As mentioned in Section 2.3, the consensus on the main mechanism of N2O emission during
wastewater treatment has not yet been achieved and there are many process design parameters and
operation conditions closely related to N2O emission, the emission factor selected in this study is based
on an average value of the measurement of N2O emissions from seven full-scale biological nutrient
removal (BNR) WWTPs in Australia [24]. The measurements found that particular design parameters,
e.g., high mixed-liquor recycle (MLR) rates and low effluent TN concentrations, potentially influence
the generation of N2O and higher MLR rates, and lower effluent TN concentrations were more likely to
have higher and variable N2O generation factors. The design of low effluent TN concentration, influent
flow balancing, high MLR rate, larger bioreactor volume, and long SRT is more likely to lead to
complete denitrification, which could result in low and stable N2O emissions. For example, a high MLR
rate tends to dilute the concentrations of all the intermediates of nitrification–denitrification, including
nitrite (NO