GSEB Class 7 Science Solutions Chapter 18 Wastewater Story

Question 1. Fill in the blanks:
Answer:
Cleaning of water is a process of removing pollutants.
Wastewater released by houses is called sewage.
Dried sludge is used as manure.
Drains get blocked by plastic items and food waste.

Exam Tip: For fill-in-the-blank questions, ensure your answers are precise and directly related to the topic of wastewater management.

Question 2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Answer: Sewage is a liquid that holds wastes, often released by homes, industries, and farms into the water. It's bad to let untreated sewage flow into rivers or seas, as it can dirty entire water sources. Sewage has harmful substances and germs that cause illnesses. So, it's risky to put untreated sewage into water bodies.

Exam Tip: Clearly define sewage and then list specific reasons for its harmful impact, such as pollution and disease-causing organisms.

Question 3. Why should oils and fats be not released in the drain? Explain.
Answer: Oils and fats should not be released into drains because they make the soil in the pipes hard and block them. Fats get stuck in the small openings of the drain soil and create blockages. This stops the water from flowing properly.

Exam Tip: Remember to mention both the hardening of pipes and the clogging of holes as reasons why oils and fats are problematic in drains.

Question 4. Describe the steps involved in getting clarified water from wastewater.
Answer: Water purification involves these steps:
1. First, all large physical items like stones, plastic bags, and cans must be taken out. This happens when water goes through bar screens.
2. Next, water moves to a grit and sand removal tank, where other unwanted bits settle down through sedimentation.
3. Solid bits and waste matter are gathered from the bottom of the water. These gathered impurities are known as sludge.
4. Finally, cleaned water is cleared of remaining impurities using an aerator. Any germs causing diseases are taken out with chlorination.

Exam Tip: List the steps in logical order and use clear, descriptive language for each stage, mentioning key processes like screening, sedimentation, aeration, and chlorination.

Question 5. What is sludge? Explain how it is treated.
Answer: Sludge is the gathered solid waste from wastewater during its treatment in a water treatment plant. Sludge is broken down in a separate tank by anaerobic bacteria. Activated sludge is then used as manure.

Exam Tip: Define sludge clearly, then detail the two main steps of its treatment: decomposition by anaerobic bacteria and its use as manure.

Question 6. Untreated human excreta is health. hazard. Explain.
Answer: Untreated human excreta can lead to many health-related issues. It pollutes water, air, and soil. Polluted water holds bacteria that cause diseases, which can spread illnesses like cholera and meningitis. It is thus a major health danger.

Exam Tip: When explaining health hazards, always link the untreated waste to specific forms of pollution (water, air, soil) and mention specific diseases that can spread.

Question 7. Name two chemicals used to disinfect water.
Answer: Chlorine and ozone.

Exam Tip: Remember these two common chemicals for disinfecting water; they are frequently asked in short-answer questions.

Question 8. Explain the function of bar screens in a wastewater treatment plant.
Answer: Bar screens clean the wastewater by removing all large physical impurities. Big waste items such as napkins, plastics, and cans are taken out from the wastewater as it passes through these bar screens.

Exam Tip: Focus on the primary purpose of bar screens: removing large physical debris to prevent damage to subsequent treatment machinery.

Question 9. Explain the relationship between sanitation and disease.
Answer: Sanitation and disease are connected to each other. Good sanitation involves the proper removal of sewage and waste from homes and public areas. If sanitation is good, no diseases will happen. However, if sanitation is poor, many types of diseases will occur and spread. So, good sanitation must be kept up to avoid illness.

Exam Tip: Explain both sides of the relationship: how good sanitation prevents disease and how poor sanitation leads to disease spread.

Question 10. Outline your role as an active citizen in relation to sanitation.
Answer: As an active citizen, we should take care of our personal environmental cleanliness. We should make people aware of the good things that come from sanitation. We should help local authorities cover all open drains and remove substances that cause diseases when left in the open.

Exam Tip: When discussing your role as a citizen, include practical actions like maintaining personal hygiene, raising awareness, and assisting local bodies.

Question 11. Here is a crossword puzzle. Good luck!
Answer:
Across:
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. The 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

Exam Tip: For crossword puzzles, always ensure that both across and down clues fit their respective words perfectly in the grid.

Question 12. Study the following statements about ozone:
(a) It is essential for the 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)
In simple words: Ozone helps clean water and blocks harmful UV rays from the sun. It is not for breathing, and its amount in air is much less than 3%.

Exam Tip: Distinguish between the functions of ozone in the stratosphere (UV absorption) and its uses in disinfection, and avoid confusing it with oxygen needed for respiration.

Extended Learning – Activities And Projects

Question 1. Construct a crossword puzzle of your own using the keywords.
Across:
1. A gas prepared by decomposition.
2. The network of sewers.
4. Solid waste which settles at the bottom.
Down:
3. Bacteria that require air.
5. A microorganism that causes cholera.
Answer:

Exam Tip: When constructing crosswords, ensure all keywords are spelled correctly and fit within the grid for both across and down clues.

Question 2. Then and now: Talk to your grandparents and other elderly people in the neighborhood. Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief report on the information you collected.
Answer: Do it yourself.

Exam Tip: For "Do it yourself" activities, focus on active participation, accurate data collection, and clear presentation of findings in your report.

Question 3. Visit a sewage treatment plant. It could be as exciting and enriching as a visit to a zoo, a museum, or a park. To guide your observation here are a few suggestions. Record in your notepad: Place Date Time Name of the official at the plant Guide/ Teacher (a) The location of the sewage plant. (b) Treatment capacity. (c) The purpose of screening as the initial process. (d) How is air bubbled through the aeration tank? (e) How safe is the water at the end of the treatment? How is it tested? (f) Where is the water discharged after treatment? (g) What happens to the plant during heavy rains? (h) Is biogas consumed within the plant or sold to other consumers? (i) What happens to the treated sludge? (j) Is there any special effort to protect nearby houses from the plant? (k) Other observations.
Answer: Do it yourself with the help of your teacher/parents.

Exam Tip: When visiting a plant, focus on asking questions from your list and observing each process carefully to understand the entire wastewater treatment cycle.