65 Figure 22 shows the polarization curves of MEAs using a HC-based polymer-bonded cathode as a function of cathode humidification. PEM dehydration and electrode flooding can be detected by hysteresis in the polarization curves when measured with increasing versus decreasing current. Driving force for the diffusion of ions is thus the electrochemical potential gradient, the sum of the chemical potential gradient, and the electrical potential gradient. The diffusion fluxes of cations and anions are interrelated, and occur in the same direction. The diffusion of each ion species occurs under a chemical potential gradient derived from a capillary pressure difference and an electrical potential gradient resulting from a difference in the mobility of the cation as well as the anion. During the densification of ionic compounds, material transport occurs mostly by diffusion with the material maintaining its stoichiometry. An electrostatic potential in the material affects the segregation of ions at the grain boundary, and further affects the grain boundary migration and grain growth. The transport of ions during the densification of ionic compounds occurs not only by a chemical potential gradient coming from a difference in capillary pressure but also by an electrical potential gradient derived from the difference in diffusivity between different ions. Kang, in Sintering, 2005 Publisher Summary 4 displays the schematic representation of the different membrane-based ZLD systems for the pretreatment and desalination of high-salinity shale gas wastewater. Their results show about 27% of decreasing in TDS levels after 7 hours of application of a low direct current electric field. have studied the efficiency of a laboratory-scale ED process as desalination treatment for flowback water from the Marcellus shale play. Their results emphasize the system suitability for long-term operation and high ion-removal efficiencies (up to 91%), which allows reaching the product water quality required for water reclamation. The authors have used coagulation as wastewater pretreatment before the ED desalination. have applied ED for the desalination of shale gas wastewater. However, further investigation on the membrane fouling mechanisms and operating conditions is still required to minimize treatment costs. Their results indicate energy consumption and related operating costs lower than those for conventional MVC evaporation.
In this study, the authors have also evaluated the optimal equipment size, energy requirements and process costs.
have developed a 10–stage ED system for the treatment of shale gas wastewater with salinities up to 192k ppm TDS. ĭespite the previous limitations, recent experimental studies in literature have demonstrated the potential of ED for the desalination of high-salinity wastewaters. Also, their high energy consumption and water production costs, along with the great fouling tendency and need for regular membrane cleaning are major drawbacks for their broad implementation in the industry. Their efficiency is very sensitive to several factors such as the wastewater salt concentration and flowrate, applied stack voltage, and membrane parameters (e.g., density, diffusion, etc. ED and EDR membrane processes can be used as post-treatment for TDS removal of treated wastewater from RO technology. The EDR separation process has the advantage of changing membrane polarity to control scaling and fouling. Caballero, in Current Trends and Future Developments on (Bio-) Membranes, 2019 4.3 Electrochemical Charge-Driven Processes: Electrodialysis and Electrodialysis ReversalĮD and EDR are electrochemical charge-driven membrane-based technologies, in which an electrical potential gradient work as driving force for the separation of dissolved ions across ion-selective membranes.
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