Study on the Synchronous Removal of Nitrogen and Phosphorus by Autotrophic/Heterotrophic Denitrification in the Presence of Pyrite

Pollution caused by N and P is a significant contributor to water eutrophication. While traditional biological treatment processes can remove some N and P elements from water, the effluent quality often fails to meet the stringent requirements of sensitive areas. The autotrophic denitrification’s simultaneous nitrogen and phosphorus removal pro-cess, known for its low operating cost and minimal sludge production, has garnered considerable attention from researchers. In this study, natural pyrite was used for the removal of nitrogen and phosphorus in a denitrification system, and the underlying mechanisms were elucidated. The results indicate that the N and P removal efficiency was influenced by empty bed contact time (EBCT) and the pH value. The highest NO 3 − -N removal rate of 90.24% was achieved at an EBCT of 8 h, while the PO 4 3− -P removal rate reached 81.58% at an EBCT of 12 h. The addition of a carbon source enhanced the synergistic autotrophic/heterotrophic denitrification, significantly improving phosphorus removal with an increasing C/N ratio. Microbial characteristics analysis revealed that, at the phylum level, Chlorobiota , Bacteroidota , and Chloroflexota played a crucial role in heterotrophic autotrophic denitrification. At the genus level, Thauera , Aridibacter , and Gemmatimonas were key players in heterotrophic denitrification, while Thiobacillus , Rhodoplanes , and Geobacter were associated with autotrophic denitrification.