ammonia-vs-ammonium-featured“Ammonia-nitrogen” includes the ionized form (ammonium, NH4+) and the un-ionized form (ammonia, NH3). Ammonium is produced when microorganisms break down organic nitrogen products such as urea and proteins in manure. This decomposition occurs in both aerobic and anaerobic environments.

One of the noticeable differences between the two is that Ammonia gives out a strong smell whereas Ammonium does not smell at all. Ammonia (NH3) is an actual gas or liquid you can see. It is not ionic. When ammonia goes ionic, which happens when you add ammonia to water, it draws a hydrogen away from a water molecule to form ammonium (NH4+).

The chemical equation that drives the relationship between ammonia and ammonium is:

NH3 + H2O ↔ NH4+ + OH-

The un-ionized Ammonia with the formula NH3  is a weak base. The iodized Ammonium with the formula NH4+, is an acid. In solution, ammonium is in chemical equilibrium with ammonia. The major factor that determines the proportion of ammonia or ammonium in water is water pH. When the pH is low, the reaction is driven to the right, and when the pH is high, the reaction is driven to the left. This is important as the unionized NH3 is the form that can be toxic to aquatic organisms. The ionized NH4+ is basically harmless to aquatic organisms.

Ammonia exerts a direct biochemical oxygen demand (BOD) on the receiving water since dissolved oxygen is consumed as ammonia is oxidized. Moderate depressions of dissolved oxygen are associated with reduced species diversity, while more severe depressions can produce fish kills.