N₂O production rate of an enriched ammonia-oxidising bacteria culture exponentially correlates to its ammonia oxidation rate

The relationship between the ammonia oxidation rate (AOR) and nitrous oxide production rate (N₂OR) of an enriched ammonia-oxidising bacteria (AOB) culture was investigated. The AOB culture was enriched in a nitritation system fed with synthetic anaerobic digester liquor. The AOR was controlled by adjusting the dissolved oxygen (DO) and pH levels and also by varying the initial ammonium (NH4+) concentration in batch experiments. Tests were also performed directly on the parent reactor where a stepwise decrease/increase in DO was implemented to alter AOR. The experimental data indicated a clear exponential relationship between the biomass specific N₂OR and AOR. Four metabolic models were used to analyse the experimental data. The metabolic model formulated based on aerobic N₂O production from the decomposition of nitrosyl radical (NOH) predicted the exponential correlation observed experimentally. The experimental data could not be reproduced by models developed on the basis of N₂O production through nitrite (NO2-) and nitric oxide (NO) reduction by AOB. © 2012 Elsevier Ltd.