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151.

The under drainage system in slow sand filters

A.	receives and collects the filtered water	B.	allows back washing for cleaning the filter
C.	both (a) and (b)	D.	none of these

152.

The under drainage system in a rapid sand filters

A.	receives and collects the filtered water	B.	allows back washing for cleaning the filter
C.	both (a) and (b)	D.	none of these

153.

Slow sand filter requires

less

154.

Which of the following statement is correct?

A.	Slow sand filters work under atmospheric pressure.	B.	Rapid sand filters require coagulation.
C.	Rapid sand filters should be cleaned after 2 to 3 days	D.	all of the above

155.

The coagulation is not required in

slow sand

rapid sand

156.

The slow sand filter should be cleaned if the loss of head becomes more than

A.	0.75 m	B.	1.2 m
C.	2.2 m	D.	3.5 m

157.

After cleaning the slow sand filter, the filtered water should not be used for a period of

A.	upto 6 hours	B.	6 hours to 12 hours
C.	12 hours to 24 hours	D.	24 hours to 48 hours

158.

Cleaning period for a slow sand filter is taken as

A.	1 hour to 3 hours	B.	1 day to 3 days
C.	1 week to 3 weeks	D.	1 month to 3 months

159.

Rate of filteration of a slow sand filter ranges from

A.	10 to 100 litres / h / m2	B.	100 to 200 litres / h / m2
C.	200 to 400 litres / h / m2	D.	400 to 1000 litres / h / m2

160.

Slow sand filter is efficient to remove the bacterias from the raw water to an extent of

A.	50%	B.	70%
C.	85%	D.	99%