Search Results (54)

Reusing treated effluent from municipal wastewater treatment plants is essential for addressing freshwater scarcity, a key objective of the United Nations Sustainable Development Goals (SDGs). While closed-circuit reverse osmosis (CCRO) has shown promise in municipal reuse facilities, the comprehensive assessment of water quality parameters, especially at higher recovery rates, is lacking. In this study, at the San Jacinto Valley Regional Water Reclamation Facility (SJVRWRF), we evaluated the performance of CCRO in treating municipal wastewater tertiary effluent, focusing on high recovery rates. Our analysis of selected chemical parameters across recovery rates ranging from 90% to 95% revealed the effective removal of suspended particles by CCRO. However, variations in removal rates were observed among ions, with chloride removal at 96.3% and nitrate removal at 79.6%, contrasting with fluoride’s complete removal and sulfate’s 99.7% removal rate. Divalent ions like calcium and magnesium exhibited better rejection than monovalent ions such as sodium and potassium. Additionally, the removal efficiency of total dissolved solids (TDSs), alkalinity, chloride, nitrate, sodium, and potassium decreased with an increasing recovery rate, while sulfate, calcium, and magnesium removal rates remained stable. These findings enhance our understanding of membrane treatment processes, providing valuable insights for future water reclamation projects to combat freshwater resource scarcity. Full article

To fulfil the goals of the circular economy, the treatment of textile wastewater should be focused on the recovery of valuable components. Monovalent anion-selective electrodialysis (MASED) was applied for the separation of reactive dyes from mineral salts. Standard cation-exchange membranes (CM membranes) and monovalent selective anion-exchange membranes (MVA membranes) were used in the electrodialysis (ED) stack. The separation efficiency was evaluated for model solutions of various reactive dyes (varying in molecular weight and chemical reactivity) containing NaCl. In the course of MASED, the mineral salt was successfully removed from the dye solutions with an efficacy of 97.4–99.4%, irrespectively of the composition of the treated solution. The transport of dye molecules through the ion-exchange membranes (IEMs) from diluate to concentrate compartments was irrelevant. Nonetheless, a significant adsorption of dye particles on the membranes was observed. Around 11–40% of the initial dye mass was deposited in the ED stack. Dye adsorption intensity was significantly affected by dye reactivity. This study showed the potential of the MASED process for the separation of the reactive dye from the mineral salt on condition that antifouling membrane properties are improved. The obtained streams (the concentrate rich in mineral salt and the diluate containing the reactive dye) can be reused in the dye-house textile operations; however, some loss of dye mass should be included. Full article

Efficient dye/salt separation poses a great challenge to nanofiltration (NF) membrane technology in the desalting sector of the dye synthesis industry. In this study, we fabricated a novel loose polyester NF membrane via an interfacial polymerization method using “hydroxyl-ammonium” biquaternary diethanolamine (MDET) and trimesoyl chloride. The molecular design of MDET provides a loose crosslinking network, showing high rejection of dyes and the passage of monovalent salt/divalent salt ions in the dye solution, exhibiting exceptional filtration efficiency with high selectivity. Furthermore, the membrane exhibits excellent operational stability for over 100 h, demonstrating superior antifouling properties and high resistance to chlorine. This study provides new insights into the role of dyes and mono- and divalent ions in desalination processes related to the dye synthesis industry. Full article

Membrane capacitive deionization (MCDI) is an electrochemical ion separation process that combines ion-exchange membranes (IEMs) with porous carbon electrodes to enhance desalination efficiency and address the limitations of conventional capacitive deionization (CDI). In this study, a cation-exchange membrane (CEM) embedded with a metal–organic framework (MOF) was developed to effectively separate monovalent and multivalent cations in influent solutions via MCDI. To fabricate CEMs with high monovalent ion selectivity, ZIF-8 was incorporated into sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) at various weight ratios. The resulting membranes were systematically characterized using diverse electrochemical methods. The ZIF-8-embedded CEMs demonstrated a sieving effect based on differences in ion size and hydration energy, achieving excellent permselectivity for monovalent ions. MCDI tests using the prepared CEMs showed a Na⁺ ion removal rate exceeding 99% in Na⁺/Mg²⁺ and Na⁺/Ca²⁺ mixed feed solutions, outperforming a commercial membrane (CSE, Astom Corp., Tokyo, Japan), which achieved a removal rate of 94.1%. These findings are expected to provide valuable insights for advancing not only MCDI but also other electro-membrane processes capable of selectively separating specific ions. Full article

Background/Objectives: Abiotic stresses such as salinity and drought significantly constrain crop cultivation and affect productivity. Quinoa (Chenopodium quinoa Willd.), a facultative halophyte, exhibits remarkable tolerance to drought and salinity stresses, making it a valued model for understanding stress adaptation mechanisms. The objective of this study was to identify and characterize Sodium/Hydrogen antiporter (NHX) genes from the quinoa genome and study their role in stress tolerance. Methods: We identified and characterized 10 NHX genes from the quinoa genome, which belong to the monovalent cation/proton antiporter 1 (CPA1) superfamily. Comprehensive analysis, including phylogenetic relationships, motif patterns, and structural characteristics, was performed to classify these genes into three subfamilies. Physicochemical properties such as isoelectric point (pI), GRAVY, and transmembrane domains were examined. Promoter analysis was conducted to identify cis-elements linked to abiotic stress responses, phytohormone signalling, and light regulation. qPCR analysis was used to assess the differential expression patterns of CqNHX genes under salt and drought stress. Results: The analysis revealed that the NHX genes were divided into three subfamilies localized to vacuolar, plasma, and endosomal membranes. These genes exhibited structural and functional diversity. Promoter analysis indicated the presence of cis-elements associated with abiotic stress responses, phytohormone signalling, and light regulation, suggesting diverse regulatory roles. qPCR analysis revealed differential expression patterns of CqNHX genes under salt and drought stress, with vacuolar NHXs showing higher induction in leaf tissues under salinity. This underscores their critical role in sodium sequestration and ion homeostasis. Evolutionary analysis indicated a high degree of conservation within subfamilies, alongside evidence of purifying selection. Conclusions: The findings enhance our understanding of the molecular basis of stress tolerance in quinoa and provide valuable targets for genetic engineering to improve crop resilience to environmental challenges. Full article

New homogeneous bilayer membranes with a thin anion-exchange layer have been developed based on the copolymer of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and ethyl methacrylate (EMA) on the surface of a membrane substrate made from polyfluorosulfonic acid (PFSA). The overall and partial current–voltage characteristics, as well as external and internal diffusion-limiting currents, were theoretically and experimentally investigated. Parameters such as specific conductivity, sorption, and diffusion permeability of individual membrane layers were determined, along with effective transport numbers and specific permselectivity of the bilayer homogeneous membranes in mixed solutions of calcium chloride and sodium chloride. It was found that applying a thin anion-exchange layer of DADMAC and EMA to the homogeneous membrane allows for the creation of a charge-selective bilayer membrane with enhanced selectivity toward monovalent metal cations. The specific selectivity of the bilayer membrane for sodium cations increases more than 6-fold (from 0.8 to 4.8). Verification of the obtained experimental data was performed within a four-layer mathematical model with quasi-equilibrium boundary conditions for the diffusion layer (I)/modifying layer (II)/membrane substrate (III)/diffusion layer (IV) in ternary NaCl+CaCl₂ solutions. Full article

The aim of this study was to analyze, both theoretically and experimentally, the material transport mechanisms governing the separation of ionic species in aqueous solutions using nanofiltration membranes. To interpret the experimental results, the Donnan Steric Partitioning Model (DSPM) and the Dielectric Exclusion Model (DSPM-DE) were applied and computationally simulated in Matlab. Experimental tests were conducted using a pilot-scale system with commercial NF90 membranes. The results indicate that the DSPM better describes the rejection of monovalent ions (sodium and chloride), while the DSPM-DE is more suitable for divalent ions (sulfate and magnesium). Additionally, both models were sensitized to explore the impact of hindrance factors on the rejection of different ionic species. For neutral molecules present in the solution, it was observed that the DSPM and DSPM-DE do not adequately interpret selectivity, suggesting that under such conditions, the electrostatic exclusion mechanism loses significance, with the steric mechanism prevailing. Full article

The high concentration of chloride ions in desulphurization wastewater is the primary limiting factor for its reusability. Monovalent anion selective electrodialysis (S-ED) enables the selective removal of chloride ions, thereby facilitating the reuse of desulfurization wastewater. In this study, different concentrations of NaCl and Na₂SO₄ were used to simulate different softened desulfurization wastewater. The effects of current density and NaCl and Na₂SO₄ concentration on ion flux, permselectivity ($P_{{\mathrm{SO}}_4^{2-}}^{{\mathrm{Cl}}^{-}}$) and specific energy consumption were studied. The results show that Selemion ASA membrane exhibits excellent permselectivity for Cl⁻ and SO₄²⁻, with a significantly lower flux observed for SO₄²⁻ compared to Cl⁻. Current density exerts a significant influence on ion flux; as the current density increases, the flux of SO₄²⁻ also increases but at a lower rate than that of Cl⁻, resulting in an increase in permselectivity. When the current density reaches 25 mA/cm², the permselectivity reaches a maximum of 50.4. The increase in NaCl concentration leads to a decrease in the SO₄²⁻ flux; however, the permselectivity is reduced due to the elevated Cl⁻/SO₄²⁻ ratio. The SO₄²⁻ flux increases with the increase in Na₂SO₄ concentration, while the permselectivity increases with the decrease in Cl⁻/SO₄²⁻ ratio. Full article

Positively charged nanofiltration (NF) technology is considered a green and low-cost method for mono/divalent cation separation. Nevertheless, the separation rejection mechanisms of these NF membranes have yet to be extensively investigated. In this work, we fabricated a thin-film composite (TFC) hollow-fiber (HF) NF membrane with a positively charged surface via modification of the nascent interfacial polymerization layer using a branched polyethyleneimine (BPEI)/ethanol solution. Then, we extensively investigated its selective separation mechanism for mono/divalent cations. We proposed and proved that there exists a double-charged layer near the membrane surface, which helps to repel the divalent cations selectively via Donnan exclusion while promoting the fast penetration of monovalent cations. Meanwhile, the membrane skin layer is loose and hydrophilic due to the loose BPEI structure and the abundance of amine groups, as well as the changed fabrication conditions. In this way, we achieved very good mono/divalent cation selectivity and relatively high water permeance for the as-prepared HF NF membrane. We also obtained good anti-fouling, anti-scaling, and acid resistance, and long-term stability as well, which are urgently needed during practical application. Furthermore, we successfully amplified this HF NF membrane and proved that it has broad application prospects in mono/divalent cation separation. Full article

In this study, novel pore-filled anion-exchange membranes (PFAEMs) modified with polypyrrole (PPy) and reduced graphene oxide (rGO) were developed to improve the energy harvesting performance of reverse electrodialysis (RED). The surface-modified PFAEMs were fabricated by varying the contents of PPy and rGO through simple spin coating and chemical/thermal treatments. It was confirmed that the PPy and PPy/rGO layers introduced on the membrane surface did not significantly increase the electrical resistance of the membrane and could effectively control surface characteristics, such as structural tightness, hydrophilicity, and electrostatic repulsion. The PPy/rGO-modified PFAEM showed excellent monovalent ion selectivity, more than four times higher than that of the commercial membrane (AMX, Astom Corp., Tokyo, Japan). This means that the PPy/rGO layer can effectively reduce the permeation of multivalent ions with a high charge intensity and a relatively large hydration radius compared to monovalent ions. The results of evaluating the performance of the surface-modified PFAEMs by applying them to a RED cell revealed that the decrease in potential difference occurring in the membrane was reduced by effectively suppressing the uphill transport of multivalent ions. Consequently, the PPy/rGO-modified membrane exhibited a 5.43% higher power density than the AMX membrane. Full article

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH₄⁺-N) from wastewater in practice. Highly efficient selective permeation of NH₄⁺ through a cation exchange membrane (CEM) is expected to be modulated via tuning the surface charge and structure of CEM. In this work, a novel CEM was designed to form a graphene oxide (GO)-polyethyleneimine (PEI) cross-linked layer by introducing self-assembling layers of GO and PEI on the surface of a commercial CEM, which rationally regulates the surface charge and structure of the membrane. The resulting positively charged membrane surface exhibits stronger repulsion for divalent cations compared to monovalent cations according to Coulomb’s law, while, simultaneously, GO forms π–metal cation conjugates between metal cations (e.g., Mg²⁺ and Ca²⁺), thus limiting metal cation transport across the membrane. During the DD process, higher NH₄⁺ concentrations resulted in a longer time to reach Donnan equilibrium and higher NH₄⁺ flux, while increased Mg²⁺ concentrations resulted in lower NH₄⁺ flux (from 0.414 to 0.213 mol·m⁻²·h⁻¹). Using the synergistic effect of electrostatic interaction and non-covalent cross-linking, the designed membrane, referred to as GO-PEI (20) and prepared by a 20 min impregnation in the GO-PEI mixture, exhibited an NH₄⁺ transport rate of 0.429 mol·m⁻²·h⁻¹ and a Mg²⁺ transport rate of 0.003 mol·m⁻²·h⁻¹ in single-salt solution tests and an NH₄⁺/Mg²⁺ selectivity of 15.46, outperforming those of the unmodified and PEI membranes (1.30 and 5.74, respectively). In mixed salt solution tests, the GO-PEI (20) membrane showed a selectivity of 15.46 (~1.36, the unmodified membrane) for NH₄⁺/Mg²⁺ and a good structural stability after 72 h of continuous operation. Therefore, this facile surface charge modulation approach provides a promising avenue for achieving efficient NH₄⁺-selective separation by modified CEMs. Full article

Graphene-based laminar membranes exhibit remarkable ion sieving properties, but their monovalent ion selectivity is still low and much less than the natural ion channels. Inspired by the elementary structure/function relationships of biological ion channels embedded in biomembranes, a new strategy is proposed herein to mimic biological K⁺ channels by using the graphene laminar membrane (GLM) composed of two-dimensional (2D) angstrom(Å)-scale channels to support a simple model of semi-biomembrane, namely oil/water (O/W) interface. It is found that K⁺ is strongly preferred over Na⁺ and Li⁺ for transferring across the GLM-supported water/1,2-dichloroethane (W/DCE) interface within the same potential window (-0.1-0.6 V), although the monovalent ion selectivity of GLM under the aqueous solution is still low (K⁺/Na⁺~1.11 and K⁺/Li⁺~1.35). Moreover, the voltammetric responses corresponding to the ion transfer of NH₄⁺ observed at the GLM-supported W/DCE interface also show that NH₄⁺ can often pass through the biological K⁺ channels due to their comparable hydration–free energies and cation-π interactions. The underlying mechanism of as-observed K⁺ selective voltammetric responses is discussed and found to be consistent with the energy balance of cationic partial-dehydration (energetic costs) and cation-π interaction (energetic gains) as involved in biological K⁺ channels. Full article

The possibility of targeted change of the properties of ion exchange membranes by incorporation of various nanoparticles into the membranes is attracting the attention of many research groups. Here we studied for the first time the influence of cerium phosphate nanoparticles on the physicochemical and transport properties of commercial anion exchange membranes based on quaternary ammonium-functionalized polystyrenes, such as heterogeneous Ralex^® AM and pseudo-homogeneous Neosepta^® AMX. The incorporation of cerium phosphate on one side of the membrane was performed by precipitation from absorbed cerium ammonium nitrate (CAN) anionic complex with ammonium dihydrogen phosphate or phosphoric acid. The structures of the obtained hybrid membranes and separately synthesized cerium phosphate were investigated using FTIR, P31 MAS NMR, EDX mapping, and scanning electron microscopy. The modification increased the membrane selectivity to monovalent ions in the ED desalination of an equimolar mixture of NaCl and Na₂SO₄. The highest selectivities of Ralex^® AM and Neosepta^® AMX-based hybrid membranes were 4.9 and 7.7, respectively. In addition, the modification of Neosepta^® membranes also increased the resistance to a typical anionic surfactant, sodium dodecylbenzenesulfonate. Full article

The selective separation of metal species from various sources is highly desirable in applications such as hydrometallurgy, water treatment, and energy production but also challenging. Monovalent cation exchange membranes (CEMs) show a great potential to selectively separate one metal ion over others of the same or different valences from various effluents in electrodialysis. Selectivity among metal cations is influenced by both the inherent properties of membranes and the design and operating conditions of the electrodialysis process. The research progress and recent advances in membrane development and the implication of the electrodialysis systems on counter-ion selectivity are extensively reviewed in this work, focusing on both structure–property relationships of CEM materials and influences of process conditions and mass transport characteristics of target ions. Key membrane properties, such as charge density, water uptake, and polymer morphology, and strategies for enhancing ion selectivity are discussed. The implications of the boundary layer at the membrane surface are elucidated, where differences in the mass transport of ions at interfaces can be exploited to manipulate the transport ratio of competing counter-ions. Based on the progress, possible future R&D directions are also proposed. Full article

This paper proposes the use of monovalent selective electrodialysis technology to concentrate the valuable sodium chloride (NaCl) component present in seawater reverse osmosis (SWRO) brine for direct utilization in the chlor-alkali industry. To enhance monovalent selectivity, a polyamide selective layer was fabricated on commercial ion exchange membranes (IEMs) through interfacial polymerization (IP) of piperazine (PIP) and 1,3,5-Benzenetricarbonyl chloride (TMC). The IP-modified IEMs were characterized using various techniques to investigate changes in chemical structure, morphology, and surface charge. Ion chromatography (IC) analysis showed that the divalent rejection rate was more than 90% for IP-modified IEMs, compared to less than 65% for commercial IEMs. Electrodialysis results demonstrated that the SWRO brine was successfully concentrated to 14.9 g/L NaCl at a power consumption rate of 3.041 kWh/kg, indicating the advantageous performance of the IP-modified IEMs. Overall, the proposed monovalent selective electrodialysis technology using IP-modified IEMs has the potential to provide a sustainable solution for the direct utilization of NaCl in the chlor-alkali industry. Full article