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141.

The process of purifying water by passing it through a bed of fine granular material, is called

A.	screening	B.	filteration
C.	coagulation	D.	sedimentation

142.

The void spaces in the filtering material act like a

A.	drain	B.	inlet
C.	tiny settling basins	D.	outlet

143.

The organic impurities in water form a layer on the top of a filtering media. Such a layer is called

A.	permeable layer	B.	filtering layer
C.	dirty skin	D.	none of these

144.

The sand, used for filteration, should not loose weight more than

A.	2.50%	B.	5%
C.	7.50%	D.	10%

145.

The rate of filteration

increases

decreases

146.

Water is forced at a preseure higher than the atmospheric pressure in rapid gravity filters.

Right

Wrong

147.

The effective size of sand particles for slow sand filters varies from

A.	0.30 to 0.35 mm	B.	0.35 to 0.50 mm
C.	0.50 to 0.65 mm	D.	0.65 to 0.75 mm

148.

The effective size of sand particles for rapid sand filters varies from

A.	0.30 to 0.35 mm	B.	0.35 to 0.50 mm
C.	0.50 to 0.65 mm	D.	0.65 to 0.75 mm

149.

The coefficient of uniformity for slow sand filters is

A.	1.35	B.	1.55
C.	1.75	D.	2.05

150.

The coefficient of uniformity for rapid sand filters is

less