Current utilization in electrodialysis: Electrode segmentation as alternative for multistaging

Electrodialysis (ED) is a membrane-based desalination technology that uses an electric field to force the migration of ions through ion-selective anion and cation exchange membranes. Salt water is highly conductive but during this desalination process, the produced water becomes more dilute and therefore less conductive. This effect causes a non-homogeneous current distribution, making the desalination performance less efficient in the direction of the flow. To mitigate this, we experimentally compare two configurations for different current distribution regimes, voltages and feed flow velocities: a fully separated system of multiple laboratory-scale ED stacks, i.e. a multistage ED, and a segmented electrode system that consists of one stack with multiple separated electrodes. The segmented electrode showed low voltage and higher desalination degree compared to multistage for operation at uniform current. For non-uniform current, no difference in efficiency was observed. For low voltage operation the segmented electrode showed, due to current redistribution, a higher desalination degree compared to the multistage ED configuration. To reach drinking water quality, a multistage operated at a potential difference of at least 4 V was necessary. The work demonstrates that electrode segmentation in ED can be effective for bulk desalination.