NCERT Grade 7-Wastewater Story-Answers – MySchoolPage

NCERT Grade 7-Wastewater Story-Answers

NCERT Solutions for Class 7 Science

Find 100% accurate solutions for NCERT Class VII Science. All questions have been explained and solved step-by-step, to help you understand thoroughly. Free Download option available!

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1.    Fill in the blanks:

(a) Cleaning of water is process of removing contaminants.

(b) Wastewater released by houses is called sewage.

(c) Dried dung is used as manure.

(d) Drains get blocked by plastic and sludge.

2.    Sewage is wastewater released by homes, industries, hospitals, offices and other users. It includes rainwater that has run down the street during a storm or heavy rain. The untreated sewage may contain harmful chemicals that may kills the organisms growing in water. The sewage also contains nutrients that cause growth of algae and leads to scarcity of oxygen. That is why it is harmful to discharge untreated sewage into rivers or seas.

3.    Oil does not mix with water. Being lighter, oil floats on water. This prevents mixing of water and air. These reduce oxygen supply for aquatic plants and animals.

4.    Treatment of wastewater involves physical, chemical and biological processes.

(a) Waste water is passed through bar screens to remove large objects like rags, sticks, cans, plastic packets, napkins etc.

(b) Water is passed to a grit and sand removal tank to allow sand, grit and pebbles to settle down.

(c) The water is then allowed to large settling tank to permit settling of solid faeces called sludge, which is removed using scarper.

(d) Air is pumped into the clarified water to help aerobic bacteria to grow and consume the wastes.

(e) This type of water is discharged into rivers or ponds.

5.    Solid wastes faeces settle at the bottom and are removed with scrapper. This is sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.

Sludge is transferred to a seperte tank where it is decomposed by the anaerobic bacteria. The biomass produced in the process can be used as fuel or can be used to produce electricity.

6.   Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and ground water get polluted. Ground water is a source of water for wells, tube wells, springs etc. thus, it becomes the most common route for water borne disease. This includes cholera, typhoid, polio etc.

7.    Ozone, chlorine.

8.    Waste water is passed through bar screens. Large objects like rags, sticks, cans, plastics and napkins are removed.

9.    Sanitation and disease are related to each other. To remain disease fee, we must observe sanitation. Clean environment is essential for preventing the growth of disease causing microbes. Dirty water around the living areas provides breeding ground for mosquito that are vectors of a number of disease. Sanitation prevents the growth of pathogens that cause disease.

10.   We all have a role to play in keeping our environment clean and healthy. We must realize our responsibility in maintaining the water sources in the healthy state. Adopting good sanitation practices should be our way of life. As an agent of change our individual initiative will make a great difference. We can influence others with our energy, ideas and optimism. A lot can be done if people work together. There is great power in collective action.


12.   (ii) (b) and (c).

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