This set of Environmental Engineering online test focuses on “Digestion of Sludge, Sludge Digestion Tank”.
1. How many stages are there in sludge digestion process?
Explanation: The sludge digestion process consists of acid fermentation, acid regression and alkaline fermentation.
2. The form of sludge which is free from pathogenic bacteria is
a) Undigested sludge
b) Digested sludge
c) Primary sludge
d) Supernatant liquor
Explanation: The digested sludge is free from pathogenic bacteria. It has the behavior of rich humus soil.
3. The BOD of supernatant liquor in a sludge digestion process is ____ ppm.
Explanation: The range of BOD of supernatant liquor in a sludge digestion process is between 2000 and 3000 ppm. It is a form of sludge that is obtained in the sludge digestion process.
4. Which of the following is correct regarding pH in different stages of the sludge digestion process?
a) Acid fermentation > Acid regression > Alkaline fermentation
b) Acid regression > Acid fermentation > Alkaline fermentation
c) Acid fermentation < Acid regression < Alkaline fermentation
d) Acid fermentation < Acid regression > Alkaline fermentation
Explanation: The pH value in Alkaline fermentation stage is 7.5 whereas in Acid regression and Acid fermentation stage, the pH>7, having the least in acid fermentation stage.
5. Which gas evolves the most in the sludge digestion process?
Explanation: Methane gas evolves the most during the sludge digestion process by approximately 70% of the total gas evolved.
6. Which of the following is incorrect about aerobic digestion in the sludge digestion process?
a) It has a low capital cost
b) It is easier to manage.
c) It has high residual energy
d) It decreases the BOD
Explanation: The residual energy in aerobic digestion is very less in comparison to anaerobic digestion.
7. The color of digestive sludge is
Explanation: The color of digestive sludge is black. It has an inoffensive odor.
8. Which of the following is correct regarding anaerobic digestion in the sludge digestion process?
a) It contains high amount of biomass
b) It is a low energy process
c) It causes infertility in soil
d) Aerobic bacteria oxidize the organic matter
Explanation: Anaerobic digestion is a low energy process which contains low amount of biomass and where both facultative and anaerobic bacteria solubilize the organic matter.
9. The maximum temperature at which thermophilic microorganisms remain active in sludge digester is
Explanation: The maximum and minimum temperature at which thermophilic microorganisms remain active in sludge digester are 60oC and 40oC respectively.
10. Which of the following is obtained in the secondary tank in two stage sludge digester?
a) Partially digested sludge
b) Partially digested sludge and supernatant liquor
c) Digested sludge and supernatant liquor
d) supernatant liquor
Explanation: In two stage sludge digester, the partially digested sludge is obtained in primary tank, whereas digested sludge is obtained in the secondary tank along with supernatant liquor.
11. The high rate sludge digestion tanks are used when the capacity of the tank is ____ million liters per day.
Explanation: High rate digesters are used when the capacity of tank is 4 million litres per day. Complete mixing and uniform feeding of raw sludge takes place in high rate digesters.
12. In which of the following, both primary and secondary tanks are used?
a) Two stage sludge digesters
b) Single stage sludge digesters
c) Low rate digesters
d) High rate digesters
Explanation: In two stage sludge digesters, the sludge is passed in primary tank for 7 days and then it is passed in the secondary tank followed by the removal of residual matter.
13. The minimum size of sludge digestion tank is
Explanation: The minimum size of sludge digestion tank is 3m. They are cylindrical in shape with a funnel shaped at the bottom.
14. The range of temperature at which mesophilic microorganism becomes active in sludge digester is
Explanation: The mesophilic microorganism becomes active at 20-40oC in the sludge digester. The rate of digestion, increases with increase in temperature.
15. The sludge digestion process is independent of which of the following?
a) Temperature of sludge
b) pH of sludge
c) Shape of tank
d) Mixing of sludge
Explanation: The sludge digestion process depends on the temperature of sludge, pH conditions and mixing of sludge and is independent of shape of tank.
Sanfoundry Global Education & Learning Series – Environmental Engineering.
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