NCERT Solutions for Class 7 Science Chapter 18 - Wastewater Story

1. Fill in the blanks: 

a. Cleaning of water is process of removing ________. 

Ans: Cleaning of water is process of removing contaminants. 

b. Wastewater released by houses is called ________. 

Ans: Wastewater released by houses is called sewage. 

c. Dried ________ is used as manure.

Ans: Dried dung is used as manure. 

d. Drains get blocked by ________ and ________.

Ans: Drains get blocked by plastic and sludge.

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

Ans: Sewage is a kind of used water or wastewater that has been emitted by houses, industries, hospitals, offices, and other users. It also features subsurface storage for rainfall. It may contain dangerous chemicals and organisms that can endanger human life.

Algae can quickly develop when given various nutrients, resulting in a decreased amount of dissolved oxygen in the water. This is why sewage should not be discharged into seas and rivers.

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

Ans: Oil and fats should not be poured down the drain since they are not dissolved in water and float on top of it. It can clog drains and, if released into bodies of water, can harm aquatic life.

4. Describe the steps involved in getting clarified water from wastewater. 

Ans: Wastewater treatment has physical, chemical, and biological processes.

a. Waste water is filtered using bar screens to eliminate large materials such as rags, twigs, cans, plastic packets, napkins, and so on.

b. Water is routed through a grit and sand removal tank, allowing sand, grit, and pebbles to settle.

c. The water is then allowed to settle in a big settling tank, where solid feces known as sludge is removed using a scarper.

d. Air is poured into the clarified water to assist aerobic bacteria in growing and consuming wastes.

e. Water of this kind is dumped into rivers or ponds.

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

Ans: Sludge is a solid waste material that settles in secondary water treatment. Generally, it is scraped out from the bottom. The clarified water is then discharged. Sludge is stored in a separate tank and treated with anaerobic bacteria, which creates biomass that can be used as bio manure.

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

Ans: Millions of bacteria live in the human stomach and expel with the feces. If human excreta is dumped directly into the soil or water, it can pollute both the water and the soil. Under favorable conditions, the bacteria divide and multiply, and when the water reaches the earth table, it might affect a bigger population that consumes it. It can induce water-borne diseases such as typhoid and cholera.

7. Name two chemicals used to disinfect water. 

Ans: Water disinfection involves removing or deactivating pathogenic bacteria, as well as killing them. Microorganisms are rendered inactive, putting an end to their development and reproduction. If germs are not removed from drinking water, humans will develop unwell from drinking water. Chlorine and ozone are the two chemicals used in water disinfection.

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

Ans: When waste water is pumped through bar screens, it serves as a large screen. In the first step of cleaning water, large materials such as rags, twigs, cans, plastics, and napkins are removed.

9. Explain the relationship between sanitation and disease. 

Ans: Sanitation is a public health issue. Sanitation includes the prevention of disease, the provision of safe drinking water, and the proper disposal of garbage. Diseases are spread when cleanliness standards are not met. Dirty water serves as a breeding ground for mosquitoes that transmit diseases. Improper sewage disposal can result in water-borne sickness. As a result, sanitation is the utmost pathogen rescue and can result in a disease-free environment.

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

Ans: All humans have a responsibility to play in keeping our environment clean as engaged and knowledgeable citizens. We can begin from home. Adopting excellent sanitation techniques should be a way of life for all of us. Our energy, ideas, and excitement can have an impact on others. And encourage people to maintain a healthy living environment for the benefit of society.

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 cause cholera. 

7. A chemical to disinfect water.

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Ans: Across:
3. Liquid waste product- Sewage
4. Solid waste extracted in sewage treatment- Sludge
6. A word related to hygiene- Sanitation
8. Waste matter discharged from human body- Excreta

Down:                                                                                                                                                    1. Used water- wastewater
2. A pipe carrying sewage- Sewer
5. Microorganisms which causes cholera- Bacteria
7. A chemical to disinfect water- Ozone

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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? 

i. a., b. and c. 

ii. b. and c. 

iii. a. and d.

iv. All four

Ans: ii.

Explanation: Ozone, often known as trioxygen, is an inorganic molecule having the formula $\mathrm{O}_{3}$. It's a pale blue gas with a pronounced unpleasant odor. Oxygen is required for living beings to breathe. As a result, statement a. is incorrect

Ozone is a powerful oxidant, even more potent than chlorine. Ozone is used in water to disinfect, deodorize, decolorize, and degrade organic compounds. As a result, statement b. is correct.

The ozone layer, also known as the ozone shield, is an area of the earth's stratosphere that absorbs the majority of the sun's UV radiation. As a result, statement c. is correct.

The concentration of ozone in the atmosphere is $0.000004 \%$. As a result statement d. is incorrect.

Therefore, the correct answer is (ii).

NCERT Solution of Class 7 Subject Science Chapter 18 - Free PDF Download

NCERT Solutions offers credible and authentic sources for students to understand, analyse, and answer the questions efficiently. NCERT Solution for Class 7th Science Chapter 18 offers students a brief comprehension of decoding the chapter and answering questions concisely. NCERT Solutions for Class 7th Science Chapter 18 PDF is an easy and scoring chapter that includes all the critical concepts and topics.

NCERT Solution Class 7 Science Chapter 18

NCERT Solutions for Class 7 Science Chapter 18 states the importance of Water in every individual's life. The chapter briefly explains the transition of clean water into dirty water and the measures that need to be implemented to reuse and recycle Wastewater. Each subtopic that falls under the NCERT Science Class 7 Chapter 18  helps students attain a brief comprehension of all the important concepts. 

NCERT Solutions for Class 7 Science Chapter 18 focuses on contaminants' issues with the natural resource water and its dire consequences. It explains the activities that lead to pollution and its adverse impact on health. The chapter also covers the conversion of wastewater generated due to human activities and leads to soil and water pollution. The implementation of a Wastewater Treatment Plant to reduce the level of pollutants in nature. The adoption and implementation of low-cost on-site Sanitation Systems to alternate the unavailability of sewage systems. However, the by-products of the Wastewater Treatment Plant are Biogas and Sludges. The Open Drainage System's consequences, which homes organisms, flies, and mosquitoes that cause multiple diseases. Thus, the chapter conveys the importance of Water, the disposal of Waste, implementation of Wastewater Treatment Plant, Sanitation, and Defecation's consequences.

NCERT Solution of Class 7 Science Chapter 18 guides students through the chapter and enlists the important measures to reduce water pollution and contamination. The NCERT Solution chapter demonstrates the importance of water balance in the ecosystem and creates awareness of sanitation among students.

NCERT Solution of Class 7 Science Chapter 18 - Weightage Marks

NCERT Class 7 Chapter 18 Science is based on the Wastewater Story, its by-products, sewage, and the role of safe disposal methods. The overall weightage for Science Class 7 Chapter 18 is primarily focused on short and long answers. The chapter Wastewater Story holds a weightage of 4 or 8 marks in the intermediate tests or annual examination. Class 7 Science Chapter 18 Solution covers all the important problems from the chapter of the NCERT textbook. The important topics included in the chapter are as follows:

• Ex 18 - Wastewater Story

• Ex 18.1 - Water, Our Lifeline

• Ex 18.2 - What is Sewage?

• Ex 18.3 - Water Freshens Up - An Eventful Journey

• Ex 18.4 - Wastewater Treatment Plant 

• Ex 18.5 - Better Housekeeping Practices

• Ex 18.6 - Sanitation and Disease

• Ex 18.7 - Alternative Arrangement for Sewage Disposal

• Ex 18.8 - Sanitation at Public Places

Benefits of Class 7 Science Chapter 18 Solution

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