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.
The efficiency of nitrification depends on how organic nitrogen transforms into ammoniacal nitrogen. Furthermore, this step can be carried out simultaneously with secondary treatment, involving oxidation and nitrification, or as tertiary treatment with separate nitrification, depending on the specific requirements of the process.

Denitrification step

Denitrification completes the nitrogen cycle by naturally transforming it from one form to another.

In this phase, a group of bacteria, such as Nitrobacter hamburgensis, converts nitrites into nitrates through oxidation.


In the absence of oxygen, microbes use nitrate from ammonium to release electrons. The Paracoccus denitrificans is an example. This reaction generates N2 gas, which is non-harmful (dinitrogen).

In fact, dinitrogen is harmless, as it makes up about 80% of the air we breathe. The nitrification/denitrification processes naturally remove ammonium and nitrate. These compounds contribute to the pollution of natural water bodies without causing harm to health or the planet.

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