162. The maximum depth of sedimentation tanks, is kept
A. 3 m
B. 3.5 in
C. 4 m
D. 4.5 in.

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163.  The detention time (t) of a settling tank, may be defined as the time required for
A. a particle to travel along its length
B. a particle to travel from top surface to bottom sludge zone
C. the flow of sewage to fill the tank
D. none of these.

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164. The detention time of a circular tank of diameter d and water depth H, for receiving the sewage Q per hour, is
A. d2(0.011d + 0.78511)
B. d(0.022d + 0.08511)
C. d(0.785d + 0.011/D
D. d(0.285d + 0.011H)

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165. The settling velocity of the particles larger than 0.06 mm in a settling tank of depth 2.4 is 0.33 m per sec. The detention period recommended for the tank, is
A. 30 minutes
B. 1 hour
C. 1 hour and 30 minutes
D. 2 hours

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166. . The dimensions of a rectangular settling tank are : length 24 m, width 6 m and depth 3 m. If 2 hour detention period for tanks is recommended, the rate of flow of sewage per hour, is
A. 204 cu m
B. 208 cu m
C. 212 cu m
D. 216 cu m

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167.  The width of a settling tank with 2 hour detention period for treating sewage 378 cu m per hour, is
A. 5 m
B. 5.5 m
C. 6 m
D. 7 m.

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168.  Pick up the incorrect statement from the following :
A. Septic tanks are horizontal continuous flow type of sedimentation tanks
B. Septic tanks are generally provided a detention period of 12 to 36 hours
C. Septic tanks are completely covered and high vent shafts are provided for the escape of foul gases
D. None of these.

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