Real-time monitoring the spatial distribution of organic fouling using fluorescence imaging technique

Abstract

Many studies have demonstrated a close relationship between fouling and fluid dynamics to control fouling formation. However, few have been carried out to validate the relationship in practice, owing to the lack of techniques to evaluate fouling with hydrodynamics. We investigated the organic fouling of humic acid (HA) and tannic acid (TA) at three crossflow velocities using a fluorescence-labelled organism bioimaging instrument (FOBI). Higher crossflow velocity generally enhanced filtration performance; however, the type of foulants induced different fouling formation patterns on the membrane. The monitoring system and computational model revealed that HA fouling had strong (R2 = 0.82) correlation with the shear rate (obtained from a velocity of 10.42 cm/s), while TA had weak correlation (R2 = 0.13). HA fouling showed a high correlation with velocity profile at 10 cm/s, but TA fouling occurred in the over 20 cm/s velocity zone. This is because TA had relatively high adhesive force acting to the membrane, resulting in irreversible fouling that was hardly mitigated by crossflow control. Therefore, this study demonstrated that fouling development was predominantly controlled by hydrodynamic conditions, but the actual fouling distribution could be influenced by the physicochemical properties of dissolved organic matters.