Study on the mechanism by which anaerobic organisms remove nitrogen and sulfur from low-C/N rare earth tail water simultaneously

The low-C/N limits the simultaneous removal of the high sulfate and high ammonia nitrogen content in the rare earth tail water. How bacteria cycle sulfur and nitrogen in this environment is still unknown. As a result, there is a pressing need to treat such complicated tail water. This study built an anaerobic reactor to treat the rare earth tail water and employed anaerobic microorganisms. Following 104 days of operation, the rates of nitrogen removal for nitrate and nitrite are above 90%, and the removal rates of ammonia nitrogen and sulfate could reach 14.36 mg/(L·day) and 21.31 mg/(L·day), respectively. To identify the nitrogen and sulfur cycle in the reactor, the bacterial population and gene abundance were characterized using 16S rRNA sequencing and functional gene prediction. The results demonstrated that nitrogen from ammonia was primarily eliminated via assimilation, while nitrogen from nitrate was primarily eliminated by denitrification, which was strongly associated with Comamonas. The principal mechanism for eliminating the sulfate is assimilation, which is linked to the bacterium SBR1031. In conclusion, the nitrogen and sulfur cycle theoretically supports the simultaneous removal of sulfate and ammonia nitrogen from rare earth tail water under low-C/N circumstances.