Exploiting electroconvective vortices in electrodialysis with high-frequency asymmetric bipolar pulses for desalination in overlimiting current regimes

Electrodialysis (ED) intensification is introduced by application of asymmetric pulses of reverse polarity. Very short pulses (10 to 100 μs) at high frequencies (from 100 to 4000 Hz) were tested, modulating the amplitude of the pulses to adjust energy consumption. Their effect in Limiting Current Density (LCD) and resulting desalination performance were investigated under various operation modes. To fully exploit electroconvective vortices, oscilloscopic profiles were used to optimize the pulsed operation. Under such conditions, the LCD increased by up to 1.6 times compared to conventional ED. The results demonstrate an effective intensification of the desalination process using pulsed electrodialysis reversal (pEDR), with a significantly reduced time in overlimiting regimes (~43% less time compared with sub-limiting conditions), while maintaining a stable pH during the operation. The energy consumed under such overlimiting current conditions, however, increased by ~56% or 14% compared to conventional ED at sub-limiting or overlimiting current regimes, respectively. This new strategy for desalination is expected to decrease the capital costs of ED plants given the prospects of operation under reduced equipment sizes.