Rapid reformation of larger aerobic granular sludge in an internal-circulation membrane bioreactor after long-term operation: Effect of short-time aeration

[Display omitted] •The average size of AGS reached a balanced distribution after long-term operation.•A suddenly external disturbance influenced the microbial composition of an MBR.•Short time aeration changed the characteristics of biomass within the bioreactor.•Larger AGS rapidly reformed after short time aeration.•Filamentous bacteria played an important role in reforming larger AGS. The investigation aimed at revealing the influence of an external disturbance on the rapid reformation of larger aerobic granular sludge (AGS) in an internal-circulation membrane bioreactor (IC-MBR) after long-term operation. The used IC-MBR was continuously operated well for more than one year, in which, the biomass was still in the state of AGS with a balanced average size at around 200 μm and an even size distribution. By providing short-time aeration to the biomass within this bioreactor, the characteristics of biomass were totally changed in a very short time, including the surface hydrophilicity, physic-chemical properties, and the structure of microbial community, which created suitable conditions for the growth of filamentous bacteria (Saccharibacteria). Such a variation was very beneficial to the reformation of larger AGS, which resulted in the average size of AGS increased to nearly 400 μm with a compact structure and clear edge in no more than one month.