141.  Pick up the correct statement from the following :
A. The materials separated by screens, is called screenings
B. The screenings are disposed off either by burning or by burial or by dumping
C. The process of burning the screenings, is called incineration
D. All the above.

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142. In a grit chamber of a sewage treatment plant,
A. flow velocity 0.15 m to 0.3 m/sec is kept
B. depth of 0.9 m to 1.20 m is kept
C. one minute of detention period is kept
D. all the above.

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143. The grit chambers of sewage treatment plants, are generally cleaned after
A. 2 days
B. 5 days
C. 7 days
D. 14 days.

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144. If the grit in grit chambers is 4.5 million litres per day, its cleaning is done
A. manually
B. mechanically
C. hydraulically
D. electrically.

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145. The grit and silt of the grit chambers, may not be used for
A. raising low lying areas by dumping
B. concreting
C. both A and B
D. neither A nor B.

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146.  In detritus tanks,
A. flow velocity is kept 0.09 m/sec
B. detention period is kept 3 to 4 minutes
C. organic and inorganic materials are separated
D. all the above.

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147.  For a grit chamber, if the recommended velocity of flow is 0.2 m/sec and detention period is 2 minutes, the length of the tank, is
A. 16 m
B. 20 m
C. 24 m
D. 30 m.

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