Overlooked role in bacterial assembly of different-sized granules in same sequencing batch reactor: Insights into bacterial niche of nutrient removal.

The unique ecosystem within different-sized granules affects microbial assembly, which is crucial for wastewater treatment performance. This study operated an aerobic granular sludge system to evaluate its performance in treating synthetic municipal wastewater. Subsequently, the microbial community within different-sized granules was characterized to investigate bacterial assembly, and elucidated their biological potential for nutrient removal. The nutrient removal efficiencies were as follows: 93.8 ± 2.8 % chemical oxygen demand, 65.4 ± 4.0 % total nitrogen, and 93.8 ± 6.8 % total phosphorus. The analysis of microbial assembly unveiled remarkable diversity among different-sized sludges, the genus relative abundance displayed 61.4 % positive and 33.0 % negative correlation with sludge size. The excellent potential for organic degradation, denitrification, and polyphosphate accumulation occurred in sludge sizes of > 0.75 mm, 0.20-0.50 mm, and < 0.20 mm, respectively. Functional annotation further confirmed the nutrient removal potential within different-sized sludges. This study provides valuable insights into the bacterial niche of different-sized sludges, which can enhance their practical application.