Ammonia removal is becoming more rigorous in permits making it one of the most important and most difficult processes to maintain in wastewater treatment plants. Ammonia can be impacted by various environmental factors, shocks, toxicity and solids loss.
Nitrification is a two-step biological process by which aerobic bacteria oxidize ammonium to nitrate. Nitrifying bacteria oxidize ammonium ions (NH4+) to nitrite (NO2-) in the first step and then oxidize nitrite to nitrate (NO3-) in the second step. The microorganisms can also be described by the step of the process they drive: ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). Many wastewater treatment systems require nitrification to occur to complete the treatment process. This is accomplished by maintaining two types of bacteria, Nitrosomonas and Nitrobacter. Both types of nitrifiers are autotrophs, which means they build cellular materials using carbon dioxide or carbonate and obtain energy from the chemical conversion of ammonia into nitrite and nitrate. Autotrophic nitrifying bacteria obtain less energy during their metabolic processes compared to more common heterotrophic (require organic carbon for growth) wastewater bacteria. This lower energy level results in slower cellular growth. This is especially true in the case of Nitrosomonas. Nitrosomonas are responsible for the conversion of ammonia into nitrite. Conversely, the growth of Nitrobacter is affected because they are responsible for taking the nitrite and converting it into nitrate.
Several parameters must be maintained for successful growth of nitrifying bacteria:
