Concentration Polarisation and Membrane Fouling Characteristics in Ultrafiltration Based on Electrical Impedance Analysis: Synergistic or Translational?

Abstract

In macromolecular ultrafiltration (UF) processes, the effects of concentration polarization (CP) and membrane fouling have been widely studied, while the impact of ion-induced CP is often overlooked. However, ion-induced CP plays a crucial role in UF systems which depends on water quality. In this study, electrochemical impedance spectroscopy (EIS) was used to monitor the membrane filtration process in real-time. Through the fitting circuit, the key parameters such as CP layer resistance (Rcp), cake layer resistance (Rf) and membrane layer resistance (Rm) were analyzed under different operating conditions. The contribution of non-ion concentration polarization (NICP), ion concentration polarization (ICP) and membrane fouling to the degradation of filtration performance can be determined by the change of different resistance values. The experimental results revealed two distinct stages in the UF process: a synergistic phase, during which NICP and membrane fouling occur simultaneously, followed by a transition to a fouling-dominated stage. In addition, ion-induced CP enhanced the synergistic interaction between NICP and membrane fouling, accelerating the transition to the fouling-dominated stage. Notably, the fouling type shifted from irreversible membrane pore plugging fouling to the more reversible cake layer fouling. Recognizing this transition in fouling behavior is crucial for optimizing membrane cleaning strategies. Furthermore, by optimizing the cleaning strategy based EIS, the study demonstrated a significant improvement in membrane flux, with the flux recovery rate increasing by 26.10% to 30.69%. This research highlighted the importance of ion-induced CP in UF systems and provided valuable insights into its role in membrane fouling.

Keywords: Concentration polarization, membrane fouling, Synergistic conversion, Membrane cleaning