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# Multiple choice question for engineering

## Set 1

1. The maximum removal of suspended and dissolved impurities from the sewage is
a) 65
b) 70
c) 92
d) 99

Answer: c [Reason:] The maximum and minimum removal of suspended and dissolved impurities from the sewage is 92% and 65% respectively.

2. The color of the secondary sludge produced from the high rate trickling filter is
a) Gray
b) Black
c) Brown
d) Green

Answer: c [Reason:] The color of the secondary sludge produced from the high rate trickling filter is brown and the secondary sludge obtained is partially oxidized.

3. _______ is the ratio of volume of recirculated sewage to the raw sewage.
a) Recirculation factor
b) Recirculation ratio
c) Food to mass ratio
d) BOD

Answer: b [Reason:] Recirculation ratio is the ratio of volume of recirculated sewage to the raw sewage. It is denoted by R/I where, ‘R’ is the recirculated sewage and I is the volume of raw sewage.

4. The range of organic loading in kg/hectare metre/ day in a high rate trickling filter is
a) 6000-18000
b) 10000-20000
c) 5000-10000
d) 900-2200

Answer: a [Reason:] The range of organic loading in high rate trickling filter lies between 6000 to 18000 kg of 5 days BOD per hectare metre of filter media per day.

5. The expression of the recirculation factor F is given by
a) F = 1 / (1+0.1 (R/I)) 2
b) F = (1+ R) / (1+0.1 (R/I)) 2
c) F = (1+ I/R) / (1+0.1(R/I))2
d) F = (1+ R/I) / (1+0.1(R/I))2

Answer: d [Reason:] The expression of the recirculation factor F is given by F = (1+ R/I) / (1+0.1 (R/I)) 2 where, R/I represents the recirculation ratio.

6. The size of filter media in a high rate trickling filter is
a) 10-20mm
b) 34-68mm
c) 25-60mm
d) 20-50mm

Answer: c [Reason:] The size of filter media in a high rate trickling filter is 25-60mm and it can be a rock, slag or any synthetic material.

7. State whether the following statement is true or false.
Recirculation increases the efficiency of high rate trickling filters.
a) True
b) False

Answer: a [Reason:] Recirculation reduces the loading in high rate trickling filter and thus, increase the efficiency infiltration process.

8. The surface loading rate of a secondary clarifier is ______ litres/m2/day
a) 1000
b) 10000
c) 20000
d) 40000

Answer: d [Reason:] The range of surface loading rate of a secondary clarifier lies between 40,000 litres/m2/day to 70,000 litres/m2/day.

9. The detention period of a secondary clarifier is
a) 30 minutes
b) 1 hour
c) 2 hours
d) 4 hours

Answer: c [Reason:] The detention period of a secondary clarifier is between 1.5 hours to 2 hours.

10. Which of the following is the cause of rising sludge?
a) Sedimentation
b) Denitrification
c) Chlorination
d) Flocculation

Answer: b [Reason:] When nitrogen is formed in the sludge, the rise of the sludge mass takes place. This phenomena is called as rising sludge.

a) 125000
b) 50000
c) 10000
d) 20000

Answer: a [Reason:] The minimum and maximum weir loading rate of primary clarifier is 125000 and 500000 m3/m/day respectively.

12. Hopper bottom vertical flow type tank is _____ in shape.
a) Circular
b) Triangular
c) Rectangular
d) Elliptical

Answer: a [Reason:] Hopper bottom vertical flow type tank is circular in shape and it consists of conical hoppers.

## Set 2

1. The minimum spacing between the bars on fine screen is
a) 0.3mm
b) 0.9mm
c) 1.5mm
d) 0.5mm

Answer: c [Reason:] The range of space between the bars in fine screen is 1.5-3mm having minimum spacing as 1.5mm.

2. The spacing between the bars in racks is
a) 30mm
b) 50mm
c) 70mm
d) 90mm

Answer: b [Reason:] The spacing between the bars in racks is 50mm. It is commonly called as coarse screen.

3. Screens are inclined to the direction of flow to
a) Increase the flow velocity
b) Increase the opening area
c) Decrease the flow velocity

Answer: c [Reason:] Screens are inclined to the direction of flow to decrease the flow velocity in order to increase the efficiency of the screen.

4. The maximum spacing between the bars in medium screen is
a) 40mm
b) 50mm
c) 70mm
d) 90mm

Answer: a [Reason:] The range of space between the bars in fine screen is 7-40mm having maximum spacing as 40mm.

5. __________ is used to cut the sewage into smaller parts.
a) Flocculator
b) Tube settlers
c) Shredders
d) Aerators

Answer: c [Reason:] Shredder is a device which is used to cut large size sewage particles into smaller size. It is composed of screens and cutting teeth.

6. What is the maximum capacity of medium screen in collecting solids?
a) 30L
b) 40L
c) 50L
d) 90L

Answer: d [Reason:] Medium screen can collect up to the maximum capacity of 90L of solids per 106 L of effluent.

7. The head loss through the screen is given by HL = k* (Vt2 – Va2), where Vt and Va are velocities through and above the screen respectively. What is the value of constant k?
a) 1
b) 0.0050
c) 0.0729
d) 0.0236

Answer: c [Reason:] The expression for the head loss through the screen is given by HL = 0.0729* (Vt2 – Va2), where Vt and Va are the velocities through and above the screen respectively.

## Set 3

1. How many types of settling are there in sedimentation tank?
a) 3
b) 4
c) 5
d) 6

Answer: b [Reason:] There are 4 types of settling in sedimentation tank, namely Flocculent, Discrete, Compression and Hindered settling.

2. In which type of settling, sedimentation of discrete particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling

Answer: d [Reason:] In Discrete settling, sedimentation of discrete particles takes place where the particles have little tendency to flocculate.

3. The settling velocity of spherical particle is given by
a) Darcy Weisbach equation
b) Hazen and William equation
c) Stokes equation
d) Bernoulli’s equation

Answer: c [Reason:] The settling velocity of spherical particle is given by stokes equation where vS = (g/18) * (G-1) d2 /v when diameter d is less than 0.1mm.

4. In the expression vS = 1.8 (g*d (G-1)) 1/2, the diameter of spherical particle is
a) 0.1mm
b) < 0.1mm
c) 1mm
d) >1mm

Answer: d [Reason:] The settling velocity of spherical particle is given by stokes law and when the diameter d of spherical particle is > 1mm, settling velocity is given by vS = 1.8 (g*d (G-1)) 1/2 where G is the specific gravity of the particle.

5. In which type of settling, settling of particles takes place by the contact of impurities with each other present in wastewater?
a) Flocculent settling
b) Hindered settling
c) Compression settling
d) Discrete settling

Answer: c [Reason:] When large amounts of impurities is present in water, they contact each other in the compression zone and compression settling takes place.

6. _______ is formed when alum is added to sewage.
a) Acid
b) Floc
c) Salt
d) Base

Answer: b [Reason:] When a coagulant is added to sewage, then a gelatinous precipitate called floc is formed and flocculent settling takes place.

7. In which settling type, dilute suspension of particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling

Answer: c [Reason:] In this type of settling, particle mass increase and it settle down due to flocculation.

## Set 4

1. How many types of sedimentation tanks are there on the basis of method of operation?
a) 2
b) 3
c) 4
d) 5

Answer: a [Reason:] There are two types sedimentation tanks on the basis of method of operation, namely Fill and draw type and Continuous flow type.

2. In which type of sedimentation, the flocculent suspension of the intermediate concentration takes place?
a) Type I sedimentation
b) Type II sedimentation
c) Type III sedimentation
d) Type IV sedimentation

Answer: c [Reason:] In type III sedimentation, the inter-particle forces hold the particle together and the flocculent suspension of the intermediate concentration takes place.

3. In which type of sedimentation,the flocculent suspension of high concentration takes place?
a) Type I sedimentation
b) Type II sedimentation
c) Type III sedimentation
d) Type IV sedimentation

Answer: d [Reason:] In type IV sedimentation,the flocculent suspension of high concentration takes place and particles comes in contact with each other resulting in the formation of structure.

4. When the impurities are separated by the gravitation of settling particles, the operation is called ______
a) Sedimentation with coagulant
b) Plain sedimentation
c) Secondary sedimentation
d) Disinfection

Answer: b [Reason:] In plain sedimentation, the impurities are separated from a suspending fluid by use of natural forces like gravitational forces.

5. What is the settling velocity of the particle in the wastewater if its diameter is 2 * 10-3cm. Given G=2.65, viscosity v=8 * 10-3cm2/Sec?
a) 0.01cm/Sec
b) 0.13cm/Sec
c) 0.24cm/Sec
d) 0.36cm/Sec

Answer: b [Reason:] Settling velocity of the particle in wastewater is given by vs=g (G-1) d2/18v Specific gravity G=1, g=981cm2/Sec, viscosity v=8 * 10-3cm2/Sec vs = 981 * (2.65-1) * 0.002 * 0.002/(18 * 0.008) = 0.13cm/Sec.

6. In a rectangular horizontal flow tank, the maximum permissible velocity is ____ m/Sec.
a) 3
b) 0.3
c) 0.03
d) 0.003

Answer: b [Reason:] In the rectangular tank, the ideal conditions are that the flow is horizontal, velocity is uniform in all directions and the maximum permissible limit of velocity is 0.03m/Sec.

7. The time period for which the water is stored in a sedimentation tank is called _____
a) Time of flow
b) Frequency of flow
c) Settling time
d) Detention period

Answer: d [Reason:] Detention period is the time period at which the water is stored in a tank. It varies for different purposes like in the septic tank or oxidation pond, its value is higher.

8. In a fill and draw type sedimentation tank, a detention period of ____ hours is provided.
a) 6
b) 12
c) 18
d) 24

Answer: d [Reason:] In this tank, water is detained for 24 hours. Then cleaning is done for 6-12 hours, so, the whole operation takes 30-36 hours.

## Set 5

1. State whether the following statement is true or false.
The intermittent sand filters have better BOD removal efficiency than trickling filters.
a) True
b) False

Answer: b [Reason:] The trickling filters have the best BOD removal efficiency in comparison to the types of filters used in aerobic treatment with a maximum value of 95%.

2. The filter material used in contact bed is
a) Sand
b) Stone ballast
c) Gravel
d) Fine sand

Answer: b [Reason:] The filter material used in contact bed is broken stones called as stone ballast.

3. Which of the following is called as contact bed?
a) Primary clarifier
b) Secondary clarifier
c) Contact filter
d) High rate digester

Answer: c [Reason:] Contact filters are water tight tanks which are used for the aerobic treatment of sewage. They are also called as contact bed.

4. How many types of trickling filters are used in sewage treatment?
a) 6
b) 5
c) 3
d) 2

Answer: d [Reason:] The trickling filters are divided into conventional and high rate trickling filters.

5. The depth of the filter media of intermittent filter is
a) 45cm
b) 60cm
c) 20cm
d) 25cm

Answer: b [Reason:] The minimum depth of filter media of intermittent filter is 60cm. These filters give highly nitrified effluent.

6. Which of the following filter is used in anaerobic treatment of sewage?
a) Intermittent sand
b) Trickling filter
c) Contact filter
d) Biological filter

Answer: d [Reason:] Biological filter is used in anaerobic treatment, whereas intermittent sand filter, trickling filter and contact filter are used in aerobic treatment of sewage.

7. The maximum size of filter media of a percolating filter is
a) 10mm
b) 25mm
c) 60mm
d) 75mm

Answer: d [Reason:] The minimum and maximum size of filter media of a percolating filter is 25mm and 75mm respectively.

8. The recirculation ratio for the low rate trickling filter is
a) 1
b) 2
c) 3
d) 0