The total and functional bacterial community of nitrogen removal in the SND ditches

- Nitrosomonas, Thauera, Arcobacter and Zoogloea were the main genera involved in oxidation ditches.
- Nitrogen removal of SND was basically relied on the function of conversion and incorporation of nitrogenous compounds.
- Ditch A presented more robust ability of conversing and incorporating ammonia.
- The functional genes encoding nitrogen cycle enzymes caused a big difference between Bitch A and Bitch B in nitrogen removal.

For a full understanding of microbial function in simultaneous nitrification and denitrification (SND), comprehensive genetic information in activated sludge from two parallel oxidation ditches (Ditches A and B) was investigated by high-throughput sequencing and quantitative real time PCR (q-PCR). Results showed that over 90% of the ammonia was removed by both oxidation ditches, and Ditch A had a higher average value of SND efficiency. Both ditches shared a similar bacterial composition, and Proteobacteria and Bacteroidetes were the dominant phyla. However ditch A had a microbial community with higher Shannon and Chao1 indices than Ditch B. At genus level, Nitrosomonas, Thauera, Arcobacter and Zoogloea were mainly involved in the SND of oxidation ditches. And more types and higher abundances of (de)nitrifiers were detected in Ditch A. The results were verified by q-PCR analysis. According to functional analysis, the metabolism of carbohydrates and proteins, clustering-based subsystems, as well as amino acids and derivatives were the major functions of activated sludge in oxidation ditches. SND was accomplished in oxidation ditches by means of conversion and incorporation of nitrogenous compounds. Furthermore, more types of Level 3 subsystems and higher efficiency of ammonia assimilation were found in the nitrogen metabolism of Ditch A. These findings provide an insight into genetic pattern of SND in the municipal sewage treatment plants.