# Waste Water Engineering Questions and Answers – Trickling Filters – 2

This set of Waste Water Engineering MCQs focuses on “Trickling Filters – 2”.

1. For rock type high filtration rate trickling filters what would be the recycling ratio assumed?
a) 0
b) 1-2
c) >2
d) >3

Explanation: For rock type high filtration, the recycling ratio would be 1-2. In case of intermediate filtration, this ratio is a little different. It is around 0-1. In case of plastic type filtration, the rate of recycle ratio is also 1-2.

2. For rock type low filtration rate trickling filters what would be depth assumed while designing it?
a) 1.8-2.4 m
b) <1.8 m
c) 3-12.2 m
d) >12.2 m

Explanation: For rock type low filtration, the depth assumed is around 1.8-2.4 m while designing it. It is assumed as 1.8-2.4 m even for intermediate filtration. It is assumed as 1.8-2.4 m for high rate filtration trickling filters also.

3. For plastic type high filtration rate trickling filters what would be depth assumed while designing it?
a) 1.8-2.4 m
b) <1.8 m
c) 3-12.2 m
d) >12.2 m

Explanation: For plastic type high filtration, the depth assumed is around 3-12.2 m while designing it. It is different for roughing type trickling filters. It is assumed as 0-2.

4. For rock type low filtration rate tricking filters what would be the BOD removal rate?
a) 50-80%
b) 50-90%
c) 80-90%
d) 40-70%

Explanation: For rock type low filtration rate trickling filters, the BOD removal efficiency is 80-90%. This is lower in case of rock type intermediate filtration trickling filters. It is around 50-80% only.

5. For rock type high filtration rate trickling filters what would be the BOD removal rate?
a) 50-80%
b) 50-90%
c) 80-90%
d) 40-70%

Explanation: For rock type high filtration rate trickling filters, the BOD removal efficiency is 50-90%. This is lower than rock type low filtration rate trickling filters. The BOD removal efficiency of high filtration rate filters is similar to that of intermediate filtration rate filters.
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6. For plastic type high filtration rate trickling filters what would be the BOD removal rate?
a) 50-80%
b) 60-90%
c) 80-90%
d) 40-70%

Explanation: For plastic type high filtration rate trickling filters, the BOD removal efficiency is 60-90%. This is lower than rock type low filtration rate trickling filters. The BOD removal efficiency rate is highest only when low filtration rate type trickling filters are used.

7. For roughing type trickling filters what would be the BOD removal rate?
a) 50-80%
b) 60-90%
c) 80-90%
d) 40-70%

Explanation: For roughing type trickling filters, the BOD removal efficiency is 40 -70 %. This roughing type filters can be both plastic and rock type. In both the cases, the removal efficiency is 40-70%.

8. In which type of trickling filter very low power is consumed?
a) Low or standard filtration rate(Rock type)
b) Intermediate filtration rate (Rock type)
c) High filtration rate (Rock type)
d) High filtration rate (Plastic type)

Explanation: Depending on the filtration rates, the trickling filters can be classified as high, low rate or intermediate filtration rate trickling filters. The minimum power consumed is when utilizing low or standard filtration rate rock type tricking filters. Around 2-4 KW/103m3 is consumed.

9. In which type of trickling filter very high power is consumed?
a) Low or standard filtration rate(Rock type)
b) Intermediate filtration rate (Rock type)
c) High filtration rate (Rock type)
d) Roughing (Plastic/Rock type)

Explanation: Depending on packing material for the trickling filters it has been classified into 2 types. Rock and plastic type. The roughing type trickling filter which can constitute either rock or plastic packing consumes the highest power. This is around 10-20 KW/ 103m3.

10. In which type of trickling filter is nitrogen oxidized?
a) Low or standard filtration rate(Rock type)
b) Intermediate filtration rate (Rock type)
c) High filtration rate (Rock type)
d) Roughing (Plastic/Rock type)

Explanation: In the low or standard filtration rate type trickling filter, the filter packing is only at the top from 0.6-1.2 m. Hence the lower portions are populated by autotrophic nitrifying bacteria. This oxidises the ammonia nitrogen to nitrite and nitrate forms.

11. When filled which of the following material only nitrogen is removed?
a) River rock (Large)
b) River rock (Small)
c) Plastic conventional
d) Plastic random packing-conventional

Explanation: The trickling filters usually constitute rock or plastic packing. The trickling filters remove BOD/ nitrogen. When it is filled only with River rock (small) then it was noticed that only the nitrogen was removed by oxidizing the ammonia nitrogen to nitrite and nitrate.

12. When filled which of the following material both nitrogen and BOD are removed?
a) River rock (Large)
b) River Rock (Small)
c) Plastic High specific area
d) Plastic random packing-high specific area

Explanation: The trickling filters usually constitute rock or plastic packing. The trickling filters remove BOD/ nitrogen. When it is filled only with River rock (large) then it was noticed that both BOD and nitrogen get removed.

13. What is the surface area of the plastic high specific surface area packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 140 m2/m3
d) 45 m2/m3

Explanation: The surface area for the plastic medium high specific surface area is about 140 m2/m3. This removes only Nitrogen. The void space is >94%.

14. What is the surface area of the plastic conventional packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 140 m2/m3
d) 45 m2/m3

Explanation: The surface area for the plastic medium of the conventional type is about 90 m2/m3. This removes both Nitrogen and BOD. The void space is >95%.

15. What is the surface area of the plastic random packing conventional packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 98 m2/m3
d) 150 m2/m3

Explanation: The surface area for the plastic random packing of the conventional type packing material is about 98 m2/m3. This removes both Nitrogen and BOD. The void space is around 80%.

16. What is the surface area of the plastic random packing high specific surface area packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 98 m2/m3
d) 150 m2/m3

Explanation: The surface area for the plastic random packing high specific area is about 150 m2/m3. This removes only Nitrogen. The void space is around 70%.

17. What is the surface area of the River rock (Small) packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 98 m2/m3
d) 150 m2/m3

Explanation: The surface area for the River rock (Small) packing material is about 60 m2/m3. This removes only Nitrogen. The void space is around 50%.

18. What is the surface area of the River rock (Large) packing material used in trickling filters as the packing medium?
a) 60 m2/m3
b) 90 m2/m3
c) 45 m2/m3
d) 150 m2/m3

Explanation: The surface area for the River rock (Large) packing material is about 45 m2/m3. This removes both Nitrogen and BOD. The void space is around 60%.

19. The settling tank which is followed after the Trickling filter has which of the following characteristic?
a) Recirculation is present
b) Low suspended solids
c) The sludge from here is returned to the primary clarifier directly.
d) Has high BOD

Explanation: The settling tank which is followed after the tricking filter usually constitutes very low suspended solids. They differ from the activated sludge process by not having a recirculation system. The sludge from these systems is processed in the sludge disposal system which is then sent to the primary clarifier.

20. What is the maximum reduced concentration of BOD obtained at the outlet of tricking filter?
a) 40 mg/L
b) 20 mg/L
c) 30 mg/ L
d) 45 mg/L

Explanation: The concentration of BOD obtained at the outlet of the trickling filter is 20 mg/L. The concentration of TSS obtained at the outlet of the trickling filter is around 20 mg/L. This is the maximum value of BOD or TSS that can be obtained at the output of a trickling filter.

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