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Class 7 Science Wastewater Story

Last updated on November 2nd, 2023 at 08:14 pm

Class 7 Science Chapter 18 Wastewater Story


Q.2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans. Sewage is a liquid waste generated from households, industries, and agriculture. Discharging untreated sewage into rivers and seas can lead to environmental pollution and harm. Sewage comprises harmful substances and disease-causing organisms that make it dangerous to release into water sources. The unprocessed waste can cause the death of aquatic life due to oxygen depletion, contamination, and harmful bacterial growth. Waterborne diseases, ranging from minor skin infections to severe illnesses, are common among people who use such water sources. Proper sewage treatment through primary and secondary processes is vital to ensure environmental safety and human health.


Q.3. Why should oils and fats be not released in the drain? Explain.
Ans. When oils and fats are poured down the drain, they often mix with other substances like soap and detergent, and the resulting mixture can create a thick, sticky mass that can harden and clog pipes over time. The fats and oils can also adhere to the inner lining of the pipes, reducing the diameter of the pipes and causing water to back up. This can lead to unpleasant smells, unsanitary conditions, and expensive repairs. It is important to properly dispose of oils and fats by storing them in containers and disposing of them in the garbage or recycling where possible.


Q.4. Describe the steps involved in getting clarified water from wastewater.
Ans. Water purification involves several steps. Firstly, physical impurities such as stones, cans and plastic bags are removed by passing the water through bar screens. The water is then taken to a grit and sand removal tank where impurities are removed by sedimentation, and sludge is collected from the bottom. Next, clarified water is cleaned of other impurities through aeration, and all disease-causing bacteria are eliminated through chlorination.


Q.5. What is sludge? Explain how it is treated.
Ans. Sludge is the solid waste produced during the treatment of wastewater in a water treatment plant. It is broken down by anaerobic bacteria in a separate tank. The resulting product, known as activated sludge, can be used as a type of fertilizer.


Q.6. Untreated human excreta is a health hazard. Explain.
Ans. Untreated human excreta can lead to health problems as it can contaminate water, air and soil. The bacteria found in polluted water can cause diseases such as cholera and meningitis, which can easily spread and cause epidemics.


Q.7. Name two chemicals used to disinfect water.
Ans. Two chemicals commonly used to disinfect water are chlorine and ozone.


Q.8. Explain the Junction of bar screens in a wastewater treatment plant.
Ans. Bar screens are used to remove physical impurities from wastewater. They are effective in removing larger items such as napkins, plastics, and cans from the wastewater before it continues on for further treatment.


Q.9. Explain the relationship between sanitation and disease.
Ans. Sanitation and disease are closely related, as proper disposal of sewage and refuse from homes and public places is crucial in preventing the spread of disease. When sanitation is present, the occurrence of diseases is minimized, but when sanitation is lacking, various types of diseases can occur and spread easily. Therefore, it is important to maintain good sanitation practices to avoid disease outbreaks.


Q.10. Outline your role as an active citizen in relation to sanitation.
Ans. As active citizens, we have a responsibility to maintain personal environmental sanitation and raise awareness about its benefits. This includes taking action to help municipal corporations cover open drains and remove disease-causing substances that are often thrown in open areas. By doing so, we can help prevent the spread of diseases and create a healthier environment for ourselves and others.


Extra Que Ans

Q- How do you define waste water?

Water that flows down drains from sinks, showers, toilets, laundry, etc., is wastewater. It is black or brown in color and contains foam and oil.

Q- How many people lack access to safe drinking water?

Over one billion people lack access to safe drinking water, according to reports.

Q- What factors contribute to the scarcity of freshwater?

Water scarcity is caused by a number of factors, such as population growth, pollution, industrial development, mismanagement, etc.

Q- What year was declared the International Decade for Action on “Water for Life”?

It was declared the International Decade for Action on “Water for Life” by the United Nations General Assembly on 22 March 2005.

Q- What is the purpose of the International Decade for Action on “Water for Life”?

The International Decade for Action on “Water for Life” aims to reduce the number of people without access to safe drinking water by half.

Q- How does sewage treatment work?

A sewage treatment process involves removing pollutants from water before it enters a waterbody or is reused. It involves physical, chemical and biological processes to remove pollutants and make the water safe.

Q- What is sewage and what does it contain?

The term sewage refers to the waste water released by industry, homes, hospitals, offices, etc. It also refers to rainfall that flows on to the roads during storms or heavy rainfall.

Q- What are the impurities present in sewage?

Sewage contains suspended solids, organic and inorganic impurities, nutrients, saprophytes, bacteria that cause disease, and other microorganisms.

Q- What is sewerage? How does it work?

A sewer system is a network of large and small pipes that transport waste from the point at which it is generated to the point where it is disposed of. In a sewage treatment plant, pollutants are removed physically, chemically and biologically before it is released into the environment or recycled. It works like a transportation system.

Q- In the sewage system, what is the role of sewers?

A sewer system is a network of pipes that transports sewage from its point of origin to its point of disposal.

Q- What are the three steps involved in treating waste water?

Wastewater treatment involves physical, chemical, and biological processes that remove physical, chemical, and biological contaminants.

Q- In order to treat waste water, what is the first step?

Water is first purified by passing through a bar screen that removes large items like clothes, sticks, cans, and plastic packets.

Q- After passing through the grit and sand removal tank, what happens to the water?

During the grit and sand removal process, the water passes through a tank that slopes toward the middle where it collects. Solids, such as feces, settle to the bottom and are removed with scrapers. Floatable solids, such as oil and grease, are removed with a skimmer. The clean water is water that is free of these impurities.

Q- Why is air pumped into pure water?

Pumping air into clean water helps aerobic bacteria grow, which breaks down organic matter.

Q- What happens to the sludge after it is removed from waste water?

The sludge is transferred to a separate tank where anaerobic bacteria decompose it. The biogas produced in this process can be used as fuel or energy. Organic matter and nutrients are returned to the soil by using dried sludge as fertilizer.

Q- What is the biological treatment process for waste water?

Bacteria consume human waste, food waste, soap, and other unwanted substances left in clean water. After several hours, the suspended microbes settle to the bottom and the water is then pumped out.

Q- Why shouldn’t cooking oils and fats be poured down the drain?

Cooking oils and fats should not be flushed down the drain, as they can harden and block the pipes. In open drains, fat clogs the pores of the soil, making it ineffective at filtering water.

Q- What are the reasons why paints, solvents, pesticides, motor oils, and medications shouldn’t be poured down the drain?

Chemicals such as paint, solvents, pesticides, motor oil, and medicines can kill the microorganisms that help purify water.

Q- What kind of waste should be thrown away in the dustbin?

Wastes such as used tea leaves, solid food leftovers, soft toys, cotton, sanitary towels, etc. should be thrown away in the dustbin because they block drains and obstruct oxygen flow.

Q- In India, what types of places generate the most garbage?

In India, busy places like fairs, train stations, bus depots, airports, and hospitals generate a large amount of waste. Thousands of people visit these places every day, and if the waste isn’t disposed of properly, epidemics can spread.

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