Effect of different feeding strategies on performance of aerobic granular sludge: From perspective of extracellular polymeric substances and microorganisms

Long-term structural stability of aerobic granular sludge (AGS) is a major challenge in AGS biotechnology. This work investigated variations in the sludge performance, structural stability, and intrinsic mechanisms of AGS under three feeding strategies (R1 direct aeration after fast feeding, R2 anaerobic stirring after fast feeding and R3 anaerobic plug-flow slow feeding). The AGS sequencing batch reactor used in this study was in stable operation with biomass of 6–10 gMLSS/L and a hydraulic retention time of 4 h. The results showed that the best sludge performance was demonstrated in R3, followed by R2 and R1. These differences were caused by extracellular polymeric substances (EPS) and microbial communities. The excellent sludge performance in R3 was attributed to the high hydrophobicity in the EPS as well as the gel properties due to the high hydrogen bonding content in the exopolysaccharide (PS). Similarly, the gel properties formed by the high hydrogen bonding content maintain the sludge stability in R1. Slow-growing dominant bacteria were enriched in the AGS of R2 and R3 with alternating anaerobic/aerobic operation modes, resulting in outstanding sludge performance. In contrast, high abundance of the filamentous bacteria Neomegalonema was enriched in the AGS of R1 without an anaerobic phase, resulting in relatively poor sludge stability. Variations in EPS characteristics and microbial community under the different feeding strategies were the main mechanisms responsible for the long-term operation of AGS. This study could provide a theoretical foundation and technical assistance for the sustainable operation of AGS reactors.