Textbook Solution: Wastewater Management | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

A. Choose the correct option.

1.
Ans: (d)

2.
Ans: (b)

3.
Ans: (a)

4.
Ans: (d)

5.
Ans: (d)

6.
Ans: (c) 

B. Fill in the blanks with the correct words.

1.
Ans: Wastewater generated from industries contain harmful.... metals and paints.

2.
Ans: Eutrophication is the bloom of... algae.

3.
Ans: In primary treatment of sewage, the material that rises to the top is called scum.

4.
Ans: The primary treatment process is a .... mechanical process.

5.
Ans: Earthworms... are used to convert human excreta into high quality compost in vermi-composting toilets.

C. Name the following.

1.
Ans: The discharge of liquid waste into water bodies - Effluent

2.
Ans: Wastewater containing dissolved and suspended impurities - Sewage

3.
Ans: The material that rises to the top in sedimentation tanks during the primary process - Scum

4.
Ans: The water that comes out of the sedimentation tanks after the completion of the primary process - Clarified water

5.
Ans: The biological process in which the organic matter in sewage is broken down with the help of bacteria - Digestion

6.
Ans: A process in which the sludge is burnt into ashes - Incineration

D. Answer the following questions.

1.
Ans: Wastewater is derived from several sources including domestic activities such as washing, cooking, cleaning, and bathing; industries that use water for various manufacturing processes; agriculture, where water is used for irrigation and also gets mixed with chemicals like insecticides, fertilizers, and pesticides; and hospitals, which may generate wastewater similar to domestic waste, potentially including disease-causing germs and radioactive wastes.

2.
Ans: Eutrophication is a condition where an increase in nutrients, such as nitrogen and phosphorus, in water bodies results in excessive growth or 'blooms' of algae. This overgrowth consumes all the nutrients present in the water, leading to depletion of oxygen in the water bodies and preventing sunlight from reaching other aquatic plants, causing them to die.

3.
Ans: A sewer system is a network of pipes, drains, and manholes that carries wastewater away from its sources to a wastewater treatment plant. The sewer pipes are laid underground and have a slight downward slope for easy movement of sewage.

4.
Ans: Wastewater treatment involves three basic processes: Primary process, which is a mechanical process that involves the removal of solid wastes; Secondary process, a biological process where the organic matter in sewage is broken down with the help of bacteria; and Tertiary process, the final step where chemicals such as chlorine are added to remove phosphorus and nitrogen, and the water is also exposed to ultraviolet light to kill remaining bacteria.

5.
Ans: Primary treatment of wastewater is a mechanical process that involves screening, pumping, and sedimentation to remove solid wastes. Secondary treatment is a biological process where the organic matter in sewage is broken down with the help of bacteria. This process, called digestion, converts the remaining organic materials into heavier particles that settle down.

6.
Ans: The tertiary process is the final stage of wastewater treatment where chemicals like chlorine are added to remove phosphorus and nitrogen, which cause eutrophication in water bodies. The water is also exposed to ultraviolet light in addition to chlorine, which destroys any remaining bacteria and disinfects the water, making it safe to be released into water bodies.

7.
Ans: Treated wastewater can be used for a variety of purposes including being released into water bodies such as streams and rivers, for drinking purposes after further purification, and for irrigation in agriculture.

8.
Ans: Sludge, which is separated from sewage and consists of human feces, organic matter, and water, can be converted into useful substances through incineration, drying, composting, and anaerobic digestion. It can be used as a soil conditioner, construction material, or as a fertilizer.

9.
Ans: Some measures to control the generation of sewage at home include adopting water conservation practices, not flushing household products into the wastewater system, and not pouring household materials like cooking oils and polythene down the drains.

10.
Ans: Problems faced due to improper management of wastes include pollution of water bodies, water-borne epidemics, eutrophication, adverse effects on aquatic life, and breeding grounds for disease-causing insects. Drinking contaminated water can also lead to diseases like gastroenteritis, dysentery, and typhoid.

11.
Ans: The sewage disposed through septic tanks is collected in the tank where the sludge is allowed to settle and lighter waste floats on the surface. The fairly clear water layer in the middle is allowed to flow out of the tank through pipes and into the grounds. Septic tanks must be emptied for solid waste every 3-5 years.

12.
Ans: Vermi-composting toilets are toilets where earthworms are used to convert human excreta into high-quality compost. These toilets use a minimal amount of water.

13.
Ans: Biogas plants convert organic wastes into biogas and manure. Human and animal excreta, as well as vegetable wastes, are fed into the plant where microorganisms act on the wastes and produce biogas, which can be used to generate electricity.

14.
Ans: While providing sanitation facilities to public at places with huge gatherings, it should be ensured that there are enough toilets with hand washing facilities and soap, sufficient dustbins, and proper refuse disposal. Public hygiene awareness should also be promoted.

15.
Ans: Garbage should not be thrown on roads as it might get into the underground drainage system leading to blockage of sewage pipes, seepage of sewage into homes and streets, water logging on the streets during monsoons, and traffic jams.