# Civil Engineering - Waste Water Engineering

### Exercise :: Waste Water Engineering - Section 4

21.

In a residential colony, sewers of diameters 100 mm, 150 mm and 225 mm were laid with a gradient 1 in 120. Which portion of the sewage system does not choke in due course of time

 A. 100 mm dia. B. 150 mm dia. C. 225 mm dia. D. all of these.

Explanation:

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22.

If D is the diameter of upper circular portion, the overall depth of New Egg shaped sewer section, is

 A. 1.250 D B. 1.350 D C. 1.425 D D. 1.625 D.

Explanation:

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23.

During putrifaction process of sewage the gas given off, is

 A. carbon dioxide B. hydrogen C. ammonia D. methane E. all the above.

Explanation:

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24.

A circular sewer section is preferred to because

 A. it is cheaper in construction B. it provides maximum area for a given perimeter C. it provides maximum hydraulic mean depth D. all the above.

Explanation:

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25.

Assertion (A) : The minimum self cleansing velocity in the sewer, at least once a day, must be generated.

Reason (R) : If certain deposition takes place and is not removed, it obstructs free flow and causes further deposition leading to complete blocking of the sewer.

 A. Both A and R are true and R is the correct explanation of A B. Both A and R are true but R is not a correct explanation of A C. A is true but R is false D. A is false but R is true.