Review: ultrasonic characterization of membranes

AbstractThis review describes the use of ultrasonic reflectometry (UR) for characterizing membranes and membrane processes. A growing body of literature documents the capabilities of UR as a versatile nondestructive, noninvasive, real-time, and low-cost methodology that can provide important information about a wide range of membrane-based separations. A compact but thorough explanation of the ultrasonic measurement concepts relevant for use of the methodology for membrane applications is first presented. This section is followed by a description of the many studies in which UR has been employed for characterization of membrane structure, formation, compaction, and inorganic and organic membrane fouling, the latter in both real-time and post-mortem modes. Examples of recent work that incorporates the innovative use of UR for scaling in nanofiltration and reverse osmosis applications as well as results that suggest the potential of the ultrasonic slow wave to monitor pore closure in early-stage fouling are then highlighted. UR is then compared with other techniques for fouling detection so that the advantages and limitations of UR can be placed in proper perspective. Finally, valuable future directions for the incorporation of UR in membrane research, development, and practice are considered.