Boron Rejection Research Articles

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.

Complexation-Enhanced Boron Removal in a Dual-Stage Nanofiltration Seawater Desalination Process

A complexation-enhanced boron removal method in a dual-stage nanofiltration (NF) seawater desalination process was investigated. A comparative experiment of five different polyols was carried out. Sorbitol was chosen as the complexation additive because of its higher equilibrium constant. The reaction between boron and sorbitol was rapid and only slightly affected by the other ions. Due to the complexation reaction, boron rejection of dual-stage NF seawater desalination process was increased from 35% to 62% in the first stage and from 42% to 55% in the second stage. Boron concentration reached 0.1 mg/L by adjusting the complexation and pH value. Molecular structures were simulated using the molecular simulation technology. The results indicated that molecular structure and molecular size played significant roles in enhancing boron removal. Meanwhile, NaOH and sorbitol had no evident effect on the chemical structure of the membrane surface. The results indicated that complexation is an effective method to reduce boron concentration in a dual-stage NF seawater desalination process.

Boron as a Surrogate for N-Nitrosodimethylamine Rejection by Reverse Osmosis Membranes in Potable Water Reuse Applications

The results of this study reveal a strong linear correlation (R(2) = 0.95) between the rejections of boron and N-nitrosodimethylamine (NDMA) by six different reverse osmosis (RO) membranes, suggesting that boron can be used as a surrogate for NDMA rejection. This proposal is based on the premise that the rejection of both boric acid and NDMA is governed by steric hindrance and that they have similar molecular dimensions. The concept proposed here is shown to be valid at pH 8 or below where boron exists as the neutral boric acid species and NDMA is also a neutral solute. Observed changes in the rejections of these two species, as a function of permeate fluxes and feed solution temperatures, were also almost identical. Boron rejection increased from 21 to 79%, and the correlation coefficient of the linear regression between boron and NDMA rejections was 0.99 as the permeate flux increased from 5 to 60 L m(-2)h(-1). Similarly, a linear correlation between boron and NDMA rejections was observed as the feed solution temperature increased from 10 to 40 °C. This linear correlation was also validated in a tertiary treated effluent matrix.

MINLP based superstructure optimization for boron removal during desalination by reverse osmosis

In this work, a model based MINLP (mixed integer nonlinear programming) optimisation framework is developed for evaluating boron rejection in a reverse osmosis (RO) desalination process. A mathematical model (for the RO process) based on solution diffusion model and thin film theory is incorporated in the optimisation framework. A superstructure of the RO network is developed which includes two passes: (a) seawater pass containing normal two-stage RO system housing seawater membrane modules and (b) the brackish water pass (BW) accommodating brackish water membrane modules. For fixed freshwater demand, the objective of this work is to demonstrate the effectiveness of the MINLP approach for analyzing and optimizing the design and operation of RO network while attaining desired limit on boron concentration in the freshwater produced. The effect of seasonal variation in seawater temperature and pH on boron removal efficiency is also discussed.

Enhanced desalination performance of polyamide bi-layer membranes prepared by sequential interfacial polymerization

A novel thin film composite (TFC) membrane featuring a polyamide bilayer was prepared on a porous polysulfone support using sequential interfacial polymerization. A conventional polyamide membrane prepared using m-phenylenediamine (MPD) in water and trimesoyl chloride (TMC) in hexane via interfacial polymerization was subsequently immersed into an alkaline aqueous solution of a hexafluoroalcohol (HFA)-containing aromatic diamine (HFA-MDA) to form an HFA-substituted aromatic polyamide layer (HFAPA) on the surface of the conventional (or reference) polyamide layer (REFPA). Water contact angle (θw) measurements indicated that the surface of the membrane becomes much more hydrophobic (θw≅140°) after forming the additional HFAPA layer onto REFPA (θw≅78°) although cross-sectional TEM images showed no significant increment in film thickness. The HFAPA-on-REFPA bilayer membrane, which features a more hydrophobic surface than the conventional REFPA membrane, exhibited improved salt rejection (ca. 50% reduction in salt passage) with a small loss in water flux (ca. 8% reduction) compared to the REFPA membrane, resulting in an excellent combination of salt rejection and water flux. Moreover, higher boron rejection was also achieved using the bilayer membrane (HFAPA-on-REFPA) compared to the REFPA membrane.

Boron removal with UTC-series reverse osmosis filtration

This study compared performance on boron rejection in seawater reverse osmosis (SWRO) membrane filtration in a high pressure cross-flow cell. Real seawaters were sampled at the north, east and south coast of Taiwan and the intake ports of SWRO plants in Penghu and Matsu islands. Four types of flat-sheet RO membranes (SG from GE Osmonics and UTC80, UTC80A, and UTC80S from Toray Industries) were tested. Permeate flux, feed flow rate and boron concentrations at room temperature were recorded over testing time. The UTC-series membranes have better performance on both boron and sodium rejection than SG membrane at all tested pH's. Test data sets were available for the first time using SWRO membrane for boron rejection from seawaters in Taiwan.

Transport model for boric acid, monoborate and borate complexes across thin-film composite reverse osmosis membrane

The transport mechanism of boric acid, monoborate and borate complexes with polyols across thin-film composite reverse osmosis (RO) membrane was investigated. The polyols applied were d-mannitol, sodium d-gluconate and N-methyl d-glucamine. A mathematical model for boric acid dissociation and complex formation equilibrium was combined with the Keedem–Katchalsky or Spiegler–Keedem model for mass transport in RO membranes. The mass transport coefficients: permeabilities and reflection coefficients for individual species were estimated. The proposed model was shown to predict boron flux with sufficient accuracy. The estimated mass transport coefficients were found to strongly depend on the species type. The highest permeability and the lowest reflection coefficient were observed for boric acid. Borate complexes with polyols were characterised by the lowest permeabilities and the highest reflection coefficients. The results of numerical calculations with the proposed model allowed for the assessment of the effect of process parameters on the effectiveness of boron rejection. The effect of retentate pH on boron rejection and boron flux is discussed. It is shown that complex formation reaction decreases the retentate pH required to achieve a given rejection of boron. The effects of permeate flux, retentate boron content and alcohol/boron molar ratio are also presented.

Boron removal in new generation reverse osmosis (RO) membranes using two-pass RO without pH adjustment

Boron removal using new generation RO membranes from several leading manufacturers under a second-pass configuration and without pH adjustment was studied. The study was conducted using seawater from the Arabian Gulf (higher salinity and temperatures than average seawater). Membranes from several manufacturers were tested under similar operational conditions and the same feed water source. It was found that significant boron rejections, as high as 96%, were successfully achieved, using readily-available commercial RO membranes under a two-pass configuration and without any pH adjustment. Moreover, single-pass configurations exhibited high salt and boron rejection results reaching 99% and 91%, respectively. First pass permeates had boron levels below 1.4ppm, which are adequate to comply with the new WHO guidelines (2.4ppm) and those of other countries such as Australia, Canada, and UAE, whose boron guideline thresholds are above 1.4ppm. The paper also assesses the influence of several operational parameters such as feed water salinity, flow velocity, temperature and feed pressure in second pass on boron removal in this process. It was found that higher boron removals were obtained with higher feed velocity, higher second-pass pressures, and lower feed temperatures.

Enhanced boron rejection by NF/RO membranes by complexation with polyols: Measurement and mechanisms

Boron rejection by nanofiltration (NF) and reverse osmosis (RO) membranes in the presence of glycerol, mannitol and sorbitol was investigated as a function of feed solution pH and boron:polyol molar ratio. In the presence of polyols, significant boron rejection improvement was obtained and the extent of the impact was directly related to the stability constant of the boron–polyol complex. Polyols could complex with boron in either the boric acid or borate anion forms; however the complexation between polyol and boric acid appeared to be incomplete. With and without the presence of polyols, boron rejection was strongly pH dependent. The increase in boron rejection due to polyol addition was higher for the NF membrane compared to the RO membrane. A boron:polyol molar ratio of 1:1 appeared to be adequate. The presence of polyols did not cause any observable membrane fouling. Results reported here suggest that the addition of polyols could allow NF membranes to be effectively used for boron removal.

Boron removal efficiency from Red Sea water using different SWRO/BWRO membranes

Seawater reverse osmosis (SWRO) desalination process provides high quality of fresh water. However, due to some operational constraints mainly scaling control some trace contaminant removal, such as acceptable boron concentration, cannot be achieved in a single pass SWRO system. The objective of this study was to investigate the efficiency of five difference reverse osmosis (RO) membranes (seawater SW and brackish water BW) provided by different manufacturers for boron removal. RO experiments using pretreated real Red Sea water were conducted in parallel to compare membrane performance under the same operating conditions. As expected, results showed that boron rejection increased as the feed pH increased. This was caused by dissociation of boric acid to negatively charged borate ions and more negatively charged membrane surface at elevated pH which enhanced boron rejection. Single pass RO system, with and without elevating the pH, may not be sufficient for two reasons. First, boron concentration in permeate does not fulfill local regulations (<0.5ppm). Second, severe scaling occurs due to operation in alkaline condition, since Ca2+ and Mg2+ concentrations are still high to cause salts precipitation. Techno-economical study was performed to select the best configuration and membrane giving the highest performance in terms of boron and TDS rejections and energy consumption.

Removal of boron from geothermal water by RO System-III-Utilization of SWRO system

In this study, desalination performance of a mini-pilot scale seawater reverse osmosis (SWRO) system installed at geothermal field was investigated. The system was analyzed in terms of product water quality and quantity using two types of FilmTech SWRO membranes (SW30-2540 and a novel high rejection SWRO membrane abbreviated as XUS SW30XHR-2540). To determine the effect of applied pressure on desalination performance of the SWRO system, the process was operated at different pressures. The boron rejection of SWRO membranes was higher than that of BWRO membranes. An average boron rejection of 88% and a salt rejection of 99% were obtained at 20bar of operating pressure by a high rejection XUS SW30XHR-2540 membrane. The average permeate recovery by XUS SW30XHR-2540 membrane was about 16% and it increased to 34% at 40bar of operating pressure. The respective average boron rejection value obtained by SW30-2540 membrane was 84% at 20bar. The average permeate recovery of SW30-2540 membrane was 20% at 20bar while it increased to 37% at 40bar. The quality of product water obtained by both membranes was good according to water standards.

Removal of boron from geothermal water by RO system-II-effect of pH

In this study, the effect of pH as a function of number of membranes employed on boron removal from geothermal water containing boron was investigated by using a mini-pilot scale brackish water reverse osmosis (BWRO) system. When the pH of geothermal water was increased to 10.5, boron rejection obtained was 94.5–95% for both single and double membrane configurations at 12bar of operating pressure. At pH 10.5, the boron concentration of the product water was around 0.5mg/L which is suitable according to irrigation standards. On the other hand, it was observed that the average permeate flux and water recovery values decreased when the pH of feed water was increased from 8.0 to 10.5 for both single and double membrane configurations.

Imino-bis-propane diol functional polymer for efficient boron removal from aqueous solutions via continuous PEUF process

Boron contamination is an environmentally serious problem especially due to its hazards on plants. In this work, newly synthesized poly (vinyl amino-N, N′-bis-propane diol) (GPVA) is presented as an excellent chelating polymer for boron removal. Boron concentration could be reduced from 10ppm down to 0.4ppm via total recycle Polymer Enhanced Ultrafiltration (PEUF). Experiments revealed that the polymer shows the highest PEUF boron rejections (96% at pH 9.0) reported so far, without precipitation in a wide concentration range. Detailed investigations such as effect of pH, loading (boron-to-polymer mass ratio) and polymer concentration showed that, the boron binding is highly pH dependent and increases with boron concentration at constant loading. Furthermore, permeate flux was found as nearly independent from polymer concentration up to 10g/L at 200kPa pressure drop. In addition, gyration radius of the polymer in solution increases while increasing pH and polymer concentration in the presence of boron as inferred from Dynamic and Static Light Scattering measurements. Regarding with high efficiency and hydrolytic stability of GPVA, its use in combination with PEUF would be of interest for large scale and long term use in boron removal.

Removal of boron from geothermal water by RO system-I—Effect of membrane configuration and applied pressure

In this study, a mini pilot scale reverse osmosis (RO) system containing two spiral wound FilmTech BW30-2540 membranes was installed at a geothermal area in Izmir, Turkey. The desalination and boron removal performances of this system were investigated. The effect of such parameters as operating pressure and the number of membranes employed during the operation on desalination performance of the system was investigated. The system performance was evaluated at 12 and 15bar of operating pressures as a function of the number of membranes used. Desalination performance of brackish water reverse osmosis (BWRO) system was determined by the quality and quantity analyses of the product water. When the operating pressure was increased, a high permeate recovery, permeate flux and salt rejection were obtained with both single and double membrane configurations. The maximum boron rejection was 47% at 12bar of applied pressure while it increased to 49% at 15bar of applied pressure using a single membrane mode of operation. The lowest average boron concentration in the product water was 4.7mg/L at 15bar of applied pressure for a single membrane configuration.

Effects of hypochlorous acid exposure on the rejection of salt, polyethylene glycols, boron and arsenic(V) by nanofiltration and reverse osmosis membranes

The separation layer of polyamide-based (PA) thin film composite (TFC) membranes can be modified by active chlorine species. The PA-TFC membranes, NF90, BW30 and NF270, were exposed to different concentrations of sodium hypochlorite (NaOCl) at pH 5 for 24 h. Elemental composition obtained from X-ray Photoelectron Spectroscopy (XPS) showed that the chlorine content in the PA layer increased with the chlorine concentrations. Treatment of membranes with 10 ppm Cl increased the membrane hydrophilicity. By contrast, when treated with 1000 ppm Cl or more, the membranes became less hydrophilic. Water permeability values for all 3 membrane types declined with increased chlorine concentrations. Filtration of polyethylene glycols (PEGs) with molecular weights of 200, 400 and 600 Daltons (Da) was performed to investigate the influence of chlorine treatment on membrane molecular weight cut off (MWCO) and rejection by size exclusion. Treatment with 10 and 100 ppm Cl lowered the MWCO while treatment with higher concentrations increased the MWCO. All chlorinated membranes experienced higher NaCl rejection compared to virgin ones. The performance of NF90 was tested with respect to the rejection of inorganic contaminants including boron (H3BO3) and arsenic (H2AsO4−). The boron rejection results paralleled PEG rejection whereas those for arsenic followed NaCl rejection patterns. The changes in membrane performance due to chlorine treatment were explained in terms of competing mechanisms: membrane tightening, bond cleavage by N-chlorination and chlorination promoted polyamide hydrolysis.

Boron transport in forward osmosis: Measurements, mechanisms, and comparison with reverse osmosis

Abstract The physical and chemical factors affecting boron solute flux behavior and membrane transport mechanisms in forward osmosis (FO) have been systematically investigated. Boron solute flux behavior in FO was further compared with that in reverse osmosis (RO) by employing identical plate-and-frame cells and membranes under the same filtration conditions. The influence of draw solution pH, draw solution type, and membrane orientation on boron solute flux was examined for FO, and the effects of water flux, cross-flow velocity, feed water boron concentration, and solution pH on boron solute flux were examined for both FO and RO. Results show that reverse salt diffusion, a unique feature of FO, is a key mechanism governing boron solute flux in FO. Boron solute flux through the FO membrane was inversely proportional to the degree of reverse salt diffusion by draw solution. The higher boron rejection observed in FO compared to RO is also attributed to reverse salt diffusion in FO. It is also shown that membrane orientation in FO plays an important role, affecting boron solute flux due to different degrees of internal concentration polarization. In both FO and RO, boron solute flux increased with increasing water flux. However, the influence of water flux on boron solute flux was less significant in FO than RO. Furthermore, boron solute flux decreased with increasing feed water pH due to the conversion of the neutral boric acid to borate anions. The findings provide new insight into the mechanisms and factors controlling boron solute transport in FO.

A comparative study of boron and arsenic (III) rejection from brackish water by reverse osmosis membranes

This study aims to compare at lab-scale the rejection efficiency of several reverse osmosis membranes (RO) toward arsenic (III) and boron during the filtration of a synthetic brackish water. The effect of pH and operating conditions on the rejection of each RO membrane was studied. Two types of membrane were investigated: “brackish water” and “sea water” membranes.Our results showed that the metalloid rejection depends on the membrane type, pH and transmembrane pressure applied. Increasing pH above the dissociation constant (pKa) of each specie improves significantly the metalloid rejection by RO membranes, whatever the membrane type. Moreover, at identical operating conditions (pH, transmembrane pressure), results showed that the brackish water membranes have a higher water flux and exhibit lower metalloid rejection. The highest As(III) rejection value for the tested brackish water membranes was 99% obtained at pH=9.6 and 40 bars, whereas it was found that the sea water RO membranes could highly reject As(III), more than 99%, even at low pH and low pressure (pH=7.6 and 24 bars).Regarding Boron rejection, similar conclusions could be drawn. The sea water RO membranes exert higher removal, with a high rejection value above 96% over the tested conditions. More generally, this study showed that, whatever the operating conditions or the tested membranes, the boron and As(III) permeate concentrations are below the WHO guidelines. In addition, new data about the boron and arsenic permeability of each tested RO membrane was brought thanks to a theoretical calculation.

Full-scale simulation of seawater reverse osmosis desalination processes for boron removal: Effect of membrane fouling

The objective of this study is to further develop previously reported mechanistic predictive model that simulates boron removal in full-scale seawater reverse osmosis (RO) desalination processes to take into account the effect of membrane fouling. Decrease of boron removal and reduction in water production rate by membrane fouling due to enhanced concentration polarization were simulated as a decrease in solute mass transfer coefficient in boundary layer on membrane surface. Various design and operating options under fouling condition were examined including single- versus double-pass configurations, different number of RO elements per vessel, use of RO membranes with enhanced boron rejection, and pH adjustment. These options were quantitatively compared by normalizing the performance of the system in terms of Emin, the minimum energy costs per product water. Simulation results suggested that most viable options to enhance boron rejection among those tested in this study include: i) minimizing fouling, ii) exchanging the existing SWRO elements to boron-specific ones, and iii) increasing pH in the second pass. The model developed in this study is expected to help design and optimization of the RO processes to achieve the target boron removal at target water recovery under realistic conditions where membrane fouling occurs during operation.

Use of methyltrioctyl/decylammonium bis 2,4,4-(trimethylpentyl)phosphinate ionic liquid (ALiCY IL) on the boron extraction in chloride media

Recent restriction of boron concentration in drinking water has produced some problems in the seawater desalinization plants because the rejection of boron in most of the plants is inadequate. Three ionic liquids derived from Cyanex 272 as an anion with different cations (from Aliquat 336, Cyphos IL 101 and Cyphos IL 167) were prepared to be used as boron extractants. Liquid–liquid extraction experiments were carried out to evaluate the viability of boron separation from high chloride media. The effect of ILs and boron concentration and pH were determined. Successive extractions, maintaining the organic phase, provided satisfactory results in order to implement these ILs on supported liquid membrane technologies. The use of the ionic liquid as a carrier can overcome the inconvenience associated with the membrane stability. In this sense, the ionic liquids ALiCY and the mixture of Cyphos IL 101 and Cyphos IL 167 with Cyanex 272 have been tested as liquid carrier for boron separation by using a flat sheet supported liquid membrane. The results obtained allow us to think about the application of this kind of ILs on the process intensification to remove boron from chloride solutions.

Boron removal and its concentration by reverse osmosis in the presence of polyol compounds

Reverse osmosis membrane (TW-30 and XLE, Filmtec™) boron removal and its concentration in the presence of chelating polyols containing a 1,2-diol group were examined in the pH range from 7 to 11 and pressure range from 5 to 20atm at an initial boron feedwater concentration of 70mg/L. The polyols applied were: d-mannitol, N-methyl d-glucamine and sodium d-gluconate, and all of them were subjected to create a dichelate ionic complexes at high pH. It was found that apparent boron rejection as well as permeate flux are strongly dependent on the above conditions. The effect of the amount of the alcohol and feedwater pH on the boron rejection was explained based on the alcohol–boric acid complex formation equilibrium reaction. The apparent boron rejection in the boric acid–alcohol mixtures was found to decrease in the following order: boric acid–N-methyl-d-glucamine mixture>boric acid–d-mannitol mixture≈boric acid–sodium d-gluconate>plain boric acid solution. On the other hand, the permeate flux values in the mixtures decreased in an alternate order: plain boric acid>boric acid–d-mannitol>boric acid–N-methyl-d-glucamine>boric acid–sodium d-gluconate. Also, the effect of other operating conditions, such as: excess pressure, feedwater recovery and concentration factor on the effectiveness of boron removal was evaluated. Finally, the possibility of reducing the boron content to less than 1mg/L even at a high feedwater recovery level of 90% has been demonstrated.