School of Environment, Guangdong Engineering Research Center of Water Treatment Processes and Materials and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University, Guangzhou 510632, China.
Environ Sci Technol. 2021 May 18;55(10):6975-6983. doi: 10.1021/acs.est.0c07279. Epub 2021 Apr 27.
Nitrous oxide (NO) is an important greenhouse gas and a dominant ozone-depleting substance. Nitrification in the activated sludge process (ASP) is an important NO emission source. This study demonstrated that a short-term low dissolved oxygen (DO) increased the NO emissions by six times, while long-term low DO operation decreased the NO emissions by 54% ( < 0.01). Under long-term low DO, the ammonia oxidizer abundance in the ASP increased significantly, and thus, complete nitrification was recovered and no NH or nitrite accumulated. Moreover, long-term low DO decreased the abundance of ammonia-oxidizing bacteria (AOB) by 28%, while increased the abundance of ammonia-oxidizing archaea (AOA) by 507%, mainly due to their higher oxygen affinity. As a result, AOA outnumbered AOB with the AOA/AOB gene ratio increasing to 19.5 under long-term low DO. The efficient nitrification and decreased AOB abundance might not increase NO production via AOB under long-term low DO conditions. The enriched AOA could decrease the NO emissions because they were reported to lack canonical nitric oxide (NO) reductase genes that convert NO to NO. Probably because of AOA enrichment, the positive and significant ( = 0.02) correlation of NO emission and nitrite concentration became insignificant ( = 0.332) after 80 days of low DO operation. Therefore, ASPs can be operated with low DO and extended sludge age to synchronously reduce NO production and carbon dioxide emissions owing to lower aeration energy without compromising the nitrification efficiency.
一氧化二氮（NO）是一种重要的温室气体和主要的消耗臭氧层物质。活性污泥工艺（ASP）中的硝化作用是 NO 排放的重要来源。本研究表明，短期低溶解氧（DO）会使 NO 排放量增加六倍，而长期低 DO 操作会使 NO 排放量减少 54%（<0.01）。在长期低 DO 条件下，ASP 中的氨氧化菌丰度显著增加，从而实现完全硝化，没有 NH 或亚硝酸盐积累。此外，长期低 DO 减少了氨氧化细菌（AOB）的丰度 28%，同时增加了氨氧化古菌（AOA）的丰度 507%，主要是因为它们对氧气的亲和力更高。结果，AOA 与 AOB 的数量比在长期低 DO 下增加到 19.5。长期低 DO 条件下，由于 AOA 的高效硝化作用和 AOB 丰度的降低，可能不会通过 AOB 增加 NO 的产生。富集的 AOA 可以减少 NO 的排放，因为它们缺乏将 NO 转化为 NO 的典型一氧化氮（NO）还原酶基因。可能是由于 AOA 的富集，在低 DO 运行 80 天后，NO 排放与亚硝酸盐浓度之间的正相关（=0.02）变得不显著（=0.332）。因此，ASP 可以在低 DO 和延长污泥龄的条件下运行，从而在不影响硝化效率的情况下，同步减少 NO 产生和二氧化碳排放，因为曝气能耗更低。
