Nitrosomonas and Nitrobacter Interactions in Biological Nitrification

Biological‐nitrification experiments using chemostats were performed with three different nitrogenous substrates: ammonia, nitrate, and various mixtures of ammonia and nitrite. The study focused on the interrelationship between two groups of nitrifying bacterial utilizing different substrates within the same environment. It was shown that the activity of the Nitrobacter population was strongly dependent on the population of Nitrosomonas, but not vice versa. Nitrite oxidation in the absence of ammonia resulted in a very unstable system and required hydraulic‐retention times of 10 days or greater to obtain complete nitrite oxidation. This is in sharp contrast to the complete oxidation of ammonia to nitrate at the hydraulic‐retention time of 2.7 days. Data are presented to show the effect of the ratio of the population of Nitrosomonas to Nitrobacter on the activity of Nitrobacter.