Enhancement of N removal by electrification coupled by Feammox and Fe (II)/Fe(III) cycle in wastewater treatment

Ammonium (NH4+) is a known toxic nitrogen pollutant in wastewater, and will result in serious water quality deterioration when discharged without treatment. Feammox is a promising new pathway to remove NH4+ by its oxidization coupling with the reduction of Fe(III) mediated by ferric reducing bacteria (FeRB). However, the low efficiency of Feammox limits the application in wastewater treatment. In this study, NH4+ removal efficiency by Feammox was promoted by introduction of Fe2O3 and AQDS (Anthraquinone-2,6-disulfonic acid) as electron shuttling molecules with and without electrification in two batch experiments Rn (Fe2O3+AQDS) and Re (Fe2O3+AQDS + electrification). Results from this study showed that NH4+ removal was significantly enhanced under electrification, with the efficiency increased up to 74.3% by day of 34. The high efficiency of NH4+ removal was discussed to be accelerated by the Fe(II)/Fe(III) cycling under electrification. Further clues were provided by the microbial community analysis by high throughput sequencing. Both the FeRB and denitrification bacteria were promoted in their relative abundance under electrification. Genus of denitrification bacteria Citrifermentans, Klebsiella, Legionella, Clicycliphilus and Ciaphorobacter were confirmed by their Feammox potential for the first time since they were clustered closely with Feammox bacteria in the phylogenetic tree. Based on the above, the combination of FeRB, NDFO and denitrifying bacteria coupled with Feammox process in the reactors all contributed to the NH4+ removal. This study provided new evidence and revealed insightful functional microbial groups for ammonium-rich wastewater treatment with amendment of AQDS under electrification.