School of the Environment, Guangdong Engineering Research Center of Water Treatment Processes and Materials, Jinan University, Guangzhou, China.
School of the Environment, Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University, Guangzhou, China.
Appl Environ Microbiol. 2021 May 11;87(11). doi: 10.1128/AEM.00154-21r.
Nitrification is an essential process for nutrient removal from wastewater and an important emission source of nitrous oxide (NO), which is a powerful greenhouse gas and a dominant ozone-depleting substance. In this study, nitrification and NO emissions were tested in two weakly acidic (pH 6.3 to 6.8) reactors: one with dissolved oxygen (DO) at over 2.0 mg/liter and the other with DO at approximately 0.5 mg/liter. Efficient nitrification was achieved in both reactors. Compared to that in the high-DO reactor, NO emission in the low-DO reactor decreased slightly, by 20%, and had insignificant correlation with the fluctuations of DO ( = 0.935) and nitrite ( = 0.713), indicating that NO might not be produced mainly via nitrifier denitrification. Based on quantitative PCR (qPCR), quantitative fluorescent hybridization (qFISH), and functional gene amplicon and metagenome sequencing, it was found that complete ammonia oxidizers (comammox), i.e., organisms, significantly outnumbered canonical ammonia-oxidizing bacteria (AOB) in both weakly acidic reactors, especially in the low-DO reactor with the comammox/AOB gene ratio increasing from 6.6 to 17.1. Therefore, it was speculated that the enriched comammox was the primary cause for the slightly decreased NO emission under long-term low DO in the weakly acidic reactor. This study demonstrated that the comammox can survive well under the weakly acidic and low-DO conditions, implying that achieving efficient nitrification with low NO emission as well as low energy and alkalinity consumption is feasible for wastewater treatment. Nitrification in wastewater treatment is an important process for eutrophication control and an emission source for the greenhouse gas NO. The nitrifying process is usually operated at a slightly alkaline pH and high DO (>2 mg/liter) to ensure efficient nitrification. However, it consumes a large amount of energy and chemicals, especially for wastewater without sufficient alkalinity. This paper demonstrates that comammox can adapt well to the weakly acidic and low-DO bioreactors, with a result of efficient nitrification and low NO emission. These findings indicate that comammox organisms are significant for sustainable wastewater treatment, which provides an opportunity to achieve efficient nitrification with low NO production as well as low energy and chemical consumption simultaneously.
硝化作用是从废水中去除营养物质的重要过程，也是氧化亚氮（N2O）的重要排放源，N2O 是一种强大的温室气体和主要的臭氧消耗物质。在这项研究中，在两个弱酸性（pH 6.3 至 6.8）反应器中测试了硝化作用和 N2O 排放：一个溶解氧（DO）超过 2.0mg/l，另一个 DO 约为 0.5mg/l。两个反应器均实现了高效硝化。与高 DO 反应器相比，低 DO 反应器中的 N2O 排放略有下降，降幅为 20%，且与 DO（=0.935）和亚硝酸盐（=0.713）的波动没有显著相关性，表明 N2O 可能不是主要通过硝化反硝化产生的。基于定量聚合酶链式反应（qPCR）、定量荧光原位杂交（qFISH）以及功能基因扩增子和宏基因组测序，发现完整氨氧化菌（comammox），即，在两个弱酸性反应器中，尤其是在 DO 长期处于低值的低 DO 反应器中，comammox 明显多于经典氨氧化菌（AOB），comammox/AOB 基因比从 6.6 增加到 17.1。因此，推测在弱酸性和低 DO 条件下，富集的 comammox 是导致长期低 DO 下 N2O 排放略有减少的主要原因。本研究表明，comammox 在弱酸性和低 DO 条件下能良好生存，这意味着在低能耗和低碱度消耗的情况下实现高效硝化和低 N2O 排放是可行的。污水处理中的硝化作用是控制富营养化和氧化亚氮（NO）温室气体排放的重要过程。硝化过程通常在略碱性 pH 值和高 DO（>2mg/liter）下运行，以确保高效硝化。然而，它消耗大量的能源和化学品，特别是对于没有足够碱度的废水。本文表明，comammox 可以很好地适应弱酸性和低 DO 生物反应器，实现高效硝化和低 N2O 排放。这些发现表明，comammox 生物对可持续污水处理具有重要意义，为同时实现高效硝化和低 NO 生成以及低能耗和低化学品消耗提供了机会。
