Mathematical modeling of the dynamic effect of denitrifying glycogen-accumulating organisms on nitrous oxide production during denitrifying phosphorus removal

• A denitrifying model was developed to simulate the dynamics of N 2 O production in a hybrid system coexisting DPAOs and DGAOs. • The model predictions matched experimental data from three independent reports on DPR. • The estimated parameter values indicated the PHA storage rate of DGAOs was higher than that of DPAOs during anaerobic stage. • The preference of DGAOs for nitrate and their cooperation in providing nitrite to DPAOs were reflected. • The source microorganisms and pathways of N 2 O production were traced for different operational conditions. The large amount of intermediate nitrous oxide (N 2 O) production from denitrifying phosphorus removal (DPR) increases the carbon footprint of wastewater treatment. However, there is a lack of detailed understanding of the interrelationships between denitrifying polyphosphate-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) on N 2 O production during DPR. In this work, a mathematical model was developed for the first time to describe dynamic N 2 O production in the DPR system coexisting DPAOs and DGAOs. The model took into account a four-step subsequent denitrification of nitrate, nitrite, nitric oxide, and N 2 O. The validity of model was fully tested by comparing simulation studies with experimental data from three independent reports on DPR, which satisfactorily described the dynamics of N 2 O production, nitrogen oxide reduction, phosphate release and uptake, and intracellular polymers turnover. The validated model could clarify the source and pathways of N 2 O production. Subsequently, the combined effects of key operational conditions on the overall N 2 O production, DPAOs and DGAOs competition, and nutrients removal efficiency were investigated by model simulation. Simulation results showed higher polyhydroxyalkanoate storage rate of DGAOs than that of DPAOs during anaerobic stage and the preference of DGAOs for nitrate electron acceptor during anoxic stage. DGAOs dominated the growth competition over DPAOs at low COD (<150 mg/L) and high nitrate (>35 mg/l) conditions, leading to the anoxic storage of glycogen by DGAOs as the main pathway of N 2 O production. In addition, both N 2 O production and generation pathways in the system possessed greater variability compared to single DGAOs or DPAOs system, further indicating the necessity of this model.