Modeling of Nitrous Oxide Production by Ammonium-Oxidizing Bacteria

Modeling is helpful for predicting nitrous oxide (N2O) accumulation and verifying the production mechanisms in wastewater treatment. A model that integrates two pathways for N2O production by ammonium-oxidizing bacteria (AOB) under extremely low dissolved oxygen (DO) conditions was proposed in this work. In this new model, a major improvement of the previously published N2O models was made to omit the intermediary compounds nitroxyl (NOH) and nitric oxide (NO) in both N2O production pathways, aiming to reduce model parameters and calibration work. The model was calibrated and validated by experimental data from four independent nitritation and nitrification studies at different DO levels. Results showed that model predictions well captured the measured N2O, ammonium, nitrite, nitrate, and DO variation trends, suggesting that this two-pathway model was able to describe the autotrophic nitritation and nitrification processes with both mixed and nitrifying cultures. N2O production by the AOB denitrification pathway occupied the dominant part in oxygen-limited nitritation processes, and incomplete hydroxylamine (NH2OH) oxidation pathway acted as the primary part in nitrification processes at high DO levels. The newly presented model would be beneficial to improve the modeling study on N2O production by autotrophic bacteria.