How is sedimentation used in the water purification process?

Sedimentation in water purification involves settling out suspended particles to make the water clearer.

In the water purification process, sedimentation is a crucial step that helps in the removal of suspended particles, colloids and flocs from the water. This process is typically carried out in a sedimentation tank or basin where the water is allowed to stand undisturbed. The principle behind sedimentation is simple: due to gravity, heavier particles settle at the bottom of the tank over time, while the clearer water remains on top.

The process begins with the addition of chemicals, often aluminium sulphate (alum), to the water. These chemicals cause the tiny particles in the water to coagulate, or come together, forming larger particles known as flocs. These flocs are heavier and thus settle to the bottom of the tank more easily. This process is known as flocculation.

The sedimentation process is not instantaneous and can take several hours. The speed at which particles settle depends on their size, shape, and density, as well as the temperature and viscosity of the water. The settled particles form a layer of sludge at the bottom of the tank, which needs to be removed periodically.

Sedimentation is an effective way to remove larger particles, but it is not sufficient to remove all impurities from the water. Therefore, it is usually followed by other purification methods such as filtration and disinfection to ensure the water is safe for consumption. Despite its limitations, sedimentation is a vital step in water purification as it significantly reduces the turbidity of the water, making subsequent treatment processes more effective.