Secondary Treatment - Aeration Tanks
After leaving the primary clarifiers, the sewage goes to any
one of ten aeration tanks. Elmhurst uses a system of sewage treatment
called activated sludge. The aeration tanks provide a location
where biological treatment of the waste water takes place. In
these tanks, microorganisms and waste water in various stages
of decomposition are mixed, aerated, and maintained in suspension.
The contents of the aeration tanks, which require a delicate
balance of food and oxygen, are commonly referred to as the mixed
liquor suspended solids (MLSS) or activated sludge. The activated
sludge converts organic substances into oxidized products and
a settleable floc which is settled out in the secondary clarifiers.
The aeration tanks have a great deal of flexibility built into
them. Raw sewage can be introduced in various locations and be
aerated and mixed for varying lengths of time and intensity.