % than that of the Polysulfone layers. On one hand, the recycled reverse osmosis membrane may be used as an alternative technique for removing turbidity and algae, while on the other hand, it reduces harmful effects and emissions

Fouling properties of reverse osmosis membranes along the feed channel in an industrial-scale system for wastewater reclamation

Membrane fouling is an inevitable disadvantage of the reverse osmosis (RO) process for wastewater reclamation. In order to clarify the development process of membrane fouling, all the fouled membranes along a feed channel of a two-stage industrial-scale RO system for wastewater reclamation (six elements in each stage) were autopsied and analyzed.The water flux and salt rejection efficiency of the fouled membranes at the head and tail were the lowest among 12 elements, thereby indicating more severe fouling on these membranes. In this RO system, most of the organic compounds deposited on the head elements of each stage were mainly composed of proteins, polysaccharides, and fulvic acid. The ATP concentrations of the foulants on the first and twelfth elements were much higher than those of the other elements, suggesting severe biofouling. Although microbes can cause organic fouling owing to extracellular polymeric substances production, no clear correlation was found between organic fouling and biofouling in this study. For example, the ATP concentrations on the second element and seventh element were similar (1.16 ng/cm2 and 1.26 ng/cm2, respectively), thereby suggesting a similar extent of biofouling, but organic fouling of the second element was relatively slight (DOC: 24.8 mg/m2) compared with that of the seventh element (DOC: 46.2 mg/m2). The seventh element (ATP: 1.26 ng/cm2) was more severely biofouled than the eighth element (ATP: 0.15 ng/cm2), but they suffered from the same level of organic fouling (DOC: 46.2 mg/m2 and 47.1 mg/m2, respectively). Approximately 70% of metallic elements, predominantly Fe, were deposited on the first element. Although the concentration of Fe in the feed water was much lower than those of Ca and Mg, the concentration of Fe on the first three elements was significantly higher than that of any other element, suggesting that Fe was more easily deposited on the RO membranes.

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

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 1×10−4m.s−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.

Microbial biofilm communities on Reverse Osmosis membranes in whey water processing before and after cleaning

The need for recovering valuable compounds and water from side streams has increased the use of Reverse Osmosis (RO) membrane filtration in the food industry. RO membranes, however, are highly susceptible to biofilm formation, which may decrease performance and increase industrial costs. In order to identify and characterize the biofilm forming communities, industrial RO membranes from whey water recovery lines in a dairy industry were investigated before and after Cleaning-In-Place (CIP) treatments. Phase contrast and Confocal Laser Scanning Microscopy (CLSM) were used to visualize the biofilms. The Heterotrophic Plate Count (HPC) and yeast population were enumerated, and 16S, 26S, and ITS rRNA sequencing was employed to identify the dominant isolates. A dense biofilm of the filamentous yeast species Saprochaete clavata and Magnusiomyces spicifer was observed together with budding yeasts and Gram-negative bacteria. The filamentous yeasts had long hyphae, which spatially dominated the biofilm on the retentate and permeate surface and they were not inactivated by the standard CIP treatment. Since neither plate counts nor DNA-based methods reflect the wide membrane coverage of the filamentous yeasts, their role in biofouling may easily be underestimated. We suggest that filamentous yeasts are included in further research on fouling of water treatment membranes in the dairy industry when investigating the effect of different CIP treatments or new RO membrane properties.

Improvement of performance and antifouling properties of reverse osmosis membranes using green additive

Improvement of performance and antifouling properties of reverse osmosis membranes using green additive

Dependence of initial silica scaling on the surface physicochemical properties of reverse osmosis membranes during bench-scale brackish water desalination

Silica scaling of reverse osmosis membranes in brackish water desalination is less understood than hardness scaling due to the complex silica behaviors at the membrane/water interface. In this study, -COOH, -SO3H, -NH2 and -OH functional groups were introduced onto polyamide membranes to create distinct surface physicochemical properties. The resulting membranes were further studied under similar scaling conditions to yield temporal flux loss data that were empirically interpreted by a logistic growth model. The scaled membranes were also characterized by complementary analytical techniques. It was found that permeate flux loss was strongly correlated to the initial silica layer formed by direct interaction between reactive silanol (Si-OH) and reciprocal groups on the membrane surface, rather than the entire scaling layer. Importantly, membrane surface properties dictated the initial silica layer formation through three possible mechanisms, i.e., electrostatic repulsion, competitive adsorption, and interfacial energy change. Of these, electrostatic repulsion was identified as the primary one. Therefore, by modifying the membrane surface properties, the three aforementioned mechanisms may be enhanced to favor the formation of a loose, disordered initial silica scaling layer. Accordingly, membrane flux loss may be mitigated. This finding provided important insights into the design heuristics of scaling-resistant reverse osmosis membrane for brackish water desalination.

Boron Can Be Used to Predict Trace Organic Rejection through Reverse Osmosis Membranes for Potable Reuse.

Potable water reuse is a viable option for communities with extreme water scarcity. Improvements in measurement capabilities and greater occurrence of contaminants of emerging concern (CECs) have made the investigation of the removal of CECs through advanced treatment facilities essential for further reuse considerations. Reverse osmosis (RO) has been demonstrated to remove many CECs, but poor removal has been observed for many low molecular weight (MW), neutral organic compounds. With the availability of many RO membrane products on the market, it is increasingly important to be able to predict organics rejection through different products without detailed information about the RO membrane's properties or structure. This laboratory-scale study investigated the rejection of low-MW, neutral organics, boron, and sodium chloride by six RO membrane products. The experimental results were used to develop a correlation between the removal of organics and boron. If the rejection of boron and a neutral organic through one reference membrane is available, then the rejection of that organic through any other membrane product can be estimated using the rejection of boron through that membrane.

Synthesis, characterization and antibacterial properties of reverse osmosis membranes from cellulose bromoacetate

The antibacterial alkyl bromide groups were introduced into cellulose diacetate (CDA) through the esterification between highly active bromoacetyl bromide and hydroxyl groups under mild conditions and the modified cellulose acetate reverse osmosis membrane (Br-CA-RO) was obtained subsequently after phase inversion process. The results of FTIR and 1H-NMR indicated the existence of alkyl bromide groups in the modified CDA powder. The optical density method was used to confirm its antibacterial ability. The chemical structure and morphology characterization demonstrated that the anchoring of bromoacetyl groups as antibacterial part brought out minimal alteration on membrane chemical structure and its asymmetric structure, but the regularity and density of membranes increased with the degree of esterification. The property testing results showed that the whole physical performance was enhanced with the thermal stability getting slightly worse. Both the flux and salt rejection of Br-CA-RO increased after modification and the latter was close to that of cellulose triacetate RO membrane. The dynamic contact antibacterial testing implied that Br-CA-RO showed much higher antibacterial ability than unmodified RO membranes, and its relative bactericidal rates against E. coli (gram negative) and S. aureus (gram positive) were higher than 73.0% and 93.5%, respectively. This method offers a new approach for antibacterial and functional modification of CA-RO membranes.

Influence of surfactant fouling on rejection of trace nuclides and boron by reverse osmosis

Recent studies have shown that contaminant rejection depends greatly on membrane surface morphology and structure. In this paper, we investigate the influence of surfactants on reverse osmosis membrane properties and the rejection of trace nuclides in low level radioactive wastewaters. The results demonstrate that surfactant deposition on membrane surfaces may change surface characteristics such as roughness and contact angle, and therefore affect trace nuclide rejection and membrane flux. After a 12h fouling test using surfactants sodium dodecyl benzene sulfonate, Tween-80 and cetyltrimethyl ammonium bromide, the permeate flux declined by ~55.8%, 44.86% and 40.61%, respectively. CTAB deposition on the membrane increases nuclide rejection, whereas sodium dodecyl benzene sulfonate and Tween-80 deposition decreases nuclide rejection. All surfactant deposition enhances boron rejection. According to a correlation coefficient analysis, the decrease in flux can be attributed mainly to a variation in membrane surface hydrophilic properties resulting from surfactant deposition. The nuclide rejection and boron transfer ability correlate with membrane roughness and hydrophilic property, respectively.

Effect of polydopamine deposition conditions on fouling resistance, physical properties, and permeation properties of reverse osmosis membranes in oil/water separation

A commercial polyamide reverse osmosis (RO) membrane was surface-modified with polydopamine deposited from buffered, aqueous dopamine solution at ambient conditions. The influence of various modification conditions (i.e., dopamine solution concentration, polydopamine deposition time, and initial pH of Tris–HCl buffer) on pure water flux, flux during filtration of an oil/water emulsion, and NaCl rejection was investigated. Dead-end filtration results showed decreased pure water flux with increasing dopamine solution concentration and polydopamine deposition time. Membranes modified at a pH of 5 exhibited no change in pure water flux or flux during fouling experiments compared to the native membranes, suggesting that polydopamine was not deposited under such acidic coating conditions. All polydopamine-modified membranes, except those coated at a pH of 5, had higher fluxes when filtering an oil/water emulsion than that of unmodified membranes. NaCl rejection values in all membranes were within the manufacturer's specification. The increased flux when filtering an oil/water emulsion was not sensitive to dopamine concentration, coating time greater than 60min, or alkaline buffer pH value. Short deposition times slightly reduced the fouling resistance of coated membranes, and membranes modified at acidic pH values showed no improvement in fouling.

Effect of surface properties of reverse osmosis membranes on biofouling occurrence under filtration conditions

Biofouling of reverse osmosis (RO) membranes, which occurs as a result of biofilm growth following initial bacterial adhesion, is well known as one of the most serious problems. Although membranes with surfaces resistant to bacterial adhesion are expected to have higher resistance to biofouling as well, our recent study reported that membrane surface properties have no significant relationship with biofouling under no filtration condition (Lee et al., 2010 [27]). The purpose of this study is to investigate the effects of surface properties of RO membranes (hydrophobicity, surface charge, and roughness) on biofouling under a lab-scale cross-flow RO membrane system using three commercial RO membranes with different surface properties. This study reports that the extent of biofouling, which was demonstrated through flux decline with time, appeared to remain constant despite the apparent difference in surface properties among the three commercial RO membranes selected. As a result, it seems that surface properties of RO membrane have no relationship with biofouling occurrence.

Evaluation of surface properties of reverse osmosis membranes on the initial biofouling stages under no filtration condition

In order to evaluate the effect of membrane surface properties on the initial stage of biofouling, in the reverse osmosis (RO) membrane process, initial bacterial adhesion and biofilm formation experiments were performed under no filtration condition. In this study, five commercialized polyamide thin-film composite RO membranes (SW30HRLE, SW30HR (Dow FilmTec Co., USA), TM820 (Toray Co., Japan), RE-BE, RE-FE (Woongjin Chemical Co., Korea)) were chosen and their surface properties such as surface charge, roughness, hydrophobicity and surface morphology were measured. For examining initial bacterial adhesion, a flow channel reactor was employed for 3 h, while for examining a biofilm formation, the CDC reactor was employed for 48 h. Pseudomonas aeruginosa PAO1 tagged with GFP was selected as a model bacterial strain. Major findings in this study indicate that although the initial bacterial cell adhesion in a flow channel reactor indicated more bacterial cells attachment on the membrane surface with higher hydrophobicity, the extent of biofilm grown in CDC reactor for 48 h became similar regardless of the difference of the membrane surface properties, indicating that the membrane surface properties become a less important factor affecting the biofilm growth on the membrane surface. This finding will be helpful in improving the understanding of biofouling issue occurring in the real RO membrane system, although practical implication is somewhat limited since this study was performed under no filtration condition.

Treatment of 137Cs liquid wastes by reverse osmosis Part I. Preliminary tests

As a consequence of an accidental fusion of a 137Cs source in a steel production factory, 40 m 3 of radioactive liquids were generated in the plant decontamination process. This radioactive liquid waste was treated by a reverse osmosis plant, managing to declassify more than 36 m 3. The remaining 4 m 3 were treated by evaporation reducing the final volume to less than 1 m 3. Prior to the waste treatment at the steel factory, preliminary tests were done in order to determine reverse osmosis membrane performance with 137Cs effluents. The influence ofgamma and electron irradiation on structure and transport properties of reverse osmosis membranes was studied; and reverse osmosis performance with a 137Cs-contaminated liquid obtained from contaminated ashes was assessed. The aim of this paper is to describe and show the results of these preliminary tests.

Effects of surface modification on antifouling and performance properties of reverse osmosis membranes

The effects of surface modification of commercial reverse osmosis (RO) polyamide membranes were studied in terms of flux/rejection and surface properties. Selected RO membranes, spanning ultra-low pressure to seawater membranes, were modified by in-situ graft polymerization using redox generation of monomer radicals. Modification of the membrane significantly reduced both receding and advancing contact angles of some of the membranes as measured by a modified Wilhelmy plate method. Lower contact angles indicate more hydrophilic membranes and such membranes will potentially show better resistance to fouling by hydrophobic foulants. This was confirmed by adsorption measurements carried out on modified and unmodified membranes with a highly fouling surface water. Modified membranes adsorbed less organic material and were more easily cleaned than unmodified membranes. Specific fluxes were not changed by more than 0–25% and NaCl rejection was unchanged or increased slightly.

Enhanced transport properties of reverse osmosis membranes by chemical treatment

The performance of thin film composite (TFCL-LP®) membranes that were treated with hydrofluoric acid (HF) improved and their flux increased significantly without any loss in ion-rejection properties. In contrast, DESAL3 membranes do not show any significant change in transport properties after similar treatment with HF. We used scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements to determine why this difference in behavior occurs. The difference in microstructure, as described by the interstitial void model, seems to be responsible for their behavior after being exposed to chemicals like HF. Therefore, we attempt to correlate transport properties with the microstructural changes (smoothing of membrane ridge-valley structure or no change in density of spherulites) observed. This method of treatment seems to be very effective in simultaneously enhancing the flux and rejection of reverse osmosis membranes which have a typical ridge and valley structure. © 1996 John Wiley & Sons, Inc.

Irradiation Effects on Properties of Reverse Osmosis Membrane Based on Crosslinked Aromatic Polyamide

Irradiation Effects on Properties of Reverse Osmosis Membrane Based on Crosslinked Aromatic Polyamide

Measuring the zeta (electrokinetic) potential of reverse osmosis membranes by a streaming potential analyzer

The use of a novel streaming potential analyzer to measure the zeta potential of cellulose acetate and composite polyamide reverse osmosis membranes is reported. Zeta potentials of these membranes were measured at various solution chemistries. These include effects of salt (NaCl) concentration, solution pH, and the presence of dissolved humic substances. It is demonstrated that streaming potential is a useful tool to measure zeta potential of reverse osmosis membrane surfaces. Results indicate that solution chemistry has a marked effect on the electrokinetic properties of reverse osmosis membranes. Humic substances strongly adsorb onto the surface of reverse osmosis membranes and thus alter the surface charge of the membranes. Furthermore, the zeta potential of reverse osmosis membranes becomes more negative as the NaCl concentration in solution increases, in a marked contrast to conventional electric double layer theories. It appears that the zeta potential of reverse osmosis membranes is strongly influenced by the presence of unreacted chemical substances or impurities on the membrane surface. Various explanations for the behavior of the membranes at the above solution chemistries are evaluated and discussed.

Irradiation Effects on Properties of Reverse Osmosis Membrane Based on Crosslinked Aromatic Polyamide.

In order to develop a membrane suitable for reverse osmotic condensation of radioactive liquid wastes, a new crosslinked aromatic polyamide composite reverse osmosis membrane (ROM) was irradiated in water, or in wet system, and its mechanical and some thermal properties, and the separation performance for inorganic salt were investigated. A membrane was degraded by irradiation more severely in wet system than in dry system, probably due to the reaction with OH-radicals. In the separation performance for NaCl, the salt rejection of the membrane was kept over 88% until irradiation reached 2MGy, maintaining about 90% of its original water flux.