This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Trickling Filters – 1”.
1. Who used the trickling filter for the first time?
a) Didden
b) Streeter
c) Thomas
d) Newton
View Answer
Explanation: Trickling filter consists of a fixed bed of rocks, lava, coke, gravel and polyurethane over which sewage or other wastewater flows downward and causes a layer of microbial slime. It was first used by Didden.
2. Splashing helps in improving aerobic conditions.
a) True
b) False
View Answer
Explanation: Splashing, diffusion, etc. increases aerobic conditions and it is increased either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.
3. Trickling filter can also be called as a biofilter.
a) True
b) False
View Answer
Explanation: The systems like trickling filter and biofilter have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.
4. The supernatant from the tank flows into a ____
a) Trickling filter
b) Dosing device
c) Pumping station
d) Sedimentation tank
View Answer
Explanation: The supernatant from the tank flows into a dosing device, often a tipping bucket which delivers flow to the arms of the filter. The flush of water flows through the arms and exits through a series of holes pointing at an angle downwards.
5. __________ in trickling filter contains many species like bacteria and round worms.
a) Treated water
b) Wastewater
c) Biofilm
d) Air influent
View Answer
Explanation: The bio-film that develops in a trickling filter may become several millimeters thick and is typically a gelatinous matrix that contains many species of bacteria, ciliates and amoeboid protozoa, annelids, round worms and insect larvae and many other micro fauna.
6. Which of the following is not used as a media for trickling filters?
a) Sand
b) Geotextiles
c) Gravel
d) Paper
View Answer
Explanation: Trickling may have a variety of types of filter media used to support the biofilm. Coke, pumice, plastic matrix material, open-cell polyurethane foam, clinker, gravel, sand and geotextiles are the most common type of media used.
7. Which of the following causes thickening of the biofilm?
a) Reduction of intake wastewater
b) Rapid growth of organisms
c) Reduction in air supply
d) Increase in acidity
View Answer
Explanation: At certain times of the year, especially in the spring, rapid growth of organisms in the film may cause the film to be too thick and it may slough off in patches leading to the “spring slough”.
8. What is the shape of a typical trickling filter?
a) Circular
b) Cylindrical
c) Square
d) Rectangular
View Answer
Explanation: A typical trickling filter is circular and between 10 meters and 20 meters across and between 2 meters to 3 meters deep. A wall, circular, often of brick, contains a bed of filter media which in turn rests on a base of under-drains.
9. What is the depth of the trickling filter?
a) 0.5-1 m
b) 1-1.5 m
c) 1.5-2 m
d) 2-3 m
View Answer
Explanation: A typical trickling filter is circular and between 10 meters and 20 meters across and between 2 meters to 3 meters deep. A circular wall, often of brick, contains a bed of filter media which in turn rests on a base of under-drains.
10. The spindle is provided at the ______ to support perforated plates.
a) Edge
b) Bottom
c) Top
d) Centre
View Answer
Explanation: On the top of the filter media, in the centre is a spindle supporting two or more horizontal perforated pipes which extend to the edge of the media.
11. While designing a trickling filter what would be the depth assumed?
a) 12-15m
b) 4-12 m
c) 16-20 m
d) 20-25 m
View Answer
Explanation: The depth for trickling filters would be mostly assumed as 4-12 m. Other than this, a trickling filter constitutes a waste water dosing system. Also it constitutes a drain.
12. What is necessary prior to trickling filters?
a) Secondary clarification
b) MBBR
c) Grit chamber
d) Primary clarification
View Answer
Explanation: Primary clarification is necessary prior to trickling filters. Screening of the materials prior to letting it into the trickling filter is necessary. This is done to prevent clogging.
13. Which type of bacteria are used in trickling filters?
a) Facultative
b) Nitrifying
c) Anaerobic
d) Blue-green bacteria
View Answer
Explanation: Facultative bacteria are used in trickling filters. Pseudomonas and Alcaligenes are some of the strains used in these filters. Also, Flavobacterium and Achromobacter are also used in this type of treatment.
14. For rock packing low- rate trickling filters what is the hydraulic loading assumed?
a) 1-4 m3/m2.d
b) 4-8 m3/m2.d
c) 8- 12 m3/m2.d
d) 12-15 m3/m2.d
View Answer
Explanation: 1-4 m3/m2.d is the hydraulic rate considered for rock type of packing in trickling filters. The other type of packing is plastic. While designing this type of packing the hydraulic rate of this would be different.
15. For rock type of packing in intermediate filtration trickling filters what is the hydraulic rate considered?
a) 4-10 m3/m2.d
b) 10-15 m3/m2.d
c) 20-25 m3/m2.d
d) 25-30 m3/m2.d
View Answer
Explanation: For rock type packing in intermediate filtration trickling type filters, the hydraulic rate considered is 4-10 m3/m2.d. In case of high filtration rock type trickling filters packing it is considered as 10-75 m3/m2.d. For plastic packing type in trickling filters, the hydraulic rate is different.
16. For rock type of roughing packing trickling filter what will be the hydraulic loading rate?
a) 40-200 m3/m2.d
b) 300 m3/m2.d
c) 500 m3/m2.d
d) 600 m3/m2.d
View Answer
Explanation: For rock type of rough packing trickling filter, the hydraulic loading rate is 40-200 m3/m2.d.High organic loaded waste water have been treated by rough packing filters. However this only partially removes the BOD.
17. For rock type low filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.4-2.4 kg BOD/m3d
d) >2.4 kg BOD/m3d
View Answer
Explanation: For rock type of low filtration rate trickling filters the organic load assumed is 0.07-0.22 kg BOD/m3d. Intermediate rate filtration filters would have different organic load. It is around 0.24-0.48 kg BOD/m3d.
18. For rock type high filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.4-2.4 kg BOD/m3d
d) >2.4 kg BOD/m3d
View Answer
Explanation: For rock type of high filtration rate tricking filters, the organic load assumed is 0.4-2.4 kg BOD/m3d. Intermediate rate filtration trickling filters would have different organic load. It is around 0.24-0.48 kg BOD/m3d.
19. For plastic type high filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.5 kg BOD/m3d
d) 0.6-3.2 kg BOD/m3d
View Answer
Explanation: For plastic type of high filtration rate trickling filters, the organic load assumed is 0.6-3.2 kg BOD/m3d. Roughing rock type of trickling filter has a different organic loading rate. It is > 1.5 kg BOD/m3d.
20. For rock type low filtration rate trickling filters what would be the recycling ratio assumed?
a) 0
b) 1-2
c) >2
d) >3
View Answer
Explanation: For rock type low filtration, the recycling ratio would be 0. In case of intermediate filtration, this ratio is a little higher. It is around 0-1.
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