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Class 7 Important Question

Science

Chapter 18: Wastewater Story

CBSE Important Questions for Class 7 Science Wastewater Story - 2025-26

Q: 3. Why is it a bad practice to throw cooking oils and fats down the drain? What is its impact on the wastewater system?

It is a bad practice because oils and fats can harden and block the pipes, leading to clogs. In the sewer system, they can interfere with the wastewater treatment process by clogging the soil pores in drains, which reduces the effectiveness of water filtration. This is a frequently asked HOTS (Higher Order Thinking Skills) question.

Q: 5. Explain the terms 'sewage' and 'sludge'. How are they different?

Sewage is the liquid waste, or wastewater, released from homes, industries, hospitals, and other sources. It contains dissolved and suspended impurities. Sludge, on the other hand, is the solid material that settles down at the bottom of a sedimentation tank or clarifier during wastewater treatment. The key difference is that sewage is the incoming wastewater, while sludge is the separated solid byproduct of its treatment.

Q: 8. Compare the function of a bar screen and a clarifier in a WWTP. Why is their operational order important?

A bar screen is used at the very beginning of the treatment process to physically remove large objects like rags, sticks, and plastic bags from the wastewater. A clarifier (or sedimentation tank) is used later to allow smaller, suspended solids like faeces to settle at the bottom as sludge. The order is critical because removing large objects first prevents damage and blockages to the pumps and equipment used in the subsequent clarifier and aeration stages, ensuring the plant runs efficiently.

Wastewater Story Class 7 important questions with answers PDF download

In CBSE Class 7 Science Chapter 13, Wastewater Story, students learn about the treatment of wastewater and its impact on health and the environment. The chapter covers the processes involved in wastewater management, including its collection, treatment, and safe disposal. These important questions will help you focus on key concepts, aiding your understanding and revision of the chapter effectively.

CBSE Class 7 Science Syllabus introduces topics related to processes involved in wastewater management. Class 7 Science Important Questions provide a great way to strengthen your knowledge and ensure your understanding of the basics. By practising these questions, students in Class 7 can develop a strong understanding of waste water management, which will be helpful for future lessons.

Access Important Questions for Class 7 Science Chapter 13 Wastewater Story

Very Short Answer Questions: (1 Marks)

Fill in the Blanks:

1. The United Nations declared the period from 2005-2015 as the International Decade for _______________.

Ans: Action on the water for life

2. The suspended impurities in sewage are called _________________.

Ans: Contaminants

3. The network of small and big pipes that is used for the transport of sewage from the point of production to the point of treatment is called __________________.

Ans: Sewerage

4. The sewage that originates from the kitchen is called as _____________.

Ans: Sullage

5. Foul waste originates from __________________.

Ans: Toilets and bathrooms

6. Wastewater generated by the industries is called as __________________.

Ans: Trade water

7. _______________ are used to remove large objects from wastewater.

Ans: Bar screens

8. Solid component of sewage is called as _______________.

Ans: Sludge

9. Aerobic bacteria that settle in the bottom of the tank after clarification are referred to as ________________.

Ans: Activated sludge

10. Septic tanks, chemical toilets and composting pits are examples of ___________________.

Ans: On-site composting

Short Answer Questions: (3 Marks)

1. What is the importance of sewage treatment?

Ans: Sewage is wastewater produced by households and businesses. As a result, it contains material that is hazardous to human health. Water and solid stuff such as faeces make up sewage. If sewage is not treated, the organic stuff in it provides ideal circumstances for the growth of bacteria and other potentially harmful carrier organisms. These organisms have the potential to cause sickness in both humans and animals. Furthermore, sewage has a foul odour that is nauseating and can induce a variety of ailments. Due to a shortage of clean water, this is impossible.

2. How is activated sludge formed?

Ans: The clarified water is then transported to an aeration tank for additional treatment. An aerator is used to introduce air into the cleared water, allowing aerobic bacteria to flourish. These aerobic bacteria then eat any organic substance that remains in the cleared water, such as human waste, food waste, soaps, and so on. These suspended aerobic bacteria settle to the bottom of the tank as activated sludge after many hours.

3. What is the role of grit and sand removal tanks?

Ans: The grit and sand removal tank is a progressively sloped tank where heavier particles such as grit and sand can settle. The pace of water in this tank is substantially slowed. Heavy particles in the wastewater, such as grit and sand, sink to the bottom of the tank when water runs at a near-stagnant rate. After that, the water is transported to the clarifier.

4. How is water clarified in a water clarifier?

Ans: The clarifier is a huge tank with a centre slope. Water is allowed to settle for several hours in this tank. During this time, the sewage's organic solid particles settle at the bottom of the tank. Sludge refers to the solid element of sewage. A scraper is used to scrape and remove the sludge. A skimmer is used to remove floatable materials like oil and grease. Clarified water is the water that is obtained at the end of this operation. The sludge is then moved to a separate tank, where anaerobic bacteria decompose it into biogas and compost. Manure can be utilised as fertiliser and biogas can be used to generate electricity.

5. What are onsite composting methods?

Ans: On-site composting systems treat sewage at the point of production rather than transporting it to a treatment facility. Septic tanks, chemical toilets, compost pits, and other on-site composting technologies include septic tanks, chemical toilets, and compost pits, among others. Such on-site solutions can be used because the volumes of sewage created by tiny units are lower than those generated by a large population. The action of bacteria composts sewage, and cleaned wastewater is subsequently reintroduced into the sewers. The burden on the sewage treatment plants is reduced as a result.

Long Answer Questions: (5 Marks)

1. Suggest better housekeeping practices that can be adopted to reduce waste generation.

Ans: We can utilise a variety of housekeeping methods to reduce sewage and our environmental impact.

1. Cooking fats and oils solidify and clog drains. As a result, they should not be flushed down the toilet.

2. Chemicals can destroy critical sewage-treatment bacteria, therefore they shouldn't be flushed down the toilet.

3. Solid wastes should not be poured down the sink since they clog it. They also obstruct oxygen flow, which has a negative impact on the deterioration process.

4. Do not pollute the environment. If there isn't a garbage bin available, the trash should be transported home and disposed of in the trash can.

2. Poor sanitation leads to diseases. Justify.

Ans: The maintenance of hygiene at the communal level is referred to as sanitation. It entails proper sewage disposal and sustaining communal cleanliness. Sanitation issues imply that hygiene is not being maintained. This happens as a result of incorrect sewage disposal. This allows disease-causing microorganisms and their vectors to reproduce. A rise in the number of pathogenic bacteria increases the chance of developing numerous diseases. Poor sanitation also has an impact on the supply and availability of safe drinking water. In the lack of safe drinking water, a variety of health issues occur, which can lead to a variety of diseases. In addition, due to a shortage of clean water, recovering from infections would be difficult.

5 Important Topics of Class 7 Science Chapter 13 You Shouldn’t Miss!

In Chapter 13 Wastewater Story, students explore essential topics related to wastewater management, treatment processes, and their impact on health and the environment.

Topic	Explanation
Wastewater Treatment Processes	Understand the various stages of wastewater treatment, including primary, secondary, and tertiary treatments. Each stage plays a crucial role in removing contaminants and ensuring water is safe for discharge or reuse.
Sources of Wastewater	Learn about the common sources of wastewater, such as households, industries, and agricultural runoff. Recognising these sources helps in understanding the scale of wastewater generation.
Impact on Health and Environment	Explore how untreated wastewater can affect human health and the environment, including the risks of disease and pollution of water bodies.
Role of Microorganisms	Discover the role of microorganisms in the biological treatment of wastewater. These organisms help break down organic matter, making the treatment process more effective.
Sustainable Water Management	Discuss the importance of sustainable practices in managing wastewater and conserving water resources. This includes methods to reduce, reuse, and recycle water to protect the environment and ensure clean water availability for future generations.

Benefits of Class 7 Science Important Questions Chapter 13 Wastewater Story

Important Questions help students focus on the main ideas of wastewater treatment, ensuring a solid understanding of the chapter.
Practising these questions prepares students for assessments by familiarising them with the types of questions they may encounter.
Answering Important Questions encourages students to think critically about wastewater management and its environmental impact.
Reviewing Important Questions aids in the long-term retention of key concepts by breaking down complex information into manageable parts.
These questions often relate to real-life scenarios, helping students understand the practical implications of wastewater treatment.
Regular practice of Important Questions boosts students' confidence in their understanding of the material, making them more prepared for exams.

Conclusion

In conclusion, the Important Questions for Class 7 Science Chapter 13, Wastewater Story, serve as a valuable resource for reinforcing key concepts related to wastewater management and its environmental significance. By actively engaging with these questions, students can enhance their understanding of the treatment processes, the importance of clean water, and the impact of wastewater on health and ecosystems.

Related Study Materials for Class 7 Science Chapter 13

S.No	Important Study Material Links for Class 7 Science Chapter 13
1.	Class 7 Wastewater Story Notes
2.	Class 7 Wastewater Story Solutions

CBSE Class 7 Science Important Questions

S.No	CBSE Class 7 Science Important Questions
1.	Chapter 1 - Nutrition in Plants Questions
2.	Chapter 2 - Nutrition in Animals Questions
3.	Chapter 3 - Heat Questions
4.	Chapter 4 - Acids, Bases and Salts Questions
5.	Chapter 5 - Physical and Chemical Changes Questions
6.	Chapter 6 - Respiration in Organisms Questions
7.	Chapter 7 - Transportation in Animals and Plants Questions
8.	Chapter 8 - Reproduction in Plants Questions
9.	Chapter 9 - Motion and Time Questions
10.	Chapter 10 - Electric Current and Its Effects Questions
11.	Chapter 11 - Light Questions
12.	Chapter 12 - Forests: Our Lifeline Questions

Other Important Study Materials for Class 7 Science

S.No	Other Important Study Material for Class 7 Science
1.	Class 7 Science Revision Notes
2.	CBSE Class 7 Sample Papers
3.	NCERT Books for Class 7 Science
4.	NCERT Exemplar for Class 7 Science Solutions

FAQs on CBSE Important Questions for Class 7 Science Wastewater Story - 2025-26

1. What are some important short-answer questions from Chapter 13, Wastewater Story, for the CBSE Class 7 exam 2025-26?

Some important short-answer (2 or 3-mark) questions include defining sewage, explaining the role of a bar screen in a Wastewater Treatment Plant (WWTP), and listing two diseases caused by poor sanitation and contaminated water. Another expected question is to explain what sludge is and how it is treated.

2. What is a likely 5-mark question from the Wastewater Story chapter?

A common 5-mark question for the 2025-26 exam would be to describe the complete process of wastewater treatment in a Wastewater Treatment Plant (WWTP). The answer should cover all the key stages in the correct order:

Primary Treatment: Bar screens, grit and sand removal, and sedimentation in a clarifier.
Secondary Treatment: Aeration to promote bacterial growth for consuming waste.
Tertiary Treatment: Disinfection using chlorine or UV light before releasing the treated water.

3. Why is it a bad practice to throw cooking oils and fats down the drain? What is its impact on the wastewater system?

It is a bad practice because oils and fats can harden and block the pipes, leading to clogs. In the sewer system, they can interfere with the wastewater treatment process by clogging the soil pores in drains, which reduces the effectiveness of water filtration. This is a frequently asked HOTS (Higher Order Thinking Skills) question.

4. How does the aeration step in a WWTP help in cleaning water, and what would happen if it were skipped?

The aeration step involves pumping air into clarified water to help aerobic bacteria grow rapidly. These bacteria are crucial as they consume the remaining organic human waste, soaps, and other unwanted matter. If this step were skipped, the organic contaminants would not be effectively removed, and the discharged water would remain polluted, causing harm to aquatic life and the environment.

5. Explain the terms 'sewage' and 'sludge'. How are they different?

Sewage is the liquid waste, or wastewater, released from homes, industries, hospitals, and other sources. It contains dissolved and suspended impurities. Sludge, on the other hand, is the solid material that settles down at the bottom of a sedimentation tank or clarifier during wastewater treatment. The key difference is that sewage is the incoming wastewater, while sludge is the separated solid byproduct of its treatment.

6. What are some expected Multiple Choice Questions (MCQs) from the Wastewater Story chapter?

Expected MCQs often test specific knowledge. For instance, a question might ask which of the following is used to disinfect water at the end of the treatment process (options: chlorine, oxygen, carbon dioxide, nitrogen). Another could be about the useful byproduct of sludge treatment, which is biogas. Questions about the definition of contaminants and types of sewers (sanitary, storm) are also common.

7. As an active citizen, what important practices can you adopt to minimise wastewater pollution?

This is an important value-based question. As an active citizen, you can adopt the following practices:

Do not dispose of cooking oils, fats, or grease down the kitchen sink.
Avoid flushing solid wastes like sanitary towels, plastics, or chemical-laden items down the toilet.
Use natural cleaning products instead of harsh chemicals to reduce the chemical load on the WWTP.

8. Compare the function of a bar screen and a clarifier in a WWTP. Why is their operational order important?

A bar screen is used at the very beginning of the treatment process to physically remove large objects like rags, sticks, and plastic bags from the wastewater. A clarifier (or sedimentation tank) is used later to allow smaller, suspended solids like faeces to settle at the bottom as sludge. The order is critical because removing large objects first prevents damage and blockages to the pumps and equipment used in the subsequent clarifier and aeration stages, ensuring the plant runs efficiently.