This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “High Rate Filtration”.
1. High rate filtrations cannot be used for wet weather conditions.
a) True
b) False
View Answer
Explanation: The purpose of this technique is to reduce contaminant load due to the discharge under wet weather conditions. In addition, by reducing the filtration rate under dry weather conditions, the process can be operated as a substitute for the primary settling tank without chemicals addition.
2. What is the filter media made of?
a) Cotton
b) Synthetic fibre
c) Geotextiles
d) Plastic
View Answer
Explanation: The filtering media is made by synthetic fibre specially processed and has a high void ratio(95% and above), which enables the trapping of debris and suspended solids in and out of the media simultaneously.
3. Filter cycle is interrupted for ______
a) Air washing
b) Back washing
c) Adding influent
d) Removing effluent
View Answer
Explanation: Filtration cycle is interrupted for air washing when filter resistance through the filter media reaches the terminal filtration.
4. ________ is shifted to keep an ample space for filtering media to rotate.
a) Drain
b) Movable plate
c) Perforated plate
d) Cylinder
View Answer
Explanation: Washing of the filtering media is made when the movable plate, which retains filter bed, is shifted to keep an ample space for filtering media to rotate. The suspended solids captured by the filtering media are removed by the air washing.
5. What is the void ratio of filter media?
a) 60-65 %
b) 65-70 %
c) 75-80 %
d) 80-85 %
View Answer
Explanation: The diameter of synthetic fiber balls used in the filter media is 1.5 cm. The void ratio of the filter media usually lies in the range of 80-85 %. The filter media is usually chemical and temperature resistant.
6. The synthetic fibres used are temperature resistant.
a) True
b) False
View Answer
Explanation: Synthetic fibre is used as the filter media. The filter media is usually chemical and temperature resistant. The filter media is usually chemical and temperature resistant.
7. Which of the following is not true in case of closing the top of the vessel?
a) Keeps out sunlight
b) Limits algal growth
c) Restricts bug access
d) Eliminates odour
View Answer
Explanation: The top of the vessel is closed to keep out the sunlight which limits algae growth and to restrict bug access to the water level. The closing of the vessel might in fact build up an odour of its own.
8. As the compression increases, the porosity in filter bed _____
a) Increases
b) Decreases
c) Remains constant
d) Alters
View Answer
Explanation: As the compression changes, the porosity in the filter bed also changes. The increase in compression results in smaller voids to capture smaller particles. Less compression leads to larger voids to capture larger particles.
9. What is the life of the media used?
a) 2 years
b) 5 years
c) 8 years
d) 10 years
View Answer
Explanation: The media used is synthetic fibre. It removes particles of size equal to 4 microns. 0% to 40% of compression can be done in the bed. The life of the media is approximately equal to 10 years.
10. What is the percentage of wash water?
a) >5%
b) >3%
c) >2%
d) <2%
View Answer
Explanation: The wash time is 30 minutes. The filter must be cleaned for every 8-24 hours. The wash water volume is less than 2% of the total volume of water used for the purpose.
11. Which of these does high rate filters not remove?
a) Phosphorous
b) Suspended Solids
c) Colloidal Solids
d) Organic matter(particulate)
View Answer
Explanation: High rate filters remove suspended solids and colloidal solids. They also remove phosphorous compounds. They don’t remove organic matter (particulate).
12. Which of these has been used as a medium for high rate filtration?
a) Polyvaniladene
b) Polypropylene
c) Polyacetylene
d) Polyvinyl
View Answer
Explanation: Polyvaniladene has been used as a medium in case of high rate filtration. This is a synthetic medium. This is highly porous.
13. What is the porosity of these synthetic media?
a) 90-92%
b) 92-94%
c) 88-90%
d) 94-96%
View Answer
Explanation: The porosity of such synthetic media is around 88-90%. These media are highly porous. Hence this is highly efficient in the removal of colloidal and suspended solids.
14. While designing a high rate filter what would be the velocity assumed?
a) 12m/h
b) 18 m/h
c) 7 m/h
d) 5 m/h
View Answer
Explanation: The velocity of the high rate filters are assumed as 5 m/h. Based on this, the diameter of the filter is fixed. Also the amount of media calculated is also based on this.
15. For a high rate filter calculate the diameter of the filter required for a flow of water of 200 m3/h.
a) 7.2m
b) 8.4 m
c) 14 m
d) 13 m
View Answer
Explanation: The calculated diameter is 7.2. Area = 200/5. Diameter =square root (area x 1.27) = 7.2 m.
16. What is the bed depth of the sand considered in such rapid filters?
a) 500 mm
b) 200- 400 mm
c) 600-760 mm
d) 900- 1000 mm
View Answer
Explanation: The bed depth is considered as 600-760 mm. The depth for the gravels is considered as 400-600 mm. These are the assumptions made while designing a rapid sand filtration.
Sanfoundry Global Education & Learning Series – Waste Water Engineering.
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