Evaluation of chemical free cleaning techniques for reverse electrodialysis stacks fed with natural waters

Reverse electrodialysis (RED) is a promising technology to harvest salinity gradient power (SGP) that is available where fresh and sea water mix, using anion (AEM) and cation exchange membranes (CEM) in a stack. Fouling of the membranes is one of the main challenges for RED, since it leads to a reduction in attainable net power output. In this study, we combined the use of profiled ion-exchange membranes (200 μm thick compartments) with a pre-treatment by a dual media filter for both natural water streams (Lake Ijssel and Wadden Sea), with four different cleaning procedures: (i) increased flow, (ii) reverse and increased flow, (iii) reverse flow and feed switch, and (iv) air sparging. Cleaning with air sparging was the most effective technique, limiting the pumping losses and not influencing the power generation capacity. The cleaning with reverse flow and feed switch also showed to be suitable, keeping the pressure drop losses lower than 100 mbar for both water streams. Post experiment membrane autopsy showed that CEMs were more subjected to particulate fouling than AEMs, and that a lower accumulation of fouling by particulate resulted in a higher concentration of humic acids and biofouling on the membrane surface.