Process flow - step 3

Biological reactor tanks

The next stage of the process is the removal of ammonia which, at high levels, is toxic to fish in the river systems.

The effluent, after primary sedimentation, enters the biological reactors tanks. It is then mixed with activated sludge containing micro-organisms. Given the right environment, these micro-organisms convert the ammonia to nitrates in a process known as nitrification.

During nitrification, the micro-organisms feed on the ammonia and other waste material in the sewage, under aerobic conditions, that is, in the presence of oxygen. This enables them to grow and reproduce.

To provide aerobic conditions in this process, air is pumped in through porous diffusers, in order to mix the sewage and activated sludge and to provide oxygen for the micro-organisms.

Next: Step 4