基于文献统计和模型拟合的污水处理厂N2O排放因子

N2O Emission Factors from Wastewater Treatment Plants Based on Literature Statistics and Model Fitting

污水处理过程中氧化亚氮(N_(2)O)的排放不容忽略.基于126个实证的文献统计数据分析发现,污水处理厂(WWTPs)的地域因素对N_(2)O排放因子有显著影响.然而,全球各地区WWTPs的N_(2)O排放因子普遍低于联合国政府间气候变化专门委员会(IPCC)推荐值.在中国,WWTPs的N_(2)O排放因子(以N_(2)O-N/N_(influent)计)约为0.000 35~0.065 20 kg·kg^(-1).同时,不同污水处理工艺的N_(2)O排放因子也存在显著差异,尤其序批式活性污泥(SBR)工艺具有较高排放.采用统一的缺省排放因子进行核算容易高估N_(2)O排放量,建议各国进行实际监测或模型研究,以制定适合本土情况的分类排放因子.此外,在126个实证数据中,基于总氮(TN)去除量的N_(2)O排放因子与TN去除率呈弱负相关,更符合生物处理化学计量学,可以提供准确的N_(2)O核算方法.为此,建立数字孪生模型对案例厌氧-缺氧-好氧(AAO)WWTP进行动态模拟,全面量化N_(2)O的动态排放行为,证明N_(2)O排放具有明显的季节性和日变化性,且仅相当于IPCC推荐排放因子计算值的11%.比较散点线性拟合和分类平均值指数拟合方法,发现后者能更准确地反映N_(2)O排放因子与TN去除率之间的负相关,进一步建立了基于TN去除量的N_(2)O平均排放因子与TN去除率的指数回归方程以预测N_(2)O的排放.本研究提供的动态模拟和分类指数拟合方法对同类WWTPs精确核算N_(2)O具有重要参考价值,可为理解和应对N_(2)O排放问题提供帮助.

The emission of nitrous oxide(N_(2)O)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 N_(2)O emission factors.However,the N_(2)O 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 N_(2)O emission factors(in N_(2)O-N/N_(influent))of WWTPs were approximately 0.00035-0.06520 kg·kg^(−1).Meanwhile,the N_(2)O 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 N_(2)O 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 N_(2)O 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 N_(2)O.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 N_(2)O,which demonstrated that N_(2)O 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 N_(2)O emission factors and the TN removal rate,and an exponential regression equation between the average N_(2)O emission factor based on the amount of TN removed and the TN removal rate was further developed to predict the N_(2)O emission.The dynamic simulation and categorical index fitting methods provided in this study are important references for the accurate accounting of N_(2)O emissions in similar WWTPs and provide help for understanding and responding to the N_(2)O emission problems.