Sedimentation in Water Treatment

The process of removal of undesirable matters and pathogens from water is called the water treatment process. The water treatment process involves different processes like screening, sedimentation, aeration, etc. We are discussing sedimentation in water treatment in this article.

  1. Introduction  

The process of the removal of suspended particles by gravitational settling is called sedimentation.

The water after screening may contain various suspended impurities like silt and clay particles. So to remove such particles sedimentation is done.

The particles whose specific gravity is greater than that of water get settles down under the action of gravity.

Sedimentation tanks are designed to reduce the velocity of the flow of water so that the suspended particles get settled under the action of gravity. Sedimentation can be achieved in two ways which are explained below.

  2. Types of Sedimentation in Water Treatment

1. Plain Sedimentation 

When the suspended particles are separated under the action of gravity only, it is called plain sedimentation.

2. Sedimentation with coagalities

Fine suspended particles and colloidal impurities are not removed by plain sedimentation. Particles of sizes 0.006 mm or less require 10 hours to settle in plain sedimentation.

Therefore we need certain chemicals to add in the water to remove such impurities which are not removed by plain sedimentation. These chemical are known as coagulants and the process is called sedimentation with coagulation.

Examples of coagulants are (Al₂SO₄) ₃, AlSO₄, sodium aluminate, etc.

  3. Advantages of Sedimentation in Water Treatment  

Some advantages of sedimentation are:

a. Requirement of fewer chemicals for subsequent water treatment.

b. Cheaper than other methods.

  4. Disadvantages of Sedimentation in Water Treatment  

Some disadvantages of sedimentation are:

a. Slower process as required more time.

b. Shows pollution trend in a specific region over time.