Effect of membrane area and membrane properties in multistage electrodialysis on seawater desalination performance

Abstract Energy consumption for seawater desalination by multistage electrodialysis (ED) is lowered last decade from 6.6 kWh/m3 to 3.6 kWh/m3. In multistage ED the driving force can be adapted to the conditions of that specific desalination stage. In this study however, we varied the membrane area, the residence time, and the membrane properties in the different stages to investigate the transport mechanisms of salt and osmotic water to improve the desalination performance of multistage ED even further. Residence time affects both salt fluxes and osmotic transport. We showed that a longer residence time is beneficial in the first stages, in combination with a shorter residence time in the later stages. The gradient in the later stages between the diluate and concentrate compartments is large, and a short residence time decreases the undesired osmotic flow, resulting in lower product (diluate) loss. Moreover, the use of membranes with lower water permeability in the last three stages results in state-of-the-art energy consumptions of 2.2 kWh/m3 for the desalination of 510 mM NaCl to 5.4 mM NaCl using multistage ED. This obtained diluate salinity more than meets the WHO standard for drinking water of 8.5 mM NaCl.