High-throughput community and metagenomic elucidate systematic performance variation and functional transition mechanisms during morphological evolution of aerobic sludge.

In this study, high-throughput sequencing and metagenomics were used to investigate the microbial succession and functional gene dynamics during aerobic sludge granulation from activated sludge (AS) to aerobic granular sludge (AGS) to algal-bacterial granular sludge (ABGS). It was found that the settleability and pollutant removal efficiency of the sludge system increased with the sludge morphology evolution. Extracellular polymeric substances (EPS) analysis showed a rise in protein from 2.1 to 17.4 mg/gSS during stage of AGS and polysaccharides from 3.3 to 5.9 mg/gSS during stage of ABGS. Microbial community analysis revealed that the sludge evolution reduced species richness but enriched functional bacteria for nitrogen/phosphorus removal, while increasing the complexity of community structure and close interactions between species. Key genes involved in the tricarboxylic acid cycle, nitrogen/phosphorus and EPS metabolism were also upregulated. This study revealed the continuity mechanism and stage dependence of the functional transition during sludge morphology evolution.