Department of Earth and Environmental Engineering, Columbia University, 500 West 120th Street, New York, NY 10027, USA.
Biochem Soc Trans. 2011 Dec;39(6):1832-7. doi: 10.1042/BST20110717.
Chemolithoautotrophic AOB (ammonia-oxidizing bacteria) form a crucial component in microbial nitrogen cycling in both natural and engineered systems. Under specific conditions, including transitions from anoxic to oxic conditions and/or excessive ammonia loading, and the presence of high nitrite (NO₂⁻) concentrations, these bacteria are also documented to produce nitric oxide (NO) and nitrous oxide (N₂O) gases. Essentially, ammonia oxidation in the presence of non-limiting substrate concentrations (ammonia and O₂) is associated with N₂O production. An exceptional scenario that leads to such conditions is the periodical switch between anoxic and oxic conditions, which is rather common in engineered nitrogen-removal systems. In particular, the recovery from, rather than imposition of, anoxic conditions has been demonstrated to result in N₂O production. However, applied engineering perspectives, so far, have largely ignored the contribution of nitrification to N₂O emissions in greenhouse gas inventories from wastewater-treatment plants. Recent field-scale measurements have revealed that nitrification-related N₂O emissions are generally far higher than emissions assigned to heterotrophic denitrification. In the present paper, the metabolic pathways, which could potentially contribute to NO and N₂O production by AOB have been conceptually reconstructed under conditions especially relevant to engineered nitrogen-removal systems. Taken together, the reconstructed pathways, field- and laboratory-scale results suggest that engineering designs that achieve low effluent aqueous nitrogen concentrations also minimize gaseous nitrogen emissions.
化能自养氨氧化细菌（AOB）是自然和工程系统中微生物氮循环的重要组成部分。在特定条件下，包括从缺氧条件到好氧条件和/或过度氨负荷的转变，以及高亚硝酸盐（NO₂⁻）浓度的存在，这些细菌也被记录为产生一氧化氮（NO）和氧化亚氮（N₂O）气体。本质上，在非限制底物浓度（氨和 O₂）存在下的氨氧化与 N₂O 的产生有关。导致这种情况的一个特殊情况是缺氧和好氧条件之间的周期性切换，这在工程氮去除系统中相当常见。特别是，从缺氧条件的恢复而不是缺氧条件的施加已被证明会导致 N₂O 的产生。然而，迄今为止，应用工程观点在很大程度上忽略了硝化作用对污水处理厂温室气体清单中 N₂O 排放的贡献。最近的现场规模测量表明，与异养反硝化相比，硝化相关的 N₂O 排放通常要高得多。在本文中，根据与工程氮去除系统特别相关的条件，从概念上重建了 AOB 可能导致 NO 和 N₂O 产生的代谢途径。总之，重建的途径、现场和实验室规模的结果表明，实现低出水含氮浓度的工程设计也可最大限度地减少气态氮排放。
