# Environmental Engineering Questions and Answers – Rapid Sand Filter

This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Rapid Sand Filter”.

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

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.

2. The effective size of a rapid sand filter is ______
a) 0.45mm
b) 0.7mm
c) 0.8mm
d) 0.9mm

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.

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

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.

4. What is the value of the uniformity coefficient in a rapid sand filter?
a) 1
b) 1.5
c) 2
d) 2.5

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.

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

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.
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6. Consider the following statement regarding the depth of sand of the rapid gravity filter?
i. It should be checked against breakage of floc
ii. The sand depth should lie between 100-200cm
iii. The floc should be attached through the sand bed
Which of the above statement is/are correct?
a) Only i
b) i, ii
c) ii, iii
d) Only ii

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

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.

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

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

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.

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

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 a finer topmost layer (2-6mm) and coarser bottom layer (20-50mm).

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

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.

11. Which device is used to supply air for the agitation of sand grains during washing of filters?
a) Rate control device
b) Tube settlers
c) Air compressors
d) Flocculator

Explanation: Air compressor is used to supply air for the agitation of sand grains at the rate of 0.6-0.8m3 per minute per m2 of filter area for 5 minutes.

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