Boron Rejection Research Articles

Predicting the boron removal of reverse osmosis membranes using machine learning

Reverse osmosis (RO) is a key technology for seawater desalination, but boron removal remains challenging due to the relatively low and varying boron rejection of RO membranes. This study explored the use of machine learning (ML) to develop predictive models for boron removal of RO membranes. Data of 11 features encompassing membrane properties, testing conditions and membrane performance were collected from journal articles. Missing data were recovered using data imputation algorithms. The predictive models were developed using five regression algorithms: linear, ridge, decision tree, random forest and XGBoost regressors, and the tree-based XGBoost regressor performed the best (R2 = 0.84). Feature importance analysis and tree diagrams revealed that membrane type, feed pH and NaCl rejection as key factors in influencing boron rejection, while membrane surface properties showed minimal impact. Partial dependence plots were generated to further analyze each feature. High NaCl rejection of >99.6 % is highly desirable for SWRO membranes to achieve high boron rejection. For BWRO membranes at pH >9, a looser structure with a NaCl rejection >95 % could be applied. The study successfully applied ML to a dataset with large portion of missing values, and the results provide valuable insights for future membrane design and boron removal processes.

More resilient polyester membranes for high-performance reverse osmosis desalination.

Thin-film composite reverse osmosis membranes have remained the gold standard technology for desalination and water purification for nearly half a century. Polyamide films offer excellent water permeability and salt rejection but also suffer from poor chlorine resistance, high fouling propensity, and low boron rejection. We addressed these issues by molecularly designing a polyester thin-film composite reverse osmosis membrane using co-solvent-assisted interfacial polymerization to react 3,5-dihydroxy-4-methylbenzoic acid with trimesoyl chloride. This polyester membrane exhibits substantial water permeability, high rejection for sodium chloride and boron, and complete resistance toward chlorine. The ultrasmooth, low-energy surface of the membrane also prevents fouling and mineral scaling compared with polyamide membranes. These membranes could increasingly challenge polyamide membranes by further optimizing water-salt selectivity, offering a path to considerably reducing pretreatment steps in desalination.

Thin-film nanocomposite membranes with polyol-functionalized layered double hydroxides for boron removal via reverse osmosis

Post-treatment of the permeate from seawater desalination using conventional reverse osmosis (RO) membranes to remove electroneutral boron species is always challenging. In this study, the surfaces of layered double hydroxides (LDHs) have been modified with polyols, namely N-methyl-d-glucamine (GLU), using tannic acid (TA) as the binding agent. By optimizing the loading of the modified LDH nanofillers, the resultant thin-film nanocomposite (TFN) membrane shows an improved water permeance of 3.0 LMH bar−1 while maintaining a high salt rejection of 99.4 %. Moreover, this newly developed TFN membrane delivers a comparable boron rejection of 78.6 % when a feed containing 2,000 ppm NaCl and 15 ppm boron at pH 8 is used. The enhanced separation performance arises from the strong and extensive interactions between the polyols and boron species. This study may provide valuable insights to design next-generation TFN RO membranes for desalination and boron removal applications.

Photosynthetic pretreatment increases membrane-based rejection of boron and arsenic

The metalloids boron and arsenic are ubiquitous and difficult to remove during water treatment. As chemical pretreatment using strong base and oxidants can increase their rejection during membrane-based nanofiltration (NF), we examined a nature-based pretreatment approach using benthic photosynthetic processes inherent in a unique type of constructed wetland to assess whether analogous gains can be achieved without the need for exogenous chemical dosing. During peak photosynthesis, the pH of the overlying clear water column above a photosynthetic microbial mat (biomat) that naturally colonizes shallow, open water constructed wetlands climbs from circumneutral to approximately 10. This biological increase in pH was reproduced in a laboratory bioreactor and resulted in analogous increases in NF rejection of boron and arsenic that is comparable to chemical dosing. Rejection across the studied pH range was captured using a monoprotic speciation model. In addition to this mechanism, the biomat accelerated the oxidation of introduced arsenite through a combination of abiotic and biotic reactions. This resulted in increases in introduced arsenite rejection that eclipsed those achieved solely by pH. Capital, operation, and maintenance costs were used to benchmark the integration of this constructed wetland against chemical dosing for water pretreatment, manifesting long-term (sub-decadal) economic benefits for the wetland-based strategy in addition to social and environmental benefits. These results suggest that the integration of nature-based pretreatment approaches can increase the sustainability of membrane-based and potentially other engineered treatment approaches for challenging water contaminants.

ANN based-model for estimating the boron permeability coefficient as boric acid in SWRO desalination plants using ensemble-based machine learning

This study examines the relationship between input conditions and the prediction of boron rejection in full-scale seawater reverse osmosis (SWRO) desalination plants using ensemble-based machine learning. While reverse osmosis is the dominant desalination technology, limited research has focused on analyzing plant performance under actual operating conditions. To address this gap, we developed and implemented machine learning algorithms to forecast boron permeability coefficient values, which are indicative of boron rejection concentrations in the permeate. Our analysis utilizes data from a SWRO desalination plant in southeast Spain, examining various input variables and their influence on the prediction of these parameters. The results demonstrate that our ensemble-based machine learning approach can predict boron permeability coefficient values with a reasonable margin of error of 1 mgL−1, as evidenced by mean average error (MAE) and mean absolute percentage error (MAPE) values of 7.93·10–8 and 11.8 %, respectively. In conclusion, an innovative application of artificial intelligence algorithms in the field of water purification under real operational conditions has been introduced, thus introducing valuable insights into the use of machine learning algorithms for forecasting boron rejection concentrations in full-scale SWRO desalination plants. The findings lay the foundation for future researches exploring automated and deep-learning methods in water purification.

Rational design of reverse osmosis membranes for boron removal: A counter-intuitive relationship between boron rejection and pore size

Owing to the toxicity of excess boron, developing reverse osmosis membranes that are capable of effectively removing boric acid, a boron specie commonly exists in seawater, is critical to advance water purification technology. To date, design principles of reverse osmosis membranes for boron removal have not yet been systematically explored. Using nanoporous graphene as a model system and by employing state-of-the-art molecular simulation techniques, this study discovers the critical role of the adsorptive competition of boric acid against water in the nanopores of membranes in their design. Specifically, the preferential adsorption of water onto the pore rims can be exploited to impede the permeation of boric acid, facilitating the size-exclusion effect for much improved boron rejection. Moreover, a well-balanced adsorptive competition is desired; water adsorption should not be too strong so that efficient water permeation can still be preserved. This results in membranes that are not only highly permeable but also capable of effectively removing boric acid. Detailed investigations on energetic, dynamics, and spatial distribution of water and boric acid as well as their free energy landscapes are also conducted for better understandings. Moreover, bilayer nanoporous graphene membranes with a heterogeneous design are identified to effectively block both boric acid and salt with a decent water permeation. Overall, the outcomes achieved herein can fundamentally guide the rational design of reverse osmosis membranes for more efficient and effective boron removal.

RO membrane with a surface tethered polymer brush layer for enhanced rejection of nitrate, boron, and arsenic

Thin-film composite (TFC) polyamide (PA) RO membrane modified with a layer of tethered poly(acrylic acid) (PAA) chains displayed intrinsic rejections of nitrate, boron, As(III), and As(V) of 98.0%, 90.7%, 96%, and 99.6%, respectively. The solute permeability coefficients for nitrate, boron, As(III), and As(V) by the SNS-PAA-PA membrane were lower by 31–38%, 49–63%, 57–72% and 87–93% relative to tested commercial membranes. The above results indicate that the SNS-PAA-PA membrane should be suitable for purification of brackish source water contaminated with nitrate, boron, As(III), and As(V) to levels 1219 ppm, 2 ppm, 95 ppb, and 948 ppb, respectively. The study results suggest that there is merit in further exploration of the potential of the present approach for enhancing RO membranes performance for targeted solute removal.

Understanding the boron rejection of cation intercalated multilayered graphene oxide (GO) membrane in reverse osmosis (RO) process: A molecular dynamics study

Cation-intercalated graphene oxide (GO) membrane has emerged as a promising candidate for desalination applications as reverse osmosis (RO) membrane. This study constructs GO membranes with different cations (K+ or Mg2+) and investigates the potential of these membranes in boron removal via nonequilibrium molecular dynamics simulations. In the aquatic environment, boron can exist in the form of boric acid or borate ion, depending on the pH of the solution. As a result, this study considers two forms of boron. This study reveals that the GO membranes effectively reject negatively charged borate ions due to their bigger hydration shell and stronger electrostatic repulsion with the membrane than neutral boric acid molecules. Moreover, K+ ion intercalated GO membranes showed higher boron rejection than Mg2+ ion intercalated GO membranes owing to weaker electrostatic attraction of K+ ions with the boric acid (or borate ions). Additionally, a summary of the effects of oxygen-containing functional groups of the GO membrane on boron rejection is provided. Since the hydroxyl and epoxy functional groups interact with boric acid molecules more strongly, these molecules are prevented from permeating through the membrane. On the other hand, the permeation rate of borate ions declines because of their stronger interactions with the carboxyl functional groups. Furthermore, Mg2+ ion intercalated GO membranes exhibited higher water permeance, excellent Na+ rejection, and poor Cl− rejection compared to K+ ion intercalated GO membranes.

In-situ rapid construction of aliphatic amine combined polyamide seawater reverse osmosis membrane for efficient boron removal

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m−2 h−1, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m−2 h−1 bar−1. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.

Solvent-activated thin-film nanocomposite membranes molecularly tuned with macrocyclic cavities for efficient water desalination and boron removal

Tuning the permeation properties of thin-film nanocomposite (TFN) membranes through the molecular redesign of their underlying nanoarchitecture is a challenging but important task for realizing reverse osmosis (RO) desalination performance above the trade-off limit. Activation by organic solvents, as one of the most facile methods to rearrange the microstructure of RO membranes, can effectively boost the water permeability but is constrained by the significant rejection loss. Here, we innovated an integrative approach whereby soluble organic macrocyclic cavitands (OMCs) with molecular-sieving open cavities were simultaneously dissolved in the activating solvent during membrane post-treatment such that their infiltration into the interfacially polymerized (IP) polyamide (PA) layer enabled the formation of a nanocomposite structure with recovered or even enhanced salt rejections. In this work, prefabricated polysulfone-supported pristine PA membranes were transformed into cavity-bearing nanocomposites after being treated with methanol solutions containing 4-sulfocalix[4]arene (SCA4), an OMC structure with a strongly size-sieving ∼ 3.0 Å cavity opening. This integrative solvent-cavitand treatment allowed their water permeability to increase by up to 129% from 1.98 to 4.53 Lm−2h−1bar−1 with uncompromised or even enhanced NaCl rejection, leading to overall separation performances that well surpassed the permeability-selectivity trade-off line. Meanwhile, these SCA4-infiltrated TFN membranes also demonstrated promising boron removal efficiency with an increase in both the water permeability and boron rejection from 1.95 to 4.17 Lm−2h−1bar−1 and 96.9% to 97.4% at pH = 10, respectively. With the wide array of solvent and soluble nanoarchitecture options, this study could provide a new and versatile direction in designing high-performance TFN membranes for environmentally important separations.

Enhancing boron rejection in low-pressure reverse osmosis systems using a cellulose fiber–carbon nanotube nanocomposite polyamide membrane: A study on chemical structure and surface morphology

Nanocomposite membranes based on carbon nanotubes (CNTs) or cellulose nanofibers (CNFs) are promising solutions for water filtration technologies such as seawater desalination, brackish water purification, and wastewater treatment. In this study, we investigated the effect of integrating CNTs and CNFs into a polyamide membrane (CNT–CNF–PA) on boron rejection in low−pressure reverse osmosis (RO) systems (0.75 MPa). A NaCl (500 ppm) and boron (5 ppm) based solution at pH = 7 was tested in an RO filtration system. The CNT–CNF–PA membrane exhibited a high boron rejection rate (up to 74%) and high permeation (greater than 1.0 m3/m2∙day). The chemical structure played a significant role in boron rejection performance. We conducted principal component analysis (PCA) to statistically study the changes in bond vibrations obtained by Fourier transform infrared (FTIR) spectroscopy, comparing the oxygenated and hydrogenated changes to sodium chloride rejection, boron rejection, and water permeation of the membranes. Additionally, the surface morphology, i.e., roughness, exhibits a direct positive effect on boron rejection, whereas the pore structure is linked to both sodium chloride and boron rejections. Molecular dynamic simulations revealed that the CNF and CNT structures suppress the hydrogen bonds between the PA matrix and boric acid, negatively affecting its diffusion and rejection. These findings help clarify the boron rejection mechanism, enabling further development of PA membranes.

Study on boron removal performance of covalent organic skeleton membrane by hydroxyl groups

Growing demand for water desalination promoted the vigorous development of reverse osmosis (RO) membrane. How to effectively remove boron from seawater is the key problem to be solved by RO membrane. It is important to select suitable membrane materials for experimental design before complicated and expensive experimental attempts. In this paper, we demonstrate that pore chemistry plays a key role in boron removal capability of RO membranes via nonequilibrium molecular dynamics simulations. This study shows that the introduction of hydroxyl (-OH) groups into the Covalent organic frameworks (COFs) pore allows for better boron removal without changing water permeability. The optimal boron rejection of AB-COF membranes is 76.67%, and that of ATFG-COF membranes with hydroxyl groups can achieve 90%. This is caused by the hydrophilic pore of ATFG-COF that will preferentially adsorb water molecules to prevent the passage of boric acid molecules through membrane zone. Additionally, -OH groups on the pore will also adsorb a part of boric acid in the membranes, reducing the amount of boric acid entering into the permeate side. The results obtained in this paper can provide guidance for the rational design of RO membranes to achieve more efficient boron removal.

Bisulfite-activated permanganate oxidation plus coagulation as a pretreatment of SWRO desalination lines to enhance boron rejection

To address the concern of high level of residual boron in the filtrate of seawater reverse osmosis (SWRO), bisulfite-activated permanganate technology (PM/BS) combined with post-coagulation/sedimentation (C/S) was evaluated as a pre-treatment strategy. The results revealed that the combination (PM/BS + C/S) can remove 37.1 % of boron under optimal conditions. For PM/BS pretreatment, there was an optimal dosage of BS (450 μM) and PM (90 μM) and pre-oxidation time (5 min) to assist C/S in achieving boron removal. For post-C/S, the optimal flocculant dose (10 mg/L), GT value (GrapidT = 45948 and GslowT = 12480), and precipitation time (20 min) were also determined. BS/PM pretreatment weakened the dependency on strict GT control and shortened the precipitation time required. Moreover, compared to C/S alone, BS/PM + C/S showed a remarkable improvement in the elimination of dissolved organic matter (19.8 %) and nutrients (19.8 % for assimilable organic carbon, 30.8 % for total nitrogen, and 16.0 % for total phosphorus), which reduced membrane fouling. The synergistic mechanism for enhanced boron removal includes destroying the organic coating of colloid or suspended particles, changing the structure of dissolved organic matter, generating MnO2 particles in situ as a boron absorbent and coagulation aid, and regulating the growth and development of flocs. A pilot-scale test integrating PM/BS into a typical SWRO process yielded an average boron rejection rate of 95.7 %. This study indicates that PM/BS + C/S may be a promising pretreatment technology for SWRO to control the amount of residual boron in the filtrate.

Superstructure based optimization of reverse osmosis desalination systems fed by decarbonated high-pH seawater under boron restrictions

This paper presents a superstructure based optimization of reverse osmosis (RO) system fed by decarbonated seawater (DS) at high pH value under boron restrictions. Each RO stage/pass could be operated with high boron rejection. The permeate split (PS) design allows permeates with different quality collecting from both sides of pressure vessel (PV). The pH variations are fitted by experiment and simulated results from the literature. The accuracy of the RO model is also validated. Results showed that about 3.48%−18.31% water cost and 3.04%−14.61% energy consumption savings are achieved by permeate split with decarbonated seawater (PSDS) design. Water cost is less influenced by pH values for PSDS design, which might be a robust solution for pH control. A two-stage stochastic model is performed to obtain robust and flexible designs considering uncertainties of the RO design problem. Both operational conditions and process flow are adjusted to save water cost and energy consumption.

Infiltration of 3D-macrocycles to integrally skinned asymmetric P84 co-polyimide membranes for boron removal

We have molecularly designed negatively charged nanofiltration (NF) membranes by chemical modification of P84 flat membranes with hyperbranched polyethylenimine (HPEI) polymers and then infiltration of sulfocalix[4]arene (SCA4) to enhance their chemical stability and molecular sieving capability. The high molecular weight HPEI polymers developed a strong cross-linked network of P84 polymer chains with extraordinary chemical stability in solvents like N-methyl-2-pyrrolidone (NMP). In addition, the amine groups of HPEI ionically bonded with the electron-accepting sulfonic acid groups of SCA4, resulting in the cross-linked membranes with a proper pore dimension and enhanced size sieving capability. The NF membrane infiltrated with SCA4 in a 0.03 wt% SCA4 solution consisting of 50/50 (wt%) water and methanol for 8 h has boron rejections of 55.37 %, 67.23 %, 87.45 %, 89.95 %, and 98.24 % at pH = 4, 7, 8, 9 and 10, respectively. These performances are comparable with or superior to literature results for membranes made from thin-film interfacial polymerization. The unique SCA4 closed-loop structure not only enhances molecular sieving capability but also achieves negatively charged NF membranes that maximize the potential for removal of toxic ions. This study may provide useful insights to design NF membranes with the aid of supramolecular macrocycles for water reuse and removal of toxic ions.

Ion Exchange Resins to Reduce Boron in Desalinated Seawater for Irrigation in Southeastern Spain

Desalinated seawater (DSW) can provide water resources for irrigation in coastal regions where freshwater is scarce. Reverse osmosis (RO) is the most common technique to obtain DSW worldwide. Nevertheless, using DSW for irrigation could pose an agronomic risk as RO permeates may have a boron concentration above the phytotoxicity thresholds of certain crops, such as woody crops (0.5 to 1.0 mg/L). In this study, an on-farm ion exchange resin system with an average flow of 1 m3/h, designed to reduce the boron concentration of DSW, was evaluated from a technical and economic perspective. The impact of variations in the feed water and operating temperatures on the boron reduction process was assessed. The results show that the system can provide an outflow with a boron concentration below the threshold of 0.5 mg/L over 92 h of operation, with boron rejections of up to 99% during the first 41 h. The estimated cost of boron removal with the on-farm system of the trial was EUR 0.992/m3. However, this cost is expected to decrease to EUR 0.226/m3 for a commercial ion exchange resin (IX) plant (20 m3/h), highlighting the importance of the scale factor. Our results provide novel guidance on the viability of using boron removal IX systems for farms irrigated with DSW, when it is provided by coastal plants with boron concentrations above the crop tolerance.

Low-pressure reverse osmosis membrane made of cellulose nanofiber and carbon nanotube polyamide nano-nanocomposite for high purity water production

Cellulose nanofiber (CNF) and multiwall carbon nanotube (CNT) nanocomposite polyamide membranes were synthesized and used in a low-pressure reverse osmosis (RO) system. Incorporating CNT and CNF into the polyamide structure (PA-CNT/CNF) allows the homogenous dispersion within the polymeric matrix, increasing its hydrophobic character and surface oxygen functionalities while reducing its surface roughness when compared to plain polyamide (PA), PA-CNT, and PA-CNF membranes. The resultant nanocomposite was tested at 0.75 MPa and sodium chloride salt concentration of 500 ppm resulting in a rejection of 99.47 % and water permeability of 1.65 m3/m2day. The rejection and permeation performance is highly competitive compared with commercial RO membranes. A 2in spiral module built with the PA-CNT/CNF membrane and tested for SiO2, NaCl, and CaCl2 rejection showed a reduction in its permeability of 24.9 % after 100 h of operations, while the commercials showed a decrease of 49.42 %. The present RO membrane module achieved a calcium rejection of 97.5 % and a boron rejection of 50.4 %. The 2in PA-CNT/CNF spiral module was tested in a two-step RO filtration system for high pure water (HPW) production and compared with a TW30 module with NSF certification. The PA-CNT/CNF module revealed a permeability reduction of 9.07% after 30 h operation, while TW30 had a reduction of 20.3%, which is about twice the durability. Molecular dynamics simulation showed that the CNF increased water hydration and boron diffusion on the membrane while CNT increased charge transfer to the PA structure. This polymeric nanocomposite has potential use in producing high purity water for brackish water or wastewater reuse for applications in the emerging semiconductor or pharmacology industry.

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse.

While reverse osmosis (RO) is the leading technology to address the global challenge of water scarcity through desalination and potable reuse of wastewater, current RO membranes fall short in rejecting certain harmful constituents from seawater (e.g., boron) and wastewater [e.g., N-nitrosodimethylamine (NDMA)]. In this study, we develop an ultraselective polyamide (PA) membrane by enhancing interfacial polymerization with amphiphilic metal-organic framework (MOF) nanoflakes. These MOF nanoflakes horizontally align at the water/hexane interface to accelerate the transport of diamine monomers across the interface and retain gas bubbles and heat of the reaction in the interfacial reaction zone. These mechanisms synergistically lead to the formation of a crumpled and ultrathin PA nanofilm with an intrinsic thickness of ~5 nm and a high cross-linking degree of ~98%. The resulting PA membrane delivers exceptional desalination performance that is beyond the existing upper bound of permselectivity and exhibited very high rejection (>90%) of boron and NDMA unmatched by state-of-the-art RO membranes.

Boron Removal from Desalinated Seawater for Irrigation with an On-Farm Reverse Osmosis System in Southeastern Spain

Seawater desalination can provide water for irrigation in coastal regions where freshwater resources are scarce. Reverse osmosis (RO) is the most common technique to obtain desalinated seawater (DSW) worldwide. However, using DSW for irrigation may pose an agronomic risk as RO permeates have a boron concentration above the phytotoxicity thresholds of some sensitive crops, such as woody crops (0.5 to 1.0 mg/L). In this study, an on-farm RO system designed to reduce the boron concentration of DSW was evaluated from a technical and economic perspective. The impact of variations in the operating parameters feed water temperature, pressure, and pH, on the boron reduction process was assessed. The results showed that boron rejections close to 99% can be obtained by increasing the feed water pH to 11 with an operating pressure of 10 bar. Looking at the affordability of the system, a total production cost of 1.076 EUR/m3 was estimated for the 1.1 m3/h on-farm system used in the trial. However, this cost is expected to decrease to 0.307 EUR/m3 for a commercial RO plant (42 m3/h), highlighting the importance of the scale factor. Our results provide novel guidance on the feasibility of implementing on-farm boron removal RO systems, when DSW is provided by coastal plants with boron concentrations above the crop tolerance.

Municipal-to-Industrial Water Reuse via Multi-Stage and Multi-Pass Reverse Osmosis Systems: A Step from Water Scarcity towards Sustainable Development

Wastewater reclamation is a promising solution to growing pressure on limited water resources. In this study we evaluated the efficiency of boron removal from effluent at a water resource recovery facility (WRRF) using a two-stage/two-pass RO membrane system. We propose using measurements of electrical conductivity (EC) as a proxy for boron concentration. We tested our approach to boron estimation and the proposed split partial second pass (SPSP) system at an established WRRF and a pilot plant we constructed at the same location. Results showed that boron in the effluent was directly related to the concentration of EC. The proposed regression equation (y = 4.959 × 10-5x + 0.138) represents a rule of thumb for wastewater plant operators. The proposed SPSP system was optimized through manipulation of operating conditions, achieving a promising total water recovery of 64% at maximum boron rejection (over 85% removal) in a manner that was both cost-effective and flexible. This study demonstrates that two-stage/two-pass split-partial permeate treatment with a high pH for boron removal offers a sustainable freshwater supply option suitable for use by the semiconductor industry.