NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story

Science is an interesting and scoring subject, but to achieve full marks, students need reliable study materials and proper guidance. The NCERT Solutions for Class 7 Science are designed to make learning easy and stress-free for students. These solutions provide clear, simplified explanations for all exercises from the NCERT textbook, ensuring that every topic in Chapter 13 – Wastewater Story is covered in a detailed and comprehensive manner.

To make learning more engaging, subject experts from Infinity Learn have carefully created these NCERT Solutions for Class 7 Science PDF, strictly following the latest CBSE syllabus. These NCERT solutions include well-labeled diagrams, illustrations, and step-by-step answers to help students understand difficult concepts easily.

Whether your child is preparing for exams or simply revising, downloading the NCERT Solutions for Class 7 Science Chapter 13 PDF will boost their preparation and build a strong foundation in Science.

NCERT Solutions for Class 7 Science PDF Download

Students looking for clear and easy explanations can now access the NCERT Solutions for Class 7 Science Chapter 13 – Wastewater Story PDF download option. This PDF is designed to provide step-by-step answers for every question from the textbook, making it easier for students to study and revise without confusion during exams. With this Class 7 Science PDF download, students can quickly review important concepts anytime, anywhere. 

The detailed solutions help explain each topic in a simple and understandable way, ensuring better learning and retention. The PDF format also allows for easy sharing and offline study support, making it a valuable resource for scoring well in Science.

NCERT Solutions for Science Class 7 Chapter 13 Textbook Solutions

1. Fill in the blanks:

(a) The process of making water free from unwanted substances is called pollutant removal.

(b) The water carrying waste materials from houses is known as sewage.

(c) After drying, sludge can be used as manure.

(d) Cooking oil and fats often block the drains.

2. What is sewage? Why should untreated sewage not be released into rivers or seas?

Answer: Sewage is dirty wastewater coming from homes, containing human waste, soap, food scraps, and harmful germs. If untreated sewage flows directly into rivers or seas, it can pollute the water, kill aquatic life, and spread diseases like cholera and typhoid among people who use that water.

3. Why should oils and fats not be poured into the drain?

Oils and fats can build up inside your drain pipes, causing them to narrow or even become completely blocked. This can result in unpleasant odors, water pooling, and potential damage to your drainage system.

4. Explain how wastewater is cleaned to get clear water.

Answer: The steps to clean wastewater include:

To start off, air is pumped through the wastewater with an aerator, which helps to eliminate any unpleasant odors.

Then, the water flows through layers of sand and gravel, effectively filtering out tiny particles and dirt.

In the final step, chemicals like chlorine are introduced to eliminate germs, ensuring the water is both safe and crystal clear.

5. What is sludge? How is it treated?

Sludge is that thick, gooey waste that settles at the bottom of a tank during the sewage treatment process. Once it’s collected, it goes into a special tank where bacteria work their magic in an oxygen-free environment (that’s called an anaerobic process), breaking it down and creating biogas in the process. The sludge that’s been treated can actually be repurposed as fertilizer later on!

6. Why is untreated human excreta dangerous?

Answer: Human excreta contains harmful germs that can spread serious diseases like typhoid, cholera, dysentery, and hepatitis. When this waste mixes with drinking water sources, it makes people sick and can even cause outbreaks.

7. Name two chemicals used to make water germ-free.

Answer: Two commonly used chemicals for disinfecting water are chlorine and ozone.

8. What do bar screens do in a sewage treatment plant?

Answer: Bar screens are like big filters that catch and remove large waste materials like plastic bags, rags, sticks, and napkins from the sewage before it moves to the next treatment stage.

9. How are sanitation and disease connected?

Answer: Poor sanitation leads to dirty surroundings and contaminated water, which can cause many diseases. Clean and proper sanitation keeps our environment healthy and helps prevent infections.

10. How can you help in keeping sanitation better as a responsible citizen?

Answer: As responsible citizens, we can:

Keep our homes and surroundings clean.

Avoid throwing garbage in open drains.

Report leaking sewage lines to authorities.

Save water and use it wisely.

Teach others about the importance of sanitation.

11. Here is a Crossword Puzzle – Wastewater Story

Ans:

12. Read the following statements about ozone and identify the correct ones:

(a) Ozone is necessary for the breathing of living beings.
(b) Ozone is used to purify and disinfect water.
(c) Ozone helps block harmful ultraviolet (UV) rays from the sun.
(d) Ozone makes up about 3% of the air around us.

Which of the following options is correct?

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

Correct Answer:
(ii) Statements (b) and (c)

Ozone is not needed for breathing, and it makes up a very tiny part of air, not 3%. However, it is commonly used to disinfect water and also plays an important role in absorbing harmful UV rays in the atmosphere.

NCERT Solutions of Class 7 Science Chapter 13 Wastewater Story Summary

This chapter teaches us about wastewater, which is the used and dirty water from homes, industries, and agricultural fields. This wastewater, often called sewage, contains many contaminants like food waste, soap, oil, harmful chemicals, and disease-causing germs.

• To make this water safe again, it is treated in a sewage treatment plant (STP). In STPs, the solid waste is removed first using bar screens. Then the water goes through processes like aeration, where air is pumped into the water to help aerobic bacteria grow and break down waste.
• The denser materials, often referred to as sludge, sink to the bottom and are gathered separately. This sludge is further broken down by anaerobic bacteria (which work without oxygen) to produce biogas, which can be used as fuel.
• Cleaned water from the plant is released into rivers or used for irrigation, but still contains small amounts of harmless substances that nature can handle safely.
• In places without underground sewer systems, low-cost on-site sanitation methods like septic tanks are used for safe waste disposal. Open drains should be avoided as they become breeding spots for mosquitoes, flies, and germs, leading to diseases.
• Finally, the chapter highlights the importance of proper sanitation and hygiene. It also stresses that we should never defecate in the open and should work towards keeping our environment clean.

Important Terms Covered: Wastewater, Sewage, Sewer, Sewerage, Sludge, Biogas, Contaminant, Aeration, Aerobic bacteria, Anaerobic bacteria, Sanitation.

NCERT Solutions for Class 7 Science – Chapter-wise PDF Download Links (Free) 

Science becomes easier with the right study material. Here, we provide chapter-wise NCERT Solutions for Class 7 Science in a free and downloadable PDF format. These solutions cover all textbook exercises with clear explanations, helping students build strong concepts and score better in exams as per the latest CBSE 2025-26 syllabus.