Category: Environmental Engineering Objective Questions

Environmental Engineering Multiple Choice Questions on “Types of Screens and Aerators”.

1. Which process of water treatment is done to avoid floating debris, branches, trees or other large particles suspended in water?
a) Screening
b) Aeration
c) Primary sedimentation
d) Secondary sedimentation
Answer: a
Clarification: Screens are used as a pretreatment process for purification of water to avoid large size suspended materials from water.

2. What is the size of the coarse screen used in pretreatment of water?
a) 25mm
b) 50mm
c) 75mm
d) 100mm
Answer: a
Clarification: Coarse screens are used in the form of bars of 25mm diameter size and are spaced at 75 to 100mm centers.

3. The coarse screen is inclined at _____ to facilitate the cleaning or raking.
a) 300
b) 350
c) 450
d) 900
Answer: c
Clarification: The coarse screen is inclined at 450-600 so that they can be easily cleaned with a rake. Moreover, it reduces the flow velocity which also helps in cleaning the screen.

4. The head loss through screen depends on _______________
a) Shape of screen elements
b) Open area, block area
c) Approach velocity
d) Nature of their construction, approach velocity
Answer: d
Clarification: The head loss through the screen is given by, h=B (w/b) 4/3h1*sinx Where h=head loss, h1=approach velocity head, b=minimum width, x=angle of rack, B=shape factor. It also depends on the nature of their construction.

5. The shape factor for circular rods in finding the head loss through the screen is _____
a) 1.79
b) 2.42
c) 1.83
d) 1.45
Answer: a
Clarification: The shape factor rectangular bar with sharp edges is 2.42, for semicircular face is 1.83 and for circular rod is 1.79.

6. Micro strainers are used to remove color in water.
a) True
b) False
Answer: b
Clarification: Micro strainers are used for screening stored water which contains plankton, algae and other microscopic particles.

7. Identify the incorrect statement regarding aeration process.
a) It removes taste and odor
b) It increases the dissolved oxygen content of water
c) It increases the carbon dioxide content of water
d) It is used for mixing chemicals with water
Answer: c
Clarification: Aeration reduces the carbon dioxide content and corrosiveness of water and hence, raises the pH value of water.

8. The reduction of carbon dioxide by cascade aerators is in the range of __________
a) 10-20%
b) 20-30%
c) 40-50%
d) 50-60%
Answer: d
Clarification: Cascade aerators are the gravity aerators in which water falls from 1-3m height such that it comes in contact with air and reduces carbon dioxide content to 50-60%.

9. In which type of aerator, the flow of water is divided into fine streams and small droplets?
a) Cascade aerator
b) Inclined apron aerator
c) Spray aerator
d) Gravel bed aerator
Answer: a
Clarification: In Cascade aerator, the flow of water is divided into fine streams and small droplets such that they come in contact with air in their trajectories and reduces CO2 by 70-90%.

10. The elapsed time in gravity filter is 1sec. What is the height of fall in a single descent?
a) 4.4m
b) 4.9m
c) 8.8m
d) 9.8m
Answer: b
Clarification: t = 1sec, g = 9.8
Elapsed time, t = (2h/g) 1/2 in a single descent.
Height of fall, H = t2g/2 = 1*1*9.8/2 = 4.9m.

11. ______ are used in fine screen so that they do not get clogged up.
a) Automatic strainers
b) Spray aerators
c) Cascade aerators
d) Gravel bed aerators
Answer: a
Clarification: Automatic strainers are self cleaning devices that remove solids from the flowing liquid continuously and help in a fine screen so that it does not get clogged up.

Environmental Engineering Multiple Choice Questions on “Chlorination”.

1. Which of the following is termed as free available chlorine?
a) Hypochlorous acid
b) Hypochlorite ions
c) Molecular chlorine
d) Hypochlorous acid, Hypochlorite ions, Molecular chlorine
Answer: d
Clarification: The chlorine existing in water as hypochlorous acid, hypochlorite ions, molecular chlorine is termed as free available chlorine.

2. At what pH, chlorine exists as molecular chlorine?
a) 3
b) 5
c) <5
d) <10
Answer: c
Clarification: When chlorine is added to water, the chlorine acts as molecular chlorine only when its pH is less than 5.

3. When the pH is between 5 and 10, the chlorine in the water acts as ______
a) Hypochlorous acid
b) Hypochlorite ions
c) Molecular chlorine
d) Hypochlorous acid hypochlorite ions
Answer: d
Clarification: When the pH is between 5 and 10, the chlorine in the water acts as hypochlorous acid and hypochlorite ions. As pH increases, the concentration of hypochlorous acid decreases while of hypochlorite ions increases.

4. At what pH, chlorine in water acts as only hypochlorite ions?
a) <5
b) >5
c) >10
d) <3
Answer: c
Clarification: HOCl <——> H⁺ + HOCl^–
Where, HOCl is hypochlorous acid and HOCl^– is hypochlorite ions.
At pH<10, only HOCl^– is produced.

5. The hypochlorous acid is ______ times effective as hypochorite ions.
a) 10
b) 30
c) 50
d) 80
Answer:d
Clarification: The hypochlorous acid is 80 times more effective as hypochorite ions, so the pH of water to be treated should be less than 7 to prevent the ionization of it.

6. Chlorine which gets consumed in the oxidation of impurities before disinfection is ______________
a) Free chlorine
b) Residual chlorine
c) Chlorine demand
d) Residual demand
Answer: c
Clarification: Chlorine has the oxidizing power which oxidizes organic and inorganic impurities present in water and the amount of chlorine, which gets consumed before disinfection is called as chlorine demand.

7. The chlorine, which serves as a disinfectant is ___________
a) Free chlorine
b) Free Residual chlorine
c) Chlorine demand
d) Residual demand
Answer: b
Clarification: When chlorine demand is fulfilled, then chlorine is available s free residual chlorine, which contains hypochlorous acid and hypochlorite ions.

8. The permissible limit of free residual chlorine is ___________
a) 0.02ppm
b) 0.2ppm
c) 1ppm
d) 2ppm
Answer: b
Clarification: The water is satisfactorily disinfected if the free residual chlorine is 0.2 ppm at the contact period of 10 minutes.

9. What is the chemical formula of bleaching powder?
a) Ca (OCl)₂
b) Ca (OCl)
c) Ca (OCl)₃
d) CaCl₂
Answer: a
Clarification: The chemical formula of bleaching powder is Ca (OCl)₂. It is called as chlorinated lime.

10. Bleaching powder contains ______ of available chlorine.
a) 16%
b) 33.3%
c) 66.6%
d) 99.9%
Answer: b
Clarification: Bleaching powder contains 33.3% of available chlorine. It loses its strength during storage and therefore, it is used during emergency conditions.

11. The process of chlorination with hypochlorites is called ___________
a) Super chlorination
b) Pre chlorination
c) Post chlorination
d) Hypo-chlorination
Answer: d
Clarification: The process of chlorination with hypochlorites is called Hypo-chlorination.
Hypochlorites are applied to water as a solution by the hypochlorite feeding apparatus.

12. Normally, the ratio of ammonia and chlorine in chloramine is?
a) 1:1
b) 1:2
c) 1:4.5
d) 1:3.5
Answer: c
Clarification: Normally, the ratio of ammonia and chlorine in chloramine is 1:4.5. They are more effective than chlorine.

13. Which type of chloramine is formed when pH of water is 4.4?
a) Monachloramine
b) Dichloramine
c) Trichloramine
d) Both monochloramine and dichloramine
Answer: b
Clarification: When the pH<4.4, then trichloramine is formed and when pH lies in the range 4.4-5, then only dichloramine is formed.

14. What is the contact period for disinfection with chloramine?
a) 1hour
b) 2hours
c) 3hours
d) 4hours
Answer: b
Clarification: The disinfecting reaction with chloramine are slower than with chlorine alone, so the contact period of 2 hours is provided.

Environmental Engineering Questions for Aptitude test on “Selection of Pumping Units”.

1. The plot of total dynamic head and discharge of a pump is called ____________
a) Dynamic head curve
b) System head curve
c) Pump curve
d) Discharge curve
Answer: b
Clarification: The plot of total dynamic head and discharge of a pump is called system head curve and each point on it denotes the head which consists of total static head, head loss in suction and delivery pipe.

2. _______ is the point of intersection of system head curve with the characteristic curve of the pump.
a) Discharge point
b) Operating point
c) Velocity head
d) Pumping point
Answer: b
Clarification: The operating point is the point of intersection of system head curve with the head – discharge characteristic curve of the pump. It is also called as operating range.

3. Which of the following is not included in the friction head?
a) Head Loss in entire length of piping
b) Total static head
c) Head Loss in bend tees
d) Head Loss in valves
Answer: b
Clarification: The friction head is the sum of head Loss in the entire length of piping, head Loss in bend tees and head Loss in valves.

4. When the pumps are in parallel operation?
a) H = H₁ + H₂
b) 1/H = 1/H₁ +1/ H₂
c) Q = Q₁ + Q₂
d) 1/Q = 1/Q₁ + 1/Q₂
Answer: c
Clarification: When the pumps are in parallel operation, then the total discharge is equal to the sum of the discharges by each pump i.e Q = Q₁ + Q₂.

5. When the pumps are in series operation?
a) H = H₁ + H₂
b) 1/H = 1/H₁ +1/ H₂
c) Q = Q₁ + Q₂
d) 1/Q = 1/Q₁ + 1/Q₂
Answer: a
Clarification: When the pumps are in series operation, then at a given discharge, total head is equal to the sum of heads added by each pump i.e H = H₁ + H₂.

6. The efficiency of the pump at half load is ____________
a) 50%
b) 70%
c) 80%
d) 100%
Answer: b
Clarification: The efficiency of a pump depends on the amount of load. At half load, the efficiency of the pump is 70%.

7. The efficiency of the pump at quarter load is ____________
a) 50%
b) 70%
c) 80%
d) 100%
Answer: a
Clarification: The efficiency of the pump at quarter load is 50% and at full load, the efficiency of the pump is 80%.

8. The installed capacity of the pump does not depend on which of the following?
a) The maximum rate of hourly demand
b) Balancing storage
c) Power of pump
d) Operation schedule
Answer: c
Clarification: The installed capacity of the pump depends on three factors, namely- balancing storage, the maximum rate of hourly demand and the operation schedule. The installed capacity of the pump is kept larger than the maximum rate of demand.

9. If the diameter of pumping mains decreases, then the total dynamic head will increase.
a) True
b) False
Answer: a
Clarification: If the diameter of pumping mains decreases, then the velocity of flow will increase for a given fixed discharge resulting in the increase of friction head loss and velocity head and ultimately increases the total dynamic head.

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Environmental Engineering Interview Questions for Experienced people on “Joints and Shapes of Sewers and Cleaning, Maintenance and Ventilation of Sewer”.

1. How many types of joints are present in the sewer?
a) 3
b) 4
c) 5
d) 7
Answer: d
Clarification: There are 7 types of joints in the sewer, namely Bell and spigot, Collar, Simplex, Flexible, Mechanical and Open joints.

2. The ratio of cement mortar used in Bell and spigot joint is?
a) 1:1
b) 1:6
c) 2:1
d) 1:3
Answer: a
Clarification: In Bell and spigot joint, the ratio of cement and mortar used is 1:1 in the space provided between bell and spigot end.

3. The ratio of cement mortar used in the Collar joint is?
a) 1:2
b) 1:6
c) 2:1
d) 1:1
Answer: a
Clarification: In the Collar joint, the ratio of cement and mortar used is 1:1 in the space provided between the collar and the ends of the pipe.

4. Which joint in the sewer is known as ring tie coupling?
a) Bell and spigot joint
b) Collar joint
c) Mechanical joint
d) Simplex joint
Answer: d
Clarification: In Simplex joint, coupling of asbestos cement pipe and two rubber ring takes place, so this joint is called as ring tie coupling.

5. In which sewer joint, bituminous compounds are added?
a) Collar joint
b) Flexible joint
c) Mechanical joint
d) Simplex joint
Answer: b
Clarification: When cement mortar is added in the joints of sewer, they get easily cracked, so bituminous compound is added to overcome this problem and the joint is called as Flexible or Bituminous joint.

6. The type of joint used for metallic sewer is __________
a) Collar joint
b) Flexible joint
c) Mechanical joint
d) Simplex joint
Answer: c
Clarification: Mechanical joints are used in metallic sewer where mechanical devices like flagged rings and bolts are used.

7. Semi elliptical sections of sewer are not used nowadays.
a) True
b) False
Answer: a
Clarification: There is no availability of factory made sections of this shape and its construction is also difficult.

8. _______ columns are used for the ventilation of sewer.
a) Aeration columns
b) Inclined columns
c) Ventilating columns
d) Vertical columns
Answer: c
Clarification: Ventilating columns are used for the ventilation of sewer. They keep the air inside the sewer pipe at atmospheric pressure.

9. The diameter of the sewer is _____ the diameter of ventilating column.
a) Equal to
b) 2 times
c) 3 times
d) 4 times
Answer: c
Clarification: The diameter of ventilating column is one third of the diameter of the sewer. They can be provided when there is a change in size of sewer.

10. Ventilating columns are provided at intervals of ______ along the sewer lines.
a) 30m
b) 50m
c) 100m
d) 150m
Answer: d
Clarification: The ventilating columns can be provided at the upper end of branch sewer at intervals of 150m to 300m along the sewer lines.

11. _______ is used to remove the waste directly from the building.
a) Branch sewer pipe
b) Outfall sewer pipe
c) Soil vent pipe
d) Main sewer pipe
Answer: c
Clarification: Soil vent pipe is used to remove the waste from toilets, sinks, bathrooms and rain water. It is placed on the exterior of the building.

12. Which of the following is called as a ventilated discharge pipe?
a) Branch sewer pipe
b) Soil vent pipe
c) Outfall sewer pipe
d) Main sewer pipe
Answer: b
Clarification: Soil vent pipe is called as ventilated discharge pipe and they help in the removal of foul smell from the sewage.

13. Which gas among the following is not produced in the sewer?
a) H₂S
b) HCL
c) CO₂
d) CH₄
Answer: b
Clarification: HCL is not produced in the sewer. H₂S, CO₂ and CH₄ are produced in a sewer which is more effective when the sewage is septic.

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Environmental Engineering Multiple Choice Questions on “Types of Settling”.

1. How many types of settling are there in the sedimentation tank?
a) 3
b) 4
c) 5
d) 6
Answer: b
Clarification: There are 4 types of settling in the 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: When large amounts of impurities are 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
Clarification: 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
Clarification: In this type of settling, particle mass increases and it settles down due to flocculation.

Environmental Engineering Multiple Choice Questions on “Air Pollutants”.

1. Which gas is mainly produced due to incomplete burning of wood?
a) CO
b) SO₂
c) NO₂
d) NO₃
Answer: a
Clarification: CO is the colorless, odorless, toxic gas produced due to incomplete burning of wood.

2. Which of the following is involved in production of carboxy haemoglobin?
a) CO
b) SO₂
c) NO₂
d) NO₃
Answer: a
Clarification: CO + Blood ——> Carboxy haemoglobin (Pink color).

3. Which of the following is a liquid form of aerosol?
a) Fume
b) Dust
c) Mist
d) Smoke
Answer: c
Clarification: Mist is a liquid form of aerosol whereas, Fume, Dust and Smoke are a solid form of aerosol.

4. X ray films are a source of which of the following gas?
a) SO₂
b) CO₂
c) NO₂
d) SO₃
Answer: c
Clarification: NO₂ is produced from X ray film. It causes irritation to eyes and cause respiratory disease.

5. The maximum size of fly ash is ___________
a) 1μm
b) 100μm
c) 1000μm
d) 10μm
Answer: c
Clarification: Fly ash is a finely divided particle produced from the combustion of coal. Its maximum size is 1000μm.

6. Which of the following leads to a disease called broncho spasm?
a) SO₂
b) SO₃
c) SO₄
d) CO₂
Answer: b
Clarification: SO₃ reacts with body fluids forming H₂SO₄ leading to Broncho spasm.

7. The minimum size of the smoke particle is ___________
a) 0.2μm
b) 1μm
c) 0.8μm
d) 0.5μm
Answer: d
Clarification: Smoke is produced due to incomplete combustion of coal. Its size lies between 0.5μm to 1μm.

8. Which of the following is a secondary air pollutant?
a) SPM
b) PAN
c) SO₂
d) NO₂
Answer: b
Clarification: Peroxy Acetyl Nitrate is a secondary air pollutant whereas, Suspended Particulate Matter, SO₂ and NO₂ are primary air pollutants.

9. The permissible concentration of PM 10 in the air is ___________
a) 60μg/m³
b) 40μg/m³
c) 50μg/m³
d) 20μg/m³
Answer: a
Clarification: The permissible concentration of PM 10 in air is 60μg/m³ whereas of PM 2.5 is 40μg/m³.