With this high concentration of ammonia, the wastewater would harm downstream ecosystems if released. It is desirable transform the ammonia as part of the waste treatment process, where aeration and other conditions, such as temperature can be controlled. The nitrification process is carried out by two different types of bacteria. These reactions, although thermodynamically favorable, occur slowly. The rate of these reactions seems to be limited by the slow growth rates of the bacteria involved.
Most nitrifying bacteria are autotrophic, with carbon dioxide serving as their carbon source.
The rates of nitrification reaction are highly dependent on a number of environmental factors. These include the substrate and oxygen concentration, temperature, pH, and the presence of toxic or inhibiting substances. The kinetics can be described with the Monod expression, and in most cases the rate is limited by the first step, the oxidation of the ammonia. At steady state, the amount of NO 2 - present is usually small and can be ignored in inital design. Rapid changes in temperature do not produce rapid changes in growth rates.