Power distribution in the single-pass multi-stage electrodialysis (SPM-ED) for brackish water desalination

Electrodialysis (ED) is able to produce drinking water from brackish sources through selective ion removal. ED can operate at different electrical potentials when configured in a single-pass multi-stage (SPM-ED) arrangement. This degree of freedom leaves doubts about how to distribute power among the stacks for better performance in salt removal and potential improvements in the system’s energy management. The limiting current density (LCD) is crucial in practical ED applications, as operating just below the LCD allows for the maximum ionic separation rate without violating electro-neutrality. This investigated the performance of a double stack SPM-ED system for brackish water desalination at varying salinities (0.58–15 g/L NaCl) and flow rates (73–100 L/h) under two distinct power distribution settings (LCD and 80 % LCD). The results indicated that increasing the salinity of the feed solution (0.58–15 g/L NaCl) and the fluid flow rate (73–100 L/h) raised the LCD for both the first and second stacks operating independently, with the second stack being more affected by the operational conditions due to its configuration. When both stacks operated together, they achieved higher salt removal. Hydraulic residence time and boundary layer thickness were identified as limiting factors affecting desalination as flow rates increased. Operating Stack 1 at 80 % LCD and Stack 2 at LCD maintained moderate SEC and higher current efficiency (CE) across all varying salinities. The findings suggest that employing staging in single-pass ED systems with different power distribution settings (80 % LCD for the first stack) can lead to enhanced salt removal, minimum specific energy consumption (SEC), and optimal current efficiency compared to operating at the LCD point.