Study on anaerobic ammonium oxidation process coupled with denitrification microbial fuel cells (MFCs) and its microbial community analysis

•Denitrifying MFC was successfully coupled with anammox process.•Further nitrite and nitrate reduction obtained based on stoichiometry relationship.•Brocadia sinica, Rhodopseudomonas palustris were the main anammox and denitrifiers.•Both sludge and biofilm performed their own duties on anammox and denitrification.•The autotrophic coupled process appears to be more promising than heterotrophic.

Denitrifying MFC was successfully coupled with anaerobic ammonium oxidation process in this study. With the help of cathode electrons, the stoichiometry relationship Δ−NH3-N:Δ−NO2−-N:Δ+NO3−-N was approximate 1:1.37:0.03 during the stable operation, which demonstrated its further nitrite and nitrate reduction. According to microbial community analysis, Candidatus Brocadia sinica was the main anammox community, and Rhodopseudomonas palustris with electrochemical driven denitrifying ability, especially enriched in biofilm. Higher abundance of nirK genes in biofilm (compare to the control) and invariable amx genes in suspended sludge were responsible for its better nitrogen removal. The sludge and biofilm performed their own duties on anammox and denitrification, respectively, according to genes quantification. Under the totally autotrophic system, electron donors were “concentrated supplied” and easy to control, which avoided the suppression of anammox growth, making this autotrophic coupling process appears to be more promising.