[NO Emission Factors from Wastewater Treatment Plants Based on Literature Statistics and Model Fitting].

The emission of nitrous oxide （NO） during wastewater treatment cannot be ignored. The analysis of statistical data from literature based on 126 empirical studies revealed that the geographical factors of wastewater treatment plants （WWTPs） had a significant impact on NO emission factors. However, the NO emission factors of WWTPs in all regions of the world were generally lower than the Intergovernmental Panel on Climate Change （IPCC） recommended values. In China, the NO emission factors （in NO-N/N） of WWTPs were approximately 0.000 35-0.065 20 kg·kg. Meanwhile, the NO emission factors of different wastewater treatment processes were also significantly different, especially since the sequencing batch reactor （SBR） process had higher emissions. The use of uniform default emission factors for accounting was prone to overestimate NO emissions, and it is recommended that countries conduct actual monitoring or modeling studies to develop categorical emission factors suitable for local conditions. In addition, the NO emission factor based on total nitrogen （TN） removal was weakly negatively correlated with TN removal in 126 empirical data, which was more in line with bioprocessing stoichiometry and could provide an accurate accounting method for NO. To this end, a digital twin model was developed to dynamically simulate a case anaerobic-anoxic-aerobic （AAO） WWTP to comprehensively quantify the dynamic emission behavior of NO, which demonstrated that NO emissions had significant seasonal and daily variability and were only equivalent to 11% of the calculated value of the emission factor based on the IPCC recommendation. Comparing the scatter linear fitting and categorical mean exponential fitting methods, it was found that the latter could more accurately reflect the negative correlation between the NO emission factors and the TN removal rate, and an exponential regression equation between the average NO emission factor based on the amount of TN removed and the TN removal rate was further developed to predict the NO emission. The dynamic simulation and categorical index fitting methods provided in this study are important references for the accurate accounting of NO emissions in similar WWTPs and provide help for understanding and responding to the NO emission problems.