Describe the steps involved in the purification of drinking water for the city water supply.
Describe the steps involved in the purification of drinking water for the city water supply.
Natural water in the form of water from rivers, lakes etc. is not considered suitable for drinking.
- Therefore, this water is treated first in the water-works which is an establishment for treating the natural water and purify it to make it suitable for human consumption and supplied to the entire city for drinking purposes.
Steps involved in the purification of drinking water for city water supply are as follows:
Screening: In this step, water from the reservoir is passed through screen like structures which have holes.
- These screens with holes allow water to pass through them but do not allow large floating materials in the water to pass through.
- Thus large pieces of waste matter like polythene, thermocol pieces etc. are screened or separated in this step.
Sedimentation: The water is then collected in a sedimentation tank.
- Sedimentation is the process of settling down of the large sediments under the force of gravity.
- In this step, large sediments settle down due to greater density than water. The water on the top i.e.; supernatant is moved to another tank called loading tank.
Loading: While large sediments gets separated in the sedimentation tank, finer particles are still present in water.
- These fine particles are separated from the water by the process of loading in the loading tank where a solution of alum is dissolved in water. Alum form insoluble gelatinous flocs by coagulating all the finer particles by absorbing them and forming their aggregates.
- These aggregates which are bigger in size are now capable of settling under the force of gravity. The supernatant water is then moved to filtration tanks.
Filtration: In the filtration tank, a set of layers of fine sand, coarse-sand or gravel and coarse-gravel is arranged in the form of the bed.
- Fine sand is at the top of the bed whereas coarse-gravel is at the bottom of this bed. Water passes through fine sand, followed by gravel, then coarse gravel.
- This process of filtration removes the colloids and other suspended material remaining in water including micro-organisms also.
Aeration: The process of addition of air to the filtered water is called aeration.
- Aeration takes place in aeration tank in which water is saturated with air which also serves the purpose of killing remaining microbes in water. The water obtained in this step is known as aerated water.
Chlorination: The process of addition of chlorine to water is known as chlorination.
- Chlorine serves the purpose of a disinfectant by killing the harmful disease causing bacteria and micro-organisms.
- The process of killing or inactivating the disease causing pathogens from water is called as sterilisation of water.
- So chlorine helps in the sterilisation of water and making it fit for human consumption.
Natural water in the form of water from rivers, lakes etc. is not considered suitable for drinking.
- Therefore, this water is treated first in the water-works which is an establishment for treating the natural water and purify it to make it suitable for human consumption and supplied to the entire city for drinking purposes.
Steps involved in the purification of drinking water for city water supply are as follows:
Screening: In this step, water from the reservoir is passed through screen like structures which have holes.
- These screens with holes allow water to pass through them but do not allow large floating materials in the water to pass through.
- Thus large pieces of waste matter like polythene, thermocol pieces etc. are screened or separated in this step.
Sedimentation: The water is then collected in a sedimentation tank.
- Sedimentation is the process of settling down of the large sediments under the force of gravity.
- In this step, large sediments settle down due to greater density than water. The water on the top i.e.; supernatant is moved to another tank called loading tank.
Loading: While large sediments gets separated in the sedimentation tank, finer particles are still present in water.
- These fine particles are separated from the water by the process of loading in the loading tank where a solution of alum is dissolved in water. Alum form insoluble gelatinous flocs by coagulating all the finer particles by absorbing them and forming their aggregates.
- These aggregates which are bigger in size are now capable of settling under the force of gravity. The supernatant water is then moved to filtration tanks.
Filtration: In the filtration tank, a set of layers of fine sand, coarse-sand or gravel and coarse-gravel is arranged in the form of the bed.
- Fine sand is at the top of the bed whereas coarse-gravel is at the bottom of this bed. Water passes through fine sand, followed by gravel, then coarse gravel.
- This process of filtration removes the colloids and other suspended material remaining in water including micro-organisms also.
Aeration: The process of addition of air to the filtered water is called aeration.
- Aeration takes place in aeration tank in which water is saturated with air which also serves the purpose of killing remaining microbes in water. The water obtained in this step is known as aerated water.
Chlorination: The process of addition of chlorine to water is known as chlorination.
- Chlorine serves the purpose of a disinfectant by killing the harmful disease causing bacteria and micro-organisms.
- The process of killing or inactivating the disease causing pathogens from water is called as sterilisation of water.
- So chlorine helps in the sterilisation of water and making it fit for human consumption.
