Removal of ammonium and nitrate through Anammox and FeS-driven autotrophic denitrification

An autotrophic denitrifying bioreactor with iron sulfide (FeS) as the electron donor was operated to remove ammonium (NH 4 + ) and nitrate (NO 3 − ) synergistically from wastewater for more than 298 d. The concentration of FeS greatly affected the removal of NH 4 + /NO 3 − . Additionally, a low hydraulic retention time worsened the removal efficiency of NH 4 + /NO 3 − . When the hydraulic retention time was 12 h, the optimal removal was achieved with NH 4 + and NO 3 − removal percentages both above 88%, and the corresponding nitrogen removal loading rates of NH 4 + and NO 3 − were 49.1 and 44.0 mg/(L·d), respectively. The removal of NH 4 + 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, NO 3 − 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.