Microbial driving mechanisms of sludge reduction in modular wastewater treatment systems under surplus aeration regulation.

-N removal rates both reaching more than 85%. 16S rRNA profiles indicated higher alpha diversity in the SA group and clear community separation from the Conv. group (PERMANOVA, p < 0.001). The SA group was enriched in taxa with documented extracellular polymeric substance (EPS) degradation potential, including Saccharimonadales, Saprospiraceae, and Caldilineaceae, whereas the Conv. group showed relatively higher abundance of taxa often associated with proliferation and EPS production (e.g., OLB17, Acinetobacter). Metagenomic functional annotation suggested higher representation of genes and pathways related to carbohydrate processing and energy metabolism in the SA group. As these omics results primarily reflect functional potential rather than confirmed in situ activity, we present a conceptual mechanism in which surplus aeration improves DO distribution and substrate utilization in the field system, thereby favoring EPS breakdown and energy-use efficiency-consistent with the observed reduction in sludge yield.