Dynamic Monitoring of Reverse Osmosis Process via Electrical Impedance Tomography: Enabling In Situ Visualization and Uncovering Distinct Roles of Concentration Polarization/Foulant Deposition in Flux Decline

Access to information about fouling in the membrane modules can provide critical insights to advance fundamental understanding and develop effective strategies for fouling mitigation. In this study, we developed a rapid, in situ, and noninvasive membrane imaging platform based on the electrical impedance tomography (EIT) technique to probe the evolution of fouling in the reverse osmosis (RO) process. This technique can be used to monitor the formation of the concentration polarization (CP) and the fouling layer without labeling. Our data demonstrate that CP reaches equilibrium within minutes of filtration initiation, whereas fouling is the primary cause of the continuous flux decline during filtration. We further show that the salt concentration is a critical factor influencing the extent of CP and scaling processes, while the presence of organic matter accelerates membrane fouling. This study also clarifies the correlation between the membrane surface impedance variation and flux decline during filtration. Leveraging impedance time-series data, a machine learning-based random forest model was developed for flux change prediction.