Fast development of microbial cultures for the anaerobic oxidation of CH4 coupled to denitrification employing widely available inocula

This work assessed the potential of two widely available inocula for the implementation of anaerobic oxidation of methane coupled with NO3 - reduction (N-AOM). Methane consumption via N-AOM was observed within the first 40-67 days of culture using secondary activated sludge (AS) and a mixture of AS and anaerobic granular sludge (AS+AGS) as inoculum. Maximum methane removal rates of 0.13 +/- 0.02 and 0.17 +/- 0.01 gCH4 m- 3 h-1 were recorded for AS and AS+AGS cultures, respectively. 16 S rRNA high throughput sequencing applied to biomass samples throughout incubation revealed the absence of the archaeon Methanoperedens nitroreducens and the bacterium Methylomirabilis oxyfera in AS and AS+AGS cultures. Instead, members from the Bacteroidetes, Chloroflexi, Proteobacteria, and Euryarchaeota lineages were predominant in the cultures. Nitrous oxide, an undesirable intermediate of nitrate reduction, was not detected in measurements performed at the end of the incubations. The methane consumption rates recorded are comparable with N-AOM systems requiring acclimation periods of up to 600 days. Therefore, this work confirmed that N-AOM processes might be implemented with inocula available in bulk amounts in short periods, which facilitates the application of this process for the treatment of residual methane in wastewater treatment plants and other waste management facilities.

Automated summary

This study assessed two widely available inocula for the anaerobic oxidation of methane coupled with NO3 reduction. It found that methane consumption via this process could be observed within a relatively short period using secondary activated sludge and a mixture of activated sludge and anaerobic granular sludge as inoculum. The study also identified the dominant microbial communities in the cultures and confirmed the absence of nitrous oxide, an undesirable intermediate, at the end of the incubations. The findings suggest that N-AOM processes can be implemented quickly and easily, making it a viable option for the treatment of residual methane in wastewater treatment plants and waste management facilities.