A consilience model to describe N2O production during biological N removal

Abstract

Nitrous oxide (N₂O), a potent greenhouse gas, is produced during biological nitrogen conversion in wastewater treatment operations. Complex mechanisms underlie N₂O production by autotrophic and heterotrophic organisms, which continue to be unravelled. Mathematical models that describe nitric oxide (NO) and N₂O dynamics have been proposed. Here, a first comprehensive model that considers all relevant NO and N₂O production and consumption mechanisms is proposed. The model describes autotrophic NO production by ammonia oxidizing bacteria associated with ammonia oxidation and with nitrite reduction, followed by NO reduction to N₂O. It also considers NO and N₂O as intermediates in heterotrophic denitrification in a 4-step model. Three biological NO and N₂O production pathways are accounted for, improving the capabilities of existing models while not increasing their complexity. Abiotic contributions from NH₂OH and HNO₂ reactions are also included. The consilient model structure can theoretically predict NO and N₂O emissions under a wide range of operating conditions and will help develop mitigation strategies.