Nitrite (not free nitrous acid) is the main inhibitor of the anammox process at common pH conditions
Nitrite is a substrate but also an inhibitor of anaerobic ammonium oxidation (anammox).There is currently no consensus on whether ionized nitrite (INi) or free nitrous acid (FNA) is the actual inhibitor of the process. The inhibition by INi and FNA on the anammox process has been analysed using a wide range of INi and FNA concentrations and by altering the pH and total nitrite conditions. The inhibitory impacts of both species were quantified through a rational inhibition equation, considering INi and FNA as substrate inhibitor and non-competitive inhibitor, respectively. Inhibitory constants were calculated with strong statistical support as 561 mg INi-N l−1 and 0.117 mg FNA-N l−1. Based on the model, INi is the main inhibiting species of the anammox process at pH > 7.1, which are the most common conditions occurring in field applications of anammox.
KeywordsAnaerobic ammonium oxidation Anammox Free nitrous acid Inhibition Kinetics Nitrite
This work has been supported by the University of Arizona Water Sustainability Program, and by the National Science Foundation (under Contract CBET-1234211). D. Puyol wishes to thank the Spanish Ministry of Education, the USA Council for the International Exchange of Scholars (CIES) and the Spanish Fulbright Commission for receiving a post-doctoral Fulbright grant. In memory of José Antonio Santos González (R.I.P.).