Nitrification and denitrification

Nitrification/denitrification is the most common biological process for removing nitrogenous substances from wastewater. MBBR biological treatment is used to clean nitrogen-rich wastewater. Most treatment systems rely on microbial activity. The purpose is to remove undesirable nitrogen and mineral compounds:
  • ammonia
  • nitrites
  • nitrates
To remove these compounds, bacteria must follow a two-step process.

Nitrification step

The first step is nitrification. The process involves Nitrosomonas europaea or similar bacteria. In this phase, bacteria oxidize ammonium to nitrite under aerobic conditions. Moreover, the efficiency of the nitrification process depends on the extent to which organic nitrogen is converted into ammoniacal nitrogen. In addition, it can be carried out at the same time as secondary treatment (oxidation and nitrification) or as tertiary treatment (separate nitrification).

Denitrification step

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.

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