High-pressure Reverse Osmosis Research Articles

Enhancing silica scaling resistance of high-pressure reverse osmosis membranes through surface grafting with various sulfonic acid monomers

Silica scaling is a major challenge in the application of high-pressure reverse osmosis (RO) membranes. In this work, we modified commercially available RO membranes by grafting different sulfonic acid monomers onto their surface using redox polymerization. We systematically studied the effects of various sulfonic acid monomers on membrane performance. Due to the different grafting abilities of sulfonic acid monomers on the membrane, the modified membranes exhibited different physicochemical properties. Simulated silica scaling experiments revealed that the initial permeate flux and sulfonic acid grafting rate of the membrane played crucial roles in its antifouling performance. Molecular dynamics (MD) simulation indicated that the adsorption of silica scale on the membrane was positively correlated with the grafting degree of sulfonic acid monomers. The membrane modified with 3-sulfopropyl potassium methacrylate (SPM) demonstrated a 14 % higher initial flux than the pristine membrane and the highest sulfonic acid grafting rate, resulting in the lowest flux decay rate. Additionally, the SPM modified membrane outperformed the pristine membrane against composite foulants with organic matters and silica. Our research demonstrated that the redox grafting polymerization of sulfonic acid monomers can simultaneously improve the flux and silica scaling resistance of RO membranes without compromising salt rejection. This provides a scalable strategy for preparing RO membranes with enhanced resistance to silica scaling.

Direct experimental comparison of batch reverse osmosis (RO) technologies

Batch RO technologies can help fulfil the growing need for high-recovery desalination. Several experimental studies have given results for batch and semi-batch RO processes individually, but under differing conditions. There is a lack of side-by-side comparisons. Here we report, for the first time, experiments with a high-pressure RO system that can be operated in batch, semi-batch, or hybrid semi-batch/batch mode. Using the same membrane and supply pump at pressures up to 110 bar, we compare performance against semi-batch mode which is used as the baseline throughout. With seawater feed, batch RO reduces electrical SEC by 10 % at recovery of 0.655. With brackish water feed, we use hybrid mode to avoid an excessively large work exchanger volume. Working at recovery of 0.94, a work exchanger volume of 20 L reduced SEC by 23 %. A work exchanger volume of 40 L reduced SEC further, resulting in SEC of 1.81, 1.89 and 2.02 kWh/m3 at recoveries of 0.9, 0.92 and 0.94 respectively, thus representing a 22–32 % reduction against the semi-batch baseline. The results also showed permeate conductivity reduced by up to 50 %. The study confirms the advantages of batch and hybrid RO over semi-batch RO, especially for brackish water desalination at high recovery.

A comprehensive assessment of the economic and technical viability of a zero liquid discharge (ZLD) hybrid desalination system for water and salt recovery

Brine, a by-product of desalination and industrial facilities, is becoming more and more of an environmental issue. This comprehensive techno-economic assessment (TEA), focusing on the technical and economic aspects, investigates the performance and viability of a novel hybrid desalination brine treatment system known as zero liquid discharge (ZLD). Notably, this research represents the first instance of evaluating the feasibility and effectiveness of integrating three distinct desalination processes, namely brine concentrator (BC), high-pressure reverse osmosis (HPRO), and membrane-promoted crystallization (MPC), within a ZLD framework. The findings of this study demonstrate an exceptional water recovery rate of 97.04%, while the energy requirements stand at a reasonable level of 17.53 kWh/m3. Financially, the ZLD system proves to be at least 3.28 times more cost-effective than conventional evaporation ponds and offers comparable cost efficiency to alternatives such as land application and deep-well injection. Moreover, the ZLD system exhibits profitability potential by marketing both drinking water and solid salt or solely desalinated water. The daily profit from the sale of generated water varies from US$194.08 to US$281.41, with Greece and Cyprus attaining the lowest and highest profit, respectively. When considering the sale of both salt and water, the profit rises by 8% across all locations.

What will it take to get to 250,000 ppm brine concentration via ultra-high pressure reverse osmosis? And is it worth it?

The possibility of ultra-high pressure reverse osmosis (UHPRO) to replace thermal brine concentration promises to reduce up to 50 % of both energy consumption and capital cost. However, commercially available reverse osmosis (RO) membranes lose up to 50 % of their water permeability when operated up to 200 bar. Higher temperature operations such as in Middle East seawater desalination and brine mining further exacerbate compaction due to softening of the polysulfone support membrane. Assuming that pressure and temperature-related compaction issues can be resolved through innovations in membrane materials and/or module designs, this study asks the questions, “What will it take to get to 250,000 ppm via ultra-high pressure reverse osmosis? And is it worth it?” Herein we comprehensively examine a three stage RO process beginning with seawater RO (SWRO) to high-pressure RO (HPRO) and ultra-high-pressure RO (UHPRO). We elucidate the influence of thermophysical properties, hydraulic pressure, permeate flux, water permeability, feed spacer design, concentration polarization (CP), salt rejection and stage design on recovery and specific energy consumption (SEC). Our analysis of high rejection (HR) and high flux (HF) RO membranes reveals that while HF RO membranes boast superior water permeability and lower trans-membrane (hydraulic) pressure (TMP), they require higher operating flux, which leads to severe CP and operating pressures of 300 to 400 bar to meet the targeted brine concentration of ~250 g/L TDS. In addition, membrane compaction drives up the TMP, SEC, and capital cost of UHPRO systems. To bring the applied pressure below 300 bar, compaction-resistant UHPRO membranes and mass-transfer enhancing feed spacers will be required. The findings herein show that it will take time, money and technological innovation to enable UHPRO at commercial scale, and it may or may not be worth it. Further, this work makes clear the technological refinements needed to enable UHPRO membrane brine concentration.

Modeling Framework for Cost Optimization of Process-Scale Desalination Systems with Mineral Scaling and Precipitation.

Cost-optimization models are powerful tools for evaluating emerging water treatment processes. However, to date, optimization models do not incorporate detailed chemical reaction phenomena, limiting the assessment of pretreatment and mineral scaling. Moreover, novel approaches for high-salinity and high-recovery desalination are typically proposed without direct quantification of pretreatment needs or mineral scaling. This work addresses a critical gap in the literature by presenting a modeling framework that includes complex water chemistry predictions with process-scale optimization. We use this approach to conduct a technoeconomic assessment on a conceptual high-recovery treatment train that includes chemical pretreatment (i.e., soda ash softening and recarbonation) and membrane-based desalination (i.e., standard and high-pressure reverse osmosis). We demonstrate how to develop and integrate accurate multidimensional surrogate models for predicting precipitation, pH, and mineral scaling tendencies. Our findings show that cost-optimal results balance the costs of pretreatment with reverse osmosis system design. Optimizing across a range of water recoveries (i.e., 50-90%) reveals multiple cost-optimal schemas that vary the chemical dosing in pretreatment and the design and operation of reverse osmosis. Our results reveal that pretreatment costs can be more than double the cost of the primary desalination process at high recoveries due to the extensive pretreatment required to control scaling. This work emphasizes the importance of and provides a framework for including chemistry and mineral scaling predictions in the evaluation of emerging technologies in high-recovery desalination.

Thin-Film Composite Membranes for Hydrogen Evolution with a Saline Catholyte Water Feed.

Hydrogen gas evolution using an impure or saline water feed is a promising strategy to reduce overall energy consumption and investment costs for on-site, large-scale production using renewable energy sources. The chlorine evolution reaction is one of the biggest concerns in hydrogen evolution with impure water feeds. The "alkaline design criterion" in impure water electrolysis was examined here because water oxidation catalysts can exhibit a larger kinetic overpotential without interfering chlorine chemistry under alkaline conditions. Here, we demonstrated that relatively inexpensive thin-film composite (TFC) membranes, currently used for high-pressure reverse osmosis (RO) desalination applications, can have much higher rejection of Cl- (total crossover of 2.9 ± 0.9 mmol) than an anion-exchange membrane (AEM) (51.8 ± 2.3 mmol) with electrolytes of 0.5 M KOH for the anolyte and 0.5 M NaCl for the catholyte with a constant current (100 mA/cm2 for 20 h). The membrane resistances, which were similar for the TFC membrane and the AEM based on electrochemical impedance spectroscopy (EIS) and Ohm's law methods, could be further reduced by increasing the electrolyte concentration or removal of the structural polyester supporting layer (TFC-no PET). TFC membranes could enable pressurized gas production, as this membrane was demonstrated to be mechanically stable with no change in permeate flux at 35 bar. These results show that TFC membranes provide a novel pathway for producing green hydrogen with a saline water feed at elevated pressures compared to systems using AEMs or porous diaphragms.

Flow-through electrochemically assisted reverse-osmosis: A new process towards low-chemical desalination

Two-pass reverse osmosis (RO) process is prevailing in seawater desalination, but each process must consume considerable amounts of chemicals to secure product water quality. Caustic soda is used to raise the pH of the first-pass RO permeate (also the second-pass RO feed) to ensure adequate removal of boron in the subsequent second-pass RO, while antiscalants and disinfectants such as hypochlorite are added in the feed seawater for scaling and biofouling control of the first-pass RO membranes. Here, we report for the first time a flow-through electrochemically assisted reverse osmosis (FT-EARO) module system used in the first-pass RO, aiming to dramatically reduce or even eliminate chemical usage for the current RO desalination. This novel system integrated an electroconductive permeate carrier as cathode and an electroconductive feed spacer as anode on each side of the first-pass RO membrane. Upon applying an extremely low-energy (< 0.005 kWh/m3) electrical field, the FT-EARO module could (1) produce a permeate with pH >10 with no alkali dosage, ensuring sufficient boron removal in the second-pass RO, and (2) generate protons and low-concentration free chlorine near the membrane surface, potentially discouraging membrane scaling and biofouling while maintaining satisfactory desalination performance. The current study further elucidated the high scalability of this novel electrified high-pressure RO module design. The low-chemical manner of FT-EARO presents an attractive practical option towards green and sustainable seawater desalination.

Unraveling Water and Salt Transport in Polyamide with Nuclear Magnetic Resonance Spectroscopy

Quantifying water and salt transport properties in polyamide is of growing importance as the use of reverse osmosis membranes grows in many industries. Here, using solid-state nuclear magnetic resonance (NMR) spectroscopy, we measure the translational diffusion coefficients using pulsed-field gradient NMR, examine ion dynamics with NMR relaxometry, and determine the activation energy barriers of hydrogen and sodium ions in ion-exchanged polyamide using variable-temperature NMR. We identify two predominant diffusion components within the spectra associated with bound and unbound hydrogen and sodium ions. We show that the diffusion coefficient of the bound hydrogen ions decreases by ∼50% while the unbound hydrogen diffusion coefficient remains constant as the salinity of the mixture doubles. Conversely, the bound sodium diffusion coefficient remained constant while the unbound sodium diffusion coefficient decreased by ∼40% as the salinity of the mixture doubled. Through examining the spin–lattice relaxation time (T1) we also report the associated activation energy for sodium and hydrogen. We believe these molecular-scale measurements can aid in extending physics-based models of salt and water transport in high-pressure reverse osmosis applications.

Inadequacy of current approaches for characterizing membrane transport properties at high salinities

Cost optimal design of osmotic membrane processes requires an accurate estimate of membrane transport parameters across their full operational range. However, standard approaches for estimating these parameters rely on empirical methods, the accuracy of which remains unquantified as a function of temperature, salinity, and measurement error. Herein, we present a systematic accuracy analysis of previously developed methods for estimation of membrane transport properties in reverse osmosis, high-pressure reverse osmosis, forward osmosis, pressure retarded reverse osmosis, and osmotically assisted reverse osmosis. We use a Monte Carlo approach to sample the full range of feasible membrane water permeabilities, salt permeabilities, structural parameters, and operating conditions for these processes. These material and process parameters are then incorporated into a physical transport model for each process. Our analysis shows that the statistical uncertainty of current empirical methods for estimating membrane parameters increases by 5 times from low-salinity to high-salinity conditions. The result of this work demonstrates that empirical methods are inadequate for precisely estimating membrane transport properties at high salinity and highlight a critical need for the development of statistically validated higher accuracy methods.

Impact of large-scale effects on mass transfer and concentration polarization in Reverse Osmosis membrane systems

We present well-resolved computational fluid dynamics simulations of a large-scale reverse osmosis membrane-spacer configuration (∼ 1 m). Our computational model solves the flow and transport equations with variable solute-dependent properties. We utilize a high resolution computational mesh to resolve all relevant length scales associated with spacer-induced mixing and thin concentration boundary layers. An important contribution of this work is the development of a modified mass-transfer correlation that accounts for the development of the concentration boundary layer along the channel. A set of 2D axisymmetric simulations were performed for a spiral wound module layer with varying cross-flow conditions and spacer diameters which indicate a significant entrance length effect for concentration profile development at lower flow rates while mixing effects dominate at higher flow rates. The mass-transfer correlations at higher flow rates compare well with published correlations while a surrogate model for Sherwood number was obtained that depends on an additional similarity variable that accounted for entrance length effects at lower flow rates. Finally, a large-scale membrane-spacer design relevant to high-pressure reverse osmosis is studied with a non-uniform arrangement of spacers, which indicate a substantial saving in pressure drop (∼ 40%) compared to traditional uniformly spaced pattern with minor variations (∼ 2%) in concentration polarization, product water quality (∼ 1%) and water recovery (∼ 7%) compared to a uniform spacer pattern.

Macrovoid resolved simulations of transport through HPRO relevant membrane geometries

Modeling the transport properties such as diffusivity and permeability of high pressure reverse osmosis (HPRO) membranes is critical for the selection and manufacture of membranes suitable for operation under high pressure. These properties can be significantly affected by the changes in heterogeneous pore structures due to compaction. The modeling platform presented in this work resolves the two scale porosity in HPRO relevant membranes. A synthetic membrane geometry is constructed based on available experimental visualizations of pore structures. The simulations directly capture the flow channeling that results from a combination of material properties and geometric features of the macrovoids. A parametric study is presented to account for the transition of flow characteristics from a material governed regime to a macrovoid governed regime. Permeability of the membrane is evaluated using the simulation data and compared with an existing model that scales with the square of tortuosity over a range of material properties. The model is found to perform well under a narrow range of tortuosity while deviating from the calculated permeabilities at extreme conditions. The effective permeability of the membrane is found to vary by at least two orders of magnitude between the two flow regimes. It is also observed that tortuosity is a bounded property with its upper limit determined by the macrovoid geometry. Consequently, the tortuosity based correlations fail near a flow regime that is mainly governed by the macrovoids. The modeled permeability can be more than an order of magnitude smaller than the simulation result. A new model based on flux-weighted porosity of a membrane is introduced and its correlation with tortuosity is studied. The model agrees with the simulated data as, in addition to tortuosity, it also accounts for the flux partition within and outside the flow channels. Such correlations enable extending the existing understanding of flow characteristics to enhance predictability of porous media models.

Process simulation and analysis of high‐pressure reverse osmosis (HPRO) in the treatment and utilization of desalination brine (saline wastewater)

Reverse osmosis (RO) is nowadays considered to be the most dominant desalination technology. Nonetheless, due to osmotic pressure constraints, conventional RO cannot desalinate brine effluents (>70 g/L of total dissolved solids [TDS]). Thus, high-pressure RO (HPRO), that is, RO operating at a pressure of more than 82 bar, has recently attracted the interest of the water and wastewater industry. To this aim, a process simulation for the HPRO process was implemented and several sensitivity analyses were conducted for the first time. The results showed that by increasing the recovery rate by 0.05, energy consumption decreased by 3.5%. An increase in the feed brine temperature from 5°C to 30°C increases the permeate flow rate (up to 0.929 m3/h), the permeate concentration (up to 468 mg/L TDS), and the recovery rate (up to 0.435). A 10-bar pressure increases the permeate flow by approximately 9.8% and decreases the permeate concentration by approximately 6 mg/L TDS. Moreover, the use of an energy recovery device significantly reduces energy consumption by 26% (from 4.93-5.10 to 3.65-3.78 kWh/m3). Overall, HPRO is a promising technology for brine treatment and valorization in zero liquid discharge and minimal liquid discharge systems.

Techno-economic assessment and feasibility study of a zero liquid discharge (ZLD) desalination hybrid system in the Eastern Mediterranean

The environmental consequences of brine disposal (i.e., marine pollution, soil salinization, and groundwater contamination) are a concern for desalination plants across the world. This techno-economic assessment and feasibility study explores for the first time both the performance and the feasibility of a zero liquid discharge (ZLD) desalination hybrid system for brine treatment and valorization in Eastern Mediterranean countries, namely, Greece, Cyprus, and Israel. The results revealed that the recovery rate (99.19%) is exceptional, while the energy demands are 20.23 kWh/m3, which is reasonable as three different desalination processes (namely, high-pressure reverse osmosis (HPRO), brine concentrator (BC), and brine crystallizer (BCr)) are integrated into the ZLD system. The ZLD system is at least 3.22 times less costly than evaporation ponds, and it is on par with deep-well injection and land application alternatives in terms of cost. Furthermore, the ZLD system is lucrative whether it markets only water or both water and solid salt. The profit gain from desalinated water sales ranges from US$196.36/day to US$285.63/day, with Cyprus and Greece having the highest and lowest profit gain, respectively. In respect of both desalinated water and salt sales, the profit gain increases by 7% for each location.

Reverse osmosis membrane compaction and embossing at ultra-high pressure operation

Herein, we describe the performance (i.e., flux and rejection) of commercially-available, thin film composite brackish water RO (BWRO), seawater RO (SWRO) and high-pressure RO (HPRO) membranes operating at pressures from 14 bar (200 psi) to 207 bar (3000 psi). For each membrane material, we elucidate the impacts to performance using a porous metal frit and woven tricot mesh permeate carrier materials from commercial HPRO, SWRO, BWRO and tap water RO (TWRO) membrane modules. The water permeability of all tested membranes declines with increasing pressure, whereas rejection behaves differently for different combinations of membrane type and permeate carrier. Cross-sectional SEM and FIB-SEM images confirm permanent reduction of the polysulfone support membrane thickness (38% to 60%) as well as collapse of support membrane skin layer pores – both of which may contribute to the observed performance decline. Also, at ultra-high pressures, permeate carrier materials with higher porosity cause greater embossing and, ultimately, coating film damage (defect formation) that leads to increased salt passage (loss of salt rejection). In contrast, the permeate carriers with lower porosity still lost water permeability, but maintained higher rejection. Finally, all of the observed compaction/embossing-related performance decline occurs within about 60 min after a membrane coupon was exposed to ultra-high pressure.

Depression, Anxiety, Quality of Life, and Coping Strategies in People Exposed to Periodic Floods of Capivara River in Imperatriz City – Maranhão State, Brazil

Trace contaminant removal is of contemporary concern in drinking water and wastewater treatment, given increasing evidence of potential toxicity of various heavy metals and metalloids in water at parts per billion (ppb) concentration levels. Currently, only high-pressure reverse osmosis can reliably remove trace concentration contaminants from water but with high energy cost. Thus, the search is on for techniques and methods able to remove trace concentration contaminants with a lower energy footprint. Adsorption, a low energy technique for water and wastewater treatment is one possibility, which when coupled with the use of low-cost biomass as adsorbent, would further improve process efficiency. This synopsis describes work done on examining the use of local marine seaweed, Sargassum sp. for removing copper at low (4 to 20 ppm, parts per million) and trace concentration (< 1000 ppb), with and without ammonium ion interference at different solution pH. Specifically, to reduce organic leaching and improve mechanical stability, formaldehyde crosslinking was used and was effective in enhancing stability of seaweed between pH 3 and 9. But, residual organic leaching of ~ 4 ppm meant that modified seaweed was not suitable for drinking water treatment. Batch kinetic and equilibrium studies revealed that up to a threshold ammonium concentration of 50 ppm [NH4+-N], there was good sorption of copper on formaldehyde crosslinked seaweed (treated seaweed), with residual copper concentration of 0.5 ppm. Residual copper concentration increased with increase in ammonium concentration (up to 2500 ppm [NH4+-N]); thereby, highlighting a competitive binding effect for treated seaweed’s surface functional groups. Attempts to remove trace concentration copper highlighted feasibility of the approach. However, significant residual equilibrium concentration of copper remained in the solution. More importantly, thermodynamic considerations point to the existence of a finite residual equilibrium concentration for copper in water; thereby, making adsorption not feasible as a method for completely removing trace concentration copper. Additionally, surface concentration of copper at the adsorbent might, in some cases, be higher than the bulk solution; thus, leading to desorption of copper from the seaweed surface back to the solution. Collectively, adsorption is not capable of completely removing a contaminant such as is the case for reverse osmosis where the non-porous membrane serves as barrier separating treated water from raw influent.

Reverse osmosis treatment of condensate from ammonium nitrate production: Insights into membrane performance

Ammonium nitrate is an important fertilizer and industrial explosive. The production of ammonium nitrate entails the generation of a large volume of condensate laden with nitrogen that must be treated before environment discharge. Results in this study show that through appropriate membrane selection, over 90% rejection of ammonium nitrate can be achieved by reverse osmosis (RO) filtration. Using RO (which is highly compact and efficient) to enrich ammonium nitrate in the condensate would significantly reduce the size of the evaporation separator for ammonia recovery. The results also highlight the importance of membrane selection for this application. Results reported here suggest that a low pressure RO membrane (e.g. ESPA2) is more suitable for the dilute condensate while a high pressure RO membrane (e.g. SW30) is recommended for the concentrated condensate to ensure adequate ammonia and nitrate rejection. Ammonia and nitrate rejections were dependent on key operating parameters including applied pressure (or water flux), temperature, feed solution pH, and initial ammonium nitrate concentration in the condensate. The impact of operating conditions on ammonia and nitrate rejections was more profound for low pressure (thus high flux) than high pressure RO membrane. An extended filtration experiment shows no evidence of membrane fouling. Results from this study are useful to the integration of a compact RO system to ammonium nitrate manufacturing for pollution prevention and improving product yield.

Comparing a Low-Fouling, High-Pressure RO Membrane with a Conventional Seawater RO Membrane for a Zero-Liquid-Discharge System

Comparing a Low-Fouling, High-Pressure RO Membrane with a Conventional Seawater RO Membrane for a Zero-Liquid-Discharge System

Design principles and challenges of bench-scale high-pressure reverse osmosis up to 150 bar

High-pressure reverse osmosis (HPRO) has been recently proposed for the energy-efficient desalination of hypersaline brines. To advance this technology, substantial innovation is needed, including the capacity to test membranes at ultra-high hydraulic pressures. Here, we report on the development of an apparatus designed and constructed specifically for coupon-scale membrane research in HPRO. The capabilities of the closed-loop crossflow system were demonstrated through desalination experiments at hydraulic pressures up to 150 bar and feed concentrations up to 2.0 M (117 g L−1) NaCl. Several safety-related design considerations are highlighted in addition to the design of a custom-built membrane test cell and high-pressure seal to ensure leak-free, safe operation. Corrosion control protocols were also developed to enable long-term system compatibility with corrosive hypersaline feed solutions. Lastly, we highlight novel experiments that are now possible with this apparatus and discuss the benefit it represents to HPRO development by the membrane community.

Desalination of brackish water using cascade Rankine cycle based reverse osmosis system

The desalination of brackish ground water using cascade Rankine cycle is proposed. A pair of a Rankine cycle like steam Rankine cycle (SRC) and organic Rankine cycle (ORC) as a waste heat recovery. The single stage steam turbine for the SRC unit while the scroll expander for ORC unit is selected. Simulation of cascade RO system performance is considered using R245fa as a working fluid for ORC unit. The saturated steam from solar Scheffler disc will expand into steam turbine, where the reject heat from steam turbine will utilize for evaporation of ORC working fluid. The high-pressure RO pumps integrated with SRC and ORC turbines to provide net driving pressure to the RO module. This type of system is well suitable for desalination of brackish water due to moderate working temperature & pressure. Result shows that the pair of Rankine cycle will increase the overall (cascade) efficiency of the system. The basic input parameters are optimised with Taguchi approach. The performance of the system shows a good agreement with variation of mass flow rate of the steam in which the permeate flow rate from RO will increase along with the cycle efficiencies.

Semi batch dual-pass nanofiltration as scaling-controlled pretreatment for seawater purification and concentration with high recovery rate

In this paper, a novel dual-pass nanofiltration (NF) as scaling-controlled pretreatment and concentration system for reverse osmosis (RO) seawater separation is reported, and a total reflux model of brine was employed to obtain more permeate. Two different NF membranes (after choosing experiments) were employed in the novel dual-pass NF, which could depart SO42− and Ca2+ into different spaces to reduce the collision chance of these ions. Thus the scaling risk was reduced obviously, and the recovery rate of the dual-pass NF could reach 90% which was higher than the reported value. The permeate of the dual-pass NF was pumped into low-pressure RO (LPRO) and high-pressure RO (HPRO) system to produce fresh water the recovery rate of RO system was (82.5%) and obtain NaCl (87.7 g/L) solution. As a consequence, high RO recovery rate was reached, and an alternative choice to solve the discharge problem of SWRO brine was provided. By combining the dual-pass NF with RO system, the total recovery rate could reach 65.7% without adding any antiscalant. The specific energy consumption (SEC) of dual-pass NF was 0.04–0.06 kWh/m3, which is economical. The SEC of LPRO and HPRO was 4.41 kWh/m3 and 7.08 kWh/m3 separately. If a EDR was employed, the SEC of RO system could be reduced from 5.55 kWh/m3 to 4.34 kWh/m3.