KSEEB Solutions for Class 7 Science Chapter 18 Wastewater Story

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Karnataka State Syllabus Class 7 Science Chapter 18 Wastewater Story

Class 7 Science Wastewater Story NCERT Textbook Questions and Answers

I. Fill in the blanks:

  1. Cleaning of water is a process of removing Pollutant
  2. Wastewater released by houses is called Sewage.
  3. Dried sludge is used as manure.
  4. Drains get blocked by oils and facts.

Question 2.
What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Sewage is wastewater containing liquid and solid wastes of dissolved and suspended impurities released by human activities from homes, industries, hospitals, offices, etc.

Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes, and disease-causing bacteria and other microbes. If untreated sewage is discharged into rivers or seas, then the water in the rivers or seas would get contaminated.

If this contaminated water is used for drinking, then it can cause diseases such as cholera, typhoid, dysentery, etc. which may lead to death. This may kill the organisms in rivers or seas. This also reduces the oxygen content in water which affects the plants and animals living in rivers and seas.

Question 3.
Why should oils and fats be not released in the drain? Explain.
Oil and fats can clog the drains reducing its effectiveness in Uttering water. In open drains, they block the pores in the soil and thus hamper the Alteration by soil. Hence, oil and fats should not be released in the drain.

Question 4.
Describe the steps involved in getting clarified water from wastewater.
Clarified water is obtained from wastewater in the wastewater treatment plants. The steps are:
(a) Wastewater is passed through bar screens which remove large objects like rags, sticks, cans, plastic packets, and napkins.

(b) Then, the water is sent to a grit and sand removal tank. The speed of the water is slowed down to allow sand, grit, and pebbles to settle down.

(c) Then, the water is allowed to settle in a large tank which is sloped towards the middle. ‘Solids like feces settle down at file bottom and are removed with a scraper. This is the sludge. The skimmers in the tank remove the floatable solids like oil and grease. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria, which produces biogas. The water so cleared is called clarified water.

(d) Air is pumped into the clarified water to help aerobic bacteria to grow. The bacteria consume human waste, food waste, soaps, and other unwanted matter which are still remaining in clarified water.

After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. Thus, the clarified water is obtained from wastewater.

Question 5.
What is sludge? Explain how it is treated.
Semi – solids such as faeces that settle down during wastewater treatment are called sludge. This sludge is removed using a skimmer and then transferred to a tank where it is decomposed by anaerobic bacreria to produce biogas. The biogas is used as a low – cost fuel for heating, cooking etc., It is also used to produce electricity.

Question 6.
Untreated human excreta is a health hazard. Explain.
Untreated human excreta is a health hazard. It contains various disease-causing microorganisms. It causes pollution of soil and water including underground water. Thus, it contaminates the sources of water from which people collect water for drinking and household purposes. When this contaminated water is used for drinking, it causes diseases such as cholera, typhoid, hepatitis, dysentery, etc., which may even lead to death.

Question 7.
Name two chemicals used to disinfect water.
Chlorine and ozone are used to disinfect water.

Question 8.
Explain the function of bar screens in a wastewater treatment plant.
In a wastewater treatment plant bar screen removes large solid objects from the water. The wastewater is allowed to pass through a bar screen so that large solid objects such as rags, napkins, sticks, cans, plastic bags, polythene ec present in wastewater can be removed.

Question 9.
Explain the relationship between sanitation and disease.
Sanitation and disease are related to each other because the lack of sanitation can cause diseases. A large fraction of our people defecates in the open fields, on dry riverbeds, on railway tracks, near fields, and also directly in water. The untreated human excreta thus pollutes soil and water sources including groundwater. This becomes the most common route for water-borne diseases like cholera, typhoid, polio, hepatitis, meningitis, and dysentery. Thus, poor sanitation and contaminated ‘drinking water is the cause of a large number of diseases.

Question 10.
Outline your role as an active citizen in relation to sanitation.

  1. Open drains be covered and keep our surroundings clean.
  2. Should not litter anywhere adopt good sanitation practices.
  3. Chemicals like paints, insecticides, motor oil etc., should not be thrown in drain which may kill useful bacteria.
  4. Used tea leaves, solid food remains, soft toys, cotton, sanitary towels, etc should also be thrown in the dustbin.
  5. Make people aware and encourage community practices to keep our environment clean.
  6. Seperate trash as recycled waste and non – recycled.

Question 11.
Here is a crossword puzzle: Good Suck! Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged front human body
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water
KSEEB Solutions for Class 7 Science Chapter 18 Wastewater Story 1

Question 12.
Study the following statements about ozone:
(a) It is essential for the breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in air is about 3%.
Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (d) (iv) All four
(ii) (b) and (c)

Class 7 Science Wastewater Story Additional Important Questions and Answers

Question 1.
Define Wastewater.
The water which is rich in a lather, mixed with oil, black-brown water that goes down the drains from sinks, showers, toilets, laundries is dirty and it is known as Wastewater.

Question 2.
What is Sewage? What are the constituents of sewage?
Sewage is nothing but wastewater. It is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprophytes, and disease-causing bacteria and other microbes.

Question 3.
What is WWTP? What is its function?
WWTP means Wastewater Treatment Plant. The treatment of Wastewater involves Physical, Chemical, and biological processes which remove physical, chemical, and biological matter that contaminates the Wastewater.

Question 4.
Which is the Alternative Arrangement for Sewage disposal?
The low – cost onsite sewage disposal systems are encouraged. The septic tanks. Chemical toilets, composting pits are the other alternate facilities. Some Organisations offer hygienic on-site human waste disposal technology. These toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The biogas produced is used as a source of energy.

Question 5.
How can we keep sanitation at Public Places?
Thousands of people visit the Public Places, so a large amount of waste is generated. It must be disposed of properly, otherwise, epidemics could break out. All of us can contribute in maintaining sanitation in public places. We should not scatter litter anywhere. If there is no dustbin insight, we should carry the litter home and throw it in the dustbin.