Environmental Engineering Multiple Choice Questions on “Design of Sedimentation Tank”.
1. 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
Answer: b
Clarification: The maximum value of the velocity of flow is 30cm/min, so it cannot be 39cm/min.
2. 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
Answer: c
Clarification: 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. The overflow rate for a plain sedimentation tank is ______ litre/day/metre2.
a) 50000
b) 40000
c) 12000
d) 30000
Answer: c
Clarification: The overflow rate for a plain sedimentation tank lies between 12000-18000 litre/day/metre2.
4. The detention period for a sedimentation tank where coagulation takes place is ____________
a) 30 seconds
b) 1 minute
c) 1hour
d) 2hour
Answer: d
Clarification: The detention period for a sedimentation tank without coagulation is 4 hours, whereas with coagulation is 2 – 2.5 hours.
5. The test for finding the optimum coagulant dose in water is ____________
a) Chromatography
b) Jar test
c) Kjeldahl test
d) Dilatancy test
Answer: b
Clarification: 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. 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
Answer: b
Clarification: 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. 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
Answer: d
Clarification: Overflow rate = Q/A where Q is discharge rate in litre per day, A is the horizontal area in m2.
8. In a rectangular horizontal flow tank, the maximum permissible velocity is ____ m/Sec.
a) 3
b) 0.3
c) 0.03
d) 0.003
Answer: b
Clarification: 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.