Mecanismos no convencionales de transformación y remoción del nitrógeno en sistemas de tratamiento de aguas residuales

A review of nitrogen transformations in wastewater treatment systems is presented, emphasizing non-conventional mechanisms, by which nitrogen is removed from wastewater. It has been observed that a fraction of nitrogen is lost under aerobic conditions in different biological processes, i.e. during the nitrification phase in biofilm systems. The mechanisms discovered until now that explain this behavior are: 1) simultaneous nitrification and denitrification (SND), 2) denitrification by autotrophic and heterotrophic nitrifying microorganisms, and 3) simultaneous co-respiration of NO_x and O₂ by denitrifiers. These and other two non-conventional nitrogen transformation mechanisms are described here: anaerobic ammonium oxidation (anammox) and chemodenitrification. A bibliographic review involving the discovery of these five mechanisms is made and the reports of its occurrence in biological and physical-chemical processes of wastewater treatment are presented. Besides, two technological processes working mainly or exclusively with non-conventional nitrogen removal mechanisms are presented and described: the Sharon-Anammox process and the Biosor process. A relevant conclusion of this paper is that non-conventional mechanisms may potentially optimize existing processes and develop better ones. Research must continue in this direction.