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 H2S from biogas as electron donors in a biotrickling filter was investigated. The influence of NO3- concentration on N2O production during this process was also evaluated. The results showed that NO3- was removed at rates up to 2.8gm(reactor)(-3)h(-1) using CH4 as electron donor. N2O production rates correlated with NO3- concentration in the liquid phase, with a 10-fold increase in N2O production as NO3- concentration increased from 50 to 200gm(-3). The use of H2S as co-electron donor resulted in a 13-fold increase in NO3- removal rates (approximate to 18gNO(3)(-)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 H2S addition, CH4 removals were not compromised and H2S removal efficiencies of 100% were achieved. This study confirmed (i) the feasibility of co-oxidising CH4 and H2S with denitrification, as well as (ii) the critical need to control NO3- concentration to minimize N2O production by anoxic denitrifiers. Biotechnol. Bioeng. 2017;114: 665-673. (c) 2016 Wiley Periodicals, Inc.