Q.1 Boojho wants to know how sewage is disposed off in an aeroplane. (Page 226)
Ans. In an aeroplane septic tanks are used for the disposal of sewage.
NCERT TEXTBOOK EXERCISE (Pages 228- 229)
Q.1 Fill in the blanks:
(a) Cleaning of water is a process of removing……….
(b) Waste water released by houses is called………..
(c) Dried……….is used as manure.
(d) Drains get blocked by ………..and……..
Ans. (a) contaminants; (b) sewage;
(c) dung; (d) plastic, sludge.
Q.2 What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans. Sewage is waste- water released by homes, hospitals, offices, industries and other users. It also includes rainwater that has run down the street during a heavy rain or storm. The water that washes off roads and rooftops carries harmful substances with it. Basically sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities which are called contaminants. That is why it is harmful to discharge untreated sewage into rivers or seas.
Q.3 Why should oils and fats not be released in the drains? Explain.
Ans. Oils and fats should not be released in the drains because they harden the soil in the pipes and block them. Fats get clogged in the holes of the soil in the drain and block it. It does not allow the waste- water to flow and thus the whole sewer system is blocked.
Q.4 Describe the steps involved in getting clarified water from waste- water.
Ans. Treatment of waste – water involves physical, chemical and biological processes, which remove the impurities that contaminates the waste-water.
(i) Waste-water is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
(ii) Water goes to a grit and sand removal tank. The speed of the incoming waste-water is decreased to allow sand, grit and pebbles to settle down.
(iii) The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faces settle at the bottom 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 this process can be used as fuel or can be used to produce electricity.
(iv) 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 down at the bottom of the tank as activated sludge. The water is the removed from the top.
Q.5 What is sludge? Explain how it is treated.
Ans. Sludge is the collected solid waste from the waste-water during the treatment in water treatment plant. Sludge is decomposed in a separate tank by the anaerobic bacteria.
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.
The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further. Sometimes, it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.
Q.6 ‘ Untreated human excreta is a health hazard’. Explain.
Ans. Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Ground water is a source of water for Wells, tubewells, springs, and many rivers. Thus, it becomes the most common route for water borne diseases. They include chlorea, typhoid, polio, meningitis, hepatitis and dysentry.
Q.7 Name two chemicals used to disinfect water.
Ans. Ozone and chlorine.
Q.8 Explain the function of bar screens in a waste-water treatment plant.
Ans. Bar screens clear the waste-water of all the physical impurities. Large waste objects like napkins, plastics, can sticks, rags, etc. are removed from the waste-water through the bar screens.
Q.9 Explain the relationship between sanitation and disease.
Ans. 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, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery. That is proper sanitation is must to avoid some of the deadly diseases.
Q.10 Outline your role as an active citizen in relation to sanitation.
Ans. As an active citizen, we should take care of our personal and environmental sanitation. We should make people around us, aware of the benefits of sanitation. We should help the municipal corporations and Gram panchayats to cover all the open drains and remove the unhygienic and disease causing substances thrown in open.
Q.11 Here is a crossword puzzle: Good luck!
Table – page 228
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body.
1. Used water
2. A pipe carrying sewage
5. Micro- organisms which causes cholera
7. A chemical to disinfect water.
Q.12 Study the following statements about ozone:
(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in 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) (b) and (c).