Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, P.O. Box 611, 8600 Duebendorf, Switzerland.
Water Res. 2012 Mar 15;46(4):1027-37. doi: 10.1016/j.watres.2011.11.080. Epub 2011 Dec 8.
Nitrous oxide (N2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions. Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment. Under anoxic conditions, nitrate reducing experiments confirmed that N2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.
一氧化二氮（N2O）是一种重要的温室气体，也是平流层臭氧的主要消耗物。在生物废水处理中，自养硝化和异养反硝化等微生物过程已被确定为主要来源；然而，其潜在途径仍不清楚。在这项研究中，采用实验室批量系统中的活性污泥处理城市废水，研究了 N2O 的产生机制。该相对复杂的混合种群系统很好地代表了硝化和反硝化条件下的全规模活性污泥处理。在好氧条件下，添加亚硝酸盐会导致强烈依赖亚硝酸盐的 N2O 产生，主要通过氨氧化细菌（AOB）的硝化反硝化作用产生。此外，通过添加羟胺表明，N2O 是通过羟胺氧化产生的。在这两组实验中，当底物（亚硝酸盐、羟胺）完全消耗时，N2O 的产生在实验开始时最高，然后连续下降并停止。在氨氧化实验中，当亚硝酸盐浓度最低时，N2O 在实验开始时达到峰值。这表明，在高氨和低亚硝酸盐浓度下，通过羟胺氧化产生 N2O 是有利的，并且与氨氧化细菌的高代谢活性（在 2 到 3mgO2/l 时）相结合；在实验结束时，随着亚硝酸盐浓度升高和氨浓度降低，AOB 的硝化反硝化作用的贡献增加。在缺氧条件下，硝酸盐还原实验证实，在异养反硝化的最佳生长条件下（例如，没有氧气输入和可生物降解有机碳没有限制），N2O 排放量很低。然而，在存在亚硝酸盐或低溶解氧浓度的情况下，N2O 和一氧化氮（NO）的产生速率显著增加。
