# Sedimentation Tank MCQ – Environmental Engineering

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

1. increasing the depth of the tank
2. decreasing the depth of the tank
3. increasing the length of the tank
4. increasing the breadth of the tank

2. The demand of water is 150 litres/head/day in a city of one lakh population. The factor of safety is taken as 1.5, detention time as 4h and overflow rate as 20,000 litres/day/m2. The area of 3m deep plain sedimentation tank

1. 1075 m2
2. 1025 m2
3. 1175 m2
4. 1125 m2

3. The velocity of flow in any sedimentation tank should not exceed

1. 0.05 mm/s
2. 0.5 mm/s
3. 50 mm/s
4. 5 mm/s

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

1. 1 to 2 hours
2. 2 to 4 hours
3. 6 to 8 hours
4. 20 to 24 hours

5. The maximum daily demand at a water purification plant has been estimated as 12 million litres per day. Find the cross-sectional area of the sedimentation tank required if a detention period of 6 hours and the velocity of flow of 0.2 m/minute is assumed

1. 51.7 m2
2. 41.7 m2
3. 61.7 m2
4. 31.7 m2

6. The maximum depth of sedimentation tank is limited up to

1. 3 m
2. 2 m
3. 4 m
4. 6 m

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

1. Increasing depth of the tank
2. Increasing surface area of the tank
3. Decreasing the depth of the tank
4. Decreasing the surface area of the tank
5. Both decreasing the depth and surface area of the tank combined

8. If the sedimentation tank is rectangular in shape having length ‘L’, Width ‘W’ and depth ‘D’, then for discharge equal to ‘Q’, the setting velocity of a particle would be

1. Q/L × W
2. Q/B × D
3. Q/B × L
4. Q/B × W

9. The dimensions for a rectangular primary sedimentation tank is, length = 30 m; breadth = 10 m and depth = 3m. If the flow rate through the tank is 0.1 m3/s, the surface overflow rate (SOR) of tank is

1. 28.8 m3/m2/d
2. 14.4 m3/m2/d
3. 21.6 m3/m2/d
4. 9.6 m3/m2/d

10. The settling of particles in a sedimentat0n tank depends upon

1. Length of tank
2. Width of tank
3. Depth of tank
4. Length and width of tank

11. Which of the following is the most important design parameter for a continuous flow rectangular sedimentation tank?

1. Surface overflow rate
2. Length of the tank
3. Depth of the tank
4. Temperature of the water to be treated

12. For a flow of 5.7 MLD (millian litter per day) and a detention of 2 hour, the surface area of a rectangular sedimentation tank to remove all particles having setting velocity of 0.33 mm/sec is

1. 40 m2
2. 20 m2
3. 200 m2
4. 100 m2

13. The maximum depth of sedimentation tank is limited to

1. 20 m
2. 4 m
3. 5 m
4. 6 m

14. The settling velocity of a particle in a sedimentation tank depends on

1. Depth of tank
2. Surface area of tank
3. Both depth and surface area of tank
4. None of the above

15. In sedimentation tank, the efficiency of sedimentation depends on

1. Depth of tank
2. Surface area of tank
3. Both depth and surface area of tank
4. None of these

16. The short circulating occurring in a sedimentation tank is represented by

2. displacement eficiency
3. recirculation ratio
4. detention time

17. The velocity of flow of water in a sedimentation tank is about

1. 15 to 30 cm/sec
2. 5 to 10 cm/sec
3. 15 to 30 cm/hour
4. 15 to 30 cm/min

18. The settling velocity 0f a particle in a sedimentation tank increases if

1. particle size is decreased
2. the surface area of tank is increased
3. the depth of tank is decreased
4. none of the above

19. The settling velocity of inorganic particles in a sedimentation tank of a water treatment plant is governed by

1. Darcy’s law
2. Stokes law
3. Dupit’s law
4. Pascal’s law

20. Surface loading or  overflow rate of a sedimentation tank, passing a discharge Q and having length = L, Depth= D, Width = B, is given by

1. Q/B L
2. Q/B D
3. Q/B D.L
4. Q/B D