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

The feasibility of NO 3 − removal by the synergistic action of a prevailing denitrifying anoxic methane oxidising (DAMO), and nitrate‐reducing and sulfide‐oxidising bacterial (NR‐SOB) consortium, using CH 4 and H 2 S from biogas as electron donors in a biotrickling filter was investigated. The influence of NO 3 − concentration on N 2 O production during this process was also evaluated. The results showed that NO 3 − was removed at rates up to 2.8 g m reactor −3  h −1 using CH 4 as electron donor. N 2 O production rates correlated with NO 3 − concentration in the liquid phase, with a 10‐fold increase in N 2 O production as NO 3 − concentration increased from 50 to 200 g m −3 . The use of H 2 S as co‐electron donor resulted in a 13‐fold increase in NO 3 − removal rates (∼18 gNO 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 H 2 S addition, CH 4 removals were not compromised and H 2 S removal efficiencies of 100% were achieved. This study confirmed (i) the feasibility of co‐oxidising CH 4 and H 2 S with denitrification, as well as (ii) the critical need to control NO 3 − concentration to minimize N 2 O production by anoxic denitrifiers. Biotechnol. Bioeng. 2017;114: 665–673. © 2016 Wiley Periodicals, Inc.