Seawater predesalination with electrodialysis

• ED seems a suitable technique to predesalinate seawater.
• Electro-osmotic water transport is proportional to the applied current density.
• Stack resistance causes the main energy loss in an electrodialysis system.
• Applied current density > 50 A/m2 leads to minor back diffusion and water losses.
• Application of ED potentially leads to desalination energy reduction compared to SWRO.

The suitability of ED for seawater desalination was investigated and we quantified the energy losses that play a role in electrodialysis. The combination of electrodialysis (ED) and brackish water reverse osmosis (BWRO) is presented as an alternative desalination strategy for seawater reverse osmosis (SWRO). Experiments have been performed with a recycling batch electrodialyzer. From this we conclude that in most cases the membrane stack is responsible for the main energy loss in the system. Energy losses due to water transport are generally low. At low applied current density, osmotic water transport is relatively large and as such the energy loss, while electroosmosis was found to be directly proportional to the applied current density. The relative energy loss caused by back diffusion was found to be only of minor importance for higher current densities and was only more pronounced at the lowest applied current density of 10 A/m2. Combining ED with BWRO in a hybrid system does not lead to a reduction in energy consumption compared to ED as standalone technique, when the applied current density becomes lower than 50 A/m2. At low applied current density (10 A/m2) ED can perform desalination energetically cheaper at lower operational costs than SWRO.