Grade 7, Science Olympiad (CBSE) - Waste water story 

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Grade 7  |   Science  |   Waste water story, Natural resources and their conservation, Olympiad, CBSE, ICSE, SOF, ITO

Waste water needs to be treated well before reusing it. The wastewater contains several impurities which are harmful to us and the environment and needs to be removed by water treatment. Wastewater from the household is treated in the water treatment plant which removes the physical, biological and chemical impurities from the plants. 
Water treatment plants

In these plants, there are several layers from which water has to pass through in order to become free from harmful impurities. These layers are-

  • Bar screens- Such screens prevent the flow of large objects in the wastewater which is an effective way to remove rags, plastic, bags, cans, napkins, etc from the sewage. 
  • Grit and sand removal tank-This tank removes impurities of small size like grit and sand but is not able to remove much smaller impurities like faeces.
  • Clarifier- This is a tank which has its central part inclined downwards to allow the faeces to settle down. The waste which has been settled at the bottom of the tank is removed using a scrapper. This waste is called sludge. The sludge is then transferred to a separate scraper where it is allowed to be decomposed with the help of bacteria. A skimmer is used to remove the oils and grease. 

When all the physical contaminants present in the sewage are removed successfully then this water is termed as clarified water. 

After the removal of physical contaminants its time for the removal of biological contaminant contaminants. For this the clarified water is passed into an aerator which pumps air into the water. After many hours the bacteria present in the clarified water settles at the bottom of the tank as activated sludge. Now the water in the top is 95% clean and is let out into a water source whereas the sludge is dried and is uses as manure. 

In the chemical process, chlorine tablets of ozone is used as a disinfectant to treat the water in treatment plants. 

People should not throw the pollutants like paints, medicine, motor oil and other solvents into the drain as it kill the microbes that help in water treatment. 

Septic tanks

These are suitable for places such as hospitals or isolated buildings where they are no sewage. The local government or private corporations provide septic tanks in areas that have no direct connection to main sewage pipes. Such tanks consists of a small sewage treatment system.

Chemical toilets

Such toilets are used in trains and aeroplanes. Here chemicals are used to disinfect human waste and remove its bad odour. 

Composting toilets

In this system, human waste is converted into organic compost and usable soil. This can be done with the help of microrganism like bacteria and fungi or macrorganism like earthworm which oxidize the organic waste and break them into essential minerals. 

Vermi composting toilets

Here, earthworm is used to treat the human excreta and it also coasts veryless in comparison to other methods of waste treatment methods. The entire human waste is converted into vermi compost. 

Sulabh toilets

An organisation Sulabh international has developed a twin pit pour flush toilet system. Here, the waste from the toilets flows through the covered drains into a biogas plant to produce biogas and bio fertilizers. Biogas is used as a source of low cost fuel. And a biogas plant offers safe and hygienic disposal of wastes. 


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