Investigation of pulsed electric field operation as a chemical-free anti-scaling approach for electrodialysis desalination of brackish water

Abstract

Pulsing the electric field is a strategy to mitigate concentration polarization in electrodialysis (ED). To evaluate the effects of the pulsed operation on the extent and kinetics of salt formation, a series of nine-day batch experiments were performed for pulsed and conventional ED (PED and CED, respectively). The pulsing duty cycle was set to 50 % and frequencies of 0.5 and 5 Hz were selected according to the divalent to monovalent ion fluxes calculated using the developed model. The results indicated that membrane scaling decreased in PED, with minimal scaling detected under 0.5 Hz. Concentration polarization moderation and lower supersaturation of the scale-forming ions in boundary layers as well as the removal of formed crystals from the stack during the pausing periods contributed to the reduction in scale formation. Considering that the scale-forming ions were transported to the concentrate channel within the first 50 % of the batch time, a novel hybrid pulsed-conventional operation was theorized that leveraged pulsing early in the batch and switched to constant voltage later to expedite the desalination process. Hybrid operation improved the desalination rate compared to a pure PED system and could potentially reduce membrane scaling by decreasing the recirculation period of the concentrate stream.