Evaluation of the impact of dissolved oxygen concentration on biofilm microbial community in sequencing batch biofilm reactor

The effect of dissolved oxygen concentration (DO) during simultaneous nitrification and denitrification (SND) was investigated in a sequencing batch biofilm reactor (SBBR). In addition, the removal rates of nitrogen and bacterial communities were investigated under different concentrations of DO (1.5, 3.5, and 4.5 mg/L). When the SND rate was 95.22%, the chemical oxygen demand and nitrogen removal was 92.22% and 84.15%, respectively, at 2.5 mg/L DO. The denitrification was inhibited by the increase of oxygen concentration. Microelectrode measurements showed that the thickness of oxygen penetration increased from 1.0 mm to 2.7 mm when the DO concentration increased from 1.5 mg/L to 5.5 mg/L. The current location of the aerobic and anaerobic layers in the biofilm was determined for analysis of the microbial community. High-throughput sequencing analysis revealed the communities of the biofilm approached similar structure and composition. Uliginosibacterium species, biofilm-forming bacteria Zoogloea species and Acinetobacter species were dominant. In the aerobic layer, phyla Betaproteobacteria and Saprospirae were predominant, the major phyla were shifted from Proteobacteria followed by Firmicutes and Bacteroidetes, which comprised 82% of the total sequences during the SND period. Anaerolineae was dominated in the anaerobic layer. The high abundance of Nitrospira in the aerobic biofilm provides evidence of the SND system performing better at ammonia oxidization. In addition, real-time PCR indicated that the amount of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) matched the Nitrospirales and Nitrosomonadales abundance well. Collectively, this study demonstrated the dynamics of key bacterial communities in the SND system were highly influenced by the DO concentration.