148.  Flow through period, in sedimentation tanks, is
A. equal to detention period
B. more than detention period
C. less than detention period
D. detention period divided by displacement efficiency

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149.  Alum is chemically
A. Copper sulphate
B. Aluminium sulphate
C. Ferrous sulphate
D. Ferric sulphate.

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150.  The process of passing water through beds of granular materials, is called
A. screening
B. sedimentation
C. filtration
D. none of these.

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151.  Filtration of water is done to remove
A. colour
B. odour
C. turbidity
D. pathogenic bacteria

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152.  The main process to purify water by filtration, is
A. mechanical straining
B. flocculation and sedimentation
C. biological metabolism
D. all the above.

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153.  An ideal sand for filters should be
A. free from dirt and other impurities
B. uniform in nature and size
C. hard and resistant
D. all the above.

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154.  The U.C.60 .C. (uniformity coefficient) Dio for the best filter media sand should be
A.2
B.3
C.4
D.5

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