Implementing Electrochemical Impedance Spectroscopy for the In Situ Analysis Of Conducting-Membrane Fouling

Abstract

AbstractAs natural resource scarcity and industrial productivity continue to rise, membrane filtration technologies provide a compelling solution for the production of clean water. Membranes are versatile, energy-efficient, and highly effective, yet they suffer from the indomitable problem of fouling. Abundant research has been conducted on this topic, but new methods for understanding and assessing fouling are still emerging, and are nevertheless needed. The present work endeavors to study membrane fouling from yet another perspective using a powerful electrochemical technique known as electrochemical impedance spectroscopy (EIS). EIS is a non-destructive electrical perturbative method, thus it can be performed during filtration. While some research groups have applied EIS for membrane characterization, none have yet incorporated conductive polymeric membranes into the electrochemical setup. The primary objectives of this study were to (1) synthesize a robust and sufficiently conductive polymeric membrane for use as a working electrode; (2) develop a non-invasive non-Faradaic EIS method to characterize membrane fouling in real time; (3) separate contributions to total fouling from processes happening on the membrane surface and within the interior pore network. Membrane fouling was studied using three model foulants, bovine serum albumin (BSA), humic acid, and colloidal silica in a supporting electrolyte of phosphate buffered saline (PBS) and potassium nitrate (KNO3), respectively. To better understand the spatial position and magnitude of fouling, EIS spectra were interpreted by fitting equivalent circuits informed by the physical structures of the membrane surface and interior. Data from the EIS fouling tests showed good agreement between changes in impedance, conductance, and capacitance and reduction in permeate flow, which is the conventional parameter used to monitor fouling severity. The conductive coating also allowed for fouling to be differentiated between the surface and interior layers of the membrane. Moreover, experiments with feed solutions containing separate foulants in different solution chemistries verified that EIS is sensitive enough to differentiate between various membrane fouling effects as well as irreversible fouling phenomena. These results suggest that conductive membranes can be used alongside EIS to spatially and temporally characterize membrane fouling as it happens in real time without the need to remove or damage the membrane for analysis.