Modelling nitrous and nitric oxide emissions by autotrophic ammonia-oxidizing bacteria

<div><p>The emission of greenhouse gases, such as N₂O, from wastewater treatment plants is a matter of growing concern. Denitrification by ammonia-oxidizing bacteria (AOB) has been identified as the main N₂O producing pathway. To estimate N₂O emissions during biological nitrogen removal, reliable mathematical models are essential. In this work, a mathematical model for NO (a precursor for N₂O formation) and N₂O formation by AOB is presented. Based on mechanistic grounds, two possible reaction mechanisms for NO and N₂O formation are distinguished, which differ in the origin of the reducing equivalents needed for denitrification by AOB. These two scenarios have been compared in a simulation study, assessing the influence of the aeration/stripping rate and the resulting dissolved oxygen (DO) concentration on the NO and N₂O emission from a SHARON partial nitritation reactor. The study of the simulated model behaviour and its comparison with previously published experimental data serves in elucidating the true NO and N₂O formation mechanism.</p> </div