Observation of membrane fouling with 3D-printed spacers using 3D optical coherence tomography

Abstract

Fouling is a common issue in membrane filtration and it greatly affects the efficiency of the separation process. A better understanding of the underlying fouling mechanisms from the observation of a filtration process is critical to investigate membrane fouling and mitigate the potential problems. This study focused on using optical coherence tomography (OCT) to investigate the effects of 3D-printed spacers (especially the 3D-printed sinusoidal spacers) on the fouling process. A series of OCT scans of a representative unit cell in a spacer was taken as a function of time to generate 3D-images illustrating the morphology of a foulant layer. With the help of some quantitative analysing methods, the formation and evolution of a foulant layer was obtained. It revealed the underlying fouling mechanisms during a fouling process. Besides the membrane flux, surface coverage and average cake thickness were adopted to compare the performance of varied spacer design under different operating conditions. The experimental results clearly indicated that the spacer designs and crossflow velocities can significantly impact the hydrodynamic conditions within the unit cells of a spacer. As a result, cake layers with different structures were formed. This study proved that OCT is a powerful tool in analyzing membrane fouling processes and evaluating different spacer designs.