Effect of C/N on the Microbial Interactions of Aerobic Granular Sludge System

The main focus of this study was to evaluate the operational stability and changes in microbial interactions of aerobic granular sludge (AGS) systems at reduced C/N (16, 8 and 4). The results showed that decreasing the C/N ratio of the influent significantly reduced the removal efficiency of total nitrogen and phosphorus. The granule settling performance and stability also deteriorated. Molecular ecological network analysis showed that the reduction of the C/N ratio made the overall network as well as the subnetworks of the Proteobacteria and Bacteroidota more complex and tightly connected. Similarly, the subnetworks of two dominant genera (Thiothrix and Defluviicoccus) became more complex as the C/N decreased. These results might be the self-regulation of the AGS system to resist the perturbation of decreased C/N ratio. Meanwhile, the decreased C/N ratio might promote competition among microbes in these overall networks and subnetworks, which might be responsible for the deterioration of pollutant removal performance at low C/N. This study adds a new direction to our understanding of the effects of C/N ratio on the operational stability and microbial interactions of AGS systems