162. Disinfection of water with ozone is not good because
A. it vanishes before water reaches the consumers
B. it removes the colour, taste and odour from water as bacterias
C. it adds taste to the water
D. it is more efficient than chlorine in killing bacterias
163. Chlorination of water does not remove
A. ammonia content
B. B.O.D.
C. organic matter content
D. dissolved oxygen.
164. The efficiency of sedimentation tank does not depend upon
A. depth of tank
B. length of tank
C. detention period
D. velocity of water,
165. The percentage of chlorine in fresh bleaching powder is roughly
A. 50 to 60
B. 30 to 35
C. 40 to 50
D. 20 to 25.
166. The detention period for plain sedimentation water tanks, is usually
A. 4 to 8 hours
B. 8 to 16 hours
C. 16 to 24 hours
D. 24 to 36 hours.
167. Water may not contain much impurities if its source is
A. reservoirs
B. stream flowing in plains
C. lakes in lower regions
D. spring along hill slopes
168. Water supply system includes
A. digging a well for water
B. construction of dams
C. construction of canals
D. entire arrangement from source to distribution.
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