Experimental visualization of leakage current in reverse electrodialysis and its effect on inorganic scaling

Abstract

In both electrodialysis (ED) and reverse electrodialysis (RED), the leakage current flowing through the feed/drain channels and liquid connections of the stack causes efficiency losses. However, there have been few reports on the effect of leakage current on inorganic scaling, a fouling phenomenon that increases the stack pressure and decreases electric power. In large-scale RED systems with high stack voltages of several tens of volts, water electrolysis is inevitable despite the presence of redox couples, and the resulting increased pH caused by the water reduction reaction leads to severe inorganic scaling. Water dissociation in a bipolar membrane (BPM) can reduce the flux of hydroxide ions across the effective working area, which allows the lateral leakage current along the BPM surface to be visualized by a specific pattern of inorganic precipitates moving from the bottom to the top of the BPM surface. In addition, the change in the area occupied by inorganic precipitates was evaluated as a function of the internal resistance of the stack and the resistance of the distributor connecting the compartment and feed channel. The findings highlight the importance of proper stack design in minimizing leakage-current-related efficiency losses and inorganic/organic fouling in real large-scale RED and ED systems.