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# Environmental Engineering MCQ – Types of Settling

How many types of settling are there in the sedimentation tank?

a) 3

b) 4

c) 5

d) 6

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Answer: b

Explanation: There are 4 types of settling in the sedimentation tank, namely Flocculent, Discrete, Compression and Hindered settling.

In which type of settling, sedimentation of discrete particles takes place?

a) Zone settling

b) Compression settling

c) Hindered settling

d) Discrete settling

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Answer: d

Explanation: In Discrete settling, sedimentation of discrete particles takes place where the particles have little tendency to flocculate.

The settling velocity of spherical particle is given by ____________

a) Darcy Weisbach equation

b) Hazen and William equation

c) Stokes equation

d) Bernoulli’s equation

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Answer: c

Explanation: The settling velocity of spherical particle is given by stokes equation where vS = (g/18) * (G-1) d2 /v when diameter d is less than 0.1mm.

In the expression vS = 1.8 (g*d (G-1))^{1/2}, the diameter of spherical particle is ____________

a) 0.1mm

b) < 0.1mm

c) 1mm

d) >1mm

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Answer: d

Explanation: The settling velocity of spherical particle is given by stokes law and when the diameter d of spherical particle is > 1mm, settling velocity is given by vS = 1.8 (g*d (G-1))^{1/2} where G is the specific gravity of the particle.

In which type of settling, settling of particles takes place by the contact of impurities with each other present in wastewater?

a) Flocculent settling

b) Hindered settling

c) Compression settling

d) Discrete settling

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Answer: c

Explanation: When large amounts of impurities are present in water, they contact each other in the compression zone and compression settling takes place.

_______ is formed when alum is added to sewage.

a) Acid

b) Floc

c) Salt

d) Base

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Answer: b

Explanation: When a coagulant is added to sewage, then a gelatinous precipitate called floc is formed and flocculent settling takes place.

In which settling type, dilute suspension of particles takes place?

a) Zone settling

b) Compression settling

c) Hindered settling

d) Discrete settling

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Answer: c

Explanation: In this type of settling, particle mass increases and it settles down due to flocculation.