Brackish Water Reverse Osmosis Membranes Research Articles

Improved Flux Performance in Brackish Water Reverse Osmosis Membranes by Modification with ZnO Nanoparticles and Interphase Polymerization.

With each passing year, water scarcity in the world is increasing, drying up rivers, lakes, and dams. Reverse osmosis technology is a very viable alternative which helps to reduce water shortages. One of the challenges is to make the process more efficient, and this can be achieved by improving the capacity by adapting membranes with nanomaterials in order to increase the permeate flux without exceeding the limits established in the process. In this research, brackish water membranes (BW30) were modified with ZnO nanoparticles by interphase polymerization. The modified membranes and BW30 (unmodified) were characterized by FTIR, AFM, contact angle, and micrometer. The membranes were tested in a cross-flow apparatus using 9000 ppm brackish water, and their permeate flux, salt rejection, and concentration polarization were determined. The salt rejection for the 10 mg ZnO NP membrane was 97.13 and 97.77% at 20 and 30 Hz, respectively, sufficient to generate drinking water. It obtained the best permeate flux of 12.2% compared to the BW30 membrane with 122.63 L m-2 h-1 at 6.24 MPa and 30 Hz, under these conditions, and the concentration polarization increased.

Multi-dimensional parametric study for enhancing Brackish Water Reverse Osmosis membrane performance suited for desalination of low salinity feeds.

Reverse osmosis (RO) effectively provides clean drinking water. Different RO membrane types are tailored to treat saline water feeds with varying characteristics. In the context of low brackish water feeds, the objective is to remove only a minimal excess of salinity through the membrane. Our study introduces a method of membrane post-treatments capable of achieving controlled salt rejection while concurrently enhancing permeate flux, which is vital for achieving effective and energy-efficient desalination of low brackish water. The post-treatments were conducted on our in-house-developed membranes using aqueous solutions of N,N-Dimethylformamide and glycerol for different drying times at the coupon level. The process was scaled up at the module level, allowing us to assess its potential for commercial application. At the coupon level, the permeate flux increased significantly from 3.7 ± 0.9 to 10.6 ± 0.2L/m2·h·bar, while the salt rejection decreased from 95.6 ± 1% to 70.5 ± 1% when measured with a feed of 2,000 ppm NaCl concentration. At the module level, we observed a higher flux of 12.8L/m2·h·bar, alongside a salt rejection of 55.5% with a similar feed. Varying post-treatment parameters at the coupon level allowed us to attain the desired salt rejection and permeate flux values. Physical changes in both pristine and post-treated membranes, including polymer swelling, were observed without chemical alterations, enhancing our understanding of the post-treatment effect and its potential for broader commercial use. PRACTITIONER POINTS: Post-treatment of RO membranes enhances flux. Physical structuring through polymer swelling was observed with the chemical structure unaltered. Post-treatment of RO opens doors for broader energy-efficient desalination application.

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

Thin Film Composite (TFC) Reverse Osmosis (RO) membranes used in desalination, reach their End-of-Life (EoL) due to fouling and chemical degradation and pose disposal problem. Their lifetime can be increased by converting them into Ultrafiltration (UF) or Nanofiltration (NF) membranes. The present work demonstrates a systematic methodology in terms of ‘ppm-h/ppm∙h exposure’ to chemically convert brackish water RO membranes into NF and subsequently into UF membranes using sodium hypochlorite (NaOCl). Post-performance studies of pure water flux, monovalent and bivalent salt rejection are carried at each treatment level. RO membrane has transformed into NF at 3000–3 ppm-h, 2000–6 ppm-h, 3000–6 ppm-h and in to UF membrane beyond 10000–3 ppm-h. Gradual changes in physicochemical properties of membrane during conversion are ascertained from Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Photoelectron Spectroscopy (XPS), contact angle, zeta potential etc. The rate of chlorination of polyamide is derived using XPS elemental data from initial stages of NaOCl exposure, and rate of hydrolysis from the membrane resistance, and pH. The overall rate equation is combination of both. The membrane thickness calculated from the kinetics match with experimental data. This study gives account of depolymerization of polyamide upon NaOCl exposure (ppm-h) which can be useful in chemical recycling/treatment of EoL membranes on a plant scale.

Application of UF and RO for power plant's wastewater treatment and recycling for environmental sustainability

Abstract Global indicators have warned of freshwater scarcity in Asia. However, the utilization of freshwater resources has skyrocketed for commercial and industrial purposes without any strategy for recycling and reuse. The power plant's wastewater/reject mainly consisted of cooling tower blowdown water and reverse osmosis (RO) plant reject water. Due to the high turbid nature of reject water, pretreatment was carried out to achieve SDI15 <3 by employing multimedia filters (MMF), activated carbon filters (ACF) and ultrafiltration (UF). Operational parameters of RO membranes were optimized (11.5 bar, 29 °C) to achieve maximum water recovery along with higher rejection rates of critical scale forming species such as 81% total dissolved solids (TDS), 73% calcium hardness and 72% silica (Si). After accounting for backwash water and other concentrate rejections, the membrane treatment plant has achieved an appreciable recovery rate of more than 44%. The RO membrane-treated water was then incorporated in the cooling tower and a 16% reduction in freshwater makeup was achieved. Reduction of microbial growth rate as well as corrosion and scaling in the cooling tower was observed due to the reuse of treated water. This is to confirm here that brackish water RO membranes can act as a strong contender for reject water reclamation and effective utilization.

Enhanced Anti-Biofouling Properties of BWRO Membranes via the Deposition of Poly (Catechol/Polyamine) and Ag Nanoparticles

The surface modification of reverse osmosis (RO) membranes to improve their anti-biofouling properties is gaining increased attention. Here, we modified the polyamide brackish water reverse osmosis (BWRO) membrane via the biomimetic co-deposition of catechol (CA)/tetraethylenepentamine (TEPA) and in situ growth of Ag nanoparticles. Ag ions were reduced into Ag nanoparticles (AgNPs) without extraneous reducing agents. The hydrophilic property of the membrane was improved, and the zeta potential was also increased after the deposition of poly (catechol/polyamine) and AgNPs. Compared with the original RO membrane, the optimized PCPA3-Ag10 membrane showed a slight reduction in water flux, and the salt rejection declined, but enhanced anti-adhesion and anti-bacterial activities were observed. The FDRt of the PCPA3-Ag10 membranes during the filtration of BSA, SA and DTAB solution were 5.63 ± 0.09%, 18.34 ± 0.33% and 34.12 ± 0.15%, respectively, much better than those of the original membrane. Moreover, the PCPA3-Ag10 membrane exhibited a 100% reduction in the number of viable bacteria (B. subtilis and E. coli) inoculated on the membrane. The stability of the AgNPs was also high enough, and these results verify the effectiveness of poly (catechol/polyamine) and the AgNP-based modification strategy for the control of fouling.

Possibility assessment of ultrafiltration membrane pre-treatment efficiency for brackish water reverse osmosis-based wastewater reuse: Lab and demonstration.

Ultrafiltration (UF) membranes are considered a pre-treatment for brackish water reverse osmosis (BWRO) membranes because of the high rejection rate of particulates and the productivity of the final water quantity. This study presents the performance and membrane surface property analysis of UF membranes for commercial membrane manufacturers, and their structural strength and chemical resistance were evaluated. Moreover, the pilot-scale UF-BWRO process was operated for two months using real wastewater based on the results of this study. Although the overall properties were similar, the poly (ether-sulfone) UF membrane showed higher tensile strength than the polyvinylidene difluoride and polyacrylonitrile UF membranes. The UF membrane showed a high removal rate of particulates (over 90%) but low rejection rate of organic compounds, such as humic acid and sodium alginate (below 30%). After exposure to high concentrations of chemicals, the contact angle of the membranes was reduced by approximately 15% compared to that of the virgin membranes. In addition, despite the exposure to low-and high-concentration chemicals, UF membranes were relatively stable in terms of tensile strength. During the operation period of the pilot-scale UF-RO process, the UF membrane showed a high turbidity removal of over 93%, and the UF-BWRO process presented a high salt rejection of over 92%. The UF membrane showed potential for the pre-treatment of BWRO membranes.

Are commercial polyamide seawater and brackish water membranes effectively charged?

New developments in modeling solute transport in reverse osmosis (RO) membranes are based on the mechanistic description of solution friction and electromigration. In these models, the membrane charge significantly impacts the separation that occurs in the membrane through Donnan partitioning. One implication of membrane charge is that the salt permeability strongly depends on the ion concentration in the feedwater. In this study, we experimentally evaluate the effect of salinity, varied over almost two orders of magnitude (ca. 10–650mM), on four commercially available polyamide seawater RO and brackish water RO membranes. We found no significant effect of feed concentration on observed salt permeability, while the membrane performance closely resembled the specification by the manufacturers. We also demonstrate that a minor leak in the membrane provides a plausible alternative explanation to trend between concentration and salt permeability reported in other studies. The standard solution diffusion model provides a satisfactory description of our data for the membranes and feedwater conditions that we tested.

Aquaporin launches its first series of brackish water RO membranes

Denmark's Aquaporin A/S, a water technology company dedicated to natural water treatment, with operations in Singapore and the USA, recently launched its first series of brackish water reverse osmosis (RO) membranes.

Practical Considerations of Wastewater-Seawater Integrated Reverse Osmosis: Design Constraint by Boron Removal.

The wastewater–seawater (WW-SW) integrated reverse osmosis (RO) process has gained much attention in and out of academia due to its energy saving capability, economic benefits, and sustainability. The other advantage of this process is to reduce boron concentration in the RO permeate that can exclude the post-treatment process. However, there are multiple design constraints regarding boron removal that restrict process design in the WW-SW integrated system. In this study, uncertainties in design factors of the WW-SW integrated system in consideration of boron removal have been explored. In comprehensive consideration of the blending ratio of between WW and SW, regulatory water quality standard, specific energy consumption (SEC), specific water cost, and RO recovery rate, a range of 15,000~20,000 mg/L feed turned out to be the most appropriate. Furthermore, boron rejection tests with SWRO (seawater reverse osmosis) and BWRO (brackish water reverse osmosis) membranes under actual WW-SW integration found a critical reduction in boron rejection at less than 20 bar of operating pressure. These findings emphasize the importance of caution in the use of BWRO membranes in the WW-SW integrated RO system.

Highly permeable thin film composite hollow fiber membranes for brackish water desalination by incorporating amino functionalized carbon quantum dots and hypochlorite treatment

A novel strategy has been demonstrated to synergistically improve the separation performance of thin film composite (TFC) hollow fiber membranes for brackish water reverse osmosis (BWRO) desalination. It consists of two steps. Firstly, a series of amino functionalized carbon quantum dots (CQDs) were synthesized and incorporated into the polyamide layer of TFC membranes. The modified TFC membrane with the optimal amino functionalized CQDs has a pure water permeability (PWP) of 5.50 LMH/bar and a NaCl rejection of 98.0% against a 2000 ppm NaCl feed solution at 15 bar. Comparing with the unmodified TFC membrane, the modified TFC membrane has a 42.1% higher PWP without compromising the salt rejection. Then the modified TFC membrane was treated by a sodium hypochlorite solution at different concentrations. Chlorine was bonded to the polyamide layers, enhancing their repulsion against charged solutes and making the polyamide network less cross-linked. As a result, both PWP and NaCl rejection of the TFC membranes could be improved. After being treated with a sodium hypochlorite aqueous solution at 4000 ppm for 3h, the aforementioned modified TFC membrane displays a PWP of 10.13 LMH/bar and a NaCl rejection of 98.9% against a 2000 ppm NaCl solution at 15 bar, which demonstrates a great potential for brackish water desalination. This study may mark a milestone for the development of future BWRO membranes based on the use of amino functionalized CQDs and hypochlorite treatment.

Flux Optimization in Reverse Osmosis via the Solution-Diffusion Model

This paper suggests a new method of predicting flux values at reverse osmosis (RO) desalination plants. The study is initiated by using the solution-diffusion model that is applied to the groundwater source at Abqaiq plant (500 RO plant) at Saudi Aramco, Dhahran, Saudi Arabia in order to calculate the osmotic pressure of the treated water for Shedgum/Abqaiq groundwater. For modelling purposes, the same technique is used to determine the osmotic pressure drops at the same plant configuration and operating conditions when using seawater sources such that of Arabian Gulf and the Red Sea waters. High rejection brackish water RO (BWRO) element Toray TM720D-400 with 8" is the RO membrane type that is used at Abqaiq plant. The calculated osmotic pressures of the three water sources, assuming that they are all treated at Abqaiq plant, are utilized to determine the appropriate flux values as well as membrane resistances of different BWRO Toray membranes. Values of numerous parameters such as water permeability constant, applied pressure, gas constant, water temperature, water molar volume and membrane thickness, water salinity/TDS are taken into account to develop our calculations through the solution-diffusion model. A comparison between low-pressure, standard and high-pressure BWRO Toray membranes performance have been established to select the ideal membrane type for the treatment of water from various sources at Abqaiq plant. The model results confirm an inverse relationship between the membrane thickness and the water flux rate. Also, a proportional linear relation between the overall water flux and the applied pressure across the membrane is identified. Higher flux rates and lower salinity indicate lower membrane resistance which yields to the higher water production. Modelled data predict that BWRO Toray TM720D-440 with 8" membrane is the optimal BWRO membrane choice for the three water sources at Abqaiq plant.

In Situ Modification of Reverse Osmosis Membrane Elements for Enhanced Removal of Multiple Micropollutants

Reverse osmosis (RO) membranes are widely used for desalination and water treatment. However, they insufficiently reject some small uncharged micropollutants, such as certain endocrine-disrupting, pharmaceutically active compounds and boric acid, increasingly present in water sources and wastewater. This study examines the feasibility of improving rejection of multiple micropollutants in commercial low-pressure RO membrane elements using concentration polarization- and surfactant-enhanced surface polymerization. Low-pressure membrane elements modified by grafting poly(glycidyl methacrylate) showed enhanced rejection of all tested solutes (model organic micropollutants, boric acid, and NaCl), with permeability somewhat reduced, but comparable with commercial brackish water RO membranes. The study demonstrates the potential and up-scalability of grafting as an in situ method for improving removal of various classes of organic and inorganic micropollutants and tuning performance in RO and other dense composite membranes for water purification.

Effect of temperature, pH and composition on nanofiltration of mono/disaccharides: Experiments and modeling assessment

The paper introduces a systematic experimental investigation on the role of temperature and composition on the membrane permeability and on the solute rejection, in association with suitable modeling. The case of Nanofiltration of aqueous solutions containing single sugars (dextrose or fructose or maltose) is considered with polyamide membranes.Real rejections are reported as a function of total volume fluxes in the complete rage from 0% to 100%, at 30°C and 50°C, at pH=4 and 6, with sugar composition from 1 to 300g/dm3, in the pressure range from 3 to 30bar. Hydraulic permeabilities are also measured at 30,40,50°C, at pH=4, for NF membranes (GE-DK and GE-DL) and for brackish water RO membranes (GE-AG and GE-AK).The wide experimentation allows to obtain general trends and to define a criterion for the experimental protocol required for a complete characterization of membrane performances.A revision of the Steric Pore Model is also introduced, in which a porous vision of the membrane is applied both to the description of the solute flux and of the total flux. The model allows to understand and to explain the nature of the solute/membrane and/or of the solvent/membrane interactions, and to develop a criterion for the primary elaboration of experimental data. Hydrodynamic coefficient of the solute becomes the main adjustable parameter of the model related to the solute type, assuming the meaning of a binary interaction parameter accounting of solute/membrane interactions, including membrane geometry and molecular dimensions.For the GE-DK and GE-DL membranes no swelling effect of temperature nor of the solute type is observed on membrane permeability, whereas solute rejection is greatly affected by temperature. Experimental results are useful to test the model and the corresponding procedure for the parameters calculation, developed in this work. A critical discussion about the validity of the procedure is presented and compared with other elaboration techniques reported in literature.

Compatibility study of nanofiltration and reverse osmosis membranes with 1-cyclohexylpiperidenium bicarbonate solutions

Any forward osmosis (FO) based water treatment process using a thermolytic draw solute requires a method to remove/recycle low concentrations of residual draw solute contained in the product water. For switchable polarity solvent forward osmosis (SPS FO) this means the removal of residual tertiary amines from the product water. This study explores membrane filtration of 1-cyclohexylpiperidenium bicarbonate (CHP-H2CO3) draw solute under conditions relevant to the SPS FO process. Fourteen commercially available nanofiltration (NF) and reverse osmosis (RO) membranes were screened. Several NF membranes displayed good chemical compatibility at CHP-H2CO3 concentrations of 2.5wt% or higher while maintaining fair selectivity, with flux normalized rejection of ~80–99% and flux normalized net driving pressure of 80–400psi for the normalized flux of 20LMH. Most sea water and brackish water RO membranes tested showed flux normalized rejection of above 98% and flux normalized net driving pressure of 300–900psi. A two-pass NF/tap water (TW) RO system is proposed as an effective low-pressure method to remove residual CHP-H2CO3 from water.

CFD modelling of electro-osmotic permeate flux enhancement on the feed side of a membrane module

Electro-osmosis has the potential to enhance mass transfer at the membrane surface, thereby minimising concentration polarisation, particularly for nanofiltration and reverse osmosis processes. Electro-osmotic flow can result in a disruption of the concentration boundary layer because of the movement of a thin layer of fluid in the vicinity of the membrane surface. A Computational Fluid Dynamics (CFD) model is used to simulate steady electro-osmotic flow with permeation inside a 2D unobstructed empty membrane channel. It is found that a slip velocity in the direction of bulk flow results in permeate flux enhancement, while a slip velocity in the opposite direction results in flux decline. A non-uniform slip velocity shows greater permeate flux enhancement than a uniform slip velocity. In addition, the results show that electro-osmosis is more effective in enhancing flux for systems with a higher level of concentration polarisation (low Reynolds number and/or high Schmidt number). The data suggests that for seawater RO, electro-osmosis is more effective as the permeability of the membrane is increased, and reaches a peak in the permeability range of brackish water RO membranes. The data also reveals better electro-osmotic enhancement for membranes with lower intrinsic rejection, which might be particularly suited for ultra-osmosis.

Modeling mass transfer using surface morphology in full-scale reverse osmosis membrane processes

The influence of surface characteristics on membrane process performance is considered significant and is not well understood. Current mass transport models generally assume constant mass transfer coefficients (MTCs) based on a homogeneous flat surface. This study evaluated membrane mass transfer by incorporating surface morphology into a diffusion-based model assuming that the MTCs are dependent on the thickness variation of the membrane’s active layer. Concentration polarization is also affected by this nonuniform surface property and was incorporated into the model. A simulation was performed using parameters from a full-scale 4.5 million gallon per day brackish water reverse osmosis membrane process. The process was simulated by modeling one thousand uniform slices of the membrane channel and the permeate water quality was determined locally through a finite difference approach. It was determined that solute mass transport is controlled by diffusion in the nonhomogeneous thinner regions (membrane valleys) of the active layer. This nonuniform surface affected the concentration polarization layer, where more solutes tended to accumulate within the valleys than on the ridges. Prediction of the permeate total dissolved solids concentration was accurate, ranging between 5 and 15%, as measured as an average percent difference between predicted and actual values.

Convective transport of boron through a brackish water reverse osmosis membrane

In this work, cross-flow filtration experiments using a brackish water reverse osmosis polyamide membrane have been performed to gather boron rejection data as function of feed concentration, pressure, pH and salinity. Increasing transmembrane pressure increases the permeation of boron indicating that convective flow is important. This result is in contrast to the normal assumption that solution diffusion dominates in such systems. The extended Nernst–Planck equation with a Donnan-steric partition coefficient is used to analyse the transport mechanisms of both neutral boric acid and negatively charged borate ions through the RO membrane. The contribution of surface charge is experimentally determined by streaming potential measurements and the electrokinetic surface charge density is then calculated as a function of ionic strength and pH. It is found that a 0.380nm pore radius and an effective membrane porosity of 0.05 shows good agreement with experimental data. Charge screening becomes more dominant with increasing ionic strength and this contribution is readily incorporated into the model. The study extends our understanding of the transport mechanism of boric acid and borate ions which can assist in predicting the performance of polyamide reverse osmosis membranes. It also raises questions as to the true mechanism of transport through such a membrane.

The Influence of Parameters Affecting Boron Removal by Electrocoagulation Process

Boron removal in seawater desalination presents a particular challenge. In seawater reverse osmosis (SWRO) systems boron removal at low concentration (<0.5 mg/L) is usually achieved by a second pass using brackish water RO membranes. However, this process requires chemical addition and important additional investment, operation and maintenance, and energy costs. Electrocoagulation (EC) process can be used to achieve such low boron concentration. In this work, the removal of boron from aqueous solution was carried out by EC process using aluminum and iron electrodes. Several operating parameters on the removal efficiency such as initial pH, current density, initial boron ion concentration, feed concentration, gap between electrodes, and electrode material, were investigated. In the case of bipolar electrocoagulation (BEC), an optimum removal efficiency of 96% corresponding to a final boron concentration of 0.4 mg/L was achieved at a current density of 6 mA/cm² and pH = 8 using aluminum electrodes. The concentration of NaCl was 2,500 mg/L and the gap between the electrodes of 0.5 cm. Furthermore, a comparison between monopolar electrocoagulation (MEC) and BEC using both aluminum and iron electrodes was carried out. Results showed that the BEC process has reduced the current density applied to obtain high level of boron removal in a short reaction time compared to MEC process. The high performance of the EC showed that the process could be used to reduce boron concentration to acceptable levels at low-cost and more environmentally friendly.

Desalination of geothermal waters using a hybrid UF-RO process. Part II: Membrane scaling after pilot-scale tests

This paper presents the results of membrane scaling studies obtained after eight months of desalinating geothermal water in an integrated system that combines iron removal, ultrafiltration and two independent reverse osmosis systems fitted with low-pressure brackish water reverse osmosis membranes that are connected in series. Scaling prediction conducted using geochemical modelling showed that at a temperature of 30°C and for neutral-pH water from the geothermal intake (GT-1 well) there were good conditions for the precipitation of aragonite, barite, calcite, chalcedony, dolomite, hydroxyapatite and quartz on the reverse osmosis membranes. A theoretically selected phosphonate scaling inhibitor failed to protect the membranes against sediment precipitation. Adjusting the pH of the water to ca. 5 by treating it with hydrochloric acid had a positive effect on the desalination process.On the basis of a morphological evaluation of sediments in the electron scanning microscope image and through the analysis of the chemical composition of the sediments crystallised on the membrane, silicates (SiO2) and aluminosilicates (Al2SiO5) as well as barite (BaSO4) and copper sulphate (CuSO4) crystalline structures were found. Calcium phosphate as well as celestite (SrSO4) and strontianite (SrCO3) sediments were also observed, which points to significant concentration polarisation. Most grains were a few to a maximum of 30μm in size. Sediment clusters were usually heterogeneous in character. Desalination was performed with a high permeate recovery ratio (75–78%) with favourable key indicator retention ratios.

Pioneering demineralized and desalinated water cost reduction with innovative brackish water RO membrane technology

Breakthrough reverse osmosis (RO) membrane chemistry and innovative materials of construction have been developed to achieve highest possible NaCl rejection while maintaining maximum element productivity. Novel brackish water reverse osmosis (BWRO) membrane element delivers to end users state-of-the-art salt rejection (99.7%) at 30% lower energy consumption compared to current high rejection BWRO membranes in addition to tailored salt passage reduction of critical solutes as nitrate, boron, silica, and ammonium. The novel module component, low differential pressure (LDP) feed spacers, provide end users with up to 15% savings in direct RO energy reductions via the lowest feed-side pressure drop available in the market. The LDP spacer outperforms other spacers by reducing pressure drop while maintaining high active area and a unique BWRO element with productivity up to 14,000 gallons per day has been achieved. A financial analysis was carried out with a refined cost model using different economic frame conditions. It shows RO plant energy costs can be reduced by up to 30% in industrial applications without compromising the product water quality. In SWRO application, the size of the BWRO pass can be reduced by 19%, resulting in an overall water cost reduction of 0.53 UScts/m3 produced water.