The presence of organic matter during autotrophic nitrogen removal: Problem or opportunity?

The simultaneous nitrification, Anammox and denitrification (SNAD) process discovered six years ago is an adaptation of the autotrophic denitrification process that allows for treating nitrogen-rich wastewater streams with moderate amounts of organic carbon. Several authors have noted that it is possible to utilize organic carbon to promote nitrogen removal via the action of denitrifying microorganisms, which can remove the remnant nitrate produced by Anammox bacteria. Thus, SNAD systems can achieve nitrogen removal efficiencies higher than 89%, which is what is expected under autotrophic conditions. Three bacterial groups are responsible for SNAD reactions: ammonium-oxidizing bacteria (AOB), anaerobic ammonium-oxidizing bacteria (AnAOB) and heterotrophic bacteria (HB). Because HB will compete with AOB and AnAOB for oxygen and nitrite, respectively, the system should be operated in such way that a balance among the different bacterial populations is achieved. Here, the results reported in the literature are analyzed to define suitable characteristics of effluents for treatment and operational conditions to allow the SNAD process to be carried out with different types of technologies.