Noninvasive monitoring of fouling in membrane processes by optical coherence tomography: A review

Optical coherence tomography (OCT) has emerged as a powerful noninvasive technique for monitoring fouling in membrane filtration systems for water and wastewater treatment and seawater desalination. This interferometric method enables real-time in-situ visualization and quantification of fouling without the need for staining agents. In the last years, the OCT has been widely applied in various filtration systems including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, forward osmosis, membrane bioreactors, and membrane distillation. In this review, we critically evaluate the potential of OCT for studying fouling in membrane processes for water treatment, including its advantages and limitations. We discuss the principle of OCT, image processing methods, and fouling morphological characterization. Furthermore, we present recent literature showcasing the versatility of OCT for visualizing various types of fouling, such as biofouling, organic and particulate fouling, and scaling. Applications of OCT include monitoring fouling development over time, evaluating spatial fouling distribution, assessing cleaning efficiency, aiding fouling characterization, and supporting modeling and simulation. Finally, we address current challenges and discuss emerging developments that may further enhance the capabilities of OCT for studying fouling in membrane filtration systems.