In water treatment, a clarifier is a settling tank used to remove solid waste particles from water. When the clarifier separates the concentrated impurities, the sludge formed by the process discharges from the bottom of the tank.
Before the waste water goes into the clarifier, it passes through a station called the headworks, where large solids and grit are removed, After this, coagulation and flocculation reagents such as polyelectrolytes and ferric sulfate are often added to the water before it is sent to the clarifier. The reagents cause fine suspended particles of waste to clump together, forming larger and denser particles called flocs that allow the waste to settle quickly, allowing the separation of the waste in the clarifier to occur more effectively.
The water now moves to the primary clarifier tank where it is slowed down to allow the remaining solid waste to settle at the bottom of the tank. A rotating sludge-raking system located at the bottom of the clarifier rakes the settled waste out of the tank, and a rotating rake-skimming system at the top of the tank removes any solids that float up to the surface. When the solids are separated from the waste water, the remaining water is slowly removed from the tank and taken to oxidation ponds. A smaller clarifier is also used if the volume of the incoming waste water exceeds the volume of the primary clarifier.