activated sludge metagenome Raw sequence reads

The simultaneous nitrification and denitrification (SND) process is efficient to achieve nitrogen removal via various reactors. Here, a simple internal circulating reactor with a high internal circulation ratio of 36:1 was designed and set up to treat wastewater containing nitrogen and COD, and the performance of the SND process was comprehensively analyzed with a long-term operation. In the bioreactor, simultaneous removal effects of COD (95.2%), TN (87.3%), and NH4+-N (96.9%) were satisfactorily obtained. According to the investigation of nitrogen removal kinetics and nitrogen balance analysis showed that traditional nitrification and denitrification, simultaneous nitrification and denitrification (SND), and nitrogen assimilation accounted for 27.4%, 68.7%, and 3.9% respectively. Microbial community analysis suggested that the proportion of aerobic bacteria (Saprospiraceae) and facultative bacteria (Comamonadaceae) in the reactor was significantly increased, indicating the system has a higher capacity for organic degradation. The relative abundance of denitrifying bacteria and bacterial groups with SND (Comamonadaceae) increased. Furthermore, the regulation of the key enzymes identified that nitrite reduction was the speed-limiting step in the denitrification process. The results of this study suggested that nitrogen removal in wastewater treatment could be accomplished successfully using the developed internal circulating reactor employing the SND process.