Biogas-based denitrification in a biotrickling filter: Influence of nitrate concentration and hydrogen sulfide.

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 mreactor-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.