The effects of dissolved oxygen (DO) and pH on nitrous oxide (N2O) production rates and pathways in autotrophic partial nitrification (PN) granules were investigated at the granular level. N2O was primarily produced by betaproteobacterial ammonia-oxidizing bacteria, mainly Nitrosomonas europaea, in the oxic surface layer (<200μm) of the autotrophic PN granules. N2O production increased with increasing bulk DO concentration owing to activation of the ammonia (i.e., hydroxylamine) oxidation in this layer. The highest N2O emissions were observed at pH 7.5, although the ammonia oxidation rate was unchanged between pH 6.5 and 8.5. Overall, the results of this study suggest that in situ analyses of PN granules are essential to gaining insight into N2O emission mechanisms in a granule.
Bibliographical noteFunding Information:
This research was financially supported by grants from the Japan Science and Technology Agency (JST) CREST, Nagase Science and Technology Foundation, and Institute for Fermentation, Osaka (IFO) to S. Okabe. We thank Reiko Hirano and Ayumi Akiyoshi for their technical assistance.
© 2015 Elsevier Ltd.
- 16S rRNA gene deep sequencing
- Autotrophic partial nitrification granule
- Dissolved oxygen effect
- NO emissions
- NO microsensor