Sedimentation:

Sedimentation is the separation of the suspended particles higher than water by gravity settling. This process is used to remove inorganic impurities from water prior to subsequent treatment process. Process of sedimentation is classified into two categories, i.e.

(a) Plain sedimentation, and

(b) Sedimentation with coagulation.

In plain sedimentation, impurities are separated from the suspended fluid by gravitational force and natural aggregation, whereas in sedimentation with coagulation, the addition of chemical substances known as coagulants increase the aggregation and finely divided suspended and colloidal matter are made to settle.

Sedimentation tanks are designed in such a way that water flows at very low velocity and inorganic impurities settle at the bottom of the tank and the lighter impurities such as colloidal particle, etc. float at the surface of the water. The settled impurities are removed from the bottom of the tank.