Understanding the Basic Principles of Nitrogen

(excerpted from an article by Robert Scott the Wastewater Technician for the Atlantic States Rural Water & Wastewater Association.)

In order to understand any conversation on nitrogen it is helpful to understand the different forms of nitrogen and some commonly referred to terms that you get used in the conversation.

Total Nitrogen (TN) is the sum of all nitrogen forms or;

Total Nitrogen = Ammonia Nitrogen (NH3) + Organic Nitrogen (Nitrogen in amino acids and proteins) + Nitrite (NO2) + Nitrate (NO3) or;

Total Nitrogen = TKN + NO2 + NO3 (This is the formula used to measure nitrogen at wastewater plants).

TKN stands for Total Kjeldahl Nitrogen which is the sum of; NH3 + Organic Nitrogen

NH3 stands for Ammonia Nitrogen

Organic Nitrogen is principally found as amino acids & proteins – this includes urea and uric acid

NO2 stands for Nitrite

NO3 stands for Nitrate

N2 stands for Nitrogen Gas

Refractory Nitrogen is the nitrogen that can’t be biologically decomposed.

Alkalinity is easiest defined as the ability to resist a drop in pH. This is very important because 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 the bug's oxygen source is derived from the nitrate (NO3) compounds.

Nitrification and denitrification are two terms that are commonly misunderstood. Both are individually distinct processes.

Nitrification is the conversion of ammonia (NH3) to nitrate (NO3). How is this done? 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)

Nitrite (NO2) + Oxygen (O2) + Alkalinity + Nitrobacter = Nitrate (NO3)

Nitrite (NO2) is the unstable form of nitrogen and is easily converted because it does not wish to be in this form. 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). How is this done? Heterotrophic bacteria utilize the nitrate (NO3) as an oxygen source under anoxic conditions to break down organic substances.

Nitrates (NO3) + Organics + Heterotrophic bacteria = Nitrogen Gas & Oxygen & Alkalinity