Factors affecting simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) system as revealed by microbial community structures

The effects of biological factors including dissolved oxygen (DO), pH, carbon/nitrogen (C/N) and hydraulic retention times (HRT) on the performance of simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) were investigated. A low DO was found to be advantageous to the SND in that nitrification was not inhibited, while pH and C/N ratio were shown to have positive effects on SND, and HRT needed to be controlled in a suitable range. A desirable SND efficiency was obtained at a DO of 2.5 mg L−1, pH of approximately 8.0, C/N ratio of 10 and HRT of 10 h in the MBSBR. High-throughput sequencing analysis showed that different operating conditions impacted microbial communities, resulting in different nitrogen removal mechanisms. Autotrophic and heterotrophic nitrification together contributed to the good nitrification performance, while denitrification was conducted by combined anoxic and aerobic processes. Furthermore, the results of principal component analyses (PCA) and the abundance of the predominant nitrification and denitrification genera both showed that DO and HRT might be regarded as the dominant variable factors influencing community structure analysis during SND, while the linear discriminant analysis (LDA) effect size (LEfSe) algorithm showed differences in abundance among the biofilm microbial communities with different DO. Overall, the results of this study improve our understanding of the bacterial community structure with different operating conditions in MBSBRs.