Aerobic process in the AOA system is a key factor affecting the storage of intracellular carbon sources and ED
Metagenomic analysis further confirmed that in the absence of O2, the functional genes related to endogenous metabolism (Polyhydroxyalkanoates synthesis, glycogen conversion, and long-chain fatty acid hydrolysis) were generally downregulated, and cells tended to secrete more extracellular polymeric substances as an alternative carbon source, but their low energy efficiency hindered ED activity. Notably, we found that the ED rates did not decline linearly with prolonged aeration, and we propose a model describing carbon transformation and replenishment in the aerobic zone. This study reveals O2 as a pivotal regulator of endogenous carbon metabolism and provides a framework for optimizing aeration and carbon management in AOA systems treating low C/N wastewater.