This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Aerobic Ponds”.
1. Aerobic ponds are similar to facultative ponds.
a) True
b) False
View Answer
Explanation: The pond is an aerobic reactor which is large in size and is similar to facultative ponds in waste stabilization pond systems, with the difference that natural oxygen is enhanced.
2. Natural oxygenation is _______ in aerated ponds while compared to facultative ponds.
a) More
b) Less
c) Equal
d) Similar
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Explanation: In aerobic ponds, natural oxygen is enhanced. Oxygen is provided by mechanical aerators to keep the aerobic organisms suspended and mixed with water to achieve a high rate of organic degradation.
3. How many types of aerate ponds are present?
a) 1
b) 2
c) 3
d) 4
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Explanation: There are two types of aerobic ponds. They are common aerated lagoons and completely mixed aerated ponds. The effluent of aerated ponds may be reused or used for recharge.
4. Aerated ponds must be shallow.
a) True
b) False
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Explanation: As natural oxygenation is enhanced, ponds can be deeper and are suited for colder climates. Mechanical aerators provide oxygen and keep the aerobic organisms suspended and mixed with water.
5. The increased aeration facilitates ________ pathogen removal.
a) Decreased
b) Increases
c) Slower
d) Faster
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Explanation: As oxygen is introduced by mechanical units, the ponds can function in northern climates. The increased aeration facilitates increased degradation and pathogen removal.
6. Which of the following is not true regarding mechanical aeration?
a) Increases oxygen
b) Enhances efficiency
c) Reduces HRT
d) Increases HRT
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Explanation: Mechanical aeration enhances the treatment efficiency and reduces the required hydraulic retention time for aerobic degradation of organics. Oxygen is introduced by mechanical units.
7. What is the outlet of TSS in ppm obtained when aerated lagoons are used for treatment?
a) 500-700
b) 100-400
c) 700-900
d) 900-1200
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Explanation: In the treated water, the TSS should be <1200ppm. When aerated lagoons are used for treatment, the TSS obtained is 100-400 ppm. This method also reduces the BOD.
8. What is the ratio of VSS/TSS in ppm obtained when aerated lagoons are used for treatment?
a) 10-20
b) 20-30
c) 70-80
d) 80-100
View Answer
Explanation: The aerated lagoon method is carried out facultatively or by solid recycling. When aerated lagoons are used for treatment, the VSS/TSS obtained is 50-80. This method also reduces the BOD present in the raw water.
9. What is the ratio of VSS/TSS in ppm obtained when partially mixed lagoons treatment are carried out facultatively?
a) 20-30
b) 40-50
c) 50-80
d) 80-100
View Answer
Explanation: Partially mixed lagoon method is carried out facultatively. This is called as partially mixed because partially the biological conversion is aerobic and partially it is anaerobic. When partially mixed lagoons are used for treatment facultatively, the VSS/TSS obtained is 50-80.
10. While designing the aerated lagoon what is the solid retention time considered?
a) 7-8 days
b) 3-6 days
c) 1-2 days
d) 10 days
View Answer
Explanation: While designing the aerated lagoon, the solid retention time considered is 3-6 days. This is generally used to remove TSS and BOD. Also because the solids are retained in the lagoon, the SRT can be higher than 3-6 days in some cases.
11. What is the outlet of TSS in ppm obtained when aerated lagoons are used for treatment?
a) 500
b) 700-1000
c) 50-200
d) 1209
View Answer
Explanation: Aerated lagoon is a method to reduce BOD in the raw water. This also reduces the TSS in the raw water. The TSS is reduced to around 50-200 ppm.
12. While designing the aerated lagoon with solid recycling what is the solid retention time considered on a warm day?
a) 10-20 days
b) 40 days
c) 25 days
d) 30 days
View Answer
Explanation: While designing the aerated lagoon with solid recycling, the solid retention time considered is 10-20 days. Depending on the temperature, the solid retention time is assumed. For a moderate day it is considered as 20-30 days.
13. While designing the aerated lagoon carried out facultatively what is the hydraulic retention time considered?
a) 3 days
b) 4-6 days
c) 10-30 days
d) 40 days
View Answer
Explanation: While designing the aerated lagoon which is carried out facultatively the hydraulic retention time considered is 4-6 days. Depending on the temperature, the solid retention time is assumed for aerated lagoons. For a moderate day it is considered as 20-30 days.
14. What is the minimum depth considered while designing an aerated lagoon?
a) 3 m
b) 2.5 m
c) 2 m
d) 1.5 m
View Answer
Explanation: The minimum depth considered for an aerated lagoon is 2.5 m. This is considered as 2.5 m even for an aerated lagoon carried out facultatively. Also for aerated lagoons with solid recycling, this is considered as 2.5 m only.
15. Which of the following methods consume the least power?
a) Aerated lagoon
b) Aerated lagoon carried out facultatively
c) Aerated lagoon with solid recycling
d) Upflow anaerobic sludge bed digestor
View Answer
Explanation: In the case of aerated lagoon carried out facultatively the least power is consumed. This is also known as partial mixing as both anaerobic and aerobic digestion takes place. Around 1-2.5 kW/1000m3 of electricity is consumed.
16. Which of the following methods consume the most power?
a) Anaerobic digestion
b) Aerated lagoon
c) Aerated lagoon carried out facultatively
d) Aerated lagoon with solid recycling
View Answer
Explanation: Aerated lagoon with solid recycling consumes very high power. Aerated lagoons consume around 5-8kw/1000m3. While aerated lagoons with solid recycling consumes around 16-20Kw/1000m3.
Sanfoundry Global Education & Learning Series – Waste Water Engineering.
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