Hydroxylamine, nitrous acid, and nitric oxide are obligate intermediates or side metabolites in different nitrogen-converting microorganisms. These compounds are unstable and susceptible to the formation of highly reactive nitrogen species, including nitrogen dioxide, dinitrogen trioxide, nitroxyl, and peroxynitrite. Due to the high reactivity and cytotoxicity, the buildup of reactive nitrogen can affect the interplay of microorganisms/microbial processes, stimulate the reactions with organic compounds like organic micropollutants (OMP) and act as the precursors of nitrous oxide (N₂O). However, there is little understanding of the occurrence and significance of reactive nitrogen during biological nitrogen conversions in engineered water systems. In this review, we evaluate the formation and fate of reactive nitrogen produced by microorganisms involved in biological nitrogen removal (BNR) processes, i.e., nitritation/nitrification, denitratation/denitrification, anammox, and the combined processes. While the formation of reactive nitrogen intermediates is entirely controlled by microbial activities, the consumption can be either biological or purely chemical. Changes in environmental conditions, such as redox transition, pH, and substrate availability, can imbalance the production and consumption of these reactive intermediates, thus leading to the transient accumulation of species. Based on previous experimental evidence, environmental relevance of reactive nitrogen in BNR systems, particularly related to abiotic N₂O production and OMP transformation, is demonstrated.

中文翻译：

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生物脱氮过程中活性氮的形成和归宿：氮循环的重要但经常被忽视的化学方面


羟胺、亚硝酸和一氧化氮是不同氮转化微生物中的专性中间体或副代谢物。这些化合物不稳定，易形成高活性氮物质，包括二氧化氮、三氧化二氮、硝氧基和过氧亚硝酸盐。由于活性氮的高反应性和细胞毒性，活性氮的积累会影响微生物/微生物过程的相互作用，刺激与有机微污染物 （OMP） 等有机化合物的反应，并充当一氧化二氮 （N₂O） 的前体。然而，人们对工程水系统中生物氮转化过程中活性氮的发生和意义知之甚少。在这篇综述中，我们评估了参与生物脱氮 （BNR） 过程的微生物产生的活性氮的形成和归宿，即硝化/硝化、反硝化/反硝化、厌氧氨氧化和联合过程。虽然活性氮中间体的形成完全由微生物活动控制，但消耗可以是生物的或纯化学的。环境条件的变化，如氧化还原转变、pH 值和底物可用性，会使这些反应性中间体的生产和消耗失衡，从而导致物种的瞬时积累。基于先前的实验证据，证明了 BNR 系统中活性氮的环境相关性，特别是与非生物 N₂O 产生和 OMP 转化有关。