Engineering Questions with Answers - Multiple Choice Questions

# Environmental Engineering MCQ’s – Design of Sedimentation Tank

1 - Question

Which of the following cannot be the velocity of flow in the horizontal flow sedimentation tank?
a) 12cm/min
b) 39cm/min
c) 5cm/min
d) 20cm/min

View Answer

Answer: b
Explanation: The maximum value of the velocity of flow is 30cm/min, so it cannot be 39cm/min.

2 - Question

The deviation from the ideal flow of wastewater in the sedimentation tank causes ____________
a) Whirlpool
b) Increase in tank efficiency
c) Short circuiting
d) Coagulation

View Answer

Answer: c
Explanation: The deviation from the ideal flow of wastewater in the sedimentation tank causes short circuiting. It results in variation in the detention period in the top and bottom layer of wastewater in the tank.

3 - Question

The overflow rate for a plain sedimentation tank is ______ litre/day/metre2.
a) 50000
b) 40000
c) 12000
d) 30000

View Answer

Answer: c
Explanation: The overflow rate for a plain sedimentation tank lies between 12000-18000 litre/day/metre2.

4 - Question

The detention period for a sedimentation tank where coagulation takes place is ____________
a) 30 seconds
b) 1 minute
c) 1hour
d) 2hour

View Answer

Answer: d
Explanation: The detention period for a sedimentation tank without coagulation is 4 hours, whereas with coagulation is 2 – 2.5 hours.

5 - Question

The test for finding the optimum coagulant dose in water is ____________
a) Chromatography
b) Jar test
c) Kjeldahl test
d) Dilatancy testAnswer: b
Explanation: Jar test is used to find the optimum coagulant concentration that is required to cause coagulation in water so that the settling of suspended impurities takes place.

View Answer

Answer: b
Explanation: Jar test is used to find the optimum coagulant concentration that is required to cause coagulation in water so that the settling of suspended impurities takes place.

6 - Question

The average time required by water to pass through the settling tank is called _______
a) Detention time
b) Flowing through period
c) Time of flow
d) Mean time

View Answer

Answer: b
Explanation: The average time required by water to pass through the settling tank is called ‘flowing through period’ which is always less than the detention period.

7 - Question

The quantity of water flowing per hour per unit horizontal area is called ____
a) Detention time
b) Flowing through period
c) Displacement time
d) Overflow rate

View Answer
Answer: d
Explanation: Overflow rate = Q/A where Q is discharge rate in litre per day, A is the horizontal area in m2.

8 - Question

In a rectangular horizontal flow tank, the maximum permissible velocity is ____ m/Sec.
a) 3
b) 0.3
c) 0.03
d) 0.003

View Answer

Answer: b
Explanation: In the rectangular tank, the ideal conditions are that the flow is horizontal, velocity is uniform in all directions and the maximum permissible limit of velocity is 0.03m/Sec.