2.2 THE BIO FILTER

Nitrifying bacteria are vital for the overall functioning of an aquaponic unit. Chapter 4 describes how the biofilter component for each aquaponic method works, and Chapter 5 describes the different bacteria groups that operate in an aquaponic unit. Two major groups of nitrifying bacteria are involved in the nitrification process: 1) the ammonia-oxidizing bacteria (AOB), and 2) the nitrite-oxidizing bacteria (NOB) (Figure 2.6).

They metabolize the ammonia in the following order:

1. AOB bacteria convert ammonia (NH3) into nitrite (NO2)
2. NOB bacteria then convert nitrite (NO2) into nitrate (NO3)

FIGURE 2.6
The nitrification process in an aquaponic system

As shown in the chemical symbols, the AOB oxidize (add oxygen to) the ammonia and create nitrite (NO2) and the NOB further oxidize the nitrite (NO2) into nitrate (NO3). The genus Nitrosomonas is the most common AOB in aquaponics, and the genus Nitrobacter is the most common NOB; these names are frequently used interchangeably in the literature and are used throughout this publication.
In summary, the ecosystem within the aquaponic unit is totally reliant on the bacteria. If the bacteria are not present or if they are not functioning properly, ammonia concentrations in the water will kill the fish. It is vital to keep and manage a healthy bacterial colony in the system at all times in order to keep ammonia levels close to zero.