Characterisation of membrane fouling deposition and removal by direct observation technique

The understanding of fouling mechanisms in membrane processes is commonly inferred via flux and rejection performances. Using direct observation (DO) allows the non-invasive, in situ, visualisation and quantification of fouling deposition and the removal from hollow fiber membranes in real time. While the advantages of the DO technique have been described previously, in this work, the effects of crossflow velocities and backwashing on particle deposition and removal are quantified under constant flux conditions. The foulant resistances are monitored along with the cake height during membrane filtration and cleaning. By measuring the cake height non-invasively, the DO technique reduces some of the assumptions required to estimate the specific cake resistance. The velocity profiles of particles near the membrane surface during filtration were observed during the formation of stagnant and fluidised fouling layers. During backwashing, the fouling layer was removed with a combination of cake expansion and gradual erosion mechanisms at low crossflow velocities and direct erosion of cake height at higher crossflow velocities. These results provide further insights into fouling dynamics in systems such as submerged hollow fiber modules.