Nitrite (NO2 -) substrate under certain conditions can cause failure of N-removal processes relying on anaerobic ammonium oxidizing (anammox) bacteria. Detoxification of NO2 - can potentially be achieved by using exogenous nitrate (NO3 -). In this work, continuous experiments in bioreactors with anammox bacteria closely related to "Candidatus Brocadia caroliniensis" were conducted to evaluate the effectiveness of short NO3 - additions to reverse NO2 - toxicity. The results show that a timely NO3 - addition immediately after a NO2 - stress event completely reversed the NO2 - inhibition. This reversal occurs without NO3 - being metabolized as evidence by lack of any 30N2 formation from 15N-NO3 -. The maximum recovery rate was observed with 5 mM NO3 - added for 3 days; however, slower but significant recovery was also observed with 5 mM NO3 - for 1 day or 2 mM NO3 - for 3 days. Without NO3 - addition, long-term NO2 - inhibition of anammox biomass resulted in irreversible damage of the cells. These results suggest that a short duration dose of NO3 - to an anammox bioreactor can rapidly restore the activity of NO2 --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.
ASJC Scopus subject areas
- Environmental Chemistry