Monitoring of colloidal fouling and its associated metastability using Ultrasonic Time Domain Reflectometry

► First application of UTDR to monitor colloidal fouling on membranes. ► Monitoring colloidal fouling and its metastability non-invasively in real-time. ► Metastability results in a rate-dependent dissolution-resistant residual layer. ► Rheological behavior of foulant layers modeled using the Bingham plastic model. ► Yield stresses of foulant layers calculated from UTDR measurements.