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.

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► Aerobic N2O production rate increases exponentially with ammonia oxidation rate.
► N2O production via the chemical breakdown of NOH could reproduce the relationship.
► The experimental data could not be reproduced by the reduction of or NO.