NPTEL Wastewater Treatment and Recycling Week 8 Assignment Answers 2024
1. Primary sludge produced from wastewater treatment plant, mainly consists of:
a. Only inorganic settleable solids
b. Dissolved inorganic and organic materials
c. Only coarser fraction of organic solids
d. Both inorganic and organic settleable solids
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2. Which of the following produces waste activated sludge:
a. Screenings and Grit
b. Primary clarifier
c. ASP and Trickling Filters
d. Multigrade filters and carbon filters
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3. The typical range of organic fraction of solids in the secondary sludge is:
a. < 20 %
b. 20-40 %
c. 40-55 %
d. 60-90 %
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4. Identify the correct statements regarding sludge digestion:
Statement 1: Sludge digestion leads to decomposition of organic solids present in
sludge into stable substances.
Statement II: Sludge digestion also significantly reduces the water content of the sludge.
a. Statement I is correct, while statement II is incorrect
b. Statement II is correct, while statement I is incorrect
c. Both, statements I and II are correct
d. Both, statements I and II are incorrect
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5.
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6. Which of the following process are expected to result in the significant decrease in the volume of the sludge:
a. Sludge conditioning
b. Sludge thickening
c. Sludge digestion
d. All of the above
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7. In aerobic sludge digestion, nitrogen in the cell mass is converted to:
a. Ammonia, and then nitrate
b. Amines
c. Nitrogen gas
d. Azo compounds
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8. The primary objective of sludge conditioning process is to:
a. Reduce the volume of the sludge by removing water from the sludge
b. Enhance the dewatering characteristics of the sludge
c. Reduce the solid content of the sludge
d. Disinfect the sludge by inactivating pathogens in it
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9. Which of the following sludge dewatering methods require large area:
a. Centrifuge
b. Belt filter press
c. Hydraulie press
d. Sludge drying beds
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10. Issues with sludge incineration is:
a. Large land area requirement
b. Risk of air pollution, if not controlled properly
c. Almost zero calorific value of wastewater sludge
d. All of the above
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11. A mechanical thickener is processing 32000 kg/d wet sludge having 1.2 % (w/w) solid content and resulting in thickened sludge with 6.4 % (w/w) solid content. The total weight of the thickened sludge would be:
a. 14,260 kg/d
b. 7,500 kg/d
c. 6.000 kg/d
d. 384 kg/d
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12. A 45,000 kg/d wastewater sludge is having two stage thickening, first a mechanical thickener to reduce it’s water content (w/w) from 98.5% to 95.4%, followed by a centrifuge to further reduce the water content (w/w) to 84.3 %. If the specific gravity of thickened sludge is 1.23, the volume of the finally thickened sludge would be:
a. 3.5 m3/day
b. 15.7 m3 /day
c. 43 m3 /day
d. 549 m3/day
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13. The residence time of the sludge in the digester (in days):
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14. Total dry weight of organic solids in the digested sludge is (in kg/d):
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15. Assuming no reduction in the inorganic fraction of solids during the digestion, the percentage
reduction in the total weight of solids during the digestion process is (in %):
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