Effect of microbubbles on microfiltration pretreatment for seawater reverse osmosis membrane

Abstract

This study focused on the application of microbubbles (Mbs) to microfiltration (MF) pretreatment for reverse osmosis (RO) desalination. Experiments were performed using seawater as the feed water to a microfiltration system. Mbs, which were generated by a pump under 4bars of pressure, were applied prior to MF treatment. The MF flux was adjusted from 15L/m2/h to 45L/m2/h. The effect of coagulant addition to the Mbs reactor on the MF efficiency was also examined. Results indicated that Mbs without using coagulant were not effective to regard MF fouling. Although the turbidity of the water decreased, the fouling rate increased after the Mbs treatment. This is attributed to an increase in the fraction of small particles, which lead to an increase in specific cake resistance by decreasing the particle size. Combined with coagulation, microbubbles showed a higher ability to control MF fouling. The removal of small particles (<10μm) was also improved and the formation of cake layer was suppressed. The SDI5 was maintained low when seawater was pretreated with a combination of coagulation–microbubble–microfiltration.