The conversion of nitrate (NO3−) to molecular nitrogen (N2) with the help of certain bacteria is called denitrification.
In wastewater treatment, the process of denitrification is used specifically to convert nitrate into molecular nitrogen.
The prerequisite for denitrification is anoxic conditions (absence of molecular oxygen (O2)), which lead to certain heterotrophic and some autotrophic bacteria using nitrate as an oxidant to generate the necessary life energy from oxidisable wastewater substances.