Nitrogen occurs naturally as a gas (N2), as well as bound up in the relatively simple molecules of Ammonia (NH3) or its ion NH4, Nitrite (NO2) and Nitrate (NO3), or in more complex molecules, principally amino acids & proteins, which include urea and uric acid.
Total Nitrogen (TN) is the sum of all nitrogen forms:
= Ammonia (NH3) + Organic Nitrogen (Nitrogen in amino acids and proteins) + Nitrite (NO2) + Nitrate (NO3)
also = TKN + NO2 + NO3 (the formula used to measure nitrogen at wastewater plants). TKN stands for Total Kjeldahl Nitrogen which is the sum of NH3 + Organic Nitrogen.
Refractory Nitrogen is nitrogen that can’t be biologically decomposed.
Alkalinity is easiest defined as the ability to resist a reduction in pH. For every 1 part ammonia (NH3) converted to nitrate (NO3), 7.1 parts of alkalinity are depleted, and for every 1 part nitrate (NO3) removed, 3.6 parts alkalinity are recovered.
An anoxic zone is an areas where the dissolved oxygen levels are less than 1.0 mg/L. In an anoxic zone an organism's oxygen source is derived from the nitrate (NO3) compounds.
Nitrification is the conversion of ammonia (NH3) to nitrate (NO3). In a wastewater plant, and similarly in the soil, this is a two‐step process that is done with oxygen and two types of bacteria, Nitrosomonas and Nitrobacter, known collectively as the nitrifiers.
Ammonia (NH3) + Oxygen (O2) + Alkalinity + Nitrosomonas = Nitrite (NO2).
Then Nitrite (NO2) + Oxygen (O2) + Alkalinity + Nitrobacter = Nitrate (NO3).
Nitrite (NO2) is an unstable form of nitrogen and is easily converted.
The total conversion of ammonia (NH3) to nitrate (NO3) takes 4.6 parts oxygen and 7.1 parts alkalinity to convert 1 part ammonia (NH3).
Denitrification is the conversion of nitrate (NO3) to nitrogen gas (N2). Heterotrophic bacteria utilize the nitrate (NO3) as an oxygen source under anoxic conditions to break down organic substances.
Nitrate (NO3) + Organics + Heterotrophic bacteria = Nitrogen Gas & Oxygen & Alkalinity.