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.