Waste Water Story Class 7 Science Part 2 Chapter 9 Questions and Answers

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Free Solutions for The Assam State School Education Board (ASSEB) Class 7 Science Chapter 9 Question Answer in English Medium

Wastewater Story - Questions and Answers
Class 7 Science Part 2 Chapter 9
Assam State Education Board Syllabus 2025-2026 Covered

This chapter explains wastewater, its treatment, and ways to reduce water pollution. Below are the important questions and answers from NCERT & SCERT Assam Class 7 Science Chapter 9 - Wastewater Story, based on the Assam State Education Board syllabus for 2025-2026.

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Introduction to Wastewater Story

Wastewater is used water that contains impurities and pollutants.
Proper treatment of wastewater is necessary to prevent water pollution.
Sanitation and hygiene play a crucial role in maintaining a clean water supply.

Class 7 Science Question Answer – Part 2

Below are the chapters of Class 7 Science Part 2. Click on the chapter name to access the respective question-and-answer content:

Waste Water Story

Exercise Questions & Answers

Q1. Fill in the blanks:

(a) Cleaning of water is a process of removing clean.

(b) Wastewater released by houses is called sewage.

(d) Drains get blocked by cooking oil and fats.

Q2. What is sewage? Explain why is it harmful to discharge untreated sewage into rivers or seas?

Ans: Sewage is wastewater released from homes, industries, and other sources. It contains harmful substances such as bacteria, chemicals, and solid waste. Discharging untreated sewage into rivers or seas can pollute water, spread diseases, and harm aquatic life.

Q3. Why should oils and fats not released in the drain? Explain.

Ans: Oils and fats can solidify and clog drainage pipes, leading to blockages. This can cause sewage to overflow and create hygiene problems. They also reduce the efficiency of wastewater treatment plants.

Q4. Describe the key steps involved in getting clarified water from wastewater.

Ans:

Aeration: Air is bubbled through the wastewater to remove foul odor.
Filtration: Water is passed through layers of sand, gravel, and stones to remove impurities.
Disinfection: Chlorine or ozone is added to kill harmful microorganisms.
Final Testing: The treated water is tested to ensure it meets safety standards before being released or reused.

Q5. What is sludge? Explain how it is treated.

Ans: Sludge is the solid waste that settles at the bottom of sewage treatment tanks. It is treated by:

Separation: Sludge is removed using skimmers.
Decomposition: Anaerobic bacteria break down sludge to produce biogas.
Usage: The treated sludge can be used as manure or fuel.

Q6. Untreated human excreta is a health hazard. Explain.

Ans: Untreated human waste contains harmful microorganisms and pollutants that can contaminate soil and water. It can cause serious diseases such as cholera, typhoid, dysentery, and hepatitis if people consume contaminated water or food.

Q7. Name two chemicals used to disinfect water.

Ans: Chlorine and ozone are commonly used to disinfect water.

Q8. Explain the function of bar screens in a wastewater treatment plant.

Ans: Bar screens are used to remove large solid objects like plastic, rags, sticks, and other debris from sewage before it undergoes further treatment.

Q9. Explain the relationship between sanitation and disease.

Ans: Poor sanitation leads to the spread of diseases like cholera, typhoid, and dysentery due to contaminated water and unhygienic conditions. Good sanitation prevents these diseases and promotes overall health and cleanliness.

Q10. Outline your role as an active citizen in relation to sanitation.

Ans:

Keep surroundings clean and dispose of waste properly.
Use toilets instead of open defecation.
Avoid throwing garbage or chemicals into drains.
Report leakage or blockages in sewage systems to authorities.
Spread awareness about proper sanitation practices.

Q11. Crossword Puzzle: Solve the following clues

Across

3. Liquid waste from households – Sewage
4. Solid waste left after sewage treatment – Sludge
6. A word related to cleanliness and hygiene – Sanitation
8. Human bodily waste – Excreta

Down

1. Water that has been used – Wastewater
2. A pipe carrying sewage – Sewer
5. Microorganisms responsible for cholera – Bacteria
7. A chemical used to disinfect water – Ozone

Q12. Which of the following statements about ozone are correct?

(a) It is essential for the breathing of living organisms.

(b) It is used to disinfect water.

(d) It makes up about 3% of air composition.

Choose the correct option:

(i) (a), (b), and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four

Ans: (ii) (b) and (c) because:

Ozone is used to disinfect water.
It also absorbs harmful ultraviolet rays from the sun.

Class 7 Science Chapter 9 - Important Questions & Answers

Q1: What is wastewater?

Answer: Wastewater is the used water that comes from homes, industries, hospitals, and other sources. It contains impurities like soap, grease, chemicals, and bacteria.

Q2: What are the main sources of wastewater?

Answer: The main sources of wastewater are:

Household waste (from kitchens, bathrooms, and laundries)
Industrial waste (factories and manufacturing units)
Agricultural runoff (pesticides and fertilizers from farms)
Hospital waste (medical and chemical contaminants)

Q3: What is sewage?

Answer: Sewage is a type of wastewater that contains human waste, food particles, chemicals, and microorganisms. It is carried away through sewers and drains.

Q4: What are the harmful effects of untreated wastewater?

Answer: Untreated wastewater can cause:

Water pollution by contaminating rivers and lakes.
Health issues like diarrhea, cholera, and skin infections.
Soil degradation due to the accumulation of harmful chemicals.
Harm to aquatic life due to toxic substances and reduced oxygen levels.

Q5: What is a sewage treatment plant (STP)?

Answer: A sewage treatment plant (STP) is a facility that removes impurities and harmful substances from wastewater before releasing it into the environment.

Q6: What are the stages of wastewater treatment?

Answer: Wastewater treatment involves:

Primary Treatment: Removal of large particles by filtration and sedimentation.
Secondary Treatment: Breakdown of organic matter using bacteria.
Tertiary Treatment: Removal of harmful chemicals and disinfection.

Q7: How can we reduce wastewater production?

Answer: We can reduce wastewater by:

Using water-efficient appliances like low-flow taps and dual-flush toilets.
Fixing leaks to avoid unnecessary wastage.
Avoiding disposal of oils and chemicals down the drain.
Recycling and reusing water whenever possible.

Q8: What is sanitation?

Answer: Sanitation refers to the safe disposal of human waste, proper sewage management, and maintaining cleanliness to prevent diseases.

Q9: Why should we not dispose of plastics in drains?

Answer: Plastics block drainage systems, leading to waterlogging, flooding, and pollution. They do not decompose and cause long-term environmental harm.

Q10: What are some methods to purify water at home?

Answer: Water can be purified at home using:

Boiling (kills germs and bacteria)
Filtration (removes dirt and large particles)
Chlorination (disinfects water using chlorine tablets)
Water purifiers (RO and UV filters)

Multiple Choice Questions (MCQs)

Q1: Which of the following is NOT a source of wastewater?

A) Factories
B) Hospitals
C) Rivers
D) Households

Answer: C) Rivers

Q2: What is the first step in wastewater treatment?

A) Chlorination
B) Filtration and sedimentation
C) Boiling
D) Water recycling

Answer: B) Filtration and sedimentation

Q3: What is the main cause of water pollution?

A) Proper waste disposal
B) Untreated sewage
C) Boiling water
D) Using water filters

Answer: B) Untreated sewage

Q4: What is the purpose of a sewage treatment plant?

A) To increase water pollution
B) To purify water before reuse or disposal
C) To generate electricity
D) To remove only solid waste

Answer: B) To purify water before reuse or disposal

Q5: Which of the following is a good practice to conserve water?

A) Leaving taps open
B) Fixing leaks immediately
C) Wasting water during washing
D) Throwing plastic in drains

Answer: B) Fixing leaks immediately

FAQs on Wastewater Story

Q1: How does wastewater affect human health?

Answer: Contaminated water can spread diseases like typhoid, cholera, and diarrhea, affecting human health.

Q2: What is the role of bacteria in sewage treatment?

Answer: Bacteria decompose organic waste in sewage, converting it into harmless substances.

Q3: Why is wastewater treatment important?

Answer: Wastewater treatment is important to:

Prevent water pollution.
Reduce the spread of diseases.
Make water reusable.

Q4: What happens if wastewater is not treated?

Answer: If untreated wastewater is released into rivers and lakes, it can cause severe pollution, harm aquatic life, and spread diseases.

Q5: How can schools promote wastewater management?

Answer: Schools can:

Educate students about water conservation.
Install water-saving devices.
Conduct awareness campaigns on proper waste disposal.

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