Notes On Water Treatment - CBSE Class 7 Science
Waste water needs to be treated before it can be reused or released into a water body. Waste water Water treatment removes impurities from waste water. Waste water from households is treated at a treatment plant to remove the physical, biological and chemical matter. Treatment of waste water reduces the toxicity of poisonous substances and pollutants in water resources.

Process of water treatment
Sewage comprises of waste water released from homes, industries, hospitals and offices and also the water collected during rains. Sewage treatment is the step wise procedure which involves removal of wastes from the water. Sewage treatment is also called as waste water treatment.

Laboratory process of water treatment
This involves filtration of water to remove large impurities. An activity is explained to show physical treatment of water.
  • Take a funnel.
  • Place a cone made up of filter paper in the funnel and wet it with water.
  • Add some sand, fine gravel and medium gravel into the funnel. These form the layers for the process of filtration of water.
  • Pour waste water into the funnel and collect clean water from the stem of the funnel.
  • Process has to be repeated for several times till the collected water looks clean.

Waste Water Treatment Plants (WWTP)
Waste water treatment involves physical, chemical and biological treatment of water. Waste water is allowed to pass through different steps in a sequence.


Physical and biological treatment of waste water:

Step 1 - Bar Screens: Bar screens are the screens that prevent the flow of large objects in waste water. These screens help to remove large objects like rags, plastic bags, cans, napkins and sticks from sewage.

Step 2 - Grit chamber: Waste water from the bar screens is allowed to pass through grit chambers in a slow manner. The slow movement of water makes grit, sand and dust particles to settle down.

Step 3 - Clarifier: A clarifier is a tank with its central part inclined downwards so as to allow faeces to settle down. The waste settled at the bottom is termed as sludge.

  • Sludge is transferred to a separate tank where it is decomposed using bacteria. Finally, a skimmer is used to remove oils and grease. Clarified water is obtained after the separation of all physical contaminants from the sewage.

Step 4 - Aerator: The clarified water is passed into an aerator. An aerator pumps air into the water to settle the bacteria to the bottom of the tank as activated sludge. Bacteria under aerated conditions consume impurities left in the water. The water present in the top is 95% clean and is let out into a water source while the activated sludge is dried in a sand bed and is used as manure.
Using bacteria in decomposing waste is the biological treatment.


Chemical treatment of waste water:

  • Chlorine tablets or chlorine gas is used to treat waste water chemically.
  • Water will be clean on the dissolution of a chlorine tablet. Hence, chlorine tablets are used to disinfect water in treatment plants.
  • Chlorine gas is introduced through many pipes into a tank with water stored after physical and biological treatment.
  • Ozone is also used in chemical purification of water.

Water treatment in olden days
The ancient Greek and Indian writings dating back to as early as 2000 BC recommended water treatment methods.
The Egyptians discovered the process of coagulation for water treatment. Eucalyptus trees are planted along the sewage ponds into which water is released. Eucalyptus trees absorbed waste water from the pond and released pure water vapour into the atmosphere.

Prevention of clogging of drains:
  • Oils and fats released from the kitchen can harden along with detergents to block water pipes. In an open drain, fats on entering the soil, clog the soil pores. This reduces the effectiveness of filtration of water or water seeping.
  • We should avoid throwing tea leaves, solid food remains and napkins into the drain. These can block the drains and also block the flow of oxygen to the useful microorganisms. Useful microorganisms bring about decomposition of organic wastes from waste water.
  • Chemicals like paints, medicines, motor oil and many other solvents kill the microbes that help in water treatment. Awareness has to be created in people about the ill effects of throwing pollutants into the drain.

Summary

Waste water needs to be treated before it can be reused or released into a water body. Waste water Water treatment removes impurities from waste water. Waste water from households is treated at a treatment plant to remove the physical, biological and chemical matter. Treatment of waste water reduces the toxicity of poisonous substances and pollutants in water resources.

Process of water treatment
Sewage comprises of waste water released from homes, industries, hospitals and offices and also the water collected during rains. Sewage treatment is the step wise procedure which involves removal of wastes from the water. Sewage treatment is also called as waste water treatment.

Laboratory process of water treatment
This involves filtration of water to remove large impurities. An activity is explained to show physical treatment of water.
  • Take a funnel.
  • Place a cone made up of filter paper in the funnel and wet it with water.
  • Add some sand, fine gravel and medium gravel into the funnel. These form the layers for the process of filtration of water.
  • Pour waste water into the funnel and collect clean water from the stem of the funnel.
  • Process has to be repeated for several times till the collected water looks clean.

Waste Water Treatment Plants (WWTP)
Waste water treatment involves physical, chemical and biological treatment of water. Waste water is allowed to pass through different steps in a sequence.


Physical and biological treatment of waste water:

Step 1 - Bar Screens: Bar screens are the screens that prevent the flow of large objects in waste water. These screens help to remove large objects like rags, plastic bags, cans, napkins and sticks from sewage.

Step 2 - Grit chamber: Waste water from the bar screens is allowed to pass through grit chambers in a slow manner. The slow movement of water makes grit, sand and dust particles to settle down.

Step 3 - Clarifier: A clarifier is a tank with its central part inclined downwards so as to allow faeces to settle down. The waste settled at the bottom is termed as sludge.

  • Sludge is transferred to a separate tank where it is decomposed using bacteria. Finally, a skimmer is used to remove oils and grease. Clarified water is obtained after the separation of all physical contaminants from the sewage.

Step 4 - Aerator: The clarified water is passed into an aerator. An aerator pumps air into the water to settle the bacteria to the bottom of the tank as activated sludge. Bacteria under aerated conditions consume impurities left in the water. The water present in the top is 95% clean and is let out into a water source while the activated sludge is dried in a sand bed and is used as manure.
Using bacteria in decomposing waste is the biological treatment.


Chemical treatment of waste water:

  • Chlorine tablets or chlorine gas is used to treat waste water chemically.
  • Water will be clean on the dissolution of a chlorine tablet. Hence, chlorine tablets are used to disinfect water in treatment plants.
  • Chlorine gas is introduced through many pipes into a tank with water stored after physical and biological treatment.
  • Ozone is also used in chemical purification of water.

Water treatment in olden days
The ancient Greek and Indian writings dating back to as early as 2000 BC recommended water treatment methods.
The Egyptians discovered the process of coagulation for water treatment. Eucalyptus trees are planted along the sewage ponds into which water is released. Eucalyptus trees absorbed waste water from the pond and released pure water vapour into the atmosphere.

Prevention of clogging of drains:
  • Oils and fats released from the kitchen can harden along with detergents to block water pipes. In an open drain, fats on entering the soil, clog the soil pores. This reduces the effectiveness of filtration of water or water seeping.
  • We should avoid throwing tea leaves, solid food remains and napkins into the drain. These can block the drains and also block the flow of oxygen to the useful microorganisms. Useful microorganisms bring about decomposition of organic wastes from waste water.
  • Chemicals like paints, medicines, motor oil and many other solvents kill the microbes that help in water treatment. Awareness has to be created in people about the ill effects of throwing pollutants into the drain.

Videos

Activities


Activity 1
Gbra.org has compiled a wonderful audiovisual version to show different steps involved in the process of  Waste water treatment. The template provides an oppurtunity to overview the plant at one sight. The process of water treatment at Waste Water Treatment Plant is divided into small parts. Each part is discussed along with animation shown on one side of the template. It is an user-friendly interface allowing the user to forward or backward or overview by just clicking on the buttons. 
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Activity 2
Aquiris.be has built a design displaying different processes under three headings. User has to click on 'Wastewater treatment channel' to view each and every step in waste water treatment as a separate animation. It also provides the information about the different equipment used in the treatment procedure. 
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References

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