Wastewater Story Class 7 Extra Questions and Answers Science Chapter 18

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In this page, we are providing Wastewater Story Class 7 Extra Questions and Answers Science Chapter 18 pdf download. NCERT Extra Questions for Class 7 Science Chapter 18 Wastewater Story with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 18 Extra Questions and Answers Wastewater Story

Extra Questions for Class 7 Science Chapter 18 Wastewater Story with Answers Solutions

Wastewater Story Class 7 Extra Questions Very Short Answer Type

Question 1.
Define pollutants.
Answer:
The harmful substances which contaminate soil, air and water, etc., are called pollutants.

Question 2.
Name three sources of water.
Answer:

  • Lakes
  • Ponds
  • Wells

Question 3.
Why can’t sea water be used for drinking purpose?
Answer:
Sea water cannot be used for drinking purpose because it contains a big amount of salt that can cause severe water loss and vomiting when consumed.

Question 4.
Why is the bleaching powder mixed with water?
Answer:
Bleaching powder is mixed with water to kill harmful bacteria present in it and make it safe for drinking purposes.

Question 5.
What do you mean by sanitation?
Answer:
Sanitation is the proper disposal of sewage and garbage away from houses and surrounding areas.

Question 6.
Give examples of onsite sewage disposal system.
Answer:
Composting pits, chemical toilets, septic tanks, etc.

Question 7.
Write the full form of WWTP.
Answer:
Waste Water Treatment Plant.

Question 8.
What is meant by chlorination?
Answer:
Chlorination is the process of adding bleaching powder in water to make it safe for drinking.

Question 9.
Give examples of some contaminants present in sewage.
Answer:
Rags, oil, human as well as animal excreta, industrial wastes, etc.

Question 10.
Give examples of some water-borne diseases.
Answer:
Cholera, meningitis, dysentery, typhoid, polio, etc.

Question 11.
Name the type of microbes present in sewage that causes diseases like typhoid and cholera.
Answer:
Bacteria

Question 12.
Name two things that can be made from sludge extracted during treatment of sewage.
Answer:

  • Manure
  • Biogas

Question 15.
What is scum?
Answer:
Floating dirt or froth on the surface of wastewater is called scum.

Wastewater Story Class 7 Extra Questions Short Answer Type

Question 1.
What is meant by sewerage?
Answer:
Sewerage is a network of big and small pipes called sewage placed under the ground. It can be considered as a transport system that carries wastewater from the point where it is produced to the point of disposal.

Question 2.
Define potable water. Write any two characteristics of potable water.
Answer:
Water that is fit for drinking is called potable water. Its characteristics are following:

  • It is odourless and colourless.
  • It is transparent.
  • It is free from germs and harmful chemicals.

Question 3.
What is clarified water. What can it be used for?
Answer:
Clarified water is the water we get from bar screening, sedimentation, aeration and skimming of the wastewater. It can be used for watering plants, flushing toilets and cleaning public places.

Question 4.
List some sources of water pollution.
Answer:

  1. Discharge of sewage
  2. Agricultural wastes
  3. Domestic wastes
  4. Industrial wastes

Question 5.
What should be done to wastewater?
Answer:
Wastewater should not be wasted. It must be cleaned up by removing pollutants.

Question 6.
How do bar screen, and grit and sand removal tank help in cleaning of water?
Answer:
Bar screen removes large objects like rags, cans, plastic packets, etc., from sewage. In grit and sand removal tank heavy solid impurities like pebbles, etc., are removed by sedimentation process.

Question 7.
How does water get polluted?
Answer:
Water is used for numerous purpose in homes, industries, agriculture, etc. It gets polluted when it is used for dying, bathing, flushing toilets, etc. During these activities; many unwanted chemicals, organic and inorganic substances get mixed with water. This pollutes water.

Question 8.
Write one word for the following:
(a) The settled solids that are removed in wastewater treatment with a scraper.
(b) Water from kitchen used for washing dishes.
(c) Wastewater released from homes, industries, hospitals and other public buildings.
Answer:
(a) sludge
(b) wastewater
(c) sewage

Wastewater Story Class 7 Extra Questions Long Answer Type

Question 1.
What is function of a septic tank?
Answer:
A septic tank consists of a big covered underground tank made of concrete. It also consists of an inlet pipe at one end and an outlet pipe at the other end. The toilet seat is connected to the inlet pipe. The human excreta enters the tank through the inlet pipe, the solid portion of the excreta gets collected at the bottom of the tank in the form of sludge whereas the liquid waste gets collected above it.

The anaerobic bacteria break down most of the solid wastes owing to which the volume of solid reduces to a great extent. The liquid waste is also decomposed by the bacteria. Bacteria deposit the digested solid at the bottom of the septic tank. The excess water goes out of the septic tank through the outlet pipe and is absorbed by the soil.

Question 2.
What is vermi-processing toilet? Explain.
Answer:
Vermi-processing toilet is a type of toilet in which the human excreta is processed by earthworms. This has been tested in India. It has proved to be a low-water use, nobel method for disposal of human ex¬creta. Toilet is operated in a very simple and hygienic way. The human excreta is converted into vermi- cakes. Hence it becomes a resource much needed for the soil.

Question 3.
List various steps involved in waste water treatment.
Answer:
Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater.

  1. First wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
  2. Water than goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
  3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This settled solid is called sludge.
  4. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.
  5. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.
  6. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.
  7. After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.
  8. The activated sludge contains about 97% water which is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.
  9. The treated water now, has a very low level of organic material and suspended matter. It is discharged into a sea, or river or into the ground.
  10. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.

Question 4.
Name various components of sewage.
Answer:
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease-causing bacteria and other microbes.

  1. Organic impurities: Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste, etc.
  2. Inorganic impurities: Nitrates, phosphates, metals.
  3. Nutrients: Phosphorus and nitrogen.
  4. Bacteria: Such as which causes cholera, typhoid, dysentery, etc.

Question 5.
How can we minimise the discharge of pollutants at their source?
Answer:
To minimise or eliminate waste and pollutants at their source we must see what we are releasing down the drain.

  1. Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water. We should throw oil and fats in the dustbin.
  2. Chemicals like paints, solvents, insecticides, motor oil, medicines may kill microbes that help purify water. So we should not throw them down the drain.
  3. Used tea leaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin.
  4. These wastes choke the drains. They do not allow free flow of oxygen. This hampers the degradation process.

Wastewater Story Class 7 Extra Questions HOTS

Question 1.
What is effluent?
Answer:
Effluent is a liquid waste or sewage discharged into a river or the sea.

Question 2.
State beneficial activity of microbes in sewage disposal.
Answer:
Microbes present in sewage water help to digest organic matter present in it and thus purifying water aerobically. Anaerobic microbes help in digestion of sludge into useful manures.

Question 3.
What are the common symptoms of water-borne diseases?
Answer:
Common symptoms of water-borne diseases are vomiting, stomachache, diarrhoea, fever, loss of appetite, etc.

Question 4.
How the terms sewage, sewers and sewerage are interlinked to each other?
Answer:
Sewage is the wastewater coming from houses and other places. Sewers are the pipes which carry sewage whereas network of sewers, manholes, pumping stations, drains, etc. form sewerage.

Question 5.
Why should we not throw
(a) Cooking oils and fats down the drains?
(b) Cotton buds, napkins and nappies down the toilets?
Answer:
(a) Cooking oils and fats can harden and block the pipes.
(b) Cotton buds, napkins and nappies are flushed with difficulties and are not easily degradable. They can block the drains.

Wastewater Story Class 7 Extra Questions Value Based (VBQs)

Question 1.
Sonam never mind to dispose her household waste like tea leaves, vegetable peels and even remaining foods from plates into the sink. Sometimes she even flush the waste from brooming or sweeping into the toilets.
(a) What will be the affects of Sonam’s practices on the process of wastewater treatment?
(b) How Sonam’s practice of throwing waste into sink and toilets will affect the sewer system?
(c) What value of Sonam is shown here?
(d) Being an active citizen, what would you like to suggest Sonam?

Answer:
(a) She is adding to the load of WWTP, by increasing waste and pollutants at their source.
(b) Throwing of tea leaves, vegetable peels and food remains may clog the sewer pipes. Waste from brooming and sweeping may also contain some non-biodegradable wastes which can choke drains or hamper in degradation processes.
(c) Sonam is impulsive, irresponsible and eco-unfriendly.
(d) Sonam must throw all the solid waste into a dustbin instead of throwing directly into sink or toilet. She must minimise or eliminate waste and pollutants at their source to decrease the load on WWTP.