Desnitrification

The biological reduction of nitrate (NO3) to nitrogen gas (N2) by facultative
heterotrophic bacteria is called Denitrification. “Heterotrophic” bacteria need a carbon source as
food to live. “Facultative” bacteria can get their oxygen by taking dissolved oxygen out of the
water or by taking it off of nitrate molecules.

Denitrification occurs when oxygen levels are depleted and nitrate becomes the primary oxygen
source for microorganisms. The process is performed under anoxic conditions, when the dissolved
oxygen concentration is less than 0.5 mg/L