NCERT Solutions for Class 7th Science Chapter 13 Wastewater Story according to the Latest Syllabus Of JKBOSE and CBSE NCERT Books
1. Fill in the blanks:
(a) Cleaning of water is a process of removing contaminants.
(b) Wastewater released by houses is called sewage.
(c) Dried sludge is used as manure.
(d) Drains get blocked by cooking oil and fats.
2. Water is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Water in sewage contains harmful chemicals, pathogens, and organic waste. Discharging untreated sewage into rivers or seas can pollute the water, harming aquatic life and making the water unsafe for human use. It can lead to the spread of diseases, deplete oxygen levels in the water, and disrupt ecosystems.
3. Why should oils and fats not be released in the drains? Explain.
Oils and fats should not be released in drains because they can solidify and cause blockages in the sewage pipes. These blockages can lead to sewage overflows, causing environmental pollution and health hazards. Additionally, oils and fats can form a layer on water bodies, preventing oxygen from dissolving in the water and harming aquatic life.
4. Describe the steps involved in getting clarified water from wastewater.
The steps involved in getting clarified water from wastewater include:
- Screening: Removing large solids like plastic, cloth, and other debris.
- Sedimentation: Allowing solids to settle at the bottom of a tank.
- Aeration: Adding air to promote the growth of beneficial bacteria that break down organic matter.
- Filtration: Passing the water through filters to remove smaller particles.
- Disinfection: Using chemicals like chlorine to kill harmful microorganisms.
5. What is sludge? Explain how it is treated.
Sludge is the solid waste that settles at the bottom of the sedimentation tanks during wastewater treatment. It is treated by:
- Thickening: Concentrating the sludge to reduce its volume.
- Digestion: Using anaerobic bacteria to break down organic matter in the sludge, reducing its volume and odor.
- Dewatering: Removing excess water from the sludge.
- Disposal: The treated sludge can be used as manure or disposed of in landfills.
6. Untreated human excreta is a health hazard. Explain.
Untreated human excreta is a health hazard because it contains harmful pathogens that can cause diseases like cholera, dysentery, and typhoid. When it contaminates water sources, it poses serious risks to public health. Proper treatment and disposal of human excreta are essential to prevent the spread of these diseases.
7. Name two chemicals used to disinfect water.
Two chemicals used to disinfect water are chlorine and ozone.
8. Explain the function of bar screens in a wastewater treatment plant.
Bar screens are used in wastewater treatment plants to remove large solid objects like sticks, plastic, and other debris from the incoming sewage. This prevents damage to the equipment and ensures the smooth operation of the treatment process.
9. Explain the relationship between sanitation and disease.
Poor sanitation can lead to the spread of diseases by providing breeding grounds for pathogens and vectors like mosquitoes and flies. Contaminated water and food can transmit diseases like cholera, diarrhea, and typhoid. Good sanitation practices, such as proper disposal of waste and access to clean water, are essential to prevent these diseases and maintain public health.
10. Outline your role as an active citizen in relation to sanitation.
As an active citizen, I can:
- Promote hygiene practices: Educate others about the importance of handwashing and proper waste disposal.
- Support sanitation initiatives: Participate in community clean-up drives and advocate for better sanitation facilities.
- Conserve water: Use water judiciously and report leaks and water wastage.
- Segregate waste: Properly separate recyclable and non-recyclable waste to facilitate efficient waste management.
- Encourage responsible behavior: Discourage littering and ensure that sewage is treated before being released into water bodies.
11. Crossword Puzzle
Across
- 3. Effluent
- 4. Sludge
- 6. Hygiene
- 8. Excreta
Down
- 1. Wastewater
- 2. Sewer
- 5. Vibrio
- 7. Chlorine
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
Answer: (ii) (b) and (c)
13. Tick mark (✓) the correct answers.
- The disease caused by polluted water
(a) Jaundice
(b) Dysentery
(c) Cholera
(d) All of these
Answer: (d) All of these
- Malaria can be triggered by
(a) Open drains
(b) Closed drains
(c) Taps
(d) Pipe lines
Answer: (a) Open drains
