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Class VII - science: Waste Water
One Word Answer Questions:
Q) Name an organic impurity present in a sewage?
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Q) Which water is called as portable water?
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Q) Which state can be represented by ice, snow, hail?
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Q) Which form of water can be converted into liquid form by heating?
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Q) What are the states of water?
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Short Answer Questions:
Q) Explain the function of a bar screen in wastewater treatment plant?
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Q) What is a sludge?
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Q) What is the role of bacteria in the treatment of water?
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Q) Explain the role of a sewerage in treating waste water?
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Q) How are euclayptus trees useful in treating water?
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Q) What is low cost onsite sewage disposal system?
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Q) How clogging of drains can be prevented?
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Q) Expalin about the Floods?
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Q) Explian briefly about the food Materials and sources?
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Long Answer Questions:
Q) What is sewage? Explain briefly?
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Q) What are the causes of contamination of water?
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Q) Explain briefly the chemical treatment of waste water?
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Q) Explain about the states of water and the uses of water?
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Q) Expalin briefly about the water cycle?
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"The water which gets contaminated after various works; like washing, bathing, mopping, etc. is called wastewater".

Water - Our Lifeline
World Water Day: 22nd March

International Decade for Action on Water for Life: (2005 - 2015) It was declared by the General Assembly of the United Nations. Its main goal was to reduce the number of people who do not have access to safe drinking water; by half.

Sewage Treatment

The liquid waste which has water as its largest component along with various types of impurities (Contaminants) is called sewage. The process of removing impurities from waste water before it can be reused or sent to the water bodies is called sewage treatment or cleaning of water.

Composition of Sewage

Types of ImpuritiesExamples
Organic ImpuritiesHuman faces,animal waste,oil urea(urine),pedticide,herbicides,fruits and vegitables
Inorganic ImpuritiesNitrates,Phosphates,metals
BacteriaVarious types such as those causing cholera,typhoid,etc
Other microbesVarious types such as those causing diarrhea,jaundice,etc

Sewers: The pipes which carry wastewater.
Sewerage: The network of sewers.
Manhole:These are the holes made in sewers at frequent intervals, so that timely inspections and cleaning of sewers can be done through them. The manhole is covered with a hard lid so that people and traffic can easily move over it.

Water Treatment Plant

These are large plants where wastewater is cleaned before being sent to the nearest water bodies or being reused. The sewage treatment involves physical, chemical and biological processes to remove impurities from the wastewater.

Physical Process:
  • The wastewater is passed through bar screen. Large objects; like rags, sticks, plastic bags, cans, etc. are removed in this process.
Bar Screen
    Grit and Sand Removal:
  • The wastewater is slowly passed through the grit and sand removal tank. Grit, sand and pebbles settle down at the bottom.
Grit And Sand Removal Tank
  • Water is then sent to the sedimentation tank.
  • Solids like faeces settle at the bottom. Floatable impurities like oil and grease float on the surface.
  • A scraper removes the faeces from the water. The impurity thus collected is called sludge; which is sent to the sludge tank.
  • The sludge can be used to produce biogas or to produce manure. A skimmer removes the floatable impurities. Now, the water is called clarified water.
Clarified Water
Biological Process:
  • Air is pumped into clarified water so that bacteria can proliferate.
  • Bacteria consume the human waste. It leaves food waste, soap and other unwanted materials in the water.
  • The microbes settle down at the bottom after several hours. Water is then removed from the top. This water is fit for irrigation and can be used for that purpose.
Chemical Process:

  • Water purified through aeration is not fit for human consumption.
  • It needs to be treated with chlorine. For this, bleaching powder is added to the water.
  • The chlorine kills whatever germs may be left in the water. After chlorination, the water is fit for drinking.

Better House Keeping Practices
  • Do not throw cooking oil and fat in the drain. This can block the drain. The fat and oil clogs the pores in the soil; in open drains. This reduces the filtering capacity of soil.
  • Do not throw chemicals; like paint, insecticides, medicines, etc. into the drain. They kill the bacteria which otherwise help in cleaning the water.
  • Do not throw used tea leaves, solid food, soft toys or napkins in the drain.
  • They can clog the drain and do not allow oxygen to enter the sewage water.
  • Oxygen is important for the natural process of decomposition.
Sanitation And Disease

  • Maintaining overall cleanliness in the home and in surroundings is called sanitation.
  • Sanitation is important for the health of a person and that of the community.
  • Many people have the habit of defecating in the open. Uncovered human excreta attract flies and other insects. These insects carry the germs of many dangerous diseases like cholera, typhoid and jaundice.
  • With constant public awareness campaign, the practice of open defecation can be stopped.
  • Poor sanitary condition also contaminated the groundwater because contaminants percolate down the ground.
  • Stagnant water is a perfect breeding ground for mosquitoes. Mosquitoes are the carriers of several diseases like malaria, dengue, chikungunya and filaria.
Alternative Arrangement For Sewage Disposal

In the absence of a sewerage system, arrangements for onsite sewage disposal can be made.

  • Septic tanks are built in which human excreta are collected. In due course of time, the human excreta get decomposed into compost.
  • Composting pits can be made to dump waste and to make manure from them. Sewage can be collected into biogas plants to produce useful biogas.
  • Chemical toilets are new discoveries. They do not require much water for the disposal of human excreta and are environment friendly. Such toilets are ideal for the trains.
Sanitation At Public Places
  • Maintaining sanitation at public places is also important. In a heavily populated country; like India; any public place is always teeming with people. More footfall at public places results in more filth.
  • Sanitation workers often work continuously to maintain cleanliness at public places. But it is our responsibility also to maintain sanitation at public places.
  • We should follow some simple rules to help the sanitation workers.
  • For example; always throw the trash in a dustbin and avoid littering. Don't spit at public places and use the dustbin or special bins marked for the purpose.
  • It is every individual's responsibility to keep the water sources in a healthy state.
  • Adopting good sanitation practices should be our way of life.
  • Our initiative will surely make a great difference to the environment.
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