# Environmental Engineering Questions and Answers – High Rate Trickling Filter and Secondary Clarifier

This set of Environmental Engineering Quiz focuses on “High Rate Trickling Filter and Secondary Clarifier”.

1. The maximum removal of suspended and dissolved impurities from the sewage is?
a) 65
b) 70
c) 92
d) 99

Explanation: The maximum and minimum removal of suspended and dissolved impurities from the sewage is 92% and 65% respectively.

2. The color of the secondary sludge produced from the high rate trickling filter is ___________
a) Gray
b) Black
c) Brown
d) Green

Explanation: The color of the secondary sludge produced from the high rate trickling filter is brown and the secondary sludge obtained is partially oxidized.

3. _______ is the ratio of volume of recirculated sewage to the raw sewage.
a) Recirculation factor
b) Recirculation ratio
c) Food to mass ratio
d) BOD

Explanation: Recirculation ratio is the ratio of volume of recirculated sewage to the raw sewage. It is denoted by R/I where, ‘R’ is the recirculated sewage and I is the volume of raw sewage.

4. The range of organic loading in kg/hectare metre/ day in a high rate trickling filter is ___________
a) 6000-18000
b) 10000-20000
c) 5000-10000
d) 900-2200

Explanation: The range of organic loading in high rate trickling filter lies between 6000 to 18000 kg of 5 days BOD per hectare metre of filter media per day.

5. The expression of the recirculation factor F is given by ___________
a) F = 1 / (1+0.1 (R/I))2
b) F = (1+ R) / (1+0.1 (R/I))2
c) F = (1+ I/R) / (1+0.1(R/I))2
d) F = (1+ R/I) / (1+0.1(R/I))2

Explanation: The expression of the recirculation factor F is given by
F = (1+ R/I) / (1+0.1 (R/I))2 where, R/I represents the recirculation ratio.
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6. The size of filter media in a high rate trickling filter is ___________
a) 10-20mm
b) 34-68mm
c) 25-60mm
d) 20-50mm

Explanation: The size of filter media in a high rate trickling filter is 25-60mm and it can be a rock, slag or any synthetic material.

7. Recirculation increases the efficiency of high rate trickling filters.
a) True
b) False

Explanation: Recirculation reduces the loading in high rate trickling filter and thus, increase the efficiency infiltration process.

8. The surface loading rate of a secondary clarifier is ______ litres/m2/day.
a) 1000
b) 10000
c) 20000
d) 40000

Explanation: The range of surface loading rate of a secondary clarifier lies between 40,000 litres/m2/day to 70,000 litres/m2/day.

9. The detention period of a secondary clarifier is ___________
a) 30 minutes
b) 1 hour
c) 2 hours
d) 4 hours

Explanation: The detention period of a secondary clarifier is between 1.5 hours to 2 hours.

10. Which of the following is the cause of rising sludge?
a) Sedimentation
b) Denitrification
c) Chlorination
d) Flocculation

Explanation: When nitrogen is formed in the sludge, the rise of the sludge mass takes place. These phenomena is called as rising sludge.

a) 125000
b) 50000
c) 10000
d) 20000

Explanation: The minimum and maximum weir loading rate of primary clarifier is 125000 and 500000 m3/m/day respectively.

12. Hopper bottom vertical flow type tank is _____ in shape.
a) Circular
b) Triangular
c) Rectangular
d) Elliptical

Explanation: Hopper bottom vertical flow type tank is circular in shape and it consists of conical hoppers.

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