Waste Water Engineering Multiple Choice Questions on “Tube Settlers”.
1. Tube settlers are used to increase the settling capacity of ______
a) Flocculation unit
b) Clarifier
c) Sand filter bed
d) Flash mixing unit
Answer: b
Clarification: Tube settlers and parallel plates increase the settling capacity of circular clarifiers and/or rectangular sedimentation basins by reducing the vertical distance a floc particle must settle before agglomerating to form larger particles.
2. A floc particle must settle after agglomerating to form larger particles.
a) True
b) False
Answer: b
Clarification: Tube settlers decrease the vertical distance of settling. Hence the floc particles settle faster. A floc particle must settle before agglomerating to form larger particles.
3. What is the angle of slope in tube settlers?
a) 30˚
b) 60˚
c) 90˚
d) 180˚
Answer: b
Clarification: Tube settlers use multiple tubular channels sloped at an angle of 60° and adjacent to each other, which combine to form an increased effective settling area. This provides for a particle settling depth that is significantly less than the settling depth of a conventional clarifier, reducing settling times.
4. The fine flocs escape and cannot b captured by tube settlers.
a) True
b) False
Answer: b
Clarification: Tube settlers capture the settleable fine floc that escapes the clarification zone beneath the tube settlers and allows the larger floc to travel to the tank bottom in a more settleable form.
5. The settling depth provided by tube settlers is _________ than the actual settling depth.
a) Less
b) Greater
c) Equal
d) Nearer
Answer: a
Clarification: The multiple tubular sections combine to form an effective settling area. This provides for a particle settling depth that is significantly less than the settling depth of a conventional clarifier, reducing settling times.
6. What is the angle at which a tube settler is usually inclined at?
a) 45-60 degree
b) 45 degree
c) 60 degree
d) >60 degree
Answer: a
Clarification: The tube settler removes suspended solids. It is classified as a secondary treatment. This is inclined at a position at 45-60 degree.
7. What would happen if the tube settler is inclined greater than 60 degrees?
a) The efficiency will increase
b) The efficiency will decrease
c) Colour will be removed
d) Odour will be removed
Answer: b
Clarification: The tube settler is usually after a flash mixer and flocculator. It is usually inclined at 45-60 degrees. In case it is inclined more than 60 degrees than the efficiency reduces.
8. What would happen if the tube settler is inclined at an angle lesser than 45 degrees?
a) Solids will accumulate in the plates
b) Efficiency Increases
c) It becomes 100 percent efficient
d) You don’t require a flocculator prior to it
Answer: a
Clarification: Usually the tube settlers are inclined at an angle 45-60 degree. This is usually classified as secondary treatment. In case the tube settlers are placed at an angle lesser than 45 degrees then this results in accumulation of solids between the plates.
9. What is the nominal spacing between the plates?
a) 1 inch
b) 2 inch
c) 3 inch
d) 4 inch
Answer: b
Clarification: The nominal spacing between the plates are 2 inches. These are inclined at a length of 2-3 m. To control biological growth, the accumulated solids must be flushed periodically.
10. Tube settlers are operated in which mode?
a) Concurrent
b) Countercurrent
c) Cross flow
d) Hindered settling
Answer: b
Clarification: Tube settlers are operated in a countercurrent mode. The water is passed from the bottom and flows upwards and exists from the basin above the modules. The solids that settle within the tube settle down due to gravity.
11. What is the mathematical representation when many plates are used?
a) V=Q/Nwb
b) V= Q x Nwb
c) V= Q/Nw
d) V=Q x Nw
Answer: a
Clarification: When a number of plates are used V= Q/Nwb. Where V = settling velocity. Q is the flowrate. N is the number of plates. w is the perpendicular distance between the surfaces. b is the dimensions of the surface at right angles to w.
12. Which of these represent the settling velocity of tubesettlers?
a) 11-15 m2/mm3
b) 20-25 m2/mm2
c) 40-45 m2/mm2
d) 30-35 m2/mm2
Answer: a
Clarification: The surface loading rate of tube settlers is 11-15 m2/mm2. Based on this the area required is calculated. Also the number of tube settlers is then calculated.
13. Calculate the area of the tube settlers for the given data:
Flow: 1500 mm3/h
Surface loading rate: 7 m2/m3/h
a) 215 m2
b) 300 m2
c) 400 m2
d) 500 m2
Answer: a
Clarification: Area= Flow rate/ Surface loading rate. This is represented as mm2. Area = 1500/7 = 215 mm2.