Question 1
__________ wastewater treatment plant may or may not need the screens.
A. Domestic
B. Industrial
C. Sewage
D. Chemical
View Answer
Answer: Option B
Explanation:
Industrial wastewater treatment plant may or may not need the screens. Screens must be provided even for industrial wastewater treatment plant to separate labels, stopper, cardboard, and other packing materials.
Question 2
At what angle generally a coarse manual screen is placed?
A. 60 degree
B. 50 degree
C. 65-70 degree
D. 30-45 degree
View Answer
Answer: Option D
Explanation:
The coarse screens are generally placed at 30-45 degree. This holds good only for a manual screen. For a mechanical screen the angle is between 0-30 degrees.
Question 3
Comminutors are usually installed in which size of water treatment plants?
A. 0.2 m3/sec
B. <0.2 m3/sec
C. 0.5 m3/sec
D. 1 m3/sec
View Answer
Answer: Option B
Explanation:
Comminutors are usually installed in plants which are <0.2 m3/sec. These are installed in order to shred material. These require high operating and maintenance cost.
Question 4
How is the headloss for a fine screen calculated?
A. hL= 1/2g(Q/CA)2
B. hL= 1/g(Q/CA)2
C. hL= 1/2g(Q/C)2
D. hL= 1/2g(Q/CA)
View Answer
Answer: Option A
Explanation:
The headloss for a fine screen is calculated as hL= 1/2g (Q/CA)2. Where hL is the headloss through the fine screen. Q is the flow rate, A is the effective open are of the submerged screen.
Question 5
How many types of screens are present?
A. 3
B. 4
C. 2
D. 5
View Answer
Answer: Option C
Explanation:
Screens can be broadly classified into two types depending upon the opening size provided as coarse screen (bar screens) and fine screens. There are manually cleaned screens and mechanically cleaned screens based on the cleaning operation.
Question 6
In drum type screen, which axis does the drum rotate?
A. Horizontal
B. Vertical
C. Irregular
D. Horizo-vertical
View Answer
Answer: Option A
Explanation:
The drum-type screen consists of a cylinder covered by a screen cloth with the drum rotating on a horizontal axis, slightly less than half submerged. Wastewater enters the inside of the drum at one end and flows outward through the screen cloth.
Question 7
Installing screens at an angle allows easier cleaning.
A. True
B. False
View Answer
Answer: Option A
Explanation:
Screens are placed either vertically or at an angle in the flow channel. Installing screens at an angle allows easier cleaning (particularly if by hand) and more screen area per channel depth, but obviously requires more space.
Question 8
From which of these type of screens there is a possibility of odour emission?
A. Catenary
B. Reciprocating rake
C. Continuous belt
D. Chain driven screen
View Answer
Answer: Option A
Explanation:
Catenary screens have an open design. Due to this construction, there is a possibility that they might emit odour. These screens also remove large objects.
Question 9
Lower the velocity through the screen, the ________ is the amount of screening that would be removed.
A. Lower
B. Greater
C. Lesser
D. Stronger
View Answer
Answer: Option B
Explanation:
The velocity of flow ahead of and through a screen varies materially and affects its operation. Lower the velocity through the screen, the greater is the amount of screening that would be removed.
Question 10
Screen is the first unit operation in wastewater treatment plant.
A. True
B. False
View Answer
Answer: Option A
Explanation:
Screen is the first unit operation in wastewater treatment plant. This is used to remove larger particles of floating and suspended matter by coarse screening. A set of inclined parallel bars, fixed at certain distance apart in a channel helps to accomplish this.
Question 11
The head lost by water flowing in a channel as a result of turbulence caused by the velocity of the flowing water is called ________
A. Putrefaction
B. Buffer
C. Head
D. Head loss
View Answer
Answer: Option D
Explanation:
The head, pressure or energy lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water, channel walls or restrictions caused by fittings.
Question 12
What is the amount of BOD removed by a fixed parabolic fine screen?
A. 25-40 %
B. 40-50%
C. 5-20%
D. 30-40%
View Answer
Answer: Option C
Explanation:
The amount of BOD removed by a fixed parabolic fine screen is 5-20%. The amount of TSS is removed 5-30%. Compared to a rotary drum fine screen, the efficiency of these screens is low.
Question 13
What is the approach velocity for grit bearing wastewaters?
A. 0.2-0.3 m/s
B. 0.6-0.75 m/s
C. 0.5-0.75 m/s
D. 0.45-0.60 m/s
View Answer
Answer: Option B
Explanation:
The approach velocity of 0.6 to 0.75 m/sec for the grit bearing wastewaters is suggested. Accordingly, the bed slope of the channel should be adjusted to develop this velocity.
Question 14
What is the headloss for fine screens?
A. 0.8-1.4m
B. 2-2.5m
C. 3-3.5m
D. <0.8 m
View Answer
Answer: Option A
Explanation:
The head loss for fine screens would be 0.8-1.4m. In many applications fine screens is limited to plants where head loss through screens is not a problem. Water sprays are supplied in order to keep the screens clean continuously.
Question 15
What is the headloss through a communitor?
A. 0.3-0.4 m
B. 0.1-0.3 m
C. 0.5-0.6 m
D. 0.6-0.7 m
View Answer
Answer: Option B
Explanation:
The headloss through the communitor is 0.1-0.3m. In large units it can approach 0.9m. These may be preceded by grit chambers.
Question 16
What is the hydraulic loading rate for a microscreen?
A. 1-3 m3/m2.min
B. 7-9 m3/m2.min
C. 3-6 m3/m2.min
D. 10-12 m3/m2.min
View Answer
Answer: Option C
Explanation:
The hydraulic loading rate for a microscreen is 3-6 m3/m2.min. The hydraulic loading rate is based on the submerged surface area of the drum. The drum diameter is 2-2.5 m.
Question 17
What is the mathematical representation of hydraulic loses through a screen?
A. hL= 1/C(V2/2g)
B. hL= 1/C(V2-v2/2g)
C. hL= 1/C(V2-v2/g)
D. hL= 1/C(V2/g)
View Answer
Answer: Option B
Explanation:
The hydraulic loss/ head loss is represented as hL= 1/C(V2-v2/2g) .Where hL is the head loss of the screen and C is the empirical discharge coefficient. V is the velocity of the bar screen through the openings, v is the approach velocity in the upstream and g is the acceleration due to gravity (9.81m/s).
Question 18
What is the maximum allowable approach velocity for a bar screen at peak flow rates?
A. >0.9 m/s
B. <0.9m/s
C. 1-2 m/s
D. 2.5m/s
View Answer
Answer: Option B
Explanation:
The approach velocity at peak flow rates for a bar screen should not exceed 0.9m/s. This is to prevent the pass-through of debris. These screens should be designed in such a way to prevent accumulation of debris or grit.
Question 19
What is the maximum allowable head loss for a manual coarse screen?
A. 150mm
B. 300 mm
C. 200 mm
D. 100mm
View Answer
Answer: Option A
Explanation:
The maximum allowable head loss for a manual coarse screen is 150 mm. For a mechanical screen, it ranges from 150-600mm. The maximum approach velocity for a manual screen is 0.3-0.6 m/s.
Question 20
What is the opening of fine screens?
A. 0.5 inch
B. 1 inch
C. 0.25 inch
D. 0.15 inch
View Answer
Answer: Option C
Explanation:
Fine screens have openings of less than 0.25 in. and are used to remove solids smaller than those retained on bar racks. They are used primarily in water or wastewater containing little or no coarse solids.
Question 21
What is the removal efficiency of TSS in case of microscreens?
A. 80-85%
B. 85-90%
C. <10%
D. 10-80%
View Answer
Answer: Option D
Explanation:
The removal efficiency of the TSS by microscreens is around 10-80%. Usually it is around 55 % in most of the cases. Microscreens can’t handle solid fluctuations.
Question 22
What is the size of the openings for a microscreen?
A. 35-50µm
B. 10-35µm
C. 50-60µm
D. 60-6µm
View Answer
Answer: Option B
Explanation:
The size of the openings for a microscreen range from 10-35µm. Microscreens utilize the use of variable low speed. This speed is up to 4r/min.
Question 23
What is the typical headloss through the microscreens?
A. 150-200mm
B. 75-150mm
C. <75mm
D. >200mm
View Answer
Answer: Option B
Explanation:
The typical headloss through the microscreens is 75-150mm. In case the headloss exceeds 200 mm then bypasss should be provided. The mesh is generally made up of stainless steel.
Question 24
What should be installed in order to control the velocity of the bar screens?
A. Sluice gate
B. Grit chamber
C. Parshall flume
D. Hoppers
View Answer
Answer: Option C
Explanation:
Parshall flumes are installed at the downstream of a bar screen. These are installed in order to control the approach velocity of a bar screen. The approach velocity is a very important factor while designing the screens to prevent the accumulation of grit and debris.
Question 25
Which of the following does the quantity of screening does not depend on?
A. Type of rack
B. Type of screen
C. Type of sewer system
D. Temperature
View Answer
Answer: Option D
Explanation:
The quantity of screening depends on the type of rack or screen used as well as sewer system and geographic location. The quantity of screening removed by bar screen is 0.0035 to 0.0375 m3 / 1000 m3 of wastewater treated (Typical value = 0.015 m3 /1000 m3 of wastewater).
Question 26
Which of the following is true for screens and comminutors?
A. Unit operation
B. Unit process
C. Chemical treatment
D. pH balancer
View Answer
Answer: Option A
Explanation:
The primary treatment incorporates unit operations for removal of floating and suspended solids from the wastewater. They are also referred to as the physical unit operations. The unit operations used are screening for removing floating papers, rages, cloths, plastics, cans stoppers, labels, etc.
Question 27
Which of these screens can handle very large particles?
A. Reciprocating rake
B. Continuous belt
C. Front clean/Front return
D. Front clean/back return
View Answer
Answer: Option A
Explanation:
Reciprocating rake is a type of mechanically driven screen. This can handle very large particles. This has relatively low operating and maintenance cost.
Question 28
Which of these screens have a very large footprint?
A. Reciprocating
B. Continuous belt
C. Catenary
D. Chain driven
View Answer
Answer: Option C
Explanation:
Catenary screens are placed at an angle 45-75 degree. Due to this reason, it has a very large footprint.
Question 29
Which of these screens is used to remove secondary suspended solids?
A. Medium drum rotary screen
B. Fine drum rotary screen
C. Tangential fine screen
D. Horizontal reciprocating screen
View Answer
Answer: Option B
Explanation:
Fine drum rotary screens are used to remove secondary suspended solids. The mesh is generally made up of stainless steel. The screen cloth would be polyester material.
Question 30
Which of these type of screen can be used both as a fine and coarse screen?
A. Continuous belt
B. Catenary
C. Reciprocating
D. Chain driven
View Answer
Answer: Option A
Explanation:
A continuous belt type screen can be used both as a fine and coarse screen. This is because the screen openings range from 0.5-30 mm. This is a continuous self- cleaning screen.
Question 31
With respect to the operation which of these screens is the most expensive?
A. Chain driven
B. Continuous belt
C. Catenary
D. Reciprocating
View Answer
Answer: Option B
Explanation:
For a continuous belt replacement of screen is a time consuming process. Also this is a very expensive process. Hence the Continuous belt screen is considered the most expensive type of screen.