4. THE BIOLOGICAL BASIS OF WASTEWATER TREATMENT
Activated sludge is a suspended growth secondary treatment
process that primarily removes dissolved organic solids as
well as settleable and non-settleable suspended solids. The
activated sludge itself consists of a concentration of
microorganisms and sludge particles that are naturally found
in raw or settled wastewater. These organisms are cultivated
in aeration tanks, where they are provided with dissolved
oxygen and food from the wastewater. The term “activated”
comes from the fact that the particles are teeming with
bacteria, fungi, and protozoa.
Like in most other wastewater treatment plants, when
wastewater enters an activated sludge treatment facility
the preliminary treatment processes remove the coarse or
heavy inorganic solids (grit) and other debris, such as rags,
and boards. Primary clarifiers (if they are provided) remove
much of the floatable and settleable organic material. The
activated sludge process can treat either primary clarified.