267.  The period of cleaning of a slow sand filter, is usually
A. 5 to 10 days
B. 2 weeks to 3 weeks
C. 1 month to 3 months
D. 3 months to 6 months

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268.  Efficiency of removing bacterias from raw water by a slow sand filter, is
A. 80% to 81%
B. 85% to 86%
C. 90% to 97%
D. 98% to 99%.

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269.  Slow sand filter is used if maximum turbidity of raw water is less than
A. 10 gm/litre
B. 20 gm/litre
C. 30 gm/litre
D. 50 gm/litre.

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270.  The yield of a rapid gravity filter as compared to that of slow sand filter, is
A. 10 times
B. 15 times
C. 20 times
D. 30 times

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271.  In a rapid gravity filter
A. raW water from the source is supplied
B. disinfected raw water is supplied
C. raw water passed through coagulation tank is supplied
D. none of these.

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272. Distribution of wash water is provided in
A. sedimentation tank
B. slow sand filter
C. rapid gravity filter
D. all the above.

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273.  A high velocity of wash water is required for
A. rapid gravity filter with strainers
B. rapid gravity filter without strainers
C. slow sand filter with strainers
D. slow sand filter without strainers

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