Terminology needed to discuss organisms responsible for removal of ammonia & nitrite in wastewater treatment plants

Almost every textbook and lecture on wastewater discusses nitrification (the conversion of ammonia into nitrate) is due to the action of two separate species of bacteria. 

Nitrosomonas sp. - are a bacterial species that oxidizes ammonia into nitrite. Nitrosomonas is a common ammonia oxidizing bacteria or (AOB). Nitrosomonas is an obligate aerobe that thrives in mesophilic waters with pH from 7.5 - 8.2 as it requires ammonia (NH3-N) form for growth. Lower pH decreases nitrogen in NH3 or free ammonia form, thereby decreasing Nitrosomonas growth rates. Other AOB include Nitrosococcus  and Nitrospira.

Nitrobacter sp. - are bacteria that oxidize nitrite into nitrate (the second step mentioned in textbooks). These organisms are also called nitrite oxidizing bacteria (NOB) Other bacteria known for nitrite oxidation include Nitrobacter, Nitrococcus, Nitrospina, and Nitrospira.

Now there is another ammonia oxidation step:

Ammonia Oxidizing Archaea (AOA) - are less well known ammonia oxidizers, but are very important in marine environments and in areas not exploited by AOB. In wastewater systems, you would find AOA in systems with lower pH as many AOA can also utilize nitrogen in the NH4+ form. Researchers are still exploring the diversity of the AOA and how they impact ammonia oxidation in wastewater treatment plants.

In addition to discovery of new organisms responsible of ammonia and nitrite removal, research and system design is moving into new directions based on ecological niche and some unusual organisms. Below are the newer ideas in ammonia and nitrite removal in wastewater treatment.

Anaerobic Ammonia Oxidation (ANAMMOX) - involves the aerobic conversion of some influent ammonia into nitrate (the action of AOB & AOA). Under anaerobic conditions, an unusual group of bacteria can use NH4+ + NO2− → N2 + 2H2O. With ANAMMOX technology, oxygen requirement for ammonia & nitrite removal are lowered. However, ANAMMOX cultures are slow growing and require monitoring to ensure proper growth conditions exist.

Complete Ammonia Oxidation (COMAMMOX) - with recent genetic testing, researchers have found Nitrospira organisms that have the ability to oxidize both ammonia to nitrate - which is both steps in one organism. At Aster Bio, we have found significantly higher concentrations of Nitrospira in industrial wastewater treatment plants than any other AOB or NOB. Our molecular testing using both 16s Microbial Community Analysis and qPCR testing has found most aerobic nitrification activity is from a combination of Nitrospira and Nitrosomonas activity.