The sludge generated during some plating/ phosphating process, flows out along with the effluent through the drain pipes. Sludge is also formed by way of precipitate during treatment of effluent. It is essential to segregate the sludge from treated liquid effluent by means of sludge separator / clarifier. 

Typically, two types of settlers are in use. One is a batch type cylindrical vessel with a slow speed blade type stirrer, which allows settlement of sludge after prolonged usage. The other is an inclined plate type Lamella clarifier, which is more popular, particularly since it allows continuous operations, thus reducing the time factor.

The settler is a tank with inclined walls, provided with inclined corrugated plates in between the walls. The effluent is made to pass parallel to the inclined plates in the vertical upward passage at pre-determined velocity. This results in settling of the suspended solids, which slide along the plates, down to the bottom of the settler. 

Both varieties of clarifiers have conical bottom. The solids are periodically pumped with the help of a screw-pump to sludge drying bed or filter press. 

The size of a settler is determined by volume of effluents and periodicity of effluent generation / disposal.