Monovalent Selective Anion Exchange Membranes Research Articles

Enhanced separation of monovalent and divalent ions in high salinity wastewater by selective electrodialysis: Experimental investigation and performance prediction

To fulfill the industrial requirements of salt fractionation and recovery from saline wastewater, a two-chamber selective electrodialysis (SED) stack incorporating commercial monovalent selective anion exchange membranes was employed and investigated in this study. Three different initial concentration ratios of NaCl/Na2SO4, namely 1:1 (10 g/L:10 g/L), 3:1 (30 g/L:10 g/L), and 5:1 (50 g/L:10 g/L) were examined to simulate various scenarios of saline wastewater. The influence of applied current density on membrane selectivity and overall system efficiency was further evaluated. The results indicated that an increase in the NaCl fraction within the feed solution directly correlates with enhanced concentration and purity of Na2SO4 in the product, achieving purities exceeding 92 %. A lower current density contributed to improved concentration and purity of Na2SO4, whereas higher current densities were conducive to augmenting the concentration and purity of NaCl. Additionally, a linear correlation was observed between the volumetric water transport and NaCl migration. Through numerical simulations, the concentrations of Na2SO4 and NaCl in the effluent were predicted, facilitating a comparative analysis with the salt fractionation efficiency of commercial nanofiltration membranes. Subsequent assessments of energy consumption and current efficiency revealed that the SED system ensured high product concentration and purity at reasonably low energy consumption (0.22–0.28 kWh per kg NaCl) alongside a high current efficiency (83–89 %). These findings offer critical insights into the optimization of salt fractionation process and highlight its economic and technical feasibility for the sustainable management of industrial saline wastewater.

Bifunctional side-chains decorating a distorted poly(aryl ether sulfone) backbone to endow an anion exchange membrane with high perm-selectivity for chloride ions

Mono-valent selective ion-exchange membrane, as the core component of selective electrodialysis (SED), has received extensive attention. In this work, we report a mono-valent selective anion-exchange membrane (AEM), which was fabricated with distorted poly(aryl ether sulfone) and decorated with bifunctional side-chains providing anion exchange groups and hydrophobic segments. By tuning the length of the hydrophobic side-chains, the nanophase separation within AEMs was finely tuned, evidenced by an ionic cluster size of about 0.47 nm from SAXS analysis. The optimized AEM (PAES-TA-7 AEM) shows a very low water swelling ratio of 6.4 %, signaling good dimensional stability. The perm-selectivity (PSO42–Cl–) of PAES-TA-7 AEM during ED reached 107 at 2.5 mA∙cm−2 (ion flux: 2.69 × 10−8 mol cm−2 s−1 at 90 min) significantly exceeding that of the commercial Neosepta ACS (11; 2.08 × 10−8 mol cm−2 s−1). It is inferred that the ion channels, resulting from nanophase separation between the side-chains and the backbone, as well as the free volume cavity created by the distorted backbone, significantly contribute to the smooth transport of the Cl− ions through the AEM with less resistance. As a result, it is believed that this work offers a useful strategy to advance the monovalent anion-selective membranes.

Electrodepositing polydopamine and iron (III) complexed polyacrylic acid for monovalent selective anion exchange membrane fabrication

Monovalent selective anion exchange membranes were efficiently prepared by two-steps electrodeposition. Firstly, a polydopamine (PDA) interlayer was formed onto the surface of a commercial anion exchange membrane (AEM), followed by the deposition of a top layer of Fe3+ complexed polyacrylic acid (Fe-PAA). The PDA interlayer formation was investigated by reversing the polarity of the electric field applied. In particular, modified membrane prepared with PDA layer facing the cathode (labeled as FC-PDA-M) exhibited lower negative charge surface density compared to the membrane prepared with DA solution close to the anode (labeled as FA-PDA-M). This effect resulted in an increased deposition of PAA, due to the diminished electrostatic repulsion, when a solution of Fe3+ complexed polyacrylic acid with a Fe/PAA ratio of 1/4 was electrodeposited on the PDA layer. After eluting the Fe3+ with EDTA, the two manufacture membranes, labeled as FC-PDA/(Fe)PAA-M and FA-PDA/(Fe)PAA-M, were characterized. The former exhibited a higher Cl−/SO42− permselectivity than the latter, although the latter demonstrated better performance compared to both the pristine AEM and a PAA-PDA-M obtained without applying any current during the deposition process. The effect the Fe3+ addition and varied the Fe/PAA ratio was also investigated. The membranes obtained using the Fe/PAA ratio of 1/4 exhibited best separation performance. Finally, the stability of this membrane was assessed by conducting ten consecutive electrodialysis (ED) experiments, revealing consistent Cl−/SO42− permselectivity values within the 5–6 range.

Simultaneous ion fractionation and concentration by selectrodialysis for saline wastewater valorization

In order to desalinate saline wastewater and achieve energy-efficient recovery of mixed salt (Na2SO4 and NaCl), selectrodialysis (SED) stack with commercial monovalent selective anion exchange membranes (MVA) was utilized in this work. The experiments proved that the final concentration and purity of Na2SO4 in Product could reach 0.84 mol·L−1 and 94.9%, respectively, under the optimal testing conditions (initial concentration of Product solution was 15 wt.% NaCl and the current density of 200 A·m−2). Simultaneously, the concentration and purity of NaCl in Brine achieved 1.90 mol·L−1 and 97.1%, respectively. In order to guide the engineering application, a formula was established to predict the termination time of SED process according to the applied current density. Furthermore, glycerol retention rate of the SED stack in Feed solution could reach more than 95%. And low energy consumption on Na2SO4 and NaCl fractionation/concentration by 0.13–0.15 kWh·kg−1 at 200 A·m−2. Hence, this work illustrated the techno-economic feasibility of using SED for saline wastewater valorization.

Cross-Linked, Monovalent Selective Anion Exchange Membrane: Effect of Prealkylation and Co-ions on Selectivity

Tuning of hydrophobicity, water uptake, and size of the ion channel is very crucial for the monovalent anion-selective membrane (MASM) preparation. In this work, we report the preparation of MASM from the cross-linked polyacrylonitrile-co-polyvinylimidazole (PAN-co-PVI) copolymer. The copolymer was in situ quaternized and cross-linked using the polyacrylonitrile-co-polychloromethylstyrene (PAN-co-PCMSt) copolymer as cross-linker. The benzyl chloride moiety (Ar-CH2Cl) of PAN-co-PCMSt reacts with imidazolium nitrogen of PAN-co-PVI and provides a positive charge on the membrane matrix, whereas the PAN moiety provides greater compatibility with the PAN-co-PVI copolymer matrix. The faster cross-linking without external prealkylation forms a strong network structure with a low ionic charge on the membrane surface. Judicious extent of prealkylation followed by cross-linking forms a controlled network structure and small-sized ionic channel with moderate water uptake and good mechanical stability. The representative AEM0Q and AEM17Q membranes with 0 and 17% prealkylation exhibited a permselectivity (PSO42–Cl–) value of 4.39 and 15.40, respectively, during the separation of 0.01 M NaCl + 0.01 M Na2SO4 by electrodialysis. Upon further increase of prealkylation to 27 and 32%, the water uptake of the membrane increased, which in turn allowed the passage of SO42– along with Cl– and decreased the PSO42–Cl–value to 4.12 and 2.45, respectively. Similar trends were observed during the separation of NaCl + MgSO4, MgCl2 + Na2SO4, and MgCl2 + MgSO4 mixtures of each 0.01 M concentration.

Designing monovalent selective anion exchange membranes for the simultaneous separation of chloride and fluoride from sulfate in an equimolar ternary mixture

Selective removal of multiple counter-ions in a single mixture is highly desirable for many industrial applications but also very challenging. This study focuses on designing monovalent selective anion exchange membranes (AEMs) for the simultaneous separation of F− and Cl− from SO42− using electrodialysis (ED). A series of brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) polymers with adjusted bromination degrees at benzyl and aryl positions were synthesized, and quaternized with different tertiary amines of varying chain lengths to produce optimized AEMs. Differences in bromination degrees and the chain lengths of the tertiary amines alter the microstructure of AEMs, which influences the anion transport through the developed membranes. Selected AEMs were modified via layer-by-layer (LbL) deposition of poly (sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) polyelectrolytes to enhance their monovalent selectivity. ED tests were carried out with an equimolar ternary mixture. When 5 layers of deposition were applied, the achieved Cl−/ SO42− and F−/ SO42− selectivities were 11.7 ± 0.2 and 8.3 ± 0.3, respectively, showing significant improvement compared to a commercial monovalent selective ASVN membrane. Experimental results confirm that simultaneously optimizing membrane microstructure and surface can be an effective strategy for the separation of similar counter-ions in an ED process.

A monovalent selective anion exchange membrane made by poly(2,6-dimethyl-1,4-phenyl oxide) for bromide recovery

Bromide recovery from waste streams is crucial for both environmental and economic reasons. Membrane technology has shown great potential in achieving efficient ion separation, credited to the use of separation membranes with well-defined pore structure down to molecular level and surface charge properties. Herein, a class of novel anion exchange membranes (AEMs) was fabricated by brominated poly (2,6-dimethyl-1, 4-phenyl oxide) (BPPO) and different content of 4-hydroxy-1-methylpiperidine (HMP) via the chemical substitution reaction for Br- recovery. The resulting membrane (HMP@BPPO-0.1) had an ion exchange capacity of 1.69 mmol g−1, a water content of 14.4 %, a swelling rate of 4.7 %, a surface electrical resistance of 3.68 Ω cm2 and a limiting current density of 28.4 mA cm−2. In addition, under a constant voltage of 15.0 V for 180 min in electrodialysis, the removal ratio of NaBr solution was 98.15 %, which was higher than that of the commercial AEM (ASE) (97.1 %) under the same testing conditions. To evaluate the Br- selectivity, the membranes were tested for an initial concentration of 50 mM of NaCl, NaBr and Na2SO4 in a mixed solution with a constant current density of 2.5 mA cm−2, 5.0 mA cm−2 and 10.0 mA cm−2. The results showed that the permselectivity of the HMP@BPPO-0.1 for 100 min was as high as 12.6 (Br-/SO42-) and 1.20 (Br-/Cl-) under the 5.0 mA cm−2 electric field, and the ion permeation rate of Cl-, Br- and SO42- were 0.78, 1.20 and 0.20 mol−1 m-2 h−1, respectively. Compared to the ASE membrane and the resulting membrane with negatively charged modification layer, this work suggests novel ideas in fabricating a membrane with Br- selectivity in view of resource recovery.

Purification of organic acids using electrodialysis with bipolar membranes (EDBM) combined with monovalent anion selective membranes

• EDBM used to purify a mixture of lactate and citrate as a simulated beet molasses solution. • The use of a monovalent selective anion exchange membrane gives higher purity than with a standard AEM. • Adjustment of the feed to pH > 9.0 improves separation due to the larger size of the citrate anion. • A volume ratio of 10:1 acid:feed gives 153 g/L lactic acid of 95% purity with <2.7 KWh per kg lactate. • The BP-A-C configuration is more energy efficient than BP-A. The feasibility of using electrodialysis with bipolar membranes (EDBM), combined with monovalent selective anion exchange membranes was investigated to purify organic acids from fermentation broths or wastewater streams. A simulated beet molasses feed containing a mixture of monobasic lactic acid and polybasic citric acid was used for this purpose. The impact of the feed pH, the configuration of the membrane stack and the voltage applied on the selectivity of the process was investigated. At a pH of 9–10 and an electric field intensity of 9 V/cm, a lactic acid product with a purity of at least 97% can be obtained by using both two chamber (BP-A) and three chamber (BP-A-C) configurations with the monovalent selective membrane. When using the BP-A configuration, the hydroxide ions generated by the bipolar membrane compete with the lactate anions to move into the acid solution and so the energy efficiency is lower than with the BP-A-C configuration. To mimic a multiple pass process and increase the lactic acid concentration of the final product, experiments were performed across a range of volume ratios between the feed and acid solutions. As this ratio is varied, the purity of lactic acid produced remains higher than 95% while the energy consumption is essentially unaffected. Due to the osmotic flow of water during experiments, the highest lactic acid concentration that can be achieved is limited to 153 g/L at a volume ratio (V A : V F ) of 1:10.

Di-quaternized graphene oxide based multi-cationic cross-linked monovalent selective anion exchange membrane for electrodialysis

A series of monovalent anion selective membranes were synthesized by crosslinking of chloromethylated polysulfone with 1,4-diazabicyclo [2.2.2] octane functionalized graphene oxide (QGO). Cross-linking of QGO provides dense polymer matrix as well as additional functional sites to the membrane. The effect of QGO on physicochemical and electrochemical properties was studied in detail. The best optimized membrane, CrPSf-3 (3 wt% of nano cross-linker) showed 2.01 mmol·g−1 ion exchange capacity, 9.90% swelling ratio, 31.20% water uptake, 72 mS·cm−1 chloride ion conductivity and 0.95 counter ion transport number along with good mechanical and thermal stability. Electrodialysis performance of membrane permselectivity between Cl− and SO42− was studied in mixed salt solution of 0.05 mol·L-1 (NaCl + Na2SO4). The CrPSf-3 membrane showed 5.7 separation factor (SF) for Cl−/SO42− which is higher than pristine QPSf (1.7) and commercial FAB-PK-130 membrane (2.01). Furthermore, higher Cl− flux (2.97 mol·m-2h−1) was observed for CrPSf-3 membrane as compare to pristine QPSf (1.45 mol·m-2h−1) and commercial membrane (1.6 mol·m−2·h−1). To achieve monovalent anion selectivity, effective cross-linking is facile approach to control compactness of the membrane and ion transport channels. Reported cross-linked membrane possesses a potential candidate for water desalination, wastewater treatment, or other monovalent selective separation processes.

Brine management from desalination plants for salt production utilizing high current density electrodialysis-evaporator hybrid system: A case study in Kuwait

The potential of producing salt and low salinity water by treating synthetic brine was investigated in a pilot-scale electrodialysis-evaporator hybrid system as part of brine management. An electrodialyzer with 25 cell pairs of monovalent selective anion exchange membranes (AEMs) and monovalent selective cation exchange membranes (CEMs) were used. Effect of three different current densities (300 to 500 A/m2) and two different flowrates (400 L/h and 450 L/h) on brine treatment were evaluated in the current study. The results indicated that the aforementioned membranes were efficient in separating monovalent ions over divalent ions. Moreover, higher current density operation was favoured during the electrodialysis (ED) operation as the operation time for producing salt was shorter. Flowrate is a crucial parameter for the operation of the ED system, where higher flowrate (by 12.5%) reduced the operation time (by 30 min), reduced energy consumption (by 32%) and reduced system resistance (by 32.42%) leading to an increase in current efficiency (by 31.4%). The concentrated brine effluent from ED was fed to an evaporator to produce coarse salt with 84.75% salt recovery and low salinity water of 1526 ppm. Thus, ED-evaporator hybrid system was found to be a good option to treat reject brine from desalination plants.

In-Situ Combination of Bipolar Membrane Electrodialysis with Monovalent Selective Anion-Exchange Membrane for the Valorization of Mixed Salts into Relatively High-Purity Monoprotic and Diprotic Acids.

The crystalized mixed salts from the zero liquid discharge process are a hazardous threat to the environment. In this study, we developed a novel electrodialysis (SBMED) method by assembling the monovalent selective anion-exchange membrane (MSAEM) into the bipolar membrane electrodialysis (BMED) stack. By taking the advantages of water splitting in the bipolar membrane and high perm-selectivity of MSAEM for the Cl− ions against the SO42− ions, this combination allows the concurrent separation of Cl−/SO42− and conversion of mixed salts into relatively high-purity monoprotic and diprotic acids. The current density has a significant impact on the acid purity. Both the monoprotic and diprotic acid purities were higher than 80% at a low current density of 10 mA/cm2. The purities of the monoprotic acids decreased with an increase in the current density, indicating that the perm-selectivity of MSAEM decreases with increasing current density. An increase in the ratio of monovalent to divalent anions in the feed was beneficial to increase the purity of monoprotic acids. High-purity monoprotic acids in the range of 93.9–96.1% were obtained using this novel SBMED stack for treating simulated seawater. Therefore, it is feasible for SBMED to valorize the mixed salts into relatively high-purity monoprotic and diprotic acids in one step.

Monovalent anion selective anion-exchange membranes with imidazolium salt-terminated side-chains: Investigating the effect of hydrophobic alkyl spacer length

Ion-conductive polymers having highly ordered and well-defined phase-separated structures are potential materials for use as monovalent anion-selective membranes (MASMs). In this work, to investigate the effect of hydrophobic spacers, four side-chain-type imidazolium salt-tethered poly(arylene ether sulfone) anion-exchange membranes (AEMs) with different alkyl spacer lengths (–CH2– number: 3, 6, 9, and 12) were fabricated for use in electrodialysis (ED). Our investigations using atomic force microscopy, small angle X-ray scattering and X-ray diffraction demonstrate that the extended alkyl spacers change the nano-phase-separated structures, with an increased ion cluster space ranging from 3.29 nm to 7.76 nm, resulting from increased immiscibility between the additional hydrophobic alkyl spacers and (i) the hydrophobic aromatic backbones and (ii) the hydrophilic ion-conductive groups. In addition, with the extension of the alkyl spacer, chloride (Cl−) ion conductivity at 25 °C decreases from 16.4 mS cm−1 to 11.4 mS cm−1 and water uptake is reduced to 12.8% (20 °C). It is found that the as-prepared AEM with a hexyl alkyl spacer shows the superior perm-selectivity (Cl−/SO42−) of 7.10 (separation efficiency: 70.3%), as compared with three others (3.48, 6.81, and 4.26). This work thus presents an efficient strategy to guide the architectural design of novel MASMs.

Monovalent Selective Anion-exchange Membranes Prepared from PVA-based Block Copolymers

Monovalent Selective Anion-exchange Membranes Prepared from PVA-based Block Copolymers

Alternating current enhanced deposition of a monovalent selective coating for anion exchange membranes with antifouling properties

In this work, a monovalent selective anion exchange membrane was prepared by a two-step modification process based on mussel inspired surface chemistry and amide condensation reactions. An alternating current electric field was employed to boost the homogeneity and stability of the coating. The membrane surface chemistry was investigated by attenuated total reflectance Fourier transform infrared spectroscopy; the surface roughness was analysed by atomic force microscopy and the hydrophilicity was evaluated by water contact angle measurement. Desalination experiments were conducted to evaluate the selectivity of the membrane for monovalent anions. The resulting membrane showed enhanced monovalent separation efficiency in comparison with the original membrane (17.33% and 4.90% SO42−/Cl−, respectively). The stability of the coating was successfully evaluated by the application of a reverse electric field in electrodialysis. The resulting membrane acquired an increased resistance to organic fouling. This work shows a facile avenue to obtain a stable monovalent selective anion exchange membrane with enhanced antifouling properties.

Fractionating various nutrient ions for resource recovery from swine wastewater using simultaneous anionic and cationic selective-electrodialysis

Different from current nutrient recovery technologies of recovering one or two nutrient components (PO43− or NH4+) from wastewater, this study aimed to fractionate various nutrient anions and cations simultaneously, including PO43−, SO42−, NH4+, K+, Mg2+ and Ca2+, into several streams. The recovered streams could be further paired together to produce high-value products. A novel electrodialysis process was developed by integrating monovalent selective anion and cation exchange membranes into an electrodialysis stack. Results revealed that nutrient recovery was achieved effectively by fractionating PO43− and SO42− into the anionic product stream, whereas bivalent cations (Mg2+ and Ca2+) were extracted in the cationic product stream and the monovalent cations (K+ and NH4+) were concentrated in the brine stream. For the permeation capabilities of anions, SO42− and Cl− possessed the higher preference, whereas PO43− permeated the membrane more difficult. As to the cations, the permeation sequence was: NH4+≈K+ >Ca2+>Mg2+≈Na+. Enhancing voltage values not only promoted ion migration rates, but also led to the increase of energy consumption. Although elevating initial phosphate concentration in the anionic product streams from 60 mg/L to 470 mg/L did not influence phosphate fractionation significantly, the current efficiency decreased from 3.55% to 0.65% and a remarkable increased of energy consumption from 29.42 kWh/kg NaH2PO4 to 160.13 kWh/kg NaH2PO4 was observed. Further experiments were conducted for phosphorus recovery by pairing two recovered product streams, which revealed that phosphate precipitation could be achieved by using inherent Ca2+ and Mg2+ in the wastewater without dosing external cation sources.

Integration of selectrodialysis and selectrodialysis with bipolar membrane to salt lake treatment for the production of lithium hydroxide

Extracting lithium from salt lakes and preparing lithium hydroxide could provide important commodities for the economic development in future. In this work, a complete system was divided into two steps of selectrodialysis (SED) and selectrodialysis with bipolar membrane (BMSED) to treat salt lakes for the production of lithium hydroxide. The effects of the applied current density, the commercial monovalent selective cation-exchange membranes (CIMS and CSO), the monovalent selective anion-exchange membranes (ACS and ASV) and the voltage drop in the SED process were investigated, respectively. The experimental results indicated that under the current density of 12 mA/cm2 can effectively avoid membrane scaling. The separation performance for Mg2+ and Ca2+ by using CIMS/ACS membrane stack was demonstrated to be superior to CSO/ASV membrane stack. Additionally, the SED stack had proven to be feasible for concentrating lithium and removing divalent ions simultaneously. In BMSED process, the purpose was to combine the monovalent selective ion-exchange membrane with bipolar membrane (FBM) inside the membrane stack to remove divalent ions and simultaneously produced LiOH. The results showed that the concentration of LiOH and current efficiency were optimized at the current density of 6 mA/cm2. Furthermore, different cation-exchange membranes (CIMS, CSO and CMX) and anion-exchange membranes (ACS, ASV and AMX) were used to evaluate the BMSED process. Compared to the FBM/ASV/CSO/FBM membrane stack and FBM/AMX/CMX/FBM membrane stack, FBM/ACS/CIMS/FBM membrane stack exhibited superior current efficiency and separation performance for Mg2+ and Ca2+.

EFFECT OF SALT COMPOSITION ON THE SEPARATION PROFILE OF CONTAMINATED GROUNDWATER IONS BY ELECTRODIALYSIS

Chloride, nitrate, sulfate, and fluoride ions are sometimes available in groundwater at an elevated level, which is harmful to humans and the environment. The membrane separation technique has been widely explored for controlling the level of those ions in drinking water, particularly the electrodialysis method. In the present study, divalent (AMX) and monovalent ion selective (ACS) anion exchange membranes were used to remove the high concentrations of chloride and other co-existent ions from groundwater samples. The study focuseson the effect of the composition of the salt in the groundwater on the reducing profile of ions, the number of deionized ions, and the rate of ion removal in the diluting compartment. To achieve these experimental objectives, two series of ion samples composed of sodium and calcium were designed. The compositions of the ions wereNaCl, Na2NO3, Na2SO4 for the Na-compound, and CaCl2, Ca(NO3)2.4H2O, CaSO4∙2H2O, and CaF2 for the Cacompound. The electrodialysis experiment was run at a constant applied voltage (8 volts), using sodium nitrate as the electrode solution. In summary, the ED performance for all the investigated parameters was better in the case of ions composed of sodium. Furthermore, a change in the applied current against the electrodialysis operation time was also observed. The results indicated that the current requirement by ED to separate ions composed of calcium needed to be slightly higher than that for ions composed of sodium.

A durable and antifouling monovalent selective anion exchange membrane modified by polydopamine and sulfonated reduced graphene oxide

Abstract Developing a durable and antifouling monovalent selective anion exchange membrane is critical in practical electrodialysis (ED) process. Herein, a commercial anion exchange membrane was modified by sulfonated reduced graphene oxide (S-rGO) and polydopamine (PDA). Inspired by biological adhesion from mussels, the PDA coating on the surface of S-rGO-PDA membrane enhanced the stability of S-rGO nanosheets due to strong adhesion. The monovalent anion selectivity was evaluated by means of the Cl - / SO 4 2 - permeselectivity, and stability property was measured by the ion concentration changes of Cl - and SO 4 2 - for a long time application of ED. Moreover, antifouling property was measured by recording the time course of the potential difference in the presence of sodium dodecyl benzene sulfonate (SDBS). The results show that permselectivity of S-rGO-PDA membrane is 2.50, which is higher than pristine membrane (1.08). In addition, S-rGO-PDA membrane is stable, the permselectivity did not change significantly during 70 h ED process. Besides antifouling property of S-rGO-PDA membranes is improved compared with S-rGO membranes.

One-pot approach to prepare internally cross-linked monovalent selective anion exchange membranes

In this study, high performance internally cross-linked monovalent selective anion exchange membranes were prepared via a one-pot approach by simply adding different amounts of sulfamerazine (SF) to partially-quaternized chloromethylated polysulfone (QPSF). The composition and structure of the prepared membranes were studied by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Atomic force microscopy (AFM). The monovalent anion selectivity was evaluated by electrodialysis using a Cl-/SO42- system. The experimental results show that all QPSF-SF-x membranes exhibit excellent monovalent anion selectivity (PSO42−Cl− = 3.98–15.90) at an average pH level of 6.0 because of the presence of sulfamerazine, which can change the compactness and electronegativity of the QPSF membranes. Especially, the optimized QPSF-SF-0.09 membrane had a permselectivity of 24.55 at pH 10.0 and showed an excellent permselectivity in alkaline condition. Based on an overall consideration of the facile synthesis procedure and the excellent monovalent ion selectivity of the resulting membranes, this process is expected to inspire the further investigation of monovalent anion selective membranes.

Upgrading groundwater for irrigation using monovalent selective electrodialysis

Desalinated water reduces salt load and water needs in irrigation but lack hardness and sulfate ions required for optimal plant growth. Mixing with groundwater adds hardness but raises chloride and sodium levels limiting the amount of groundwater that can be used in the blend. Monovalent selective electrodialysis (SED) allows reducing chloride and sodium while preserving most of the hardness ions. This study examined under what conditions monovalent selective membranes are effective in treating groundwater for irrigation. All monovalent selective anion exchange membranes tested showed excellent selectivity for sulfate over chloride. Monovalent selective cation exchange membranes worked less well at the lower conductivities typical of brackish water, with only CSO membrane showing significant monovalent permselectivity (Pdm<1) at conductivities<4.5dS/m. Keeping current densities for treating groundwater below limiting current found for solutions of pure sodium chloride at sodium levels found in the groundwater was key to preserving monovalent selectivity. Poisoning of CSO membranes monovalent cation selectivity could be reversed by acid wash and electrically driven re-deposition of polyethyleneimine on the membrane. When compared to irrigation with mix of groundwater and RO water, mix of SED and RO water used in irrigation gave better results in growing bell peppers.