Aerated Biological Nitrogen Removal

Mike Rousey, Hach Company

Excess ammonia in receiving waters causes algal blooms that decrease oxygen levels. For this reason, many wastewater treatment plants (WWTPs) must limit ammonia in discharge.

Aerated nitrification, or the conversion of ammonia to nitrate, requires a specific population of beneficial bacteria and the proper environment to maintain that population:

Microorganisms
Bacteria from the Nitrosomas group – nitrogenous bacteria that convert ammonia to nitrite, the first stage of biological decomposition.

Bacteria from the Nitrobacter group – carbonaceous bacteria that convert nitrite to nitrate, the second stage of the nitrification process.

These microorganisms exist together in the aeration basin, after a first-stage activated sludge process or a trickling filter (primary clarifier) that removes the carbonaceous biological oxygen demand (BOD) and 90-95% of the suspended solids.