Question

How is water purified at a water purification plant?

Answer 1

In conventional water treatment plants, water is subjected to different processes. They are:

Sedimentation:

1. Water from lakes or rivers is collected in large sedimentation tanks.

2. There, it is allowed to stand undisturbed so that suspended impurities settle down at the bottom of the tank.

3. Sometimes, a chemical substance such as potash alum is added to water to speed up the process of sedimentation, this is called loading.

4. The particles of potash alum combine with the suspended impurities and make them settle down at a faster rate.

Filtration:

1. Water from the sedimentation tanks is then pumped to the filtration tanks.

2. Filtration tanks contain filter beds made up of gravel, sand, pebbles, activated charcoal and concrete.

3. Water passes through these layers and becomes free from any remaining dissolved or suspended impurities completely.

sterilisation:

1. The filtered water is treated chemically to remove the remaining germs or bacteria, this process is called sterilisation.

2. The chemicals that are used in this process are chlorine and ozone.

3. The process of adding chlorine in adequate amounts to water is called chlorination.

4. The water from filtration tanks is pumped into chlorination tanks, where chlorine is added to remove harmful bacteria and other germs.

5. Ozonisation is a process in which water is treated with ozone gas to kill the germs present in it.

6. The sterilisation of water can also be done by exposing it to air and sunlight.

7. Oxygen from the air and sunlight destroy the germs present in water.

8. Aeration is the process in which air under pressure is blown into filtered water, this also helps to kill the germs.