The feasibility of NO₃^- removal by the synergistic action of a prevailing denitrifying anoxic methane oxidising (DAMO), and nitrate-reducing and sulfide-oxidising bacterial (NR-SOB) consortium, using CH₄ and H₂ S from biogas as electron donors in a biotrickling filter was investigated. The influence of NO₃^- concentration on N₂ O production during this process was also evaluated. The results showed that NO₃^- was removed at rates up to 2.8 g m_reactor^-3 h^-1 using CH₄ as electron donor. N₂ O production rates correlated with NO₃^- concentration in the liquid phase, with a 10-fold increase in N₂ O production as NO₃^- concentration increased from 50 to 200 g m^-3 . The use of H₂ S as co-electron donor resulted in a 13-fold increase in NO₃^- removal rates (∼18 gNO₃^- m^-3 h^-1 ) and complete denitrification under steady-state conditions, which was supported by higher abundances of narG, nirK, and nosZ denitrifying genes. Although the relative abundance of the DAMO population in the consortium was reduced from 60% to 13% after H₂ S addition, CH₄ removals were not compromised and H₂ S removal efficiencies of 100% were achieved. This study confirmed (i) the feasibility of co-oxidising CH₄ and H₂ S with denitrification, as well as (ii) the critical need to control NO₃^- concentration to minimize N₂ O production by anoxic denitrifiers. Biotechnol. Bioeng. 2017;114: 665-673. © 2016 Wiley Periodicals, Inc.

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