21. The detention time for an ordinary plain sedimentation tank is

- 6 to 8 hours
- 20 to 24 hours
- 1 to 2 hours
- 2 to 4 hours

22. If the temperature of a sedimentation tank is increased, the sedimentation speed will

- get hastened
- get slowed down
- not be affected at all
- none of the above

23. The length of rectangular sedimentation tank should not be more than

- 2B
- B
- 8B
- 4B

24. The efficiency of a sedimentation tank should not depend upon

- depth of the tank
- detention time
- length of the tank
- horizontal velocity of water

25. For a given discharge, the efficiency of sedimentation tank can be increased by

- increase the depth of tank
- decrease the depth of tank
- increasing the surface area of tank
- decreasing the surface area of tank

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