A focused ultrasonic sensor for in situ detection of protein fouling on tubular ultrafiltration membranes

One of the greatest challenges in membrane fouling studies is the development of non-invasive methods that allow for in situ detection of protein fouling, especially in tubular membrane modules. This study describes the extension of ultrasonic time-domain reflectometry (UTDR) for the real-time measurement of protein fouling on tubular ultrafiltration (UF) membranes. A specially designed focused transducer with a frequency of 7.5 MHz was used in this study. The tubular membrane was a polyethersulphone (PES) UF membrane with MWCO 40 kDa. The feed used was 0.08 and 3 g/l bovine serum albumin (BSA) solutions. The results show that the UTDR technique can distinguish and recognize the acoustic response signals from the various curve surfaces of the housing holder, steel support and membrane within a tubular membrane module. Changes in the amplitude of the differential signals obtained provide useful quantitative information about the deposited BSA on the membrane. A linear relationship between the amplitude of the observed signals and fouling resistance exists in the fouling experiment with 0.08 g/l BSA. The rate at which the ultrasonic amplitude increased became faster at fouling operation with 3 g/l BSA than with 0.08 g/l BSA. Flux measurements and UV analysis corroborate the ultrasonic testing.