Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Bioresour Technol. 2010 Jun;101(11):3958-63. doi: 10.1016/j.biortech.2010.01.030. Epub 2010 Feb 6.
Nitrous oxide (N(2)O) is emitted during the aerated nitrification process of wastewater treatment, but its mechanism is not understood. In this study, we employed a model system to clarify the mechanism of N(2)O emission, utilizing the activated sludge derived from a piggery effluent. Aerated incubation of the sludge with ammonium (NH(4)(+)) or hydroxylamine (NH(2)OH) resulted in the emission of a significant amount of N(2)O. The emission stopped when the nitrification substrate (NH(4)(+) or NH(2)OH) was exhausted. When NH(4)(+) was replaced with nitrate (NO(3)(-)) and nitrite (NO(2)(-)), no N(2)O was emitted. This result suggests that the N(2)O emission under nitrifying conditions did not depend on the oxidation of NO(2)(-) by nitrite-oxidizing bacteria (NOB) or denitrification by heterotrophic denitrifiers but depended on the oxidation of NH(4)(+) by ammonia-oxidizing bacteria (AOB). When NO(2)(-), the product of nitrification by AOB, was added to the NH(4)(+)-oxidizing system, N(2)O emission was enormously enhanced, suggesting that N(2)O was formed via denitrification. Diethyldithiocarbamate (DCD), an inhibitor of copper-containing nitrite reductase (NirK), strongly blocked N(2)O emission from NH(2)OH. Furthermore, the expression of the gene (nirK) encoding NirK of AOB was detected in the sludge exposed to the nitrifying conditions. The results showed that N(2)O emission during the nitrification process depends on denitrification by AOB that reside in the activated sludge. This study provides direct evidence for the cause of N(2)O emission from activated sludge (non-pure culture).
一氧化二氮（N(2)O）是在废水处理的充氧硝化过程中排放的，但它的机制尚不清楚。在这项研究中，我们采用模型系统来阐明 N(2)O 排放的机制，利用来自养猪场废水的活性污泥。在有氧条件下，用氨（NH(4)(+)）或羟胺（NH(2)OH）孵育污泥，会导致大量 N(2)O 的排放。当硝化基质（NH(4)(+)或 NH(2)OH）耗尽时，排放停止。当用硝酸盐（NO(3)(-)）和亚硝酸盐（NO(2)(-)）替代 NH(4)(+)时，不会产生 N(2)O。这一结果表明，在硝化条件下，N(2)O 的排放并不依赖于亚硝酸盐氧化菌（NOB）对 NO(2)(-)的氧化或异养反硝化作用，而是依赖于氨氧化菌（AOB）对 NH(4)(+)的氧化。当向 NH(4)(+)氧化系统中添加 AOB 硝化的产物亚硝酸盐时，N(2)O 的排放会大大增加，这表明 N(2)O 是通过反硝化作用形成的。二乙基二硫代氨基甲酸盐（DCD），一种含铜的亚硝酸盐还原酶（NirK）抑制剂，强烈阻止了 NH(2)OH 产生的 N(2)O 排放。此外，在暴露于硝化条件下的污泥中检测到编码 AOB 的 NirK 基因（nirK）的表达。结果表明，硝化过程中的 N(2)O 排放取决于存在于活性污泥中的 AOB 的反硝化作用。这项研究为活性污泥（非纯培养物）中 N(2)O 排放的原因提供了直接证据。
