This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Theory of Sedimentation”.
1. When impurities are separated by the gravitation of settling particles, the operation is called _____
a) Sedimentation with coagulant
b) Plain sedimentation
c) Secondary sedimentation
d) Disinfection
View Answer
Explanation: In plain sedimentation, impurities are separated from a suspending fluid by use of natural forces like gravitational forces.
2. In which type of settling, sedimentation of discrete particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling
View Answer
Explanation: In Discrete settling, sedimentation of discrete particles takes place where the particles have little tendency to flocculate.
3. In which settling type, dilute suspension of particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling
View Answer
Explanation: In this type of settling, particle mass increase and it settle down due to flocculation.
4. In which type of sedimentation, flocculent suspension of intermediate concentration takes place?
a) Type I sedimentation
b) Type II sedimentation
c) Type III sedimentation
d) Type IV sedimentation
View Answer
Explanation: In type III sedimentation, inter-particle forces hold the particle together and flocculent suspension of intermediate concentration takes place.
5. In which type of sedimentation, flocculent suspension of high concentration takes place?
a) Type I sedimentation
b) Type II sedimentation
c) Type III sedimentation
d) Type IV sedimentation
View Answer
Explanation: In type IV sedimentation, flocculent suspension of high concentration takes place and particles comes in contact with each other resulting in the formation of structure.
6. What is the settling velocity of the particle if its diameter is 2 * 10-3cm. Given G=2.65, viscosity v=8 * 10-3cm2/sec?
a) 0.011cm/sec
b) 0.045cm/sec
c) 0.024cm/sec
d) 0.036cm/sec
View Answer
Explanation: Settling velocity of the particle is given by vs=g (G-1) d2/18v
Specific gravity G=1, g=981cm2/sec, viscosity v=8 * 10-3cm2/sec
vs = 981* (2.65-1) *0.002*0.002/(18*.008) = 0.0449cm/sec ~ 0.045cm/sec.
7. 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
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 .03m/Sec.
8. The time period for which the water is stored in a sedimentation tank is called _____
a) Time of flow
b) Frequency of flow
c) Settling time
d) Detention period
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Explanation: Detention period is the time period at which the water is stored in a tank. It varies for different purposes like in the septic tank or oxidation pond, its value is higher.
9. Settling velocity of a spherical body in a viscous fluid is given by ___________
a) Reynolds law
b) Newton’s law
c) Stokes law
d) Charles law
View Answer
Explanation: According to Stokes law, settling velocity of the particle is given by
vs=g (G-1) d2/18v where G is the specific gravity, d is the diameter of spherical particles and v is the viscosity.
10. In a fill and draw type sedimentation tank, a detention period of ____ hours is provided.
a) 6
b) 12
c) 18
d) 24
View Answer
Explanation: In this tank, water is detained for 24 hours. Then cleaning is done for 6-12 hours, so, the whole cycle of operations takes around 30-36 hours.
11. Which of the following represents the correct relation between displacement velocity and diameter of the particle?
a) v1 = (8Bg (G-1) d/f) 1/2
b) v1 = (8Bg (G-1) d2/f)2
c) v1 = (8Bg (G-1) d/f)
d) v1 = (8Bg (G-1) d/f)2
View Answer
Explanation: Displacement velocity is given by v1 = (8Bg (G-1) d/f)1/2 where B is a constant with value range 0.04-0.06, G is specific gravity, d is the diameter of the particle and f is the Darcy Weisbach friction factor.
Sanfoundry Global Education & Learning Series – Environmental Engineering.
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