Question
How is water purified at a water purification plant?
✓
Answer
In a conventional water treatment plant, water is subjected to a different process. They are:
Water treatment
- Sedimentation:
- Water from lakes or rivers is collected in large sedimentation tanks.
- There, it is allowed to stand undisturbed so that suspended impurities settle down at the bottom of the tank.
- Sometimes, a chemical substance such as potash alum is added to water to speed up the process of sedimentation, this is called loading.
- The particles of potash alum combine with the suspended impurities and make them settle down at a faster rate.
- Filtration:
- Water from the sedimentation tanks is then pumped to the filtration tanks.
- Filtration tanks contain filter beds made up of gravel, sand, pebbles, activated charcoal, and concrete.
- Water passes through these layers and becomes free from any remaining dissolved or suspended impurities completely.
Water treatment - sterilisation:
- The filtered water is treated chemically to remove the remaining germs or bacteria, this process is called sterilisation.
- The chemicals that are used in this process are chlorine and ozone.
- The process of adding chlorine in adequate amounts to water is called chlorination.
- The water from filtration tanks is pumped into chlorination tanks, where chlorine is added to remove harmful bacteria and other germs.
- Ozonisation is a process in which water is treated with ozone gas to kill the germs present in it.
- The sterilisation of water can also be done by exposing it to air and sunlight.
- Oxygen from the air and sunlight destroys the germs present in water.
- Aeration is the process in which air under pressure is blown into filtered water, this also helps to kill the germs.
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