Enhanced permeate flux by air micro-nano bubbles via reducing apparent viscosity during ultrafiltration process

Micro-nano bubbles (MNBs) play important roles in the reduction of membrane fouling during membrane separation; however, such improvements are always attributed to the reduced concentration polarization on the surface of membranes and little attention has been paid on the variations of physicochemical properties of the feed caused by MNBs. In this study, the separation efficiencies of the feed containing humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) or dyes can be improved by MNBs during ultrafiltration, and the normalized fluxes can be maximally increased to 139% and 127% in the dead-end and cross-flow modes, respectively in the treatment of HA solution. We further reveal that the decreased apparent viscosity of the feed in the presence of MNBs is the key factor that enhances the normalized flux during ultrafiltration. This study gives new insight on the importance of MNBs in membrane separation and provides valuable clues for other chemical processes. [Display omitted] •Enhanced normalized fluxes of NOMs are observed with MNB input during UF processes.•The apparent viscosity of NOMs is reduced with MNB input.•The apparent viscosities of MNB-BSA increase with MNB decaying.•Enhanced fluxes of NOMs are due to decreased apparent viscosities with MNB input.