Nitrogen gets from organisms back into the atmosphere through a process called denitrification. Denitrification is performed by bacteria that live in aerobic or anaerobic environments. Denitrification converts nitrate (NO3-) and nitrite (NO2-), into nitrogen gas (N2). This process is the final step in the nitrogen cycle, and it returns nitrogen to the atmosphere.

The process of denitrification can be described by the following chemical equation:

2 NO3- + 10 e- + 12 H+ → N2 + 6 H2O

In this equation, nitrate (NO3-) is reduced (gains electrons) to form nitrogen gas (N2). The electrons that are needed for this reaction are typically obtained from organic matter, which is broken down by bacteria.

Denitrification is a very important process in the nitrogen cycle because it helps to regulate the amount of nitrogen that is available to plants and other organisms. Denitrification also helps to reduce the amount of nitrate pollution that can enter waterways and cause problems for aquatic ecosystems.