High-throughput measurement and analysis of streaming potential and electroviscous effects in an alumina microfiltration membrane

Electrokinetic phenomena in microfiltration (MF) are among the key factors governing process performance and are recognized as important for understanding fouling phenomena and for developing mitigation technologies, including membrane design, process design, and optimization of operating conditions. However, due to the inconvenient nature of conventional methods for observing electrokinetic phenomena in MF systems, the relationship between electrokinetic phenomena and MF performance remains insufficiently understood. In this study, a high-throughput measurement setup for streaming potential (SP) and the electroviscous effect in an MF membrane over a wide range of KCl concentrations and pH values was developed. The KCl dependence of the SP and electroviscous effect, as well as the pH dependence of the zeta potential, were measured for an alumina MF membrane, and the analysis of the obtained profiles was demonstrated. From the analysis of KCl profile of SP, the surface charge density and pore radius were determined by curve fitting using a theoretical charged-capillary model, in addition to the determination of the zeta potential. Analysis of the pH profile of zeta potential revealed a dependence of pH history, and this pH hysteresis was elucidated by differences in the reaction rates of hydrogen and hydroxide ions with surface hydroxyl groups. Furthermore, analysis of the KCl profiles of the electroviscous effect showed a stronger effect at lower KCl concentrations under negative surface charge conditions, whereas no significant effect was observed under positive surface charge conditions.