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Abstract: Recent electrodialysis (ED) research put forward the way a mineral fouling growth occurring on cation-exchange membrane (CEM) was reduced by a pulsed electric field (PEF) ratio of repetitive current pulsation (ton/toff=10s/10s). The current study applies a set of PEF on-duty ratios of even higher frequencies to further control membrane fouling, and to maximize the process performance during the ED of a solution containing a high Mg/Ca ratio (2/5). The on-duty ratios were two PEFs ratio 0.5 (ton/toff=5s/10s, and 10s/20s), two PEFs ratio 1 (ton/toff=5s/5s, and 10s/10s), and two PEFs ratio 2 (ton/toff=10s/5s, and 20s/10s). The repetitive pulsation of the ratios 10s/5s and 5s/5s enhanced the process performance (DRs of 58.48% and 59.64%), and suppressed CEM fouling on the diluate side. The ratio 10s/5s having a pause shorter than the pulse reduced fouling also on the concentrate side through steady water splitting proton generation that neutralized OH− leakage through CEM. No severe mineral precipitation occurred on AEM. The application of optimized water splitting proton-barriers for mineral fouling control is crucial. [Copyright &y& Elsevier]

Abstract: Mineral fouling of cation-exchange membrane (CEM) was recently reduced by pulsed electric fields (PEFs) during the electrodialysis (ED) of solutions containing high Mg2+/Ca2+ ratios. However, a fouling layer appeared on the diluate side of anion-exchange membrane (AEM) once the pause lapse surpassed certain duration. Recent studies presented a multilayer mineral growth on CEM, but the case of AEM needs yet to be cleared. The current study reveals the mechanisms involved in AEM fouling growth when applying pulse modes of current in comparison with dc current. The results showed that dc current generated steady proton barriers given by water splitting at AEM interfaces that impeded fouling on both membrane sides. The higher frequency of PEF ratio 1 (Ton/Toff=10s/10s) acted removing completely an initial mineral deposit on the concentrate side of AEM, keeping it clean after two and three consecutive runs. Particularly, an undesirable brucite layer was formed on the AEM-diluate side for longer pause lapses as for a PEF ratio 0.3 (Ton/Toff=10s/33.3s) current regime. This structure caused violent water splitting resulting in amorphous magnesium hydroxide formation and consequently in fouling precipitation on the concentrate side during a third run through current exaltation. [Copyright &y& Elsevier]

Abstract: Pulsed electric fields (PEFs), hashed modes of current consisting in the application of a constant current density during a fixed time (Ton) followed by a pause lapse (Toff), were recently demonstrated as an effective alternative for mineral fouling mitigation and process intensification during electrodialysis (ED) treatments. Recent ED studies have continuously reported a considerable mineral fouling formation on ion-exchange membranes, especially during the demineralization of solutions containing a high Mg/Ca ratio and a basified concentrate solution. The aim of this study was to evaluate the process performance under two different PEF conditions on a mineral solution containing a mineral mixture giving a high Mg2+/Ca2+ ratio of 2/5. Two different pause-lapse durations (PEF ratio 1 (Ton/Toff 10s/10s); PEF ratio 0.3 (Ton/Toff 10s/33.3s)) during consecutive ED treatments and their comparison with dc current were evaluated at a current density of 40mA/cm2. Our results showed that PEFs resulted in an intensification of ED process, enhancing the demineralization rates (DRs), reducing the system resistance (SR), and reducing the fouling and energy consumption (EC). PEF ratio 1 was the most optimal condition among the current regimes applied, leading to faster and higher demineralization rates due to a lower fouling and with low energy consumption during all consecutive runs. [Copyright &y& Elsevier]

Abstract: The present study aimed the characterization of the fouling formed on anion-exchange membrane during electrodialysis treatment of model salt solutions at different Mg/Ca ratio (0, 1/20, 1/10, 1/5 and 2/5). The membrane fouling was characterized by membrane parameters (membrane thickness and electrical conductivity) and identified by membrane surface analysis (elemental analysis and X-ray diffraction). The mineral deposit was identified as Ca(OH)2 when no magnesium was present in the model salt. As soon as magnesium was present in the model salt solution for neutral pH(concentrate) conditions a mix between CaCO3 and Ca(OH)2 was formed. This study is the first one to report the influence of magnesium in solution on the formation of CaCO3 fouling at the interface of anion-exchange membrane during electrodialysis. [Copyright &y& Elsevier]

Abstract: Electrodialysis is based on the migration of charged species through perm-selective membranes under an electric field. Fouling, which is the accumulation of undesired solid materials at the interfaces of these membranes, is one of the major problems of this process. The aim of the present work was to investigate the nature and the morphology of fouling observed at different Mg/Ca ratios (, 1/20, 1/10, 1/5, 2/5) on cation-exchange membranes (CEM) during conventional electrodialysis treatments. It appeared that for , the fouling observed on the surface in contact with the basified concentrate was formed of only Ca(OH)2. As soon as magnesium was introduced into the solution treated, CaCO3 was observed. Furthermore, the X-ray diffraction results also identified the CaCO3 observed as calcite. To our knowledge, this is the first time that the presence of magnesium has been demonstrated to induce a CaCO3 fouling on CEM during electrodialysis. [Copyright &y& Elsevier]

Abstract: The aim of this work was to study the effect on the fouling of anion-exchange membranes (AEM) of (1) the pH value of the concentrate solution and (2) the composition in calcium, carbonate, and protein of the diluate solution to be treated by conventional electrodialysis. It appeared that after demineralization of solutions containing CaCl2 using a concentrate solution maintained at a pH value of 7 or 12, mineral fouling appeared on the AEM surface in contact with the concentrate. The mineral deposits presented a cylindrical filament shape for conditions with a concentrate solution pH value of 7, while, for a pH value of 12, the mineral deposit had a crumbly and spongy texture formed by irregular aggregates. The nature of the fouling was identified as a calcium phosphate with or without calcium hydroxide. In addition, gel-like protein fouling was detected on the AEM surface in contact with the diluate after demineralization procedures using a concentrate pH value of 2 or 7, regardless of the mineral composition of the diluate. [Copyright &y& Elsevier]

Abstract: The aim of this work was to study the effect of a concentrate solution pH value and of the composition in calcium, carbonate, and protein of a diluate solution to be treated by conventional electrodialysis on the fouling of cation-exchange membranes (CEM). It appeared that after demineralization of solutions containing CaCl2 and CaCl2 +Na2CO3 using a concentrate solution maintained at a pH of 12, mineral fouling appeared on both sides of the CEM. The nature of the deposits was identified as calcium hydroxide and/or carbonate on both surfaces. The mineral fouling presented an aggregation-like crystal following a carnation-like pattern of aggregates of small rhombohedral crystals with CaCl2 added alone, while CaCl2 +Na2CO3 yielded a smoother spherical crystal. Protein fouling was detected only on the CEM surface in contact with the diluate after demineralization of a solution containing CaCl2 +Na2CO3 using a concentrate pH value of 2. [Copyright &y& Elsevier]

Abstract: During electrodialysis (ED) treatment of solutions with different Mg/Ca ratios (R =0, 1/20, 1/10, 1/5 and 2/5) and in different pH conditions (acid, neutral and basic), foulings on ion-exchange membranes were previously characterized and identified, by the way of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. A mineral fouling was observed in neutral and basic conditions (for R =1/5 and 2/5) on the anion-exchange membrane (AEM) concentrate side and in basic conditions on the cation-exchange membrane (CEM) concentrate side as well as on the diluate side for R =1/5 and 2/5. The objectives of this present work were to link the morphological characterization and identification of membrane fouling to electrodialytic parameters and cation migration kinetics. It appeared that the CEM permselectivity was severely affected in basic conditions for R ≥1/5. The consequence of this alteration was the migration of OH− through the CEM, a pH increase in the diluate compartment and different treatment durations. The calcite observed on AEM concentrate side for Mg/Ca≥1/5 would be due first to the particular operating conditions such as the recirculation of the concentrate solution, and also to the supersaturated conditions reached or not at the AEM interface and favourable pH conditions. [Copyright &y& Elsevier]

Abstract: The aim of this work was to study the effect of the concentrate solution pH and the composition in calcium, carbonate and protein of the diluate solution to be treated by conventional electrodialysis on the fouling of ion-exchange membranes. Conductivity, system resistance, pH of the diluate and cation migration were monitored to follow the evolution of the demineralization. Total cation migration was similar for all conditions although different forms of fouling were identified after three consecutive 100min electrodialysis treatments. The nature of fouling and the membrane surface fouled depended on the concentrate pH value, the diluate mineral composition and the intrinsic composition of the whey isolate. Once conditions leading to membrane fouling were identified, an alternative configuration for our electrodialysis stack is proposed to prevent fouling onset. [Copyright &y& Elsevier]

Abstract: Recent work carried-out on conventional electrodialysis of model solutions containing whey proteins and/or salts (CaCl2, MgCl2) showed significant ion-exchange membrane foulings, one of the major problems of this process. The purpose of this study was to demonstrate the feasibility of using pulsed electrical field in a new electrodialysis (ED) configuration to prevent the ion-exchange membrane fouling and to enhance the ED process. The main objectives of the present work were to test a new cell configuration and to study the effect of pulsed electrical field on fouling and electrodialytic parameters. The results obtained showed that a pulsed electrical field coupled to a separated feed of the concentrate compartments led to the higher demineralization rate (79.5%) without membrane fouling and excessive energy consumption compared to the other treatments. This study also showed that the pulsed electrical field applied in combination with the classical configuration decreased the mineral fouling observed in basic conditions (16% for Ca and 24% for Mg) and the protein fouling observed in acidic condition (decrease by 18%). [Copyright &y& Elsevier]

Abstract: Electrodialysis (ED) is a membrane process used on a large scale. However, one of the common problems is fouling of ion-exchange membranes stacked in the cell. The use of pulsed power, consisting in applying a constant current density during a fixed time of application (T on) followed by a pause duration (T off), was demonstrated recently as an effective fouling mitigation method for electrodialysis. Up until now, no work has investigated the potential of electrodialysis using pulsed electric field on protein fouling. The aim of the present work was to study the influence of pulsed electric field (PEF) with a low frequency square shaped periodic signal (T on =10s–T off =10s, T on =10s–T off =40s) in comparison with dc current during electrodialysis of a casein solution at different current densities (10, 20 and 30mA/cm2) on membrane fouling. It appeared from these results that PEF, under certain conditions of pulse, would avoid fouling on anion-exchange membranes. For 10s–40s pulsed electric field conditions, no fouling was observed with any density, while for 10s–10s PEF conditions, fouling appeared only at current density over 10mA/cm2. dc current, whatever the current density conditions, led to a fouling on the diluate side of the AEM. Furthermore, when fouling occurred, magnitude layer thickness and dry weight increased with the applied current density. The nature of the fouling was identified as 97% protein. The protein fouling would be due to the dissociation of water molecules and/or heat increase at the anion-exchange membrane interface. The relaxation time of the pulse would limit both phenomena on the membrane. [Copyright &y& Elsevier]