Control of scale formation in reverse osmosis by membrane rotation

Scale formation of soluble salts is one of the major factors limiting the application of reverse osmosis (RO) membranes. In this study, rotating RO, which takes advantage of Taylor-Couette flow instabilities to reduce concentration polarization and membrane fouling, was investigated as a novel method to control CaSO4 scale formation. The permeate flux for rotating RO at omega = 180 rpm remains constant up to a volume concentration factor (VCF) of 4.2, while the permeate flux declines steadily with increasing VCF for no rotation. This is probably because vortices in rotating RO induce bulk crystallization and prevent scale particle deposition on the membrane surface. The anti-scaling effect in rotating RO increases with increasing rotational speed and depends to some extent on transmembrane pressure.