An Electrochemical Impedance Spectroscopy Study on Ion-Fouling of Forward Osmosis Membranes

Forward osmosis (FO) has been rapidly developed and employed in the industrial and environmental wastewater treatment, whose performance is affected profoundly by membrane fouling. Electrochemical impedance spectroscopy (EIS), as a nondestructive and low-cost evaluation technique, has been increasingly used for the characterization of membrane structures and membrane fouling. However, monitoring ion fouling of FO membranes is difficult with EIS due to the weak signal. In this work, the ion-fouling of various FO membranes was successfully characterized by EIS and the inductance variation was firstly utilized to interpret the degree of FO membrane fouling. Multi-walled carbon nanotubes (MWCNTs) and polydopamine (PDA) were modified onto the thin film nanofibrous composite membrane (#FO-0) as anti-fouling modification (#FO-MWCNTs and #FO-PDA), respectively. The structural measurements of #FO-0, #FO-MWCNTs, and #FO-PDA were achieved by a two-electrode EIS system. Then the ion fouling of FO membranes was monitored by a four-electrode EIS system. Through the equivalent circuit fitting, the correlation between the inductance variation and the membrane fouling was established. The FO experiments further validated the effectiveness of the proposed EIS method. The results indicate that inductance as a detection index is expected to be a convenient tool for studying the ion-fouling phenomenon in the FO process.