Engineering Questions with Answers - Multiple Choice Questions

Environmental Engineering MCQ’s – Sludge Thickening, Sludge Dewatering

1 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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

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

7 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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