In situ membrane monitoring

A method of in situ monitoring of a membrane separation system wherein the membrane separation system includes a separation membrane, and a pair of electrodes separated by the separation membrane, the method comprising:

• using the membrane separation system to separate a feed solution into a permeate and a residue, where the permeate passes through the separation membrane and the residue remains on a feed side of the separation membrane;
• applying an electrical alternating current stimulus through the separation membrane at one or more frequencies by applying the electrical stimulus between the pair of electrodes separated by the separation membrane;
• measuring a response electrical potential between the pair of electrodes separated by the separation membrane;
• comparing the electrical stimulus and the response electrical potential to determine a complex electrical impedance of the separation membrane at the one or more frequencies;
• determining electrical conduction and electrical polarization properties of the separation membrane from the complex electrical impedance of the separation membrane at the one or more of frequencies;
• and
• monitoring changes of the electrical conduction and electrical polarization properties of the separation membrane indicative of changes in performance of the separation membrane.