Sedimentation is a physical water treatment process that uses gravity to remove suspended solids from water). Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans). Sedimentation tanks, also known as settling basins or clarifiers, are designed to retain water so that suspended solids can settle). Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation). Sedimentation in potable water treatment generally follows a step of chemical coagulation and flocculation, which allows grouping particles together into flocs of a bigger size. This increases the settling speed of suspended solids and allows settling colloids). Sedimentation of water is one of the most basic processes of purifying water, making it a process that is commonly used and understood throughout the world.

The following are the types of sedimentation processes based on the size and density of particles and physical properties of the solids):

• Type 1 – Dilutes, non-flocculent, free-settling (every particle settles independently)
• Type 2 – Concentrated, non-flocculent, hindered settling (particles settle with interference from other particles)
• Type 3 – Dilutes, flocculent, free-settling (particles settle in flocs)
• Type 4 – Concentrated, flocculent, hindered settling (particles settle in flocs with interference from other particles)

Sedimentation is used to treat wastewater and drinking water. It provides the following benefits to municipalities that employ it:

• Fewer chemicals are required for subsequent water treatment.
• It makes any subsequent process easier.
• The cost is lower than some other methods.

Sedimentation is not and cannot be used for all water treatment applications. It’s essential to understand the characteristics of wastewater to determine if it’s an effective treatment process. When sedimentation is used to treat wastewater, this primary step is followed by secondary treatment, such as a trickling filter, activated sludge, or another purification process that is used to remove soluble impurities.