Regenerant Brine Research Articles

A new pretreatment approach for applying high-recovery reverse osmosis desalination to highly scaling brackish groundwater

A new approach is presented for pretreating very hard, divalent-ion-laden brackish-water, to allow applying reverse-osmosis desalination at reasonable recovery-ratio and competitive cost. The approach consists of a cation-exchange step applied on the raw-water to reduce the divalent-cation concentrations thereby enabling operation at high recovery (>80 %) without chemical scaling. For cost-effectiveness, the exhausted ion-exchange regeneration solution undergoes nanofiltration separations to recover the NaCl, enabling multi-cycle usage. The process was exemplified on brackish groundwater from New-Mexico's National-Desalination-Research-Facility. Two treatment alternatives were considered for the exhausted regeneration brine, consisting of several NF in series (alternative 1) and additional NF-retentate treatment (alternative 2). Following simulation and selection of alternative 1, empirical-evaluation and cost-assessment ensued. The results showed that when the regeneration-solution contained total-hardness < 2 % of the total-cation concentration (eq/eq), the cation-exchange breakthrough curves did not deteriorate. To maintain this criterion the exhausted regeneration-solution should undergo 3–4 sequential NF passes after each regeneration cycle. This approach enables operating the BWRO plant with RR = 81 % at additional cost of ∼US$0.4/m3 (CAPEX+OPEX), which ∼doubles the overall brackish desalination cost, but also produces more desalted water and much less retentate. The approach is competitive when the brackish water is laden with divalent ions and the retentate discharge-cost is high.

Physicochemical model for simulating the chemical processes during the crystallization of minerals from spent ion exchange regenerant

Traditionally, industrial processes produce wastes that, even though often containing useful materials, are discarded, contributing to environmental pollution and depletion of natural resources. An example of such wastes are brines, flows of concentrated salts, produced in water treatment processes, which are now routinely discharged into receiving water bodies. Brines however can also be considered as flows of reusable materials which should be recovered, and the Zero Brine cooperation project aims to develop processes for that purpose. For a demineralized water production plant in the port of Rotterdam (the Netherlands), a closed water processing cycle was proposed to treat the large volume of spent Ion Exchange (IEX) regenerant brine which, apart from recovering demineralized water, is also intended to produce magnesium (Mg2+) and calcium (Ca2+) salts, with the highest purity possible, from the otherwise discharged brine. The process scheme includes nanofiltration (NF) for separating mono- and multivalent ions, followed by sequential chemical precipitation of Mg2+ and Ca2+ ions from the NF concentrate, and production of demineralized water by evaporation of the NF permeate. The concentrate of monovalent ions produced in the evaporator, essentially a concentrated sodium chloride solution, in its turn might be reused for IEX regeneration. Part of the supernatant of the sequential precipitation may be fed to the evaporator as well, but bleeding the other part of this supernatant is essential in order to maintain process stability, avoid accumulation of minor pollutants, and reduce scaling. In this study, various scenarios to operate the process were modeled, using PHREEQC and Excel. According to the simulation results, recovery of ≈97% of Mg2+ and Ca2+ is possible, the latter with a higher purity than the former. The main factors affecting the results are the concentration of carbonate present in the spent IEX regenerant, as well as characteristics of the NF membrane and the dosing of sodium hydroxide in the sequential precipitation steps. The results of the simulations were used for the design and operation of a pilot plant, comprising all mentioned process steps.

Removal of Zwitterionic PFAS by MXenes: Comparisons with Anionic, Nonionic, and PFAS-Specific Resins.

Zwitterionic per- and polyfluoroalkyl substances are increasingly detected in aquatic environments. The magnitude of their concentration and increased frequency of detection worldwide raise questions on their presence in drinking water and associated health risk. Scientific knowledge on the identification of treatment technologies to effectively capture such zwitterionic PFAS from contaminated water sources remains largely unknown. In this study, we investigated the application of anionic organic scavenger ion exchange (IX) resins (A860), nonionic IX resins (XAD 4 and XAD 7), PFAS-specific resins (A694 and A592), and Ti3C2 MXenes (novel two-dimensional metal carbides) for the removal of select fluorotelomer zwitterionic PFAS from natural waters. The cumulative removal of zwitterionic PFAS at pH ∼ 7 follows the order: Ti3C2 MXenes > A694 > A592 > A860 > XAD 4 ∼ XAD 7. Ti3C2 MXenes were able to capture >75% of the total influent zwitterionic PFAS and the performance remained consistent in natural and synthetic water. Ti3C2 MXenes also exhibited efficient regeneration (>90% recovery) with 0.4 M Na2SO3 solution, while the regeneration efficacy of other IX resins generally remained below 20%. Treatment with ∼180 J/cm2 UV dosage in the 0.4 M Na2SO3 regenerant brine solution yielded >99.9% reduction in the zwitterionic PFAS concentration indicating that UV-sulfite systems exhibit promising potential for the treatment of zwitterionic PFAS concentrates.

Impact of resin loading on ion exchange equilibrium for removal of organic matter and inorganic ions

Ion Exchange (IEX) applications for drinking water can be limited due to high volumes of brine, brine waste and treated water corrosivity. Reusing the resin by operating at reduced regeneration frequency can overcome this. However, assessing changes on the resin loading over reuse cycles is complex because multiple presaturant ions participate in the exchange and existing models only account for the exchange with one presaturant ion. This study developed a theoretical multicomponent model for the determination of IEX equilibria when the resin loading increases due to reuse. The model suggested that both electrostatic interactions and admicelle formation were the separation mechanisms. The model revealed that under reduced regeneration frequencies, brine use and waste generation can be reduced by more than 90%, where the bicarbonate-form resin offered the potential for lower corrosivity. However, changes in resin loading after 5 reuse cycles showed that the risk of corrosion increased. For the tested source water, reusing the bicarbonate-form resin every 5 cycles would achieve the most sustainable option with 41% NOM removal and 79% brine and waste reduction. Under these conditions, almost 100% of exchange capacity is recovered after regeneration

ECONOMICAL AND ENVIRONMENTAL BENEFITS OF POINT-OF-USE NaCl BRINE REUSE BY NEW MEMBRANE TECHNOLOGY

Cation exchange water softening is one of the most widely used technologies of water treatment. However, its environmental impact related to discharge of highly concentrated regeneration brine draws more attention as overall quality and availability of water resources decreases. Bearing in mind high levels of reusable NaCl in brine discharge, technology that will reduce the environmental impact and help reuse brine is required. To develop such technology composition of spent brine solution from Na-cation exchanger was investigated and conditioning of such solution with use of nanofiltration membranes of different types under different temperatures, pressures and recovery values was tested. Results show that optimal conditions for NaCl recovery include usage of DuPont (Dow) Filmtec Fortilife XC-N membrane elements at temperature 23-27 °С, pressure of 23-25 bar and recovery of 55-60 %. Under these conditions purity of NaCl in permeate over 90 % and productivity by NaCl of 13.1 kg/h were achieved. Principal technological scheme of the process of membrane conditioning of the spent regeneration solution was proposed that allows achieving reduction of NaCl consumption by 40 % and reduction of NaCl discharge into sewage by 72 % with corresponding economic and environmental benefits.

Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein

A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.

Separating NOM from salts in ion exchange brine with ceramic nanofiltration

In drinking water treatment, natural organic matter (NOM) is effectively removed from surface water using ion exchange (IEX). A main drawback of using IEX for NOM removal is the production of spent IEX regeneration brine, a polluting waste that is expensive to discharge. In this work, we studied ceramic nanofiltration as a treatment for the spent NOM-rich brine, with the aim to reduce the volume of this waste and to recycle salt. Compared to polymeric nanofiltration, the fouling was limited. When NOM is rejected and concentrated, a clean permeate with the regeneration salt (NaCl) could be produced and reused in the IEX regeneration process. Bench scale studies revealed that NOM could be effectively separated from the NaCl solution by steric effects. However, the separation of NaCl from other salts present in the brine, such as Na2SO4, was not sufficient for reuse purposes. The low sulphate rejection was mainly due to the low zeta potential of the membrane at the high ionic strength of the brine. The permeate of the ceramic nanofiltration should be treated further to obtain a sodium chloride quality that can be recycled as a regenerant solution for ion exchange. Further treatment steps will benefit from the removal of NOM from the brine.

ECONOMIC AND ENVIRONMENTAL BENEFITS OF NACL BRINE REUSE BY NEW MEMBRANE TECHNOLOGY

Article history:Received 23 April 2019 Accepted 18 May 2019Print 24 June 2019Cation exchange water softening is one of the most widely used technologies of water treatment. However, its environmental impact related to discharge of highly concentrated regeneration brine draws more attention as overall quality and availability of water resources decreases. Bearing in mind high levels of reusable NaCl in brine discharge, technology that will reduce the environmental impact and help reuse brine is required. To develop such technology composition of spent brine solution from Na-cation exchanger was investigated and conditioning of such solution with use of nanofiltration membranes of different types under different temperatures, pressures and recovery values was tested. Results show that optimal conditions for NaCl recovery include usage of Dow Filmtec Fortilife XC-N membrane elements at temperature 23–27 °C, pressure of 23–25 bar and recovery of 55–60%. Under these conditions purity of NaCl in permeate over 90% and NaCl yield of 13,1 kg/h were achieved. Principal technological scheme of the process of membrane conditioning of the spent regeneration solution was proposed that allows achieving reduction of NaCl consumption by 40% and reduction of NaCl discharge into sewage by 72% with corresponding economic and environmental benefits.

Computational and experimental study for the desalination of petrochemical industrial effluents using direct contact membrane distillation

The petrochemical, mining and power industries have reacted to the recent South African water crisis by focussing on improved brine treatment for water and salt recovery with the aim of achieving zero liquid effluent discharge. The purpose of this novel study was to compare experimentally obtained results from the treatment of synthetic NaCl solutions and petrochemical industrial brines such as spent ion exchange regenerant brines and reverse osmosis (RO) brines to the classical well-known Knudsen diffusion, molecular diffusion and transition predictive models. The predictive models were numerically solved using a developed mathematical algorithm that was coded using MATLAB® software. The impact of experimentally varying the inlet feed temperature on process performance of the system is presented here and compared to simulated results. It was found that there was good agreement between the experimentally obtained results, for both the synthetic NaCl solution and the industrial brines. The mean average percentage error (MAPE) was found to be 7.9% for the synthetic NaCl solutions when compared to the Knudsen model. The Knudsen/molecular diffusion transition theoretical model best predicted the performance of the membrane for the industrial spent ion exchange regenerant brine with a mean absolute percentage error (MAPE) of 13.3%. The Knudsen model best predicted the performance of the membrane (MAPE of 10.5%) for the industrial RO brine. Overall, the models were able to successfully predict the water flux and can be used as potential process design tools.

Thermodynamic optimization of a vacuum multi-effect membrane distillation system for liquid desiccant regeneration

The regenerator is one of the key components in the liquid desiccant air-conditioning system, and improvement of the regenerator performance is key to promoting the overall system energy efficiency. This study entails the investigation of a vacuum multi-effect membrane distillation system (V-MEMD) for liquid desiccant regeneration. The V-MEMD regenerator possesses the merits of high energy efficiency and zero desiccant carry-over. A thermodynamic model has been developed to study the regeneration process based on the principles of heat and mass transfer and heat and mass balances. The model is validated with experimental data, and the discrepancies are observed to be within 10% and 5% for regeneration rate and brine concentration, respectively. Employing the developed and validated model, several V-MEMD configurations have been investigated and the effects of key operating parameters are evaluated. The regenerator performance is observed to degrade at higher feed concentrations, while a higher hot water temperature promotes regeneration rate and thermal efficiency. The proposed configurations expand the operation range of the V-MEMD regenerator to greater than 40 wt% under a heat source temperature of 70 °C. Compared with existing liquid desiccant regeneration systems, the specific energy consumption is reduced by 10–50%.

Evaluating Options for Regenerant Brine Reuse in Magnetic Ion Exchange Systems

The purpose of this work was to provide an empirical foundation for decisions regarding regenerant brine management in anion exchange systems for the removal of compounds that absorb ultraviolet (UV) light at a wavelength of 254 nm (UV254) in drinking water treatment. Regenerant performance was assessed for fresh regenerant brine, reused regenerant brine, and used brine that had been treated with aluminum sulfate (alum) before reuse. Jar tests were conducted to examine the UV254 reduction achieved by resins treated with each of these regenerants. Over three regeneration cycles, resin treated with continuously reused regenerant did not display a significant decline in UV254 reduction. While treatment with alum was effective for removing UV254‐absorbing compounds from used regenerant brine, this treatment did not improve the brine's performance as a regenerant. These results demonstrate that regenerant brine may be reused several times without any intermediate treatment, which provides a cost‐saving solution for treatment plants seeking to install anion exchange systems.

Evaluation of a pilot plant for removal of nitrate from groundwater using ion exchange and recycled regenerant

A combined system of ion exchange (IX) and advanced biophysical treatment of a recirculating regenerant was tested for nitrate removal from groundwater with minimal brine discharge and chloride addition to the product water. Using well water containing 21.5 ± 1.4 mg NO3−-N/L, optimal IX operation was found at a service cycle of 500 bed volumes (BV). Product water nitrate concentrations (7.4 ± 1.4 mg/L as N) met regulations while minimizing both Cl− addition to the treated water (1.03 meq Cl− added per meq NO3−-N removed) and waste brine production (0.2% of the water volume treated). The total organic carbon in the product water was slightly higher (1.5 ± 0.5 vs. 1.3 ± 0.4 mg/L) than the well water and before disinfection the bacterial count was 10–700 cfu/ml. Brine used to regenerate the IX columns was treated first in a sequential batch reactor (SBR) for biological denitrification followed by ozonation for polishing. The SBR was operated at 8 hour cycles and achieved complete nitrate removal. An ozone dose of 3 to 5 mg/L brine allowed for efficient recycling of the denitrified regenerant by removing suspended solids by foam fractionation. In spite of the low brine blow-down, DOC in the recycled regenerant brine after a year of continuous operation was maintained at relatively low levels of 61.0 ± 11.6 mg/L.

Improvement of MCDI operation and design through experiment and modelling: Regeneration with brine and optimum residence time

Membrane Capacitive Deionization (MCDI) is an energy efficient, electrochemical desalination technology, in which ions are removed from a salty stream upon applying a constant voltage or current. The ions are stored in carbon electrodes and then released back into the stream by reversing the polarity. In this work, we aimed to assess the feasibility of using a brine stream to regenerate the MCDI unit in order to improve water recovery. We further aimed to determine the optimum residence time in the MCDI unit. To achieve these objectives, we first enhanced the ion transport model previously developed for MCDI by independently measuring the counter-ion and co-ion diffusion coefficients in the ion-exchange membranes. These experiments allowed for an asymmetric model of the MCDI unit where the voltage drop across the cation exchange membrane was greater than that across the anion exchange membrane. Using this revised model, we found that in batch operation, a brine to feed water concentration ratio of around two was optimum. In continuous operation, over 40% enhancement in water recovery could be achieved when the regeneration brine was partially recycled, but water productivity dropped. We further showed that the maximum desalination capacity did not increase beyond a critical residence time in the MCDI cell, while the water recovery decreased.

Removal of Nitrate from Drinking Water by Ion-Exchange Followed by nZVI-Based Reduction and Electrooxidation of the Ammonia Product to N2(g)

Ion-exchange (IX) is common for separating NO3− from drinking water. From both cost and environmental perspectives, the IX regeneration brine must be recycled, via nitrate reduction to N2(g). Nano zero-valent iron (nZVI) reduces nitrate efficiently to ammonia, under brine conditions. However, to be sustainable, the formed ammonia should be oxidized. Accordingly, a new process was developed, comprising IX separation, nZVI-based nitrate removal from the IX regeneration brine, followed by indirect ammonia electro-oxidation. The aim was to convert nitrate to N2(g) while allowing repeated usage of the NaCl brine for multiple IX cycles. All process steps were experimentally examined and shown to be feasible: nitrate was efficiently separated using IX, which was subsequently regenerated with the treated/recovered NaCl brine. The nitrate released to the brine reacted with nZVI, generating ammonia and Fe(II). Fresh nZVI particles were reproduced from the resulting brine, which contained Fe(II), Na+, Cl− and ammonia. The ammonia in the nZVI production procedure filtrate was indirectly electro-oxidized to N2(g) at the inherent high Cl− concentration, which prepared the brine for the next IX regeneration cycle. The dominant reaction between nZVI and NO3− was described best (Wilcoxon test) by 4Fe(s) + 10H+ + NO3− → 4Fe2+ + NH4+ + 3H2O, and proceeded at &gt;5 mmol·L−1·min−1 at room temperature and 3 &lt; pH &lt; 5.

BDST modelling of sodium ion exchange column behaviour with strong acid cation resin in relation to coal seam water treatment

Reverse osmosis is the dominant technology utilized for desalination of saline water produced during the extraction of coal seam gas. Alternatively, ion exchange is of interest due to potential cost advantages. However, there is limited information regarding the column performance of strong acid cation resin for removal of sodium ions from both model and actual coal seam water samples. In particular, the impact of bed depth, flow rate, and regeneration was not clear. Consequently, this study applied Bed Depth Service Time (BDST) models to reveal that increasing sodium ion concentration and flow rates diminished the time required for breakthrough to occur. The loading of sodium ions on fresh resin was calculated to be ca. 71.1gNa/kg resin. Difficulties in regeneration of the resin using hydrochloric acid solutions were discovered, with 86% recovery of exchange sites observed. The maximum concentration of sodium ions in the regenerant brine was found to be 47,400mg/L under the conditions employed. The volume of regenerant waste formed was 6.2% of the total volume of water treated. A coal seam water sample was found to load the resin with only 53.5g Na/kg resin, which was consistent with not only the co-presence of more favoured ions such as calcium, magnesium, barium and strontium, but also inefficient regeneration of the resin prior to the coal seam water test.

Evaluation of a hybrid ion exchange-catalyst treatment technology for nitrate removal from drinking water

Ion exchange (IX) is the most common approach to treating nitrate-contaminated drinking water sources, but the cost of salt to make regeneration brine, as well as the cost and environmental burden of waste brine disposal, are major disadvantages. A hybrid ion exchange-catalyst treatment system, in which waste brine is catalytically treated for reuse, shows promise for reducing costs and environmental burdens of the conventional IX system. An IX model with separate treatment and regeneration cycles was developed, and ion selectivity coefficients for each cycle were separately calibrated by fitting experimental data. Of note, selectivity coefficients for the regeneration cycle required fitting the second treatment cycle after incomplete resin regeneration. The calibrated and validated model was used to simulate many cycles of treatment and regeneration using the hybrid system. Simulated waste brines and a real brine obtained from a California utility were also evaluated for catalytic nitrate treatment in a packed-bed, flow-through column with 0.5 wt%Pd–0.05 wt%In/activated carbon support (PdIn/AC). Consistent nitrate removal and no apparent catalyst deactivation were observed over 23 d (synthetic brine) and 45 d (real waste brine) of continuous-flow treatment. Ion exchange and catalyst results were used to evaluate treatment of 1 billion gallons of nitrate-contaminated source water at a 0.5 MGD water treatment plant. Switching from a conventional IX system with a two bed volume regeneration to a hybrid system with the same regeneration length and sequencing batch catalytic reactor treatment would save 76% in salt cost. The results suggest the hybrid system has the potential to address the disadvantages of a conventional IX treatment systems.

Minimizing brine discharge in a combined biophysical system for nitrate removal from inland groundwater

Abstract Health concerns regarding microbial contamination on the one hand and brine disposal regulations on the other limits the application of both biological and physico-chemical techniques for nitrate removal from polluted inland groundwater. In the current work, a combined system consisting of ion exchange (IX) and advanced biophysical treatment of the recirculated regenerant was investigated to achieve a safe and reliable process for nitrate removal from groundwater with minimal brine discharge and chloride addition to the product water. Using a feed water composing 26 mg NO 3 − –N/L, Cl − 243 mg/L and 16 mg SO 4 − 2 –S/L, optimal IX operation was found to be at a service cycle length of 380 bed volumes with ‘full treatment’ of the water source rather than a ‘split treatment’ option with shorter service cycle and final product water blending. ‘Full treatment’ resulted in nitrate concentrations meeting regulations while minimizing both Cl − addition to the treated water (1.11 meq Cl − added per meq NO 3 − –N removed) and waste brine production (0.25% of the water volume treated). In the product water, the DOC was 0.5 mg/L lower than the feed (tap) water and before disinfection the bacterial count was 10–700 cfu/mL. Spent regenerant was first treated in a sequential batch denitrification bioreactor followed by ozonation for polishing. The SBR unit achieved complete nitrate removal in 8 h with nitrate removal rates of 2.6 ± 0.4 g N/L reactor /d and a low average ethanol to nitrate mass ratio of 1.68 ± 0.18. An ozone dose of 3–5 mg/L brine allowed for efficient recycling of the denitrified regenerant by removing suspended solids by foam fractionation. In spite of the low brine blow-down, DOC in the recycled regenerant brine after more than a year of continuous operation was maintained at relatively low levels of 61.0 ± 11.6 mg/L.

Photocatalytic reduction of nitrate using titanium dioxide for regeneration of ion exchange brine

Nitrate is often removed from groundwater by ion exchange (IX) before its use as drinking water. Accumulation of nitrate in IX brine reduces the efficiency of IX regeneration and the useful life of the regeneration brine. For the first time, we present a strategy to photocatalytically reduce nitrate in IX brine, thereby extending the use of the brine. Titanium dioxide (Evonik P90), acting as photocatalyst, reduced nitrate effectively in both synthetic brines and sulfate-removed IX brine when formic acid (FA) was used as the hole scavenger (i.e., electron donor) and the initial FA to nitrate molar ratio (IFNR) was 5.6. Increasing the NaCl level in the synthetic brine slowed the nitrate reduction rate without affecting by-product selectivity of ammonium and gaseous N species (e.g., N2, N2O). In a non-modified IX brine, nitrate removal was greatly inhibited owing to the presence of sulfate, which competed with nitrate for active surface sites on P90 and induced aggregation of P90 nanoparticles. After removing sulfate through barium sulfate precipitation, nitrate was effectively reduced; approximately 3.6 × 1024 photons were required to reduce each mole of nitrate to 83% N Gases and 17% NH4+. To make optimum use of FA and control the residual FA level in treated brine, the IFNR was varied. High IFNRs (e.g., 4, 5.6) were found to be more efficient for nitrate reduction but left higher residual FA in brine. IX column tests were performed to investigate the impact of residual FA for brine reuse. The residual FA in the brine did not significantly affect the nitrate removal capacity of IX resins, and formate contamination of treated water could be eliminated by rinsing with one bed volume of fresh brine.

Application of a Re–Pd bimetallic catalyst for treatment of perchlorate in waste ion-exchange regenerant brine

Concentrated sodium chloride (NaCl) brines are often used to regenerate ion-exchange (IX) resins applied to treat drinking water sources contaminated with perchlorate (ClO4−), generating large volumes of contaminated waste brine. Chemical and biological processes for ClO4− reduction are often inhibited severely by high salt levels, making it difficult to recycle waste brines. Recent work demonstrated that novel rhenium–palladium bimetallic catalysts on activated carbon support (Re–Pd/C) can efficiently reduce ClO4− to chloride (Cl−) under acidic conditions, and here the applicability of the process for treating waste IX brines was examined. Experiments conducted in synthetic NaCl-only brine (6–12 wt%) showed higher Re–Pd/C catalyst activity than in comparable freshwater solutions, but the rate constant for ClO4− reduction measured in a real IX waste brine was found to be 65 times lower than in the synthetic NaCl brine. Through a series of experiments, co-contamination of the IX waste brine by excess NO3− (which the catalyst reduces principally to NH4+) was found to be the primary cause for deactivation of the Re–Pd/C catalyst, most likely by altering the immobilized Re component. Pre-treatment of NO3− using a different bimetallic catalyst (In–Pd/Al2O3) improved selectivity for N2 over NH4+ and enabled facile ClO4− reduction by the Re–Pd/C catalyst. Thus, sequential catalytic treatment may be a promising strategy for enabling reuse of waste IX brine containing NO3− and ClO4−.

Application of UF, NF and ED in natural organic matter removal from ion-exchange spent regenerant brine

The objective of the study was to compare the efficiency of pressure and electrically driven membrane processes in the treatment of brines containing high concentrations of NOM. In the pressure driven processes 6 ultrafiltration and 2 nanofiltration Nadir polymeric membranes were tested. Electrodialysis was performed using Neosepta AMX and CMX ion-exchange membranes. Experiments were carried out on a model solution containing 12% NaCl and 1 g of humic substances per liter. Electrodialytic treatment of spent regenerant brought an almost 100% recovery of NaCl when the feed to receiver volume ratio amounted to 5:3. The retention of NOM particles reached 91%. The increase of volume ratio up to 5:5 resulted in the decrease of salt recovery to 79%. In the same time organic macromolecules separation increased to 97%. UF and NF membranes were very effective in NOM separation from spent regenerant. The reduction of color reached 88% for UF membranes and 99% for NF ones. Pressure membrane filtration only slightly influenced the NaCl concentration in the permeate.