Monitoring of hollow fiber module velocity field and fouling inside individual fibers using benchtop MRI

Ultrafiltration (UF) membrane modules are a viable pre-treatment technology for reverse osmosis processes; they however are susceptible to fouling. In the current study, we demonstrate the use of benchtop MRI to provide quantitative structural and velocity images of an UF membrane module showing velocity inside each individual fiber and proceed to provide unique insights into both subsequent fouling and cleaning events. The module consists of 400 fibers, these all were correctly identified from the MRI images based on an implemented fiber identification algorithm. Velocity imaging of the UF module, revealed significant water flow in only 91% of the fibers. Following fouling with a calcium alginate gel, only 73% of the fibers were observed to be active which only recovered to 79% on application of a cleaning protocol using acetic acid. Fouling was clearly isolated to specific fibers in which flow was effectively eliminated; this is not consistent with the assumption of uniform fouling deposition on the inner fiber walls. This also restricts the access of cleaning solutions which effectively by-pass the fouled fibers. This level of novel, quantitative insight is available on benchtop MRI equipment, which displays significant promise for further hollow fiber UF module design, manufacturing and fouling development and control studies.