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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: The aim of this study was to reveal the mechanisms ruling a fouling growth on both sides of a CMX-SB cation-exchange membrane (CEM), run after run during three consecutive electrodialysis (ED) treatments. A model solution containing a high magnesium/calcium ratio (2/5) was demineralized under two different pulsed electric field (PEF) on-duty ratios and dc current. The results showed a series of mechanisms ruling a multilayer mineral fouling growth and its delay by PEFs. The nature of the fouling layer, during a first run, depended on the diluate pH-value evolutions and the ion migration rates through the membrane. A subsequent multilayer fouling growth during consecutive treatments was ruled by the already formed mineral layers, where gradual sieving effects inverted the migration rates and led to a multistep crystal growth. Calcium carbonate grew on the diluate side of CEM, starting from its amorphous phase to then crystallize in a coexisting presence of aragonite and calcite. Amorphous magnesium hydroxide appeared on CEM apparently through fouling dehydration ruled by the mineral layers themselves and by overlimiting current regimes. A delayed fouling growth was observed for PEF ratio 0.3. A long pause lapse during pulse modes was demonstrated as an important parameter for fouling mitigation. [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]

Pulsed electric field (PEF) can affect positively the membrane scaling mitigation and the intensification of electrodialytic (ED) process. Recent studies considered the use of PEF with relatively long pulse/pause conditions (5-40 s). The present work was focused on the application of specific PEF conditions with short pulse/pause duration as a following perspective step in improving demineralization. Therefore, in this study six conditions were tested (1 s/0.33 s, 1 s/1 s, 2 s/0.5 s, 2 s/0.67 s, 3 s/0.33 s, 3 s/1 s) in order to investigate the influence of short PEF lapses and to find the optimum among all PEF conditions. Results indicate that PEF conditions of 2 s/0.5 s and 2 s/0.67 s allowed the highest demineralization rates. A decrease of scaling on the cation-exchange membrane surface in comparison with previous data was observed in all PEF conditions. In addition, absence of scaling on the anion-exchange membrane was observed for the first time in such extreme conditions of demineralization and solution composition. These results highlighted the successful use of short pulse/pause lapses during electrodialysis. [ABSTRACT FROM AUTHOR]

Abstract: Electromembrane process yields can be enhanced by using pulsed electric field. Electrodialysis experiments carried out on brackish water solutions show that the same level of desalination can be reached faster under pulsed field conditions. A model based on the Nernst–Planck equations is developed to explain this behavior. [Copyright &y& Elsevier]

Two different lots of cation-exchange membranes (CMX-SB-1 and -2) were compared in terms of physico-chemical and electrochemical properties. Further, electrodialysis with both membrane lots was carried out under pulsed electric field (PEF) on model solution containing Ca 2 + and Mg 2 + ions. It was found that CMX-SB-1 was more scaled with prevalence of Ca compounds on both membrane sides. CMX-SB-2 contained less scaling with prevalence of Ca compounds on diluate side and Mg compounds on concentrate side. The different behavior of membranes was hypothesized to be due to the differences in their intrinsic structure and surface properties. The CMX-SB-2 has higher concentration of fixed charges and water content, which cause larger size of inner channels and easier transport of Mg 2 + ; the structural organization of CMX-SB-1 with presumably narrower nanochannels leads to the slower Mg 2 + migration and their low quantity on CMX-SB-1 concentrate side. Additionally, the surface hydrophobicity and heterogeneity of CMX-SB-2 is higher than that of CMX-SB-1 what allow easier water slip on CMX-SB-2 surface facilitating electroconvection. Thus, more scaled CMX-SB-1 membrane with less developed electroconvection yielded lower values of demineralization (59.0% and 57.2% for 2 s/0.5 s and 2 s/0.67 s PEF respectively) than the less scaled CMX-SB-2 with better developed electroconvection (77.3% and 75.2% respectively). [ABSTRACT FROM AUTHOR]

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]