1. 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.
2. 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.
3. 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.
4. 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
5. 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)
6. 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
7. 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
8. The loss of head during cleaning operation of a rapid sand filter is __________
a) 15-30cm
b) 1-5cm
c) 10-20cm
d) 10-25cm
Explanation: When cleaned bed is put into operation, the loss of head through it is 15-30cm and it goes on increasing as impurities are arrested in filter media
9. The thickness of the suspended matter on top of the sand bed is __________
a) Directly proportional to head loss
b) Inversely proportional to head loss
c) Independent of the head loss
d) Directly proportional to the square of head loss
Explanation: As the thickness of suspended matter on top of the sand bed increases, the head loss is increased. So, it is directly proportional to head loss
10. When the loss of the head exceeds the static head, the head becomes _____
a) Positive
b) Negative
c) Constant
d) Zero
Explanation: The head becomes negative when the loss of the head through the bed depth exceeds the static head. The negative head is the fall of liquid level in the piezometric tube below the center line of under drainage system.