NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story

NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 18
Chapter Name	Wastewater Story
Number of Questions Solved	12
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story

Question 1.
Fill in the blanks:

1. Cleaning of water is a process of removing ________
2. Wastewater released by houses is called __________
3. Dried _________ is used as manure.
4. Drains get blocked by ________ and _______

Solution:

1. pollutants
2. sewage
3. sludge
4. cooking oil; fats.

Question 2.
What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Solution:
Sewage is wastewater released by homes, industries, hospitals, offices, and other users.
Sewage is harmful if discharged untreated into rivers or seas because sewage is a complex mixture of suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease-causing bacteria, and other microbes.

Question 3.
Why should oils and fats be not released in the drain? Explain.
Solution:
Oils and fats should not be released in drains because they can harden and block the pipes. In an open drain, the fats clog the soil pores, reducing its effectiveness in filtering water.

Question 4.
Describe the steps involved in getting clarified water from wastewater.
Solution:
Step 1: When wastewater passes through bar screens, large objects like rags, sticks, cans, plastic packets are removed.
Step 2: Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit, and pebbles to settle down.
Step 3: The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces, settle at the bottom and are removed with a scraper.
Step 4: Air is pumped into clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soap, and other unwanted matter that still remains in clarified water.
After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

Question 5.
What is sludge? Explain how it is treated.
Solution:
Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.  Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps, and other unwanted matter still remaining in clarified water.

After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

Question 6.
Untreated human excreta is a health hazard. Explain.
Solution:
Human excreta may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tube-wells, springs, and many rivers. Thus it becomes the most common route for water-borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis, and dysentery.

Question 7.
Name two chemicals used to disinfect water.
Solution:

1. Ozone
2. chlorine.

Question 8.
Explain the function of bar screens in a wastewater treatment plant.
Solution:
When wastewater passes through the bar screens, large objects like rags, sticks, cans, plastic packets, napkins are removed under the filtration process.

Question 9.
Explain the relationship between sanitation and disease.
Solution:
Sanitation and disease are related to each other. Sanitation involves proper disposal of sewage released from houses and public places. If sanitation is there, no disease will occur, but if sanitation is not there various types of diseases will occur and spread. Therefore, sanitation is necessary to avoid disease.

Question 10.
Outline your role as an active citizen in relation to sanitation.
Solution:
An active citizen has many responsibilities regarding sanitation. An active citizen should do the following to maintain proper sanitation:

• Surroundings should be clean (both inside and outside).
• The sewage system in the home should be properly managed.
• Some leakage or other problem in the sewage system should be reported to the municipality.
• If the sewage of any particular house makes the neighbourhood dirty, we should request them to be more considerate about the health of others.

Question 11.
Here is a crossword puzzle: Good luck!

Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from the human body

Down
1. Used water
2. A pipe carrying sewage
3. Micro-organisms which causes cholera
7. A chemical to disinfect water
Solution:

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 the air is about 3%.
Which of these statements are correct?

1. (a), (b) and (c)
2. (b) and (c)
3. (a) and (d)
4. All four

Solution:
2.  (b) and (c).

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