250+ TOP MCQs on Sludge Characteristics, Thickening and Concentration – 2 and Answers

Waste Water Engineering Questions and Answers for Entrance exams on “Sludge Characteristics, Thickening and Concentration – 2”.

1. _________ is an aerobic process of mixing sewage sludge with agricultural by-product sources.
a) Aerobic digestion
b) Anaerobic digestion
c) Composting
d) Incineration
Answer: c
Clarification: Composting is an aerobic process of mixing sewage sludge with agricultural by-product sources of carbon such as sawdust, straw or wood chips. Bacteria digesting both the sewage sludge and the plant material generate heat to kill disease-causing micro-organisms and parasites.

2. Which of the following processes is rarely used?
a) Aerobic digestion
b) Anaerobic digestion
c) Composting
d) Incineration
Answer: d
Clarification: Incineration of sludge is less common because of air emissions concerns and the supplemental fuel (typically natural gas or fuel oil) required to burn the low calorific value sludge and vaporize residual water.

3. What is the thickened concentration of the primary sludge?
a) 1-2%
b) 2-3%
c) 3-5%
d) 5-10%
Answer: d
Clarification: The unthickened primary sludge is around 2-6%. In most cases, it is considered 2%. The thickened sludge is around 5-10%. In most cases, it is considered 5%.

4. What is the thickened concentration of the trickling filter sludge?
a) 3-6%
b) 1-3%
c) 6-9%
d) 0.5%
Answer: a
Clarification: The unthickened sludge from the trickling filter is around 1-4%. In most cases, it is considered 2%. The thickened sludge is around 3-6%. In most cases, it is considered 5%.

5. What is the thickened concentration of the thickened sludge from the rotating biological contractor?
a) 1-2%
b) 3-5%
c) 5-7%
d) 7-9 %
Answer: b
Clarification: The unthickened sludge from rotating biological contractor is around 1-3.5%. In most cases, it is considered 2%. The thickened sludge is around 3-5%. In most cases, it is considered 5%.

6. What is the thickened concentration of air activated sludge?
a) 1%
b) 5%
c) 2-3%
d) 3-6%
Answer: c
Clarification: The unthickened air activated sludge is around 0.5-1%. The thickened sludge is around 2-3%. In most cases, it is considered 2%.

7. What is the thickened concentration of extended aeration sludge?
a) 1%
b) 2-3%
c) 5%
d) 5-7%
Answer: b
Clarification: The unthickened sludge from the extended aeration is around 0.5-1%. The thickened sludge is around 2-3%. In most cases, it is considered 2%.

8. What is the thickened concentration of high purity oxygen activated sludge?
a) 1%
b) 10%
c) 2-3%
d) 3-5%
Answer: c
Clarification: The unthickened sludge from the high purity oxygen activated sludge is around 0.5-1%. The thickened sludge is around 2-3%. In most cases, it is considered 2%.

9. What is the thickened concentration of anaerobically digested primary sludge from primary digestor?
a) 1-3%
b) 5-7%
c) 10%
d) 12%
Answer: d
Clarification: The unthickened anaerobically primary digested sludge from the primary digestor is around 8%. The thickened sludge is around 12%. In anaerobic digestion, the amount of sludge produced is very high.

10. What is the thickened concentration of primary sludge combined with trickling filter humus?
a) 1-3%
b) 4%
c) 5-9%
d) 10%
Answer: c
Clarification: The unthickened primary sludge combined with trickling filter humus is 2-6 %. The thickened sludge is around 5-9%. In this case, the trickling filter humus is recycled back to the primary clarifier which gets combined with the primary sludge formed.

11. What is the thickened concentration of primary sludge combined with rotating biological contractor?
a) 1-2%
b) 3-4%
c) 5-8%
d) 9-11%