Microbial Community Dynamics During Two Sludge Granulation Processes

: Aerobic granular sludge (AGS) was cultivated in a sequencing batch reactor (SBR). In this study, AGS was broken during the formation process and then mature AGS formed again. The microbial community dynamics during two sludge granulation processes were investigated using high-throughput sequencing to reveal the dominant bacteria beneficial to AGS formation. The abundance dynamics of nitrifying microorganisms were analyzed by a quantitative polymerase chain reaction (qPCR). The results showed that the amount of extracellular protein and polysaccharides increased during two sludge granulation processes. The abundance of ammonia oxidizing archaea (AOA) increased during the first AGS formation process and during the process of AGS maturation. The abundance of ammonia oxidizing bacteria (AOB) decreased during the first AGS formation process, while it maintained a higher abundance than AOA during AGS cultivation. Microbial diversity decreased with AGS formation. The relative abundance of Proteobacteria increased by 12.29% and 5.90% during two sludge granulation processes, respectively. Candidatus Competibacter belonging to Proteobacteria was enriched during two sludge granulation processes, accounting for 14.20% in mature AGS. Overall, extracellular protein and polysaccharides may have contributed to the sludge granulation. Both AOA and AOB might have been involved in ammonia oxidation. This study indicated that Ca. Competibacter might contribute to AGS formation.