Secondary Clarifiers - Waste Water Engineering Questions and Answers

This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Secondary Clarifiers – 1”.

1. Which is the special feature of secondary clarifier?
a) Sludge collection
b) Sludge withdrawal
c) Launder covers
d) Spiral scraper
View Answer

Answer: d
Explanation: The features such as sludge collection and sludge withdrawal are present in both primary and secondary clarifiers. Secondary clarifiers include special features such as a spiral scraper, density current baffle, etc.

2. What does SSCC stand for?
a) Spiral scraper clarifier type
b) Suction header clarifier type
c) Up-flow pipe clarifier type
d) Perimeter feed clarifier
View Answer

Answer: a
Explanation: SSCC stands for Spiral Scraper Clarifier type. SHSC stands for Suction Header Clarifier type. Up-flow Pipe Clarifier type. PIBC stands for Perimeter Feed Clarifier type.

3. What is the mixed liquor?
a) Influent
b) Effluent
c) Intermediate
d) Liquid
View Answer

Answer: a
Explanation: Typically the influent will be mixed liquor from an aeration tank incorporating an activated sludge process. Micro-organisms metabolize the biological waste that exists after primary clarification.

4. Micro-organisms metabolize the _______that exists after primary clarification.
a) Chemicals
b) Coagulant
c) Ions
d) Biological waste
View Answer

Answer: d
Explanation: Micro-organisms metabolize the biological waste that exists after primary clarification. Typically the influent will be mixed liquor from an aeration tank incorporating an activated sludge process.

5. What does EDI stand for?
a) Energy discharge inlet
b) Energy diode indicator
c) Effluent discharge inlet
d) Energy dissipating inlet
View Answer

Answer: d
Explanation: A central energy-dissipating inlet (EDI) can be used, or Monroe Environmental will design a peripheral feed system that distributes influent around the perimeter of the tank, and aids in activated sludge secondary settling.

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6. What does MLSS stand for?
a) Mixed Liquor Soluble Solvents
b) Mixed Liquor Suspended solids
c) Mixed Liquor Suspended Solvents
d) Major Liquid Soluble Solids
View Answer

Answer: b
Explanation: Liquor suspended solids (MLSS) that are broken up during transport from the aeration basin to recombine can be used to design an enlarged flocculation zone. The larger floc that results will settle more effectively.

7. Radial tube header is designed to remove _______
a) Suspended solids
b) Backwash water
c) Settled solids
d) Floating matter
View Answer

Answer: c
Explanation: All settled solids from the tank and return them either to the head of the activated sludge process (Return Activated Sludge) or to further solid waste treatment (Waste Activated Sludge) by a radial tube header.

8. Orifice placement is critical to the successful operation of the clarifier.
a) True
b) False
View Answer

Answer: a
Explanation: Proper design of the suction header (header geometry as well as orifice placement and sizing) is critical to the successful operation of the clarifier.

9. Hindered zone settling refers to the suspensions of intermediate concentration.
a) True
b) False
View Answer

Answer: a
Explanation: Hindered zone settling refers to the suspensions of intermediate concentration. Inter particles forces are sufficient to hinder the settling of neighbouring particles.

10. The liquid tends to move up through the interstices of contacting particles because of _______
a) High turbidity
b) Low turbidity
c) High concentration of particles
d) Low concentration of particles
View Answer

Answer: c
Explanation: The liquid tends to move up through the interstices of contacting particles because of the high concentration of particles. A zone or blanket is developed by settling particles.

11. Calculate the volume of the flocculation zone for a clariflocculator for the following data.
Flow: 500 m³/h.
a) 250 m³
b) 325 m³
c) 425 m³
d) 525 m³
View Answer

Answer: a
Explanation: The retention time is considered as 30 mins for the flocculation zone in case of a flocculator. The volume is calculated by multiplying retention time and flow. The area is then calculated by dividing the volume by the height.

12. Calculate the diameter of the flocculation zone for the following data:
Flow: 200 m³/h.
Height considered (SWD):3.5 m
a) 6.1 m
b) 9.8 m
c) 10.8 m
d) 10.7 m
View Answer

Answer: a
Explanation: The retention time is considered as 30 mins for the flocculation zone. The volume is calculated by multiplying retention time and flow. The area is then calculated by dividing the volume by the height. From the area the diameter can be calculated.

13. Calculate the surface area of the flocculation zone for the following data.
Flow: 300 m³/h.
Rise rate :1.2 m/h
a) 240 m²
b) 250 m²
c) 350 m²
d) 160 m²
View Answer

Answer: b
Explanation: The surface area of the clariflocculator is found out based on the rise rate. Area = Flow/rise rate. Area = 300/1,2 = 250 m².

14. Calculate the flocculation volume for an HRSCC for the following data.
Flow: 300 m³/h.
a) 40 m³
b) 90 m³
c) 75 m³
d) 100 m³
View Answer

Answer: c
Explanation: The retention time is considered as 15 mins for the flocculation zone. The volume is calculated by multiplying retention time and flow. The area is then calculated by dividing the volume by the height. From the area the diameter can be calculated.

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