NCERT Class 7 Science Chapter 13 Wastewater Story: Notes, Solutions, Free PDF

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Class 7 Science Chapter 13

The final chapter of Class 7 Science deals with wastewater and its management. We will begin NCERT Class 7 Science Chapter 13 with the definition of important terms- wastewater, contaminant, and sewage. Thereafter, we will learn about sewage systems and the “Water for Life” campaign of the United Nations. Further, we will walk through the wastewater treatment process in a wastewater treatment plant. Also, we learn about sanitation and tips to dispose of waste effectively at home. Let us explore all these elements in our CBSE notes. Let us begin!!

Download NCERT Solutions Class 7 Science Chapter 13 Important Questions and Answers PDF

Also Read: Essay on Water Pollution: Samples in 200, 500 Words

Introduction to Class 7 Science Chapter 13: Wastewater Story

In Class 7 Science Chapter 13 we begin with the definition of wastewater and water cleaning process. Also, we will explore the “Water for Life” campaign of the United Nations Organisation. 

What is Wastewater?

Abundant foam, combined with oil, the dark-brown liquid that flows away through pipes from sinks, showers, toilets, and washing machines is considered unclean liquid. This liquid is known as wastewater.

Contaminant

A contaminant is a substance or agent that pollutes or degrades the quality of another substance, such as water or food.

What is Sewage?

Sewage comprises wastewater discharged from residential areas, industrial facilities, hospitals, offices, and various other sources. It also includes rainwater that flows along streets during storms or heavy rain. This runoff from roads and rooftops often carries impure substances. 

Thus, “sewage” is a liquid waste, which primarily contains water with dissolved and suspended impurities.

Sewage Systems

Sewage from each house is gathered via the drainage system. It is then transported to wastewater treatment plants through a network of pipes known as “sewers”. After treatment, the wastewater is released into natural water bodies.

Sewage Treatment

The purification of water involves eliminating contaminants before it is discharged into a body of water or recycled. This procedure for treating wastewater is commonly known as sewage treatment.

Water for Life

Before we dive into the “Water for Life” initiative by the UNO, let us learn about the reasons for global water scarcity. 

Here are some common reasons for the increasing scarcity of freshwater

  • Population growth
  • Pollution
  • Industrial development
  • Mismanagement, and other elements. 

Recognising the pressing nature of this issue, the United Nations General Assembly (UNGA) declared March 22, 2005, as World Water Day. Furthermore, the UNGA designated the period from 2005 to 2015 as the International Decade for Action on “Water for Life.” The primary objective during this decade was to halve the number of people lacking access to safe drinking water. Although there has been noticeable progress toward this goal, there is still much work to be done.

Read More: Class 8 Pollution of Air and Water: Notes and PDF

Wastewater Treatment

In this part of NCERT Class 7 Science Chapter 13, we will learn about the different stages of wastewater treatment in a wastewater treatment plant (WWTP). 

What is Wastewater Treatment?

The process of removing impurities from polluted water to make it usable is known as wastewater treatment. This process includes a combination of physical, chemical, and biological processes designed to eliminate physical, chemical, and biological impurities that are present in the wastewater.

Stages of Wastewater Treatment

Here are the different stages of wastewater treatment:

Wastewater Collection

Firstly, wastewater is collected from different sources in large containers. The water is collected through pipes connecting houses, factories, and other production facilities. 

Screening

Thereafter, screening of wastewater takes place. In this process, large substances are separated from wastewater. After this, the large objects are transferred to the sand and grit removal tank. 

Removal of Organic Waste or Primary Treatment

After the initial screening process, wastewater undergoes primary treatment, during which all organic waste is eliminated. This primary treatment involves directing the wastewater into large tanks where solid materials settle at the top surface of the tanks.

The solids that settle after the primary treatment are called “sludge”. After the collection of sludge, it is decomposed using bacteria. In this process of decomposition, a gas is produced. The gas produced in this process is known as “biogas”. Furthermore, biogas can serve as a fuel source or be used for electricity generation.

Aeration or Secondary Treatment 

Following the primary treatment, the water is directed through a tank known as an “aeration lane” where air is introduced into the water to promote the growth of aerobic bacteria. These bacteria are responsible for breaking down small particles of sludge that may have escaped during the primary treatment process.

Following the secondary treatment, the decomposed sludge settles at the bottom of a large tank known as the “activated sludge” tank, and it contains air within it.

Filtration

Finally, the activated sludge is transferred through a sand-drying machine to remove moisture and separate the water from it. The water is then allowed to flow over a wall, where it is filtered through a sand bed to eliminate any remaining particles. The purified water is subsequently discharged into the river.

Also Read: What are Different Types of Water Pollution?

Household Practices to Minimise or Eliminate Water Pollution

Moreover, NCERT Class 7 Science Chapter 13 also gives ideas to reduce or eliminate water pollution in our houses. Let us pledge to practice these in our daily lives.

  • Do not dispose of cooking oil and fats down the drain as they can block pipes. Also, oil and fats reduce the effectiveness of soil in filtering water. Instead, throw them in the dustbin.
  • Similarly, chemicals like paints, solvents, insecticides, motor oil, and medicines should not be poured down the drain, as they can harm the microbes responsible for purifying water. Properly dispose of these chemicals following recommended guidelines to protect the water treatment process.
  • Also, dispose of used tea leaves, leftover food, soft toys, cotton products, sanitary towels, and similar items in the trash. This is because, these types of waste can block drains, restrict the flow of oxygen, and hinder the decomposition process.

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Sanitation and Disease

Sanitation typically involves offering facilities and services for the safe disposal of human urine and faeces. Inadequate sanitation causes numerous diseases and health risks.

As a large population in developing countries like India and Pakistan and underdeveloped nations like Syria and Palestine consume polluted water, they are often affected by the following water-borne diseases:

  • Dysentery
  • Cholera
  • Meningitis
  • Typhoid
  • Hepatitis
  • Polio

Also Read: Water Image Questions & Tips to Crack them

Alternative Arrangement for Sewage Disposal

In efforts to improve sanitation, the promotion of affordable on-site sewage disposal systems is underway. Some examples include septic tanks, compositing pits, and chemical toilets.

Septic Tanks

A septic tank is an underground, watertight container typically constructed from concrete or polyethene. It is designed to collect sewage and facilitate its decomposition through bacterial processes before allowing the treated effluent to drain through a soak-away system.

On-Site Human Disposal

Certain organizations provide hygienic on-site human waste disposal technology in the form of toilets that do not necessitate manual scavenging. Excreta from these toilets flows through covered drains into a biogas plant, where the produced biogas serves as an energy source.

Read More: Essay on Water Conservation

NCERT Solutions Class 7 Science Chapter 13: Wastewater Story

In the final section of Class 7 Science Chapter 13, we have tried to answer all the questions. All solutions adhere to the latest CBSE curriculum. 

Ques 1. Fill in the blanks:

a. Cleaning of water is a process of removing_______________.

b. Wastewater released by houses is called________________.

c. Dried______________ is used as manure.

d. Drains get blocked by_(1)____________ and_(2)____________.

Ans:

a. Pollutant

b. Sewage 

c. Sludge

d. (1) Cooking oil; (2) fats

Ques 2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Ans: Sewage” is a liquid waste, which primarily contains water with dissolved and suspended impurities.

The discharge of untreated sewage into rivers and seas will contaminate the water in these water bodies. Further, the consumption of polluted water by humans, terrestrial animals and aquatic animals will cause several diseases in these organisms. 

Ques 3. Why should oils and fats be not released in the drain? Explain.

Ans: Do not dispose of cooking oil and fats down the drain as they can block pipes. Also, oil and fats reduce the effectiveness of soil in filtering water.

Ques 4. Describe the steps involved in getting clarified water from wastewater.

Ans: Here are the steps to get clarified water from wastewater:

  • To improve the quality of the wastewater, you can use an aquarium aerator to bubble air through the sample in a glass jar. 
  • For effective aeration, you must leave the aerator attached overnight, although several hours can also be effective. Alternatively, you can also use a mechanical stirrer or mixer to reduce the unpleasant odour of the wastewater.
  • Following aeration, the water undergoes filtration through layers of sand, fine gravel, and medium gravel. This filtration process effectively removes various types of pollutants, and it is continued until the water becomes clear.
  • Finally, water disinfection is achieved by employing a chlorine tablet.

Ques 5. What is sludge? Explain how it is treated.

Ans: The solids that settle after the primary treatment are called “sludge”. 

After the collection of sludge, it is decomposed using bacteria. In this process of decomposition, a gas is produced. 

Ques 6. Untreated human excreta is a health hazard. Explain.

Ans: Untreated human excreta is a significant health hazard due to the presence of several disease-causing microorganisms and pollutants. These contaminants can pollute the soil and water resources that people rely on for drinking and domestic purposes. When we use water that has been contaminated with human excreta, they are at risk of contracting diseases such as Cholera, Typhoid, Dysentery, and Hepatitis.

Ques 7. Name two chemicals used to disinfect water.

Ans: Ozone and Chlorine

Ques 8. Explain the function of bar screens in a wastewater treatment plant.

Ans: Bar screens are designed to separate large objects such as napkins, rags, cans, sticks, and plastic pouches from the wastewater.

Ques 9. Explain the relationship between sanitation and disease.

Ans: Sanitation typically involves offering facilities and services for the safe disposal of human urine and faeces. Inadequate sanitation causes numerous diseases and health risks as we consume water that is discharged from sewage systems. 

Inefficient sanitation causes the following waterborne diseases:

  • Polio
  • Typhoid
  • Cholera
  • Dysentery 

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

Ans:  As an active citizen, I must contribute to the sanitation process in the following ways:

  • I will keep my surroundings clean.
  • I will manage my household sanitation system properly.
  • I will dispose of waste properly and after segregation.
  • I will report to the concerned authorities about leakages in the sewage system in my neighbourhood. 

Ques 11. Here is a crossword puzzle: Good luck!

Class 7 Science Chapter 13

Across:

3. Liquid waste products

4. Solid waste extracted in sewage treatment

6. A word related to hygiene

8. Waste matter discharged from the human body

Down:

1. Used water

2. A pipe carrying sewage

5. Micro-organisms which cause cholera

7. A chemical to disinfect water

Ans:

Across:

3. Sewage

4. Sludge

6. Sanitation

8. Excreta

Down:

1. Wastewater

2. Sewer

5. Bacteria

7. Ozone

Ques 12. Study the following statements about ozone:

a. It is essential for 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

Ans: Option (ii) b and c

Also Read:

NCERT Class 7 Science Chapter 1 Nutrition in Plants: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 2 Nutrition in Animals: Notes, Solutions, Free PDF
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NCERT Class 7 Science Chapter 4 Acids, Bases, and Salts: Notes, Solutions, Free PDF 
NCERT Class 7 Science Chapter 5 Physical and Chemical Changes: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 6 Respiration in Organisms: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 7 Transportation in Animals and Plants: Notes, Solutions, Free PDF
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NCERT Class 7 Science Chapter 9 Motion and Time: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 10 Electric Current and its Effect: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 11 Light: Notes, Solutions, Free PDF
NCERT Class 7 Science Chapter 12 Forests: Our Lifeline: Notes, Solutions, Free PDF

FAQs

Q1. What is activated sludge?

Ans: Following the secondary treatment in wastewater treatment plants, the decomposed sludge settles at the bottom of a large tank known as the “activated sludge” tank, and it contains air within it.

Q2. What is wastewater?

Ans: Abundant foam, combined with oil, the dark-brown liquid that flows away through pipes from sinks, showers, toilets, and washing machines is considered unclean liquid. This liquid is known as wastewater.

Q3. What is a contaminant?

Ans: A contaminant is a substance or agent that pollutes or degrades the quality of another substance, such as water or food.

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