This set of Tricky Energy Engineering Questions and Answers focuses on “Anaerobic Fermentation – 2”.
1. How are systems intended for the digestions are filled and emptied?
a) Manually
b) By evaporation
c) By pumps and pipes
d) By channels and pits
View Answer
Explanation: Systems intended for the digestion of liquid or suspended solid waste (cow manure is a typical example of this variety) are mostly filled or emptied using pumps and pipe work. A simple version is simply to gravity feed the tank allow the digested slurry to overflow the tank.
2. Cow manure is rich in __________
a) Hydrogen
b) Phosphorus
c) Nitrogen
d) Potassium
View Answer
Explanation: Cow dung is the undigested residue of plant matter which has passed through the animal’s gut. The resultant fecal matter is rich in minerals. Color ranges from greenish to blackish, often darkening soon after exposure to air. And it is very rich in nitrogen.
3. How many weeks does complete digestion of cow manure takes about?
a) 1
b) 2
c) 4
d) 8
View Answer
Explanation: The complete anaerobic digestion of cow manure takes about 8 weeks at normally warm temperatures. One third of the total biogas will be produced in the first week, another quarter in the second week and the remainder of the biogas production will be spread over the remaining 6 weeks.
4. How many weeks does a batch digester need to produce biogas?
a) 1 week
b) 2 – 4 week
c) 12 week
d) 4 – 8 week
View Answer
Explanation: Depending on the waste material and operating temperature, a batch digester will start producing biogas after 2 – 4 weeks, slowly increase in production then drop off after three or 4 months. Batch digesters are therefore best operated in groups.
5. Which of the following matter has a much higher carbon – nitrogen ratio?
a) Vegetable matter
b) Cow dung
c) Plant waste
d) Organic waste from industry
View Answer
Explanation: Most vegetable matte has a much higher carbon – nitrogen ratio than dung has, so some nitrogen producers (preferably organic) must generally be added to vegetable matter, especially when batch digestion is used.
6. Which of the following waste produces more gases comparatively?
a) Vegetable matter
b) Cow dung
c) Plant waste
d) Organic waste from industry
View Answer
Explanation: Vegetable matter produces about 8 times more gas, so the quantity required is much smaller in batch production for the same gas production from any other wastes. A mixture of dung and vegetable matter is hence ideal in most ways, with a majority of vegetable matter to provide the biogas and the valuable methane contained in it.
7. How much thick layer of insulation is done inside of digester?
a) 10 cm
b) 15 – 25 mm
c) 8 mm
d) 50 – 100 cm
View Answer
Explanation: In hot regions it is relatively easy to simply shade the digester to keep it in the ideal range of temperature, but cold climates present more of a challenge. The first action is, naturally, to insulate the digester with straw or wood shavings. A layer about 50 – 100 cm thick, coated with a waterproof covering is a good start.
8. What happens if the organic matter is not stirred while in process of digestion?
a) It will evaporate
b) It solidifies
c) It will form hard scum on layer
d) It gets struck to digester walls
View Answer
Explanation: Some method of stirring the slurry in a digester is always advantageous, if not essential. If not stirred, the slurry will tend to settle out and form a hard scum on the surface, which will prevent release of biogas.
9. How is biogas from an anaerobic digester collected?
a) In a compressor
b) In the pipelines
c) In inverted drum
d) In a storage tank
View Answer
Explanation: The biogas in an anaerobic digester is collected in an inverted drum. The walls of the drum extended down into the slurry to provide a seal. The drum is free to move to accommodate more or less gas needed.
10. Which type of valve is used to prevent air being drawn into the digester?
a) Non return valve
b) Poppet vale
c) Return valve
d) Check valve
View Answer
Explanation: A non return valve is a valuable investment to prevent air being drawn into digester, which would destroy the activity of bacteria and provided a potentially explosive mixture inside the drum. Larger plants may need counterweights of some sort to ensure that the explosive mixture inside the drum.
11. Which types of plants are filled and then emptied completely after fixed retention time?
a) Batch plants
b) Continuous plants
c) Floating gas holder plants
d) Flexible bag biogas plant
View Answer
Explanation: Batch plants are filled and then emptied completely after a fixed retention time. Each design and each fermentation material is suitable for batch filling, but batch plants require high labor input.
12. What is the major disadvantage of batch plants?
a) Their output is not steady
b) Comes to frequent breakdown
c) They are not efficient
d) They are very costly
View Answer
Explanation: Batch biogas plants are loaded with substrate completely and after some determined digestion time are fully unloaded. For this loading method any design of biogas plant and any design of biogas plant any substrate can be used, but such plants are distinguished by unstable biogas production. The major disadvantage of batch plant is the output is not steady.
13. Which among the following best suitable treatment of waste products?
a) Aerobic fermentation
b) Anaerobic fermentation
c) Autolysis
d) Thermal reaction
View Answer
Explanation: Anaerobic process is especially considered as a suitable treatment option due to low-energy requirements and little quantities of sludge production. Therefore, anaerobic process has become increasingly demanding in the treatment of complex industrial wastes.
14. What does PSD stand for?
a) Post source decay
b) Particle size distribution
c) Polystyrene deuterated
d) Post synaptic density
View Answer
Explanation: The particle-size distribution (PSD) of a powder, granular material, or particles dispersed in fluid is a list of values or a mathematical function that defines the relative amount, typically by mass, of particles present according to size.
15. Which is the third stage of anaerobic digestion?
a) Acetogenesis
b) Methanogenesis
c) Acidogenesis
d) Hydrolysis
View Answer
Explanation: The third stage of anaerobic digestion is acetogenesis. Here, simple molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.
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