Sedimentation Process

In Water Treatment Process Sedimentation is the process of removal of suspended particles that are heavier than water by gravitational settling. Most raw water will contain mineral and organic particles. The density of mineral particles is usually between 2000 to 3000 kg/m3 and can easily settle out by gravity. Organic particles, on the other hand, have densities ranging from 1010 to 1100 kg/m3and take a long time to settle by gravity. In conventional water treatment, coagulants are used to destabilize particle to form larger and settlable solids. The relevant terms with respect to sedimentation are:



Plain Sedimentation

refers to the separation of suspended particles from liquid by gravitation and natural aggregation of settling particles. Examples are settling of sand in filtration and the settling of grits, and sandy and silty particles in pre-sedimentationtreatment. Such particles  are usually greater than 10 μm in size.

Coagulation and Flocculation

the addition of chemicals or other substances to induce or hasten aggregation and settling of finely divided suspended matter, colloidal substances, and large molecules. Examples are the removal of colour and turbidity in water



Chemical precipitation:



the addition of chemicals to remove dissolved impurities such as hardness, Fe, Mn, etc. out of the solution

The sedimentation process can be used to treat raw water containing suspensions ranging from a very low concentration of nearly discrete particles to a high concentration of flocculent solids