class 7 worksheet science water story

1. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
2. Why should oils and fats be not released in the drain? Explain.
3. Describe the steps involved in getting clarified water from wastewater.
4. What is sludge? Explain how it is treated
5. Untreated human excreta is a health hazard. Explain.
6. Name two chemicals used to disinfect water.
7. Explain the Junction of bar screens in a wastewater treatment plant.
8. Explain the relationship between sanitation and disease.
9. Special type of toilets has been designed in aeroplanes, name it.
10. Name the toilets used in areas with limited water supply.
11. The Eucalyptus trees are planted along sewage ponds. Give reason.
12. Mention the use of dried sludge.
13. Sewage contains some organic impurities in it. Name them.
14. World Water Day is celebrated on
15. Name the three processes involved in treatment of wastewater.
16. Explain sewers and sewage.
17. Bleaching powder is mixed in water, why? Think and give appropriate reason for it.
18. Protozoa is causative organism of which waterborne disease?
19. Animal waste, oil and urea are some of the organic impurities present in sewage. Name two more organic impurities present in sewage. 
20. Recall and enlist some better house keeping practices to prevent water pollution
21. Water in a river is cleaned naturally. Do you agree? Think and explain
22. Describe septic tank. How does it function?
23. There are many alternative sewage disposal systems which have been developed as per needs of the community, persons, occasions, etc.. Few situations/specifications of the sewage need are given below. Write the name of sewage which can be used in the following conditions.
24. (a) A toilet which can provide high quality manure.
25. (b) The toilet which is used in aeroplane during flight.
26. (c) A toilet which can be used in some out door gathering.
27. (d) A toilet used in limited water supply.
28. (e) A toilet which contaminates water of hand pump installed nearby
29. Fill in the Blanks

1. Untreated human excreta is a ………………. hazard.

2. Vermi-composting toilets use ………………. to treat human waste.

3. Poor sanitation is crowded public places can result in spread of ………………. .

4. Dried sludge is used as ………………. .

5. Wastewater is treated in ………………. treatment plant.

6. Wastewater released by houses is called ………………. .

7. Stagnant water blocked in drains is good breeding place for ………………. .

8. All portable toilets are ………………. toilets.

9. The full form of WWTP is ………………. .

10. Bacteria play important ………………. in sewage treatment.