Knapp Charles W, Graham David W
School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, UK.
FEMS Microbiol Ecol. 2007 Nov;62(2):195-201. doi: 10.1111/j.1574-6941.2007.00380.x. Epub 2007 Sep 14.
Nitrification is an important process for nitrogen removal in many wastewater treatment plants, which requires the mutualistic oxidation of ammonia to nitrate by ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). However, this process can be quite unpredictable because both guilds are conditionally sensitive to small changes in operating conditions. Here, dynamics are examined within the NOB guild in two parallel chemostats operated at low and high dilution rates (0.10 and 0.83 day(-1), respectively) during periods of varying nitrification performance. NOB and AOB guild abundances and nitrogen-oxidation efficiency were relatively constant over time in the 0.10 day(-1) reactor; however, the 0.83 day(-1) reactor had two major disturbance episodes that caused destabilization of the NOB guild, which ultimately led to nitrification failure. The first episode caused the extinction of Nitrospira spp. from the system, resulting in chronic incomplete ammonia oxidation and nitrite accumulation. The second episode caused complete loss of nitrification activity, likely resulting from metal toxicity and the previous extinction of Nitrospira spp. from the system. These results exemplify the types of changes that can occur within the NOB guild that result in process impairment or failure, and provide one possible explanation for why nitrification is often unstable at higher dilution rates.
硝化作用是许多污水处理厂中氮去除的重要过程，这需要氨氧化细菌（AOB）和亚硝酸盐氧化细菌（NOB）将氨相互氧化为硝酸盐。然而，这个过程可能非常不可预测，因为这两个菌群对操作条件的微小变化都有条件敏感性。在此，在不同硝化性能期间，对两个分别以低稀释率和高稀释率（分别为0.10和0.83天⁻¹）运行的平行恒化器中NOB菌群的动态进行了研究。在0.10天⁻¹的反应器中，NOB和AOB菌群丰度以及氮氧化效率随时间相对恒定；然而，0.83天⁻¹的反应器有两次主要干扰事件，导致NOB菌群不稳定，最终导致硝化作用失败。第一次事件导致系统中硝化螺菌属灭绝，导致长期不完全氨氧化和亚硝酸盐积累。第二次事件导致硝化活性完全丧失，可能是由于金属毒性以及系统中先前硝化螺菌属的灭绝。这些结果例证了NOB菌群内可能发生的导致过程受损或失败的变化类型，并为为什么硝化作用在较高稀释率下往往不稳定提供了一种可能的解释。
