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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 2.8 g mreactor−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 200 g m−3. The use of H2S 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 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. This article is protected by copyright. All rights reserved

The feasibility of NO

The reproducibility and stability of low- temperature anaerobic wastewater treatment systems undergoing transient perturbations was investigated. Three identical anaerobic expanded granular sludge bed-based bioreactors were used to degrade a volatile fatty acid and glucose-based wastewater under sub-ambient (15 degrees C) conditions. The effect of a variety of environmental perturbations on bioreactor performance was assessed by chemical oxygen demand removal. Temporal microbial community development was monitored by denaturation gradient gel electrophoresis (DGGE) of 16S rRNA genes extracted from sludge granules. Methanogenic activity was monitored using specific methanogenic activity assays. Bioreactor performance and microbial population dynamics were each well replicated between both experimental bioreactors and the control bioreactor prior to, and after the implementation of most of the applied perturbations. Gene fingerprinting data indicated that Methanosaeta sp. were the persistent, keystone members of the archaeal community, and likely were pivotal for the physical stability and maintenance of the granular biofilms. Cluster analyses of DGGE data suggested that temporal shifts in microbial community structure were predominantly independent of the applied perturbations.