This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Anaerobic Digestion”.
1. Anaerobic digestion occurs in the presence of oxygen.
a) True
b) False
View Answer
Explanation: Anaerobic digestion is a collection of processes by which micro-organisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels.
2. Anaerobic digestion can be used to produce fuel.
a) True
b) False
View Answer
Explanation: Anaerobic digestion process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation uses anaerobic digestion.
3. _________ uses anaerobic digestion.
a) Incineration
b) Combustion
c) Fermentation
d) Oxygenation
View Answer
Explanation: In industries, fermentation is used to produce food and drink products. Anaerobic digestion occurs naturally in some soils and in a lake and oceanic basin sediments, where it is usually referred to as “anaerobic activity”.
4. What is biogas composed of?
a) O2 and CO2
b) CO2 and NO2
c) CH4 and O2
d) CH4 and CO2
View Answer
Explanation: Anaerobic digestion is a biological process. A gas is produced that is composed of methane and carbon-dioxide which is called as biogas. These gases are produced from organic wastes such as livestock manure, food processing waste, etc.
5. What is the percentage of methane in the biogas?
a) 10-20 %
b) 20-40 %
c) 45-65 %
d) 55-75 %
View Answer
Explanation: Anaerobic processes could either occur naturally or in a controlled environment such as a biogas plant. Depending on the waste feedstock and the system design, biogas is typically 55 to 75 percent pure methane.
6. How many steps are present in anaerobic digestion?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: There are three steps present in the anaerobic digestion process. The first step is the decomposition of plant or animal matter and the second step is the conversion of decomposed matter to organic acids. In the final step, the acids are converted to methane.
7. What is the temperature that needs to be maintained during the process?
a) 90˚F
b) 95˚F
c) 100˚F
d) 105˚F
View Answer
Explanation: Process temperature affects the rate of digestion and should be maintained in the mesophilic range (95 to 105 degrees Fahrenheit) with an optimum of 100 degrees Fahrenheit.
8. The pathogens in digestate are _________
a) Highly active
b) Inactive
c) Partly inactive
d) Neutral
View Answer
Explanation: The pressure exerted by the rising gas can be used to transport the gas to the collection vessel or directly to where it is going to be sued. The digestate is rich in organics and nutrients, almost odourless and pathogens are partly inactivated.
9. What is the range of retention time during anaerobic digestion?
a) 10-20 days
b) 20-30 days
c) 40-80 days
d) 40-100 days
View Answer
Explanation: The range of retention time during anaerobic digestion is 40-100 days. Biogas reactors are often installed at household or community level in rural areas for the co-digestion of animal manure and toilet products.
10. How much is the cow yield from anaerobic digestion that can be obtained?
a) 0.1 m3/Kg dung
b) 0.2 m3/Kg dung
c) 0.3 m3/Kg dung
d) 0.4 m3/Kg dung
View Answer
Explanation: The cow yield from anaerobic digestion is 0.4 m3/Kg dung. Animal manure and kitchen waste contain a lot of organic matter and generally, the process produces enough biogas for the family to cover cooking requirements.
11. In anaerobic digestion system which of the following statement holds good?
a) Acids are necessary to be added to make the pH neutral
b) Alkalines are necessary to be added to make the pH neutral
c) A flocculant is to be added to bring about flocculation
d) A coagulant is necessary to be added in order to bring about coagulation
View Answer
Explanation: Alkalines are necessary to be added to make the pH neutral. The pH in these systems drops very low. Hence the addition of such alkaline to increase the pH becomes necessary.
12. What is the optimum temperature at which anaerobic digestion is carried out?
a) 25-35 degree Celsius
b) 55 degree Celsius
c) 45 degree Celsius
d) 40-50 degree Celsius
View Answer
Explanation: Anaerobic digestion is carried out at 25-35 degree Celsius. At lower temperatures, higher Solid retention time is expected. Attached or suspended growth anaerobic digestion is carried out at temperatures as low as 10-20 degree Celsius.
13. For what range of COD level anaerobic digestion is carried out?
a) 400-800
b) 900-1200
c) 1500-2000
d) 300-400
View Answer
Explanation: The COD level would be around 1500-2000 mg/L if it is subjected to anaerobic digestion. In case if it is around 1300 mg/L then aerobic digestion is carried out. In anaerobic digestion, methane is produced.
14. What is the percentage of Carbon dioxide produced during anaerobic digestion?
a) 70-80%
b) 80-90%
c) 30-50%
d) 50-60%
View Answer
Explanation: Around 30-50% of gas is produced. This carbon dioxide produced reduces the pH. Hence alkaline is required to be added.
15. What is the rate limiting step in anaerobic digestion?
a) Methanogenesis
b) Hydrolysis
c) Acidification
d) Biogas production
View Answer
Explanation: In the case of anaerobic digestion, methanogenesis is the rate limiting step. This results in longer solid retention time. In the case of acid fermentation, hydrolysis is the rate limiting step.
16. What is the volumetric organic loading in Kg COD/ m3 day for a completely mixed anaerobic digestion process?
a) 1-5
b) 5-7
c) 7-9
d) 9-12
View Answer
Explanation: The volumetric organic loading in Kg COD/ m3 day for a completely mixed anaerobic digestion process is 1-5. This is the loading rate obtained at 30 degree Celsius. This value holds good for suspended growth anaerobic digestion.
17. What is the volumetric organic loading in Kg COD/ m3 day for an anaerobic contact digestion process?
a) 1-8
b) 8-10
c) 10-12
d) 12-15
View Answer
Explanation: The volumetric organic loading in Kg COD/ m3 day for an anaerobic contact digestion process is 1-8. This is the loading rate obtained at 30 degree Celsius. This value holds good for suspended growth anaerobic digestion.
18. What is the volumetric organic loading in Kg COD/ m3 day for an anaerobic sequence batch reactor?
a) 4-6
b) 1.2-2.4
c) 2.6-3.4
d) 6.4-7.6
View Answer
Explanation: The volumetric organic loading in Kg COD/ m3 day for an anaerobic sequence batch reactor digestion process is 1.2-2.4. This is the loading rate obtained at 30 degree Celsius. This value holds good for suspended growth anaerobic digestion.
19. What is the hydraulic retention time for a completely mixed anaerobic digestion process?
a) 15-30 days
b) 40-50 days
c) 50-60 days
d) 60-80 days
View Answer
Explanation: The hydraulic retention time for a completely mixed anaerobic digestion process is 15-30 days. This is dependent on the influent COD. This is mostly assumed as 20 days in most cases.
20. What is the hydraulic retention time for a completely mixed anaerobic contact type process?
a) 8-10 days
b) 5-8 days
c) 0.5-5 days
d) 10-12 days
View Answer
Explanation: The hydraulic retention time for a completely mixed anaerobic digestion process is 0.5 -5days. This is dependent on the influent COD. This is mostly assumed as 3 days in most cases.
Sanfoundry Global Education & Learning Series – Waste Water Engineering.
To practice all areas of Waste Water Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
- Check Waste Water Engineering Books
- Practice Civil Engineering MCQs
- Check Civil Engineering Books
- Apply for Civil Engineering Internship
