Insights into the Mass Transfer Improvement of a Submerged Forward Osmosis System with Vibration-Induced Shear Enhancement

Abstract

External and internal concentration polarizations are critical bottlenecks in the application of forward osmosis. This study examines the overall mass transfer performance of a submerged membrane vibration system for flat sheet and hollow fiber configurations. The application of membrane vibration at 14.3 Hz resulted in a flux enhancement of at least 43% at different membrane orientations and configuration modes in the flat sheet module. Interestingly, it was found that the membrane vibration can improve the shear force in the channel side of a plate-and-frame configuration, with the presence of a mesh spacer, with up to a 49% increase in the overall mass transfer coefficient at a vibration frequency of 21.8 Hz. Variation of shear forces and configurations revealed complex interactions between internal and external concentration polarizations. In addition, the application of membrane vibration can mitigate the effects of accelerated cake-enhanced concentration polarization as observed by a stable flux performance at 5 L/m2 h over 17 h as opposed to a flux decline to 3 L/m2 h for the case without vibration using a seawater model feed with the presence of silica colloids.