Characterization of fouling and concentration polarization in ion exchange membrane by in-situ electrochemical impedance spectroscopy

The electrochemical impedance spectroscopy (EIS) was used to monitor the ion transport of the ion exchange membrane (IEM) interface with ectopic monitoring. But the general monitoring methods were lack of the information in concentration polarization (CP) and fouling formation. In this paper, an in-situ method for monitoring the ion mass transfer by EIS was established which can distinguish the contribution of membrane fouling and CP. The results showed that the in-situ EIS could more comprehensively monitor the desalination process. Membrane fouling, especially the formation of fouling layer on membrane surface, promoted the CP at membrane/solution interface. This was mainly because the ion mass transfer was hindered by serious membrane fouling, so that the ion concentration near the membrane surface was higher than that of the solution, and this phenomenon was gradually aggravated with the increase of membrane fouling. The recovery of membrane performances were assessed by different cleaning methods, it was found that the chemical cleaning effect was superior to inverted electrode according to online EIS. When irreversible fouling was formed in the membrane and then the fouled membrane was chemically cleaned, the formation of the fouling layer was accelerated and the CP was aggravated during membrane reuse.