Category: Environmental Engineering Objective Questions

Environmental Engineering Multiple Choice Questions on “Design of Sedimentation Tank”.

1. Which of the following cannot be the velocity of flow in the horizontal flow sedimentation tank?
a) 12cm/min
b) 39cm/min
c) 5cm/min
d) 20cm/min
Answer: b
Clarification: The maximum value of the velocity of flow is 30cm/min, so it cannot be 39cm/min.

2. The deviation from the ideal flow of wastewater in the sedimentation tank causes ____________
a) Whirlpool
b) Increase in tank efficiency
c) Short circuiting
d) Coagulation
Answer: c
Clarification: The deviation from the ideal flow of wastewater in the sedimentation tank causes short circuiting. It results in variation in the detention period in the top and bottom layer of wastewater in the tank.

3. The overflow rate for a plain sedimentation tank is ______ litre/day/metre².
a) 50000
b) 40000
c) 12000
d) 30000
Answer: c
Clarification: The overflow rate for a plain sedimentation tank lies between 12000-18000 litre/day/metre².

4. The detention period for a sedimentation tank where coagulation takes place is ____________
a) 30 seconds
b) 1 minute
c) 1hour
d) 2hour
Answer: d
Clarification: The detention period for a sedimentation tank without coagulation is 4 hours, whereas with coagulation is 2 – 2.5 hours.

5. The test for finding the optimum coagulant dose in water is ____________
a) Chromatography
b) Jar test
c) Kjeldahl test
d) Dilatancy test
Answer: b
Clarification: Jar test is used to find the optimum coagulant concentration that is required to cause coagulation in water so that the settling of suspended impurities takes place.

6. The average time required by water to pass through the settling tank is called _______
a) Detention time
b) Flowing through period
c) Time of flow
d) Mean time
Answer: b
Clarification: The average time required by water to pass through the settling tank is called ‘flowing through period’ which is always less than the detention period.

7. The quantity of water flowing per hour per unit horizontal area is called ____
a) Detention time
b) Flowing through period
c) Displacement time
d) Overflow rate
Answer: d
Clarification: Overflow rate = Q/A where Q is discharge rate in litre per day, A is the horizontal area in m².

8. 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
Clarification: 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.

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

1. Coning plume occurs under which conditions?
a) Super adiabatic
b) Sub adiabatic
c) Neutral
d) Inversion
Answer: b
Clarification: Coning occurs under sub adiabatic conditions. The plume is of conical shaped.

2. In which of the following plumes, stable condition prevails?
a) Lofting
b) Fanning
c) Neutral
d) Fumigating
Answer: b
Clarification: The stability prevails in the Fanning plume. It occurs during inversion conditions.

3. The upward vertical rise prevails in which of the following plume?
a) Trapping
b) Fanning
c) Looping
d) Neutral
Answer: d
Clarification: In Neutral plume, the Environmental lapse rate is equal to the Adiabatic lapse rate.

4. Which of the following plume is worst for the dispersion of pollutants?
a) Trapping
b) Fanning
c) Neutral
d) Fumigating
Answer: d
Clarification: In Fumigating plume, the pollutants come down near the ground due to turbulence instead of escaping above the stack. This makes it the most dangerous plume.

5. In which of the following plumes, unstable condition prevails?
a) Trapping
b) Fanning
c) Looping
d) Neutral
Answer: c
Clarification: Rapid dispersion of pollutants takes place under Looping plume. It occurs under super adiabatic conditions.

6. Which of the following are contradictory plume?
a) Lofting and fumigating
b) Looping and coning
c) Neutral and lofting
d) Fumigating and trapping
Answer: a
Clarification: In Lofting plume, the super adiabatic lapse rate occurs above the stack, whereas, in Fumigating plume, it occurs below the stack.

7. The maximum efficiency of the electrostatic precipitator is ___________
a) 95%
b) 80%
c) 99%
d) 100%
Answer: c
Clarification: The efficiency of electrostatic precipitator lies between 95% to 99%. They are used in thermal power plants.

8. The minimum particle size removes by the gravitational chamber is ___________
a) >50μm
b) >10μm
c) >25μm
d) >0.5μm
Answer: a
Clarification: The minimum particle size removes by the gravitational settling chamber is >50μm and its efficiency is less than 50%.

Environmental Science Multiple Choice Questions on “Aerosols”.

1. Formation of aerosols by nucleation produces particles of size __________
a) Less than 0.1 micron
b) Greater than 0.1 micron
c) Less than 1 micron
d) Greater than 1 micron
Answer: a
Clarification: Aerosol formation by molecular nucleation leads to the production of particles with size less than 1 micron.

2. The size of aerosol particles formed mechanically is minimum 1 micron.
a) True
b) False
Answer: a
Clarification: Due to surface tension, the minimum size of particles formed mechanically is limited to 1 micron.

3. What is the statement of the Kelvin effect in fluid droplets?
a) Vapour pressure about a droplet decreases with decrease in diameter of the droplet
b) Vapour pressure about a droplet increases with decrease in diameter of the droplet
c) Vapour pressure of the droplet is independent of the diameter of the droplet
d) Vapour pressure of the droplet varies with the diameter of the droplet as well as the temperature
Answer: b
Clarification: The Kelvin effect is a phenomenon where the vapour pressure of the droplet increases with decrease in diameter of the droplet.

4. When a given gas has a temperature gradient, the aerosol particles move from higher temperature regions to low temperature regions. This effect is known as __________
a) Photophoresis
b) Diffusiophoresis
c) Thermophoresis
d) Diffusiophoresis or Thermophoresis
Answer: c
Clarification: Based on the temperature gradient, by the effect of thermophoresis, aerosol particles move from high temperature regions to low temperature regions.

5. Particle movement due to photophoresis depends on _________
a) Shape and size of the particle
b) Optical properties of the particle
c) Wavelength and intensity of incident light
d) All of the mentioned
Answer: d
Clarification: Particle movement due to photophoresis depends on the shape, size and optical properties of the particle, as well as wavelength and intensity of incident light.

6. The movement of particles from region of lower vapour to high vapour molecule concentration is known as diffusiophoresis.
a) True
b) False
Answer: b
Clarification: Movement of particles from higher vapour to low vapour molecule concentration is known as diffusiophoresis.

7. Which of the following scattering phenomena is responsible for the blue colour of the sky?
a) Mie scattering
b) Diffraction
c) Rayleigh scattering
d) All of the mentioned
Answer: c
Clarification: Due to Rayleigh’s scattering shorter wavelength radiations are scattered more, and hence makes the sky appear blue.

8. When light is passed through a suspension, it’s intensity decreases due to _________
a) Both scattering and diffraction
b) Both diffraction and absorption
c) Absorption only
d) Both scattering and absorption
Answer: d
Clarification: Light intensity decreases when passed through a suspension due to scattering and absorption of light by suspended particles.

9. What is/are the inertial method(s) used to measure size of aerosol particles?
a) Particle acceleration method
b) Pulsation method
c) Multi cyclone
d) All of the mentioned
Answer: d
Clarification: Inertial methods such as particle acceleration, pulsation and multi-cyclones are used to measure size of aerosol particles larger than 5 microns.

10. What does CNC stand for in the context of aerosol particles?
a) Cloudy nucleic condensation
b) Condensation nucleus counter
c) Chemical nucleic coagulation
d) Cloudy nucleic coagulation
Answer: b
Clarification: To measure the number concentration of aerosol particles, we use a condensation nucleus counter which counts particles of even 0.003 micron diameter.

11. What type of colloid is an aerosol?
a) Solid in gas
b) Gas in solid or fluid
c) Fluid in gas
d) Fluid or solid in gas
Answer: d
Clarification: Aerosol is a colloid formed by the presence of fluid or solid particles suspended in the air/atmosphere.

12. Aerosols contribute to global warming.
a) True
b) False
Answer: b
Clarification: Aerosols help in scattering radiations from the sun back into outer space and help cool down the atmosphere.

13. What is the size of the particles categorised as aerosols?
a) Greater than 1 micron
b) Less than 1 micron
c) Between 0.01-1 micron
d) Less than 0.01 micron
Answer: c
Clarification: Aerosol consists of solid/fluid particles of size ranging between 0.01-1 microns.

14. What does the aerodynamic diameter of an aerosol indicate?
a) Size of the aerosol particle when floating in air
b) Equivalent diameter of a sphere having same volume as that of the aerosol
c) Average diameter of aerosol particles present in unit volume of air
d) Maximum size of aerosol particle that can float in the air
Answer: b
Clarification: The aero-dynamic diameter gives the equivalent diameter of a sphere having the same volume as that of the aerosol.

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Environmental Engineering Multiple Choice Questions on ” Sedimentation with Coagulation”.

1. What is formed when coagulant is added to water?
a) Scum
b) Soap
c) Bubbles
d) Floc
Answer: d
Clarification: When coagulant is added to water, then white gelatinous precipitate is formed called floc.

2. The chemical composition of Alum is _____________
a) Al₂ (SO₄)₃.18H₂O
b) Al₂ (SO₄)₂.18H₂O
c) Al₃ (SO₄)₂.18H₂O
d) Al₄ (SO₄)₃.18H₂O
Answer: a
Clarification: Alum is the most common and universal coagulant used in water treatment having chemical composition Al₂ (SO₄) ₃.18H₂O.

3. The chemical compound which is insoluble in water, formed when alum is added to water is _____________
a) Al (OH)₃
b) CaSO₄
c) CO₂
d) Ca (OH)₃
Answer: a
Clarification: Al₂ (SO₄)₃.18H₂O + 3Ca (HCO₃)₂ = 2Al (OH)₃ + 3CaSO₄ + 18H₂O + CO₂
Where Al (OH)₃ is insoluble in water.

4. Which gas is released when alum is added to water?
a) Al (OH)₃
b) CaSO₄
c) CO₂
d) Ca (OH)₃
Answer: c
Clarification: Carbon dioxide gas is released when alum is added to water, which is corrosive to metals.

5. What indicates the permanent hardness when alum is added to water?
a) Al (OH)₃
b) CaSO₄
c) CO₂
d) Ca (OH)₃
Answer: b
Clarification: The presence of calcium sulfate indicates the permanent hardness in water when alum is added to water.

6. Alum is effective when pH of water is between ____
a) 8-10
b) 6-8
c) 6.5-8.5
d) 7-9
Answer: c
Clarification: Alum is effective when pH of water is between 6.5-8.5. Its dose depends on turbidity, color, taste, pH and temperature of water.

7. Why Alum is preferred over other coagulants?
a) It is easy to dewater the sludge formed
b) It imparts corrosiveness to water
c) It reduces taste and odor in addition to turbidity
d) The time required for floc formation is less
Answer: c
Clarification: Alum is preferred over other coagulants because it reduces the taste and odor in addition to turbidity and produce lighter flocs that can be broken easily.

8. The chemical composition of Chlorinated Copperas is __________
a) Fe₂ (SO₄)₃ + FeCl₃
b) FeSO₄.9H₂O
c) FeSO₄.18H₂O
d) Fe₂ (SO₄)₃
Answer: a
Clarification: 6FeSO₄.7H₂O₂ +3Cl₂ = 2Fe₂(SO₄) ₃ + 2FeCl₃ + 7H₂O
The ferric sulfate and ferric chloride so formed are called as Chlorinated Copperas.

9. Ferric chloride is effective over a pH range of __________
a) 3.5-6
b) 6.5-8
c) 3.5-6.5
d) 2-5
Answer: c
Clarification: Ferric chloride is effective over a pH range of 3.5-6.5 and above 8.5 whereas if Ferric sulfate is used then, it is effective over a pH range of 4-7 and above 9.

10. Why Magnesium carbonate is not commonly preferred as coagulant?
a) It is expensive
b) It does not remove color
c) Formation of sludge
d) The time required for floc formation is less
Answer: c
Clarification: When magnesium carbonate and lime are dissolved in water, magnesium hydroxide and calcium carbonate are formed which are soluble in water and sludge is formed in slurry form, so they are not commonly used.

11. Which of the following statement is wrong regarding Iron salt?
a) Iron salt produces less floc than Alum
b) Detention time for sedimentation by using Iron salt as coagulant is less
c) Handling of Iron salt requires some skills
d) Iron removes H₂S, taste and odor
Answer: a
Clarification: Iron salt produces heavy floc due to which more suspended matter is removed than with alum.

Environmental Engineering Multiple Choice Questions on “Kinetics of Chemical Disinfection”.

1. Consider the following variables.
i. Concentration of disinfectant
ii. Concentration of organisms
iii. Temperature
iv. Time of contact
Disinfection is the function of which of the following variables?
a) i, ii
b) i, ii, iii
c) i, ii, iii, iv
d) ii, iii, iv
Answer: c
Clarification: The process of disinfection is the function of concentration of disinfectant, organisms, temperature of disinfection and time of contact.

2. According to which of the following, organism destroyed by disinfection is proportional to organism remaining?
a) Hazens equation
b) Chicks law
c) Darcy’s law
d) Rose equation
Answer: b
Clarification: According to Chicks law of disinfection, the number of organisms destroyed in unit time is proportional to the number of organisms remaining.

3. Which of the following is the expression of Chicks law?
a) Dy/Dt = k (N – y)
b) Dy/Dt = k/(N – y)
c) Dy/Dt = k (N + y)
d) Dy/Dt = k (N * y)
Answer: a
Clarification: The expression of Chicks law is given by Dy/Dt = k (N – y) Where, N is the number of organisms initially present, ‘y’ is the number of organisms remaining after time t and k is the coefficient of proportionality.

4. The integration of the expression of Chicks law is given by ____________
a) N1/N = e^kt
b) N1/N = kt
c) N1/N = k/t
d) N1/N = e^-kt
Answer: d
Clarification: According to Chicks law, Dy/Dt = k (N – y), by integration,
loge N1/N = -kt
= N1/N = e^-kt Where, N1 = N – y.

5. The dimensional formula of rate constant used in Chicks law is ____________
a) 1/t
b) 1/t²
c) 1/t³
d) t²
Answer: a
Clarification: According to Chicks law, Dy/Dt = k (N – y) where, k is the rate of proportionality or rate constant having dimensional formula 1/t.

6. The number of organisms destroyed is equal to the number of organisms remaining at time t = __________
a) 0
b) 1
c) 2
d) 10
Answer: a
Clarification: According to Chicks law, N1/N = e^-kt, when t=0,
N1/N = 1 or N1 = N, Where, N1 represents the remaining organisms.

7. The expression loge N1/N = – kt m Where m is a constant such that m>1 represents ____________
a) Rate of the kill will remains constant with time
b) Rate of the kill will increase with time
c) Rate of the kill will decrease with time
d) Rate of the kill is directly proportional to time
Answer: b
Clarification: The expression loge N1/N = -kt^m Where m is a constant such that m>1 represents that rate of kill will increase with time whereas m<1 represents rate of the kill decrease with time.

8. For changing the concentration of disinfectant, the disinfecting efficiency is expressed by ____________
a) C n *t p = Constant
b) C n/ t p = Constant
c) C q * Np = Constant
d) C q / Np = Constant
Answer: a
Clarification: The disinfecting efficiency is expressed by C n *t p = Constant where, C is the concentration of disinfectant, t p is the time required to kill the organism and n is the coefficient of dilution.

9. The number of organisms in disinfection process can be expressed by ____________
a) Cⁿ *t _p = Constant
b) C ⁿ / t_p = Constant
c) C ^q * N_p = Constant
d) C ^q / N_p = Constant
Answer: c
Clarification: The number of organisms in disinfection process can be expressed by C^q * N_p = Constant where, C is the concentration of disinfectant, the N_p is the reduced concentration of organisms and q is the coefficient of disinfectant strength.

10. Efficiency of dilution decreases rapidly when the coefficient of dilution is ____________
a) 0
b) 1
c) <1
d) >1
Answer: d
Clarification: Efficiency of dilution decreases rapidly when the coefficient of dilution n is greater than 1 which is a measure of order of reaction.

11. When the coefficient of dilution is 1, then which of the following statement is correct?
a) Time of contact is more important than dosage
b) The dosage is more important than time of contact
c) Concentration and time are equally important
d) Efficiency of dilution decreases.
Answer: c
Clarification: When the coefficient of dilution is 1, concentration and time are equally important and a first order will proceed.

12. The temperature of disinfection is inversely proportional to the killing of organisms.
a) True
b) False
Answer: b
Clarification: The temperature of disinfection is directly proportional to the killing of organisms and the increase in temperature results in more rapid killing of organisms.

Environmental Engineering Multiple Choice Questions on “Layout of Distribution System”.

1. The method of distribution of water is divided into how many types?
a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: The method of distribution of water is divided into 3 types and it includes gravity system, pumping system and combined gravity and pumping system.

2. In which of the following distribution system, the clean water flows entirely under gravity?
a) Gravity system
b) Pressure system
c) Combined gravity and pumping system
d) Pumping system
Answer: a
Clarification: The purified water in gravity system flow entirely under gravity. It is the most reliable and economical distribution system.

3. The pressure in the distribution mains does not depend on ____________
a) Altitude to supply water
b) Fire fighting requirements
c) Availability of funds
d) Quality of water
Answer: d
Clarification: The pressure in the distribution mains depends on the height to which water is required to be supplied, fire fighting requirements, whether the supply is metered or not and availability of funds.

4. The pressure in distribution mains in a residential building up to three storeys is ____________
a) 2kg/cm²
b) 5kg/cm²
c) 7kg/cm²
d) 10kg/cm²
Answer: a
Clarification: The pressure in distribution mains in a residential building up to three storeys is 2kg/cm² and when it is between 3-6 storeys, the pressure is 3kg/cm².

5. There is a 8 storey residential building in Lucknow. What is the pressure in the distribution mains?
a) 2kg/cm²
b) 5kg/cm²
c) 7kg/cm²
d) 10kg/cm²
Answer: b
Clarification: When the height of residential building is between 6 to 10 storey, the pressure in the distribution mains lies between 4 to 5.5kg/cm².

6. The velocity of water in a 10 cm diameter pipe should be ____________
a) 0.2m/Sec
b) 0.5m/Sec
c) 0.9m/Sec
d) 1.2m/Sec
Answer: c
Clarification: The velocity of water in a 10 cm diameter pipe should be 0.9m/Sec
Which is 1.2m/Sec when the diameter of pipe is 15cm.

7. In which system of water supply, water is available for 24 hours but uneconomically used?
a) Continuous supply
b) Fixed supply
c) Intermittent supply
d) Low supply
Answer: a
Clarification: In continuous water supply, water is wasted due to a continuous supply of water for 24 hours of the day or long duration of flow.

8. In which system of water supply, water is supplied only during fixed hours of the day?
a) Continuous supply
b) Fixed supply
c) Intermittent supply
d) Low supply
Answer: c
Clarification: In Intermittent supply, water is supplied to the consumer during fixed hours of the day and is adopted when sufficient pressure is not available or sufficient quantity of water is not available.

9. The velocity of water in the pipe is 1.8m/Sec. What is the diameter of pipe used?
a) 10cm
b) 15cm
c) 25cm
d) 40cm
Answer: d
Clarification: It is the maximum diameter of the pipe for which the velocity of water should not be less than 1.8m/Sec.

10. The hourly demand rate is constant throughout the day.
a) True
b) False
Answer: b
Clarification: The hourly demand rate is not constant throughout the day, it is more during morning and evening and less during other parts of the day.

11. According the mass curve method, the storage capacity is defined as ____________
a) Maximum excess of supply / Maximum excess of demand
b) Maximum excess of supply * Maximum excess of demand
c) Maximum excess of supply – Maximum excess of demand
d) Maximum excess of supply + Maximum excess of demand
Answer: d
Clarification: A mass curve of demand is the cumulative demand curve, which is obtained by continuously adding the hourly demands and plotting it against time.

12. _______ causes hoop tension in pipe shell.
a) Internal water pressure
b) External water pressure
c) Water hammer
d) Longitudinal stress
Answer: a
Clarification: Internal water pressure causes hoop tension in pipe shell and its magnitude is given by f = pd/2t where p is the internal pressure of water, d is the diameter of the pipe and t is the thickness of pipe shell.

13. The water supply pipes are buried underground. The load on the buried pipe due to earth filling is given by ____________
a) W = C*Y*B
b) W = C*Y/B
c) W = C*Y*B²
d) W = C*Y2*B
Answer: c
Clarification: According to Marston, the load W on buried pipes due to earth filling is given by W = C*Y*B² where, ‘C’ is the coefficient which depends on soil, ‘Y’ is the unit weight of back fill material and ‘B’ is the width of the trench.

14. Which of the following stress in pipe depends on temperature?
a) Internal water pressure
b) Stress due to foundation reaction
c) Longitudinal stress
d) Temperature stress
Answer: d
Clarification: Temperature stress is caused in pipes when they are laid above ground. When they are subjected to temperature variation, changes in the length of pipe takes place.

15. Pipe corrosion can be minimized by ____________
a) Removal of copper sulfate
b) Addition of calcium carbonate
c) Addition of carbon dioxide
d) Removal of dissolved oxygen
Answer: d
Clarification: Pipe corrosion can be minimized by pH adjustment, control of calcium carbonate, removal of dissolved oxygen, removal of carbon dioxide and by the addition of sodium silicate.