An N2O emissions model featuring newly integrated abiotic pathways in nitrification

Abstract

Nitrification in biological wastewater treatment is a significant source of nitrous oxide (N2O), a potent greenhouse gas (GHG). There are some models that describe the biological N2O production process, but they don't include abiotic N2O production pathways which, remarkably, contribute up to 50% of the total N2O emissions under high nitrite (NO2-) conditions. This limitation frequently results in pronounced predictive biases under high influent ammonium (NH4+) and intermediate NO2- conditions (such as in the partial nitrification + Anammox system), leading to the misidentification of N2O emissions, undermining the development of effective mitigation strategies. To address this gap, a key abiotic N2O production pathway was integrated into an existing model of nitrification which includes biological N2O emissions. The upgraded model was systematically evaluated using literature-derived case studies, and can effectively predict the contributions of the abiotic pathway to N2O emissions (49%), compared to experimental data (51%). A local sensitivity analysis confirms that the upgraded model has a resilience to perturbations within most parameters, although very high concentrations of NO2- (>1,000 mg N/L) necessitate a precise calibration of ammonium oxidation to nitrite (the AOB process), in which related parameters can more easily be measured in experiments. Moreover, a global sensitivity analysis demonstrates that dissolved oxygen (DO) and alkalinity are the most sensitive of the four key environmental factors (NH4+, NO2-, DO and alkalinity) which control N2O emissions.