Nitrogen Removal Performance and Metagenomic Analysis of Sequencing Batch Reactor Under Different Dissolved Oxygen Concentrations at Aerobic Phase

The effects of dissolved oxygen (DO) concentration at aerobic phase on nitrogen removal performance, enzymatic activities, microbial community and nitrogen metabolism functional genes were investigated in a sequencing batch reactor (SBR). With the DO concentration at aerobic phase decreased from 5~6 to 2~3 mg·L^-1, the nitrification rates and nitrifying enzymatic activities of SBR activated sludge system gradually decreased, while the denitrification rates and denitrifying enzymatic activities gradually increased. Metagenomic analysis revealed that the microbial community of the activated sludge system changed significantly with the decrease of DO concentration at aerobic phase. The relative abundance of typical nitrifying bacteria decreased gradually, while that of multiple denitrifying bacteria increased gradually. In the process of nitrogen metabolism, the decrease of DO concentration at aerobic stage inhibited the relative abundance of functional genes and key enzymes related to the nitrification process, but promoted the relative abundance of functional genes and key enzymes related to the denitrification process, which explained the reasons for the decreased nitrification performance and the increased denitrification performance of SBR from the perspective of genes. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database analysis, the decrease of DO concentration at aerobic phase significantly inhibited the carbon metabolism process of activated sludge system and promoted the process of energy generation and electron transfer to some extent. This study further explored the effect of DO concentration at aerobic phase on biological nitrogen removal process of SBR, and provided a theoretical basis for the DO parameter setting of SBR.