High diversity of potential nitrate-reducing Fe(II)-oxidizing bacteria enriched from activated sludge.

Nitrate-dependent Fe(II) oxidation (NDFO) has been discovered in various environments including activated sludge and can potentially be used to remove nitrate from wastewater. In this study, NDFO sludge was successfully enriched from activated sludge under high Fe(II) concentrations over 100 days and the denitrification rate achieved 1.37 mmol N/(gVSS day). High-throughput sequencing of the bacterial 16S rRNA gene was used to investigate the microbial community structure dynamics during the enrichment process. The results showed that the microbial community changed significantly and high diversity of potential Fe(II)-oxidizing bacteria (FeOB) was observed in the enriched sludge. Thermomonas and Gallionella were the dominant bacterial genera in the enriched sludge and their relative abundances accounted for 9.49 and 4.08%, respectively. Furthermore, it was found that potential FeOB were also abundantly present in activated sludge samples of common municipal wastewater treatment plants. Collectively, this study demonstrated that NDFO could be successfully performed by enriched activated sludge and high diversity of bacteria is involved in this process, and the results also provide baseline information for future research and engineering application of NDFO process.