Abstract: | ● Simultaneous NH4+/NO3– removal was achieved in the FeS denitrification system ● Anammox coupled FeS denitrification was responsible for NH4+/NO3– removal ● Sulfammox, Feammox and Anammox occurred for NH4+ removal ● Thiobacillus, Nitrospira , and Ca. Kuenenia were key functional microorganisms An autotrophic denitrifying bioreactor with iron sulfide (FeS) as the electron donor was operated to remove ammonium (NH4+) and nitrate (NO3?) synergistically from wastewater for more than 298 d. The concentration of FeS greatly affected the removal of NH4+/NO3?. Additionally, a low hydraulic retention time worsened the removal efficiency of NH4+/NO3?. When the hydraulic retention time was 12 h, the optimal removal was achieved with NH4+ and NO3? removal percentages both above 88%, and the corresponding nitrogen removal loading rates of NH4+ and NO3? were 49.1 and 44.0 mg/(L·d), respectively. The removal of NH4+ mainly occurred in the bottom section of the bioreactor through sulfate/ferric reducing anaerobic ammonium oxidation (Sulfammox/Feammox), nitrification, and anaerobic ammonium oxidation (Anammox) by functional microbes such as Nitrospira, Nitrosomonas, and Candidatus Kuenenia. Meanwhile, NO3? was mainly removed in the middle and upper sections of the bioreactor through autotrophic denitrification by Ferritrophicum, Thiobacillus, Rhodanobacter, and Pseudomonas, which possessed complete denitrification-related genes with high relative abundances. |