Membrane Fouling and Electrochemical Regeneration at a Sub-Stoichiometric TiO2 Reactive Electrochemical Membrane

In this study, a non-invasive and non-destructive electrochemical impedance spectroscopy (EIS) characterization method was used to study membrane fouling at a novel ultrafiltration (UF) reactive electrochemical membrane (REM). The REM was fabricated from a titanium dioxide UF precursor and converted to a substoichiometric titanium dioxide using a high temperature reduction method. The EIS method was used to spatially characterize membrane fouling by interpreting the EIS data using a theoretical transmission line model. Model simulations indicate that different modes of membrane fouling (e.g., pore blocking, pore constriction, and cake layer formation) produced distinct EIS spectra. The model was used to interpret experimental EIS data collected during filtration experiments in the presence of two model membrane foulants, humic acid and polystyrene microspheres. Results indicate that the transmission line model could accurately characterize membrane fouling and was used to aid in the development of a chemical free electrochemical regeneration method. Electrochemical regeneration was able to recover the flux of a fouled REM from 3% to between 76% and 99% of the initial flux over 5 continuous fouling/regeneration cycles for humic acid fouling and full flux recovery for polystyrene microsphere fouling. The operating cost of the electrochemical regeneration method is estimated at 1.3% of that for NaOH cleaning, which indicates the great promise of this new method for separation processes.