denitrify

verb (used with object), de·ni·tri·fied, de·ni·tri·fy·ing. Chemistry.

1. to remove nitrogen or nitrogen compounds from.
2. to reduce (nitrates) to nitrites, ammonia, and free nitrogen, as in soil by microorganisms.

verb -fies, -fying or -fied

1. to undergo or cause to undergo loss or removal of nitrogen compounds or nitrogen