Effect of temperature gradients in (reverse) electrodialysis in the Ohmic regime

Electrodialysis (ED) and reverse electrodialysis (RED) are processes for the production of desalinated water (ED) and power (RED). Temperature of the feed streams can strongly influence the performance of both processes. In this research, commercial membranes are used for the investigation of temperature and temperature gradients on ED and RED processes. We find that the energy required for ED processes can be reduced by 9% if the temperature of one of the feed streams is increased by 20 degrees C, while maintaining the charge-selectivity of the membranes. The direction of the temperature gradient did not have a significant influence on the efficiency and selectivity of ED in the Ohmic regime. In RED, we find an increase in obtained gross power density over 25% for the process when one feed stream is heated to 40 degrees C instead of 20 degrees C. This work experimentally demonstrates that utilization of low-grade waste heat from industrial processes can yield significant reduction of energy costs in ED processes, or result in higher power densities for RED systems where the increase in temperature of a single feed stream already yields significant efficiency improvements.