Nitrification and denitrification
Denitrification is the last stage in the nitrogen cycle. This is a natural biological process by which nitrogen changes from one form to another.
For this step, another group of bacteria such as Nitrobacter hamburgensis will oxidize nitrite to nitrate.
Under anaerobic conditions, the nitrate produced during ammonium oxidation is used as a terminal electron acceptor by microbes. Paracoccus denitrificans is a good example. This reaction produces a non-toxic N2 gas (diazote).
This is because nitrous oxide is harmless, since it represents around 80% of the air we breathe in.
Thanks to nitrification/denitrification, ammonium and nitrate, responsible for the eutrophication of natural waters, are eliminated naturally and without any consequences for our health and our planet.