Influence of phosphorus on the performance of sulfur autotrophic denitrification

In order to explore the minimum requirement of phosphorus for sulfur autotrophic denitrification, the sulfur autotrophic denitrification system was first treated with phosphorus starvation, and then the influents of different phosphorus concentrations were provided to investigate the influence of phosphorus concentration on the sulfur autotrophic denitrification performance and microbial community structure. The results showed that with the extension of the phosphorus starvation period, $ {\mathrm{N}\mathrm{O}}_{x}^{-} $-N removal efficiency declined gradually from 98.1%-99.6% before phosphorus starvation to 24.8%-49.6% after phosphorus starvation, accompanied by an accumulation of nitrite in the effluent. After phosphorus addition, $ {\mathrm{N}\mathrm{O}}_{x}^{-} $-N removal efficiency increased significantly with increasing influent phosphorus concentration. The higher the influent phosphorus concentration, the faster the $ {\mathrm{N}\mathrm{O}}_{x}^{-} $-N removal efficiency and effluent nitrite concentration recovered to the level before phosphorus starvation, with more than 98% and less than 0.05 mg/L, respectively. The efficiency of sulfur autotrophic denitrification was not limited by phosphorus concentration when the influent phosphorus concentration was not lower than 0.200 mg/L. The phosphorus concentration affected the microbial diversity of the sulfur autotrophic denitrification system, and the community diversity and richness of the sulfur autotrophic denitrification group recovered from phosphorus starvation were significantly higher than that of the group under phosphorus starvation. The functional genera related to sulfur autotrophic denitrification were the predominant genera in the sulfur autotrophic denitrification group recovered from phosphorus starvation, with the relative abundance accounting for 45.78%, while the relative abundance only accounted for 4.67% in the group under phosphorus starvation. The phosphorus concentration greatly affected the relative abundance of functional genera related to sulfur autotrophic denitrification in the sulfur autotrophic denitrification system.