Department of Civil and Environmental Engineering and Earth Science, University of Notre Dame , 156 Fitzpatrick Hall, Notre Dame, Indiana 46556 United States.
Environ Sci Technol. 2015 Feb 3;49(3):1486-94. doi: 10.1021/es5046919. Epub 2015 Jan 15.
Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. However, little is known about N2O emissions from biofilm processes. We adapted an existing suspended-growth mathematical model to explore N2O emissions from nitrifying biofilms. The model included N2O formation by ammonia-oxidizing bacteria (AOB) via the hydroxylamine and the nitrifier denitrification pathways. Our model suggested that N2O emissions from nitrifying biofilms could be significantly greater than from suspended growth systems under similar conditions. The main cause was the formation and diffusion of hydroxylamine, an AOB nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. In the anoxic regions, hydroxylamine oxidation by AOB provided reducing equivalents used solely for nitrite reduction to N2O, since there was no competition with oxygen. For a continuous system, very high and very low dissolved oxygen (DO) concentrations resulted in lower emissions, while intermediate values led to higher emissions. Higher bulk ammonia concentrations and greater biofilm thicknesses increased emissions. The model effectively predicted N2O emissions from an actual pilot-scale granular sludge reactor for sidestream nitritation, but significantly underestimated the emissions when the NH2OH diffusion coefficient was assumed to be minimal. This numerical study suggests an unexpected and important role of hydroxylamine in N2O emission in biofilms.
污水处理厂可能是氧化亚氮（N2O）的重要来源，氧化亚氮是一种强效温室气体。然而，人们对生物膜工艺中 N2O 的排放知之甚少。我们对现有的悬浮生长数学模型进行了改编，以探讨硝化生物膜中的 N2O 排放。该模型包括氨氧化细菌（AOB）通过羟胺和硝化反硝化途径形成 N2O。我们的模型表明，在相似条件下，硝化生物膜中的 N2O 排放可能明显大于悬浮生长系统。主要原因是羟胺的形成和扩散，羟胺是 AOB 硝化过程中的一种中间体，从好氧区向生物膜的缺氧区扩散。在缺氧区，AOB 氧化羟胺提供了仅用于将亚硝酸盐还原为 N2O 的还原当量，因为没有与氧气竞争。对于连续系统，非常高和非常低的溶解氧（DO）浓度会导致排放减少，而中间值会导致排放增加。较高的基质氨浓度和较大的生物膜厚度会增加排放。该模型有效地预测了实际中试规模侧流亚硝化颗粒污泥反应器中的 N2O 排放，但当假设 NH2OH 扩散系数最小时，排放明显被低估。这项数值研究表明，羟胺在生物膜中 N2O 排放中具有意想不到的重要作用。
