Test: Rapid Sand Filter

QUESTION: 1

The depth of an enclosed tank of a rapid sand filter lies in the range of ______

A.
1-2m
B.
2.5-3.5m
C.
2-5m
D.
3-5m

Solution:

Explanation: The depth of an enclosed tank of a rapid sand filter lies in the range of 2.5-3.5m and its surface area lies between 20-50m².

QUESTION: 2

The effective size of a rapid sand filter is ______

A.
0.45mm
B.
0.7mm
C.
0.8mm
D.
0.9mm

Solution:

Explanation: The effective size of a rapid sand filter lies in the range of 0.35-0.6mm and its common value is 0.45mm.

QUESTION: 3

The finer the suspended impurities to be removed,

A.
Larger will be the sand size
B.
Smaller will be the sand size
C.
Smaller will be the surface area of sand grains
D.
Narrow will be the sand depth of the bed

Solution:

Explanation: The finer the suspended impurities to be removed, smaller will be the sand size in order to increase the surface area of sand grains in the sand bed.

QUESTION: 4

What is the value of uniformity coefficient in a rapid sand filter?

A.
1
B.
1.5
C.
2
D.
2.5

Solution:

Explanation: The value of uniformity coefficient in a rapid sand filter lies between 1.2 and 1.7 and its common value is 1.5.

QUESTION: 5

What is the effective size of Anthracite when used as a filter material?

A.
0.1-0.2mm
B.
0.2-0.4mm
C.
0.4-0.6mm
D.
0.7-0.75mm

Solution:

Explanation: The effective size of Anthracite when used as a filter material lies between 0.7-0.75mm and its uniformity coefficient is 1.75.

QUESTION: 6

Consider the following statement regarding depth of sand of the rapid gravity filter?
1. It should be checked against breakage of floc
2. The sand depth should lie between 100-200cm
3. The floc should be attached through the sand bed
Which of the above statement is/are correct?

A.
Only 1
B.
1, 2
C.
2, 3
D.
Only 2

Solution:

Explanation: Sand depth should be such that floc do not break through the sand bed and the depth of sand should vary between 60-90 cm.

QUESTION: 7

Which of the following statement is wrong regarding Anthracite?

A.
It requires less water
B.
It is less inert to caustic solutions than sand
C.
It is more costly per tonne than sand
D.
It is used in industrial filters.

Solution:

Explanation: Anthracite is a costlier filter material used in industrial filter which is more inert to hot caustic solutions than sand.

QUESTION: 8

The minimum depth of sand of a rapid sand filter is given by

A.
Stokes formula
B.
Clark’s formula
C.
Hudson formula
D.
Emden formula

Solution:

Explanation: The minimum depth of sand of a rapid sand filter is given by
Qd³h/l=B*29323, Where Q=filtration rate, d =sand size, H= head loss, l=depth of sand bed, B=break through index.

QUESTION: 9

The thickness of the base material of a rapid sand filter on which filter media are supported is

A.
45-60cm
B.
20-80cm
C.
30-75cm
D.
10-30cm

Solution:

Explanation: The base material of a rapid sand filter consists of 45-60 cm thick gravel bed which is laid in layers of 15 cm with finer topmost layer (2-6mm) and coarser bottom layer (20-50mm).

QUESTION: 10

In which type of under drainage system of rapid sand filter, laterals are provided with strainers?

A.
Perforated pipe system
B.
Pipe and strainer system
C.
Wheeler system
D.
Wagner system

Solution:

Explanation: In Perforated pipe system, laterals are provided with strainers. Strainers are made of brass or bronze and are in umbrella shape, having a small perforation. They distribute the wash water without jet action.