# Environmental Engineering Questions and Answers – Sludge Thickening, Sludge Dewatering

This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Sludge Thickening, Sludge Dewatering”.

1. The design solid surface loading in an activated sludge process is ___________
a) 10 kg/m2/day
b) 25 kg/m2/day
c) 15 kg/m2/day
d) 35 kg/m2/day

Explanation: The design solid surface loading during a gravity thickening process in an activated sludge plant lies between 25 to 30 kg/m2/day.

2. Which of the following plant nutrient is not found in municipal sewage?
a) Arsenic
b) Phosphorous
c) Potassium
d) Nitrogen

Explanation: Potassium, Phosphorous and Nitrogen are found in municipal sewage having maximum plant nutrient concentration of 3.3% of total municipal waste as nitrogen.

3. The design pressure of ____ is applied on pressure type flotation device.
a) 1kg/cm2
b) 2kg/cm2
c) 3kg/cm2
d) 6kg/cm2

Explanation: In pressure type flotation device, 3-5kg/cm2 pressure is applied to the sludge thickening process.

4. The design Hydraulic loading rate of the gravity thickener is _______ m3/m2/day.
a) 20
b) 39
c) 40
d) 85

Explanation: The range of design Hydraulic loading rate of the gravity thickener is 20-25m3/m2/day.

5. Which of the following process is not involved in sludge thickening?
a) Gravity thickening
b) Vacuum filter
c) Air flotation
d) Centrifugation

Explanation: The process involved in sludge thickening are gravity thickening, air flotation and centrifugation.

6. 7% of solids concentration of thickened sludge is obtained from gravity thickener. What is the type of sludge?
a) Primary sludge
b) Secondary sludge
c) Tertiary sludge
d) Activated sludge

Explanation: When the thickened sludge, solid concentration is between 7-9, the type of sludge obtained from gravity thickner is activated.

7. Which of the following is not used for drying of sludge?
a) Multiple effect evaporation
b) Dual effect evaporation
c) Rotary dryer
d) Spray dryer

Explanation: The process used for drying of sludge is multiple effect evaporation, rotary dryer, spray dryer and flash dryer.

8. In which of the following method, the sludge is rotated for dewatering process?
a) Centrifugation
b) Drying lagoon
c) Drying bed
d) Vacuum filter

Explanation: In the centrifugation process, the force is applied so that rotation of sludge takes place which helps in the dewatering of sludge.

9. The dewatered sludge cannot be disposed by ___________
a) Composting
b) Heat drying
c) Acid fermentation
d) Incineration

Explanation: Acid fermentation is a sludge digestion process and composting, heat drying and incineration are the methods of disposal of dewatered sludge.

10. In which of the following process, the sludge is dried and disposed in land?
a) Centrifugation
b) Drying lagoon
c) Drying bed
d) Vacuum filter

Explanation: Good amount of dried solids is produced by drying bed process and they are commonly used in the sludge dewatering process due to their low cost and better efficiency.

11. Which of the following is not a drying bed?
a) Wedwire beds
b) Artificial media
c) Filter press
d) Conventional sand

Explanation: There are 5 types of drying beds, namely wedwire beds, artificial media, conventional sand, paved and vacuum assisted drying bed.

12. Which of the following is not suitable for dewatering of raw sludge?
a) Centrifugation
b) Drying lagoon
c) Drying bed
d) Vacuum filter

Explanation: In drying lagoon, if raw sludge is used that contains supernatant liquor, foul smell and fly nuisance occur in the dewatering process.

13. Which of the following is not a part of dewatering process?
a) Drying bed
b) Air flotation
c) Vacuum filter
d) Drying lagoon

Explanation: Air flotation is a part of the sludge thickening process and drying bed, drying lagoon and vacuum filter are part of the dewatering process.

Sanfoundry Global Education & Learning Series – Environmental Engineering.

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