Response of aerobic granular sludge to loading shock: Performance and proteomic study

In this work, the response of aerobic granular sludge (AGS) to organic loading rate (OLR) shock was investigated from proteomic level for the first time. Results showed that OLR shock destabilized AGS system in terms of sludge properties, nutrient removal and microbial community, while they reached a new stability eventually. The AGS system exhibited larger-size granules (4 mm), higher biomass retention (6.9 g/L), enhanced nitrogen removal (97%-99%) and abundant Candidatus_Competibacter (30.7%) under OLR shock. Proteomic analysis demonstrated that AGS system responded to OLR shock by activating protection mechanism through up-regulating numerous metabolic pathways related to amino acid synthesis, aminoacyl-tRNA biosynthesis and gluconeogenesis. With the extension of OLR-shocking tests, AGS up-regulated metabolic pathways associated with glycogen synthesis and denitrification, which were mainly contributed by Candidatus_Competibacter based on species annotation analysis. This study offers an in-depth mechanistic insight into response of AGS to OLR shock and relevant regulation mechanisms, which will provide fundamental information and important implications for practically relevant cases.