The sludge thickening is a process used to increase the solid content in the sludge by separating and remaining the liquids.

The gravity thickening makes the use of the force of gravity, as the main agent in thickening process of sludge.

A)The gravity thickening process:-

• It is accomplished in a tank like the conventional sedimentation tank.

• Generally for the thickening purpose another tank is used.

• The diluted sludge is fed to the feed-well.

• The sludge is allowed to settle at the bottom of bank.

• This thickened sludge is pumped into the dewatering equipment. It is the most effective process of sludge thickening.

B)The floatation thickening process:-

There are three basic variation of the flotation thickening operation i.e.

1) Dissolved-Air flotation

2) Vacuum flotation

3) Depressed-Air flotation

• Among the above three dissolved air flotation is widely accepted for specially activated sludge.
• The air is introduced into the solution which is being at an elevated pressure.
• When the solution is depressurized the dissolved air is released as finely divided bubbles which carry the sludge to the top, from where it is removed.
• In case of flotation thickness, higher loading of sludge is possible. Than the conventional gravity thickness because of its capacity to separate solids from waste water is fast.