Switching selectivity of carboxylic acids and associated physico-chemical changes with pH during electrodialysis of ternary mixtures

Electrodialysis as a potential technology for 4-nitrophenol abatement from wastewater

4-Nitrophenol is a widely used emerging pollutant in various industries, including the production of agrochemicals, drugs, and synthetic dyes. Due to its potential environmental harmful effects, there is a need to study its reuse and removal from wastewater. This study used electrodialysis technology to separate 4-nitrophenol ions using a four-compartment stack. The effects of supporting electrolyte concentration, pH, voltages, and current density on the performance of electrodialysis for separating 4-nitrophenol were investigated. A high extraction percentage of 77% was achieved with low energy consumption (107 kWh kg-1) when high 4-nitrophenol flows and transport numbers were reached.

Comparison of the Electrodialysis Performance in Tartrate Stabilization of a Red Wine Using Aliphatic and Aromatic Commercial and Modified Ion-Exchange Membranes

The application of electrodialysis for tartrate stabilization and reagent-free acidity correction of wine and juices is attracting increasing interest. New aliphatic membranes CJMC-3 and CJMA-3 and aromatic membranes CSE and ASE were tested to determine their suitability for use in these electrodialysis processes and to evaluate the fouling of these membranes by wine components for a short (6-8 h) operating time. Using IR spectroscopy, optical indication and measurement of surface contact angles, the chemical composition of the studied membranes, as well as some details about their fouling by wine components, was clarified. The current-voltage charsacteristics, conductivity and water-splitting capacity of the membranes before and after electrodialysis were analyzed. We found that in the case of cation-exchange membranes, complexes of anthocyanins with metal ions penetrate into the bulk (CJMC-3) or are localized on the surface (CSE), depending on the degree of crosslinking of the polymer matrix. Adsorption of wine components by the surface of anion-exchange membranes CJMA-3 and ASE causes an increase in water splitting. Despite fouling under identical conditions of electrodialysis, membrane pair CJMC-3 and CJMA-3 provided 18 ± 1 tartrate recovery with 31 · 10^-3 energy consumption, whereas CSE and ASE provided 20 ± 1% tartrate recovery with an energy consumption of 28 · 10^-3 Wh, in addition to reducing the conductivity of wine by 20 ± 1%. The casting of aliphatic polyelectrolyte films on the surface of aromatic membranes reduces fouling with a relatively small increase in energy consumption and approximately the same degree of tartrate recovery compared to pristine CSE and ASE.

Effect of Pulsed Electric Field on the Electrodialysis Performance of Phosphate-Containing Solutions

A comparative analysis of mass transfer characteristics and energy consumption was carried out for the electrodialysis recovery of P^V from of NaH₂PO₄ solutions and multicomponent (0.045 M Na_xH_(3-x)PO₄, 0.02 M KCl, 0.045 M KOH, 0.028 M CaCl₂, and 0.012 M MgCl₂, pH 6.0 ± 0.1) solution in conventional continuous current (CC) and pulsed electric field (PEF) modes. The advantages of using PEF in comparison with CC mode are shown to increase the current efficiency and reduce energy consumption, as well as reduce scaling on heterogeneous anion-exchange membranes. It has been shown that PEF contributes to the suppression of the "acid dissociation" phenomenon, which is specific for anion-exchange membranes in phosphate-containing solutions. Pulse and pause lapse 0.1 s-0.1 s and duty cycle 1/2 were found to be optimal among the studied PEF parameters.

Recovery of Nutrients from Residual Streams Using Ion-Exchange Membranes: Current State, Bottlenecks, Fundamentals and Innovations

The review describes the place of membrane methods in solving the problem of the recovery and re-use of biogenic elements (nutrients), primarily trivalent nitrogen N^III and pentavalent phosphorus P^V, to provide the sustainable development of mankind. Methods for the recovery of NH₄⁺ − NH₃ and phosphates from natural sources and waste products of humans and animals, as well as industrial streams, are classified. Particular attention is paid to the possibilities of using membrane processes for the transition to a circular economy in the field of nutrients. The possibilities of different methods, already developed or under development, are evaluated, primarily those that use ion-exchange membranes. Electromembrane methods take a special place including capacitive deionization and electrodialysis applied for recovery, separation, concentration, and reagent-free pH shift of solutions. This review is distinguished by the fact that it summarizes not only the successes, but also the “bottlenecks” of ion-exchange membrane-based processes. Modern views on the mechanisms of NH₄⁺ − NH₃ and phosphate transport in ion-exchange membranes in the presence and in the absence of an electric field are discussed. The innovations to enhance the performance of electromembrane separation processes for phosphate and ammonium recovery are considered.

Influence of Electroconvection on Chronopotentiograms of an Anion-Exchange Membrane in Solutions of Weak Polybasic Acid Salts

Visualization of electroconvective (EC) vortices at the undulated surface of an AMX anion-exchange membrane (Astom, Osaka, Japan) was carried out in parallel with the measurement of chronopotentiograms. Weak polybasic acid salts, including 0.02 M solutions of tartaric (NaHT), phosphoric (NaH₂PO₄), and citric (NaH₂Cit) acids salts, and NaCl were investigated. It was shown that, for a given current density normalized to the theoretical limiting current calculated by the Leveque equation (i/i_lim^theor), EC vortex zone thickness, d_EC, decreases in the order NaCl > NaHT > NaH₂PO₄ > NaH₂Cit. This order is inverse to the increase in the intensity of proton generation in the membrane systems under study. The higher the intensity of proton generation, the lower the electroconvection. This is due to the fact that protons released into the depleted solution reduce the space charge density, which is the driver of EC. In all studied systems, a region in chronopotentiograms between the rapid growth of the potential drop and the attainment of its stationary values corresponds to the appearance of EC vortex clusters. The amplitude of the potential drop oscillations in the chronopotentiograms is proportional to the size of the observed vortex clusters.

Electro-membrane separations in biotechnology

Membrane processes are of crucial importance for downstream processing in biotechnology. This is due to their selectivity and the mild operating conditions, enabling to extract target products without damages caused by overheating and chemical agents. Besides the most spread membrane processes like ultrafiltration and reverse osmosis, electrodialysis is very important for removal and extraction of electrically charged products, i. e. anions of organic acids, some antibiotics, etc. The electrodialysis process can be organized in batch or continuous mode. On the other hand, in the electro-crossflow filtration, the transport of target solutes across the membrane is guided by two main driving forces, the transmembrane pressure and the electric potential. This combination enables various possibilities for more selective and efficient downstream processing in biotechnology. This chapter provides a brief overview of recent achievements of electrodialysis in selected bioproducts separations and recovery. A special focus, including original experimental data, is then given to electro-filtration, which is a powerful tool creating new opportunities for performing separations on the basis of both electric charge and particle size differences.

Partial Fluxes of Phosphoric Acid Anions through Anion-Exchange Membranes in the Course of NaH2PO4 Solution Electrodialysis

Electrodialysis (ED) with ion-exchange membranes is a promising method for the extraction of phosphates from municipal and other wastewater in order to obtain cheap mineral fertilizers. Phosphorus is transported through an anion-exchange membrane (AEM) by anions of phosphoric acid. However, which phosphoric acid anions carry the phosphorus in the membrane and the boundary solution, that is, the mechanism of phosphorus transport, is not yet clear. Some authors report an unexpectedly low current efficiency of this process and high energy consumption. In this paper, we report the partial currents of H2PO4-, HPO42-, and PO43- through Neosepta AMX and Fujifilm AEM Type X membranes, as well as the partial currents of H2PO4- and H+ ions through a depleted diffusion layer of a 0.02 M NaH2PO4 feed solution measured as functions of the applied potential difference across the membrane under study. It was shown that the fraction of the current transported by anions through AEMs depend on the total current density/potential difference. This was due to the fact that the pH of the internal solution in the membrane increases with the growing current due to the increasing concentration polarization (a lower electrolyte concentration at the membrane surface leads to higher pH shift in the membrane). The HPO42- ions contributed to the charge transfer even when a low current passed through the membrane; with an increasing current, the contribution of the HPO42- ions grew, and when the current was about 2.5 ilimLev (ilimLev was the theoretical limiting current density), the PO43- ions started to carry the charge through the membrane. However, in the feed solution, the pH was 4.6 and only H2PO4- ions were present. When H2PO4- ions entered the membrane, a part of them transformed into doubly and triply charged anions; the H+ ions were released in this transformation and returned to the depleted diffusion layer. Thus, the phosphorus total flux, jP (equal to the sum of the fluxes of all phosphorus-bearing species) was limited by the H2PO4- transport from the bulk of feed solution to the membrane surface. The value of jP was close to ilimLev/F (F is the Faraday constant). A slight excess of jP over ilimLev/F was observed, which is due to the electroconvection and exaltation effects. The visualization showed that electroconvection in the studied systems was essentially weaker than in systems with strong electrolytes, such as NaCl.