4.4. Air scouring
Air scouring is used to provide a certain surface shear or enough
mass transferring motion to avoid the foulants from compacting on the
membrane surface, especially when a high TMP is applied. Air scouring
is often coupled with rinsing and used intermittently or continuously; it
is demonstrated to be an effective cleaning method in the filtration
process. The core of air scouring is how to control the rate, i.e. the
velocity for air passing by the surface of the membrane, the size and
direction of the provided bubble, and to achieve a high utilization ratio.
New products or way for a better air transition among the liquid–solid
phase surface are necessary for higher efficiency of air scouring. Psoch et
al. [73] introduced sponge ball combinationwith air scouring for fouling
control in ultrafiltration; it was reported that the repeated sponge ball
application and the air sparging were significant for almost the total
fouling reduction. Overall, there is not enough literature for the
mechanismor detailed reaction process, probably because of its uneasy
control during the experiment.