Sustain. Environ. Res., 24(2), 117-128 (2014)
Hui-Ping Chuang, Jer-Horng Wu, Akiyoshi Ohashi, Kenichi Abe and Masashi Hatamoto
Nitrous oxide, ammonia oxidizer, microbial community structure
Nitrous oxide (N2O), an important intermediate or by-product in the nitrogen cycle is among the priority greenhouse gas to be mitigated. It can be produced from the aerobic nitrification processes but whether converted under aerobic conditions remains unclear. This study set up the batch and down-flow hanging sponge (DHS) reactor experiments to investigate the aerobic conversion potential of N2O. The results of batch assays indicated that the significant decrease of N2O along with oxygen consumption was attributed to the biological reactions. After a 270-d operation of the DHS reactor with N2O as the sole substrate, it could achieve a removal rate of 6.99 g N g-1 VSS d-1 with high N2O efficiency (~95%). In the reactor, nitrate was accumulated in the effluent up to 7.8 mg N L-1 at the loadings < 1 mmol N2O-N d-1, whereas gaseous N2 turned out to be the end product at the loadings > 2 mmol N2O-N d-1. The cloning library analysis of 16S rRNA gene sequence revealed a complex community structure, comprising abundant Nitrososphaera gargensis and Nitrospira spp. developed in the DHS system. The quantitative PCR analysis further showed that the bacterial and archaeal ammonia-oxidizing populations could greatly increase with the reactor operations, suggesting an important role in the N2O-converting consortia. Overall, these results suggested the feasibility of N2O conversion in the bioreactor systems under aerobic conditions.