Experimental verification on real-time fouling analysis in crossflow UF of protein solutions by electrical impedance spectroscopy

Background: Fouling control and monitoring of the membranes during a pressure-driven separation process is critical for practical operation and applications. Methods: In this work, a non-constructive technique electrical impedance spectroscopy (EIS) was applied to detect fouling development during crossflow ultrafiltration (UF) of bovine serum albumin (BSA) solutions using polyethersulfone and cellulose acetate membranes with a molecular weight cut-off of 10 kDa and 20 kDa, respectively. Various electrical impedances due to the electrolyte solution, the fouled layer, and the membrane itself were determined at different transmembrane pressures (68.9, 137.9, and 206.8 kPa), BSA concentrations (100, 500, and 1000 mg/L), and pH values (3.0, 5.0, and 8.6) based on a proposed equivalent circuit diagram. On the other hand, the filtration resistances due to the solute adsorption, concentration polarization, cake formation, and membrane itself were also determined according to a resistance-in-series model. Significant findings: Correlations between the variations of various electrical impedances and filtration resistances with time were finally examined to justify the validity of EIS technique applied in crossflow UF processes. This work has verified from flux decline experiments that EIS was a powerful tool in monitoring fouling development in crossflow UF processes, particularly with a predominant contribution of the fouled layer resistance of to the overall transport.