337.  In sludge digestion tank, the gas evolves, is
A. methane
B. hydrogen sulphide
C. ammonia
D. nitrogen

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338. The most efficient method of BOD removal, is
A. oxidation ditch
B. trickling filter
C. oxidation pond
D. aerated lagoon

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339.  Pick up the correct statement from the following :
A. The flow velocity in Imhoff tanks is limited to 0.3 m/min
B. The effluent of a septic tank is not fit for discharge any open drain
C. A septic tank can be used either as a settling tank or a digestion tank
D. All the above.

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340.  Consider the following statements regarding the peaks in the sewers 1. The peaks get damped because of the storage space in the sewers 2. The peaks get damped because time is required for the sewage to the point of gauging 3. The peak flow is quite pronounced near its origin 4. The peak hourly flows decrease as the tributary area increases Of these statements:
A. 1 and 2 are correct
B. 2 and 3 are correct
C. 3 and 4 are correct
D. All of these are correct

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341. Consider the following statements regarding water supply pipes and sewer pipes 1. The water supply pipes carry pure water without any contamination 2. The sewer pipes carry particles in suspension and the heavier ones settle down at(the bottom of the sewer resulting in the clogging of the sewers 3. The water supply pipes carry water under gravity 4. The sewer pipes carry sewage under pressure Of these statements:
A. 1 and 2 are correct
B. 2 and 3 are correct
C. 3 and 4 are correct
D. None of these is correct

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342.  Consider the following statements regarding swears 1. The sewer pipes of sizes less than 0.7 m dia are designed as running half full at maximum discharge 2. The sewer pipes of sizes greater than 0.7 m dia, are designed as running 2/3rd or 3/4th full at maximum discharge 3. The extra space aboveffie?designed full supply line, acts as a factor of safety for unexpected increase of sewage 4. The flow in the sewers is under gravity Of these statements:
A. land 2 are correct
B. 2 and 3 are correct
C. 1 and 4 are correct
D. 1, 2, 3 and 4 are correct

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343.  Consider the following statements : A. The flow velocities in the sewers should be such that neither the suspended materials in sewage get silted up nor the sewage pipe materials get scoured out. R. The first condition limits the minimum velocity and second condition limits the maximum velocity. Of these statements:
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

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