Nitrate Reverses Severe Nitrite Inhibition of Anaerobic Ammonium Oxidation (Anammox) Activity in Continuously-Fed Bioreactors

摘要

Nitrite (NO_2~- ) substrate under certain conditions can cause failure of N-removal processes relying on anaerobic ammonium oxidizing (anammox) bacteria. Detoxification of NO_2~- can potentially be achieved by using exogenous nitrate (NO_3~-). In this work, continuous experiments in bioreactors with anammox bacteria closely related to "Candidatus Brocadia caroliniensis" were conducted to evaluate the effectiveness of short NO_3~- additions to reverse NO_2~- toxicity. The results show that a timely NO_3~- addition immediately after a NO_2~- stress event completely reversed the NO_2~- inhibition. This reversal occurs without NO_3~- being metabolized as evidence by lack of any ~(30)N_2 formation from ~(15)N-NO_3~-. The maximum recovery rate was observed with 5 mM NO_3~- added for 3 days; however, slower but significant recovery was also observed with 5 mM NO_3~- for 1 day or 2 mM NO_3~- for 3 days. Without NO_3~- addition, long-term NO_2~- inhibition of anammox biomass resulted in irreversible damage of the cells. These results suggest that a short duration dose of NO_3~- to an anammox bioreactor can rapidly restore the activity of NO_2~--stressed anammox cells. On the basis of the results, a hypothesis about the detoxification mechanism related to narK genes in anammox bacteria is proposed and discussed.