Influence of Aggregate Size on Core Microbial Communities and Functional Group Selection in Full-Scale Aerobic Granular Sludge Systems

Aerobic granular sludge (AGS) technology is gaining attention as an effective solution for biological wastewater treatment due to its low energy consumption, compact design, and efficient nutrient removal. AGS systems consist of microbial aggregates of various sizes, with granules making up 80%, each supporting distinct microbial communities. However, it remains unclear whether full-scale AGS WWTPs select core microbial communities across different aggregate sizes and how these communities differ. This study addresses this gap by analyzing samples from nine high-performing AGS WWTPs. The results reveal that site-specific conditions influence microbial composition in smaller aggregates, while larger granules form stable, site-independent communities. Despite this, all aggregates shared 128–139 core operational taxonomic units, including key functional groups involved in organics and nutrient removal. Enrichment patterns showed aerobic heterotrophs in flocs, polyphosphate-accumulating organisms in small granules, and glycogen-accumulating organisms and nitrifiers in large granules.