Clarifiers                                                                                                                     

Water clarification is the process of removing suspended solids from water using large tanks to
let the solids settle down .Most of the suspended matter in water would settle, given enough time,
but in most cases the amount of time required would not be practical. The time required for settling
is dependent on many factors, including:

1. Weight of the particle
2. Shape of the particle
3. Size of the particle
4. Viscosity and/or frictional resistance of the water, which is a function of temperature.

Chemicals are often added to water to neutralize particle charge and enhance particle settling. Chemicals used to promote suspended particle settling in the clarification process are commonly called coagulants; the particle charge neutralization process is called coagulation. Coagulation, the first step in complete clarification, is the neutralization of the electrostatic charges on colloidal particles. Because most of the smaller suspended solids in surface waters carry a negative electrostatic charge, the natural repulsion of these similar charges causes the particles to remain dispersed almost indefinitely. To allow these small suspended solids to agglomerate, the negative electrostatic charges must be neutralized. The most common inorganic coagulants is:
Alum-aluminum sulfate-Al2(SO4)3
Once the negative charges of the suspended solids are neutralized, flocculation begins. Charge
reduction increases the occurrence of particle-particle collisions, promoting particle agglomeration.
After flocculation, sedimentation takes place.