This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Sedimentation Tanks – 1”.
1. Sedimentation is a process using gravity to remove suspended solids from water.
a) True
b) False
View Answer
Explanation: Sedimentation is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans.
2. What are the ponds constructed for removing entrained solids called?
a) Clarifiers
b) Settling basins
c) Eco-ponds
d) Ditches
View Answer
Explanation: Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation.
3. The tanks built with mechanical means for continuous removal of solids being deposited by sedimentation are called _________
a) Clarifiers
b) Settling basins
c) Sedimentation tanks
d) Eco-pons
View Answer
Explanation: Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation.
4. Sedimentation tank is also called as settling tank.
a) True
b) False
View Answer
Explanation: Sedimentation tank, also called settling tank or clarifier is a component of a modern system of water supply or wastewater treatment. The suspended particles settle down thereby providing some degree of purification.
5. What is the accumulated layer at the bottom of the tank called as?
a) Flocs
b) Sediment
c) Sludge
d) Sewage
View Answer
Explanation: A layer of accumulated solids called sludge forms at the bottom of the tank and is periodically removed. Prior to sedimentation, coagulants are added to the water in order to facilitate the settling process, which is followed by filtration and other treatment steps.
6. How many types of sedimentation tanks are there based on the method of operation?
a) 2
b) 4
c) 5
d) 7
View Answer
Explanation: Based on the method of operation, there are two types of sedimentation tanks. The first one is filled and draw type tank and the second one is the continuous flow type tank.
7. How many types of sedimentation tanks are present based on the shape of the tank?
a) 2
b) 3
c) 4
d) 5
View Answer
Explanation: Based on the shape of the sedimentation tank, there are two types of sedimentation tank. They are circular sedimentation tank and rectangular sedimentation tank.
8. What is the time period for which the water is stored in fill and draw type of sedimentation tank?
a) 48 hours
b) 24 hours
c) 52 hours
d) 76 hours
View Answer
Explanation: In case of fill and draw type sedimentation tank, water from the inlet is stored for some time. The time may be 24 hours. The suspended particles settle down. After 24 hours, the water is discharged through the outlet.
9. How many hours does the removing of Settleable particles require in fill and draw type of sedimentation tanks?
a) 3-6
b) 6-9
c) 6-12
d) 12-15
View Answer
Explanation: Then settled particle is removed. This removal action requires 6-12 hours. 30-40 hours is required for one complete action in case of fill and draw type sedimentation tank.
10. In which of the following sedimentation tanks, the flow may be either horizontal or vertical?
a) Circular
b) Rectangular
c) Fill and draw type
d) Continuous flow
View Answer
Explanation: In the case of continuous flow type, water is not allowed to rest. Flow always takes place but with a very small velocity. During this flow, suspended particles are settling at the bottom of the tank. The flow may be either in a horizontal direction or vertical direction.
11. What is the maximum permissible velocity in horizontal flow type sedimentation tank?
a) 0.2 m/s
b) 0.3 m/s
c) 0.5 m/s
d) 1 m/s
View Answer
Explanation: Horizontal flow type sedimentation tanks generally in rectangular shape. They have more length twice its width. Because they need to flow more distance to settle all suspended particles. The maximum permissible velocity in this case is 0.3m/sec.
12. The vertical type of sedimentation tanks are usually in _________ shape.
a) Circular
b) Rectangular
c) Semi-circular
d) Cylindrical
View Answer
Explanation: The vertical flow type sedimentations tanks are generally in circular shape and flow takes place in vertical direction. The flow is usually horizontal generally in rectangular tanks.
13. Why are the baffle walls provided?
a) Prevent short circuit
b) Abstruct flow
c) Reduce velocity
d) Collect sediment
View Answer
Explanation: The sedimentation tanks preferred are rectangular and are used widely. The flow takes place in horizontal direction that is length wise in rectangular tanks. Sometimes baffle walls are provided for rectangular tank to prevent short circuiting.
14. Sludge is disposed through _______
a) Hopper bottom
b) Sludge pump
c) Deflector
d) Launder
View Answer
Explanation: A deflector box located at the top. This deflects the influent from central pipe downwards in case of hopper bottom tanks. Sludge is collected at the bottom and it is disposed of through sludge pump.
15. ________ is provided after activated sludge process.
a) Primary sedimentation tank
b) Flocculation tank
c) Secondary sedimentation tank
d) Sand filter
View Answer
Explanation: The suspended particles present in the wastewater contains microbes and are removed and reflected towards aerobic filter to maintain high microbe concentration in an aerobic filter.
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