Category: Environmental Engineering Objective Questions

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.

Environmental Engineering test on “Inverted Siphon, Storm Regulator and Sewage Pumping”.

1. Which of the following is called as depressed sewer?
a) Lateral sewer
b) Outfall sewer
c) Inverted siphon
d) Main sewer
Answer: c
Clarification: Inverted siphon is also caused as depressed sewer as the pipes between the inlet and the outlet chamber is depressed due to obstruction like roads, bridges etc.

2. The sewage in inverted siphon will flow under __________
a) Air
b) Vacuum
c) Pressure
d) Gravity
Answer: c
Clarification: The sewage in inverted siphon will flow under pressure greater than the atmospheric pressure and it will not flow under gravity.

3. The design self cleansing velocity of an inverted siphon is __________
a) 0.9m/Sec
b) 0.6m/Sec
c) 0.7m/Sec
d) 0.4m/Sec
Answer: a
Clarification: The design self cleansing velocity of an inverted siphon is 0.9m/Sec for caring minimum, maximum and combined sanitary sewage.

4. The minimum diameter of an inverted siphon is __________
a) 5cm
b) 10cm
c) 15cm
d) 25cm
Answer: c
Clarification: The inverted siphon has a minimum diameter of 15cm and it is made of siphon tubes.

5. Which sewer appurtenance discharges the excess sewage flow to relief sewer?
a) Flushing tank
b) Drop manhole
c) Lamp hole
d) Storm regulators
Answer: d
Clarification: Storm regulators prevents the overloading of sewage treatment plants by discharging the excess sewage flow into relief sewer.

6. Storm regulators are classified into how many types?
a) 2
b) 3
c) 4
d) 6
Answer: b
Clarification: Storm regulator is classified into 3 types, namely Overflow weir, Siphon spillway and Leap weir.

7. Which of the following is most effective in preventing the overloading of treatment plants?
a) Street inlets
b) Overflow weir
c) Siphon valley
d) Leap weir
Answer: b
Clarification: In Siphon valley, the siphonic action takes place when the sewage quantity in combined sewer exceeds the fixed level and it get stopped as soon as it falls below that fixed level.

8. Which of the following is called a sewage ejector pump?
a) Solid handling pump
b) Air lift pump
c) Diaphragm pump
d) Reciprocating pump
Answer: a
Clarification: Solid handling pump is also called as sewage ejector pump where pumping of raw sewage takes place which are mostly in solid form.

9. Which of the following pump is used for the removal of grit?
a) Centrifugal pump
b) Pneumatic ejector
c) Rotary screw pump
d) Air lift pump
Answer: c
Clarification: At Rotary screw pump, the motor rotates on a shaft to lift the solid waste material to a higher level and they are used in grit chambers for removing grit.

10. The septic tank and pump chamber should be kept as deep as possible.
a) True
b) False
Answer: b
Clarification: The septic tank and pump chamber should be placed at shallow depth as it will result in easier inspection, repairment and maintenance of them.

11. Which part of the pump chamber allows to easily disconnect from the pipeline?
a) Gate valve
b) Check valve
c) Union
d) Pump lift chain
Answer: c
Clarification: Union is a device that is placed in the pump discharge pipe that allows the pump to easily disconnect from the pipe in the pump chamber.

12. Which device warns that the liquid is above the pump level?
a) High level alarm
b) Check valve
c) Union
d) Pump lift chain
Answer: a
Clarification: High level alarms give a red light as a warning signal that warns the user that wastewater is above the pump level.

13. Which of the following device prevents the back flow of wastewater?
a) Gate valve
b) Check valve
c) Union
d) Pump lift chain
Answer: b
Clarification: Check valve allows the flow of wastewater in one direction and prevents the back flow of water.

14. Which component of the pumping chamber prevents ground water from entering the septic tank?
a) Pump lift chain
b) Access riser
c) Check valve
d) Union
Answer: b
Clarification: Access riser are large diameter riser with a 61cm diameter that prevents the ground and surface water from entering the septic tank.

15. Which of the following represents the correct order in terms of the maximum efficiency of the pump?
a) Centrifugal > Airlift > Diaphragm
b) Diaphragm > Airlift > Centrifugal
c) Airlift > Centrifugal > Diaphragm
d) Centrifugal > Diaphragm > Airlift
Answer: d
Clarification: The maximum efficiency of the centrifugal pump is 85%, while of Diaphragm and Airlift pumps are 30% and less than 25% respectively.

To practice all areas of Environmental Engineering for tests, .

Environmental Engineering Multiple Choice Questions on “Chemical Clarification”.

1. Which of the following represents the coagulant pipe in the following figure?

Figure: Flash mixer
a) A
b) B
c) C
d) D
Answer: a
Clarification: ‘A’ represents the coagulant pipe which is used for discharging the coagulant into the flash mixer.

2. Which of the following represents the device which is used for sludge removal in the following figure?

Figure: Flash mixer
a) F
b) E
c) D
d) B
Answer: c
Clarification: ‘D’ represents the drain valve which is used for the removal of sludge from the mixer.

3. _________ is the average of velocities at a point over a definite period of time.

Figure: Flash mixer
a) Mean velocity
b) Relative velocity
c) Velocity gradient
d) Temporal mean velocity
Answer: d
Clarification: Temporal mean velocity is the average of velocities at a point over a definite period of time. It is represented by G.

4. Which of the following goes to the flocculation tank in the following figure?

Figure: Flash mixer
a) B
b) C
c) E
d) F
Answer: b
Clarification: ‘B’ represents the outlet of the mixer which goes to the flocculation tank.

5. Which of the following is the correct expression regarding temporal mean velocity in the following figure?

Figure: Flash mixer
a) G = (P/μV)^1/2
b) G = (P/μV)
c) G = (P/μV)²
d) G = (Pμ/V)^1/2
Answer: a
Clarification: Temporal mean velocity G = (P/μV)^1/2, where P is the power, μ is the dynamic viscosity and V is the volume of the tank. It is measured in per second.

6. Which of the following is correctly paired in the following figure?

Figure: Flash mixer
a) C – Impeller
b) D – Outlet
c) F – Deflecting wall
d) E – Impeller
Answer: d
Clarification: E represents the Impeller which is driven by the electric motor to revolve in the tank.

7. The speed of impeller in a flash mixer is ___________

Figure: Flash mixer
a) 45rpm
b) 60rpm
c) 110rpm
d) 200rpm
Answer: c
Clarification: The speed of impeller in a flash mixer is between 100 to 120 rpm and the propeller type impeller is used.

8. ‘C’ in the following figure represents the ________

Figure: Flash mixer
a) Impeller
b) Impeller shaft
c) Deflecting wall
d) Flash mixer wall
Answer: c
Clarification: ‘C’ represents the deflecting wall, whereas the boundary below the inlet and outlet of the tank is the flash mixer wall.

9. The detention period of a flash mixer is _________________

Figure: Flash mixer
a) 2 minutes
b) 30 minutes
c) 1 hour
d) 2 hours
Answer: a
Clarification: The detention period of flash mixer lies between 30 seconds to 2 minutes.

10. Which of the following represents the impeller shaft in the following figure?

Figure: Flash mixer
a) F
b) E
c) C
d) B
Answer: a
Clarification: Impeller is connected to impeller shaft which is further connected to electric motor so as to drive the impeller and mixing of coagulant in water takes place.

Environmental Engineering Multiple Choice Questions on “Devices to Control Air Pollution”.

1. Which of the following is used in ceramic industries?
a) Electrostatic precipitator
b) Dynamic precipitator
c) Spray tower
d) Wet cyclonic scrubber
Answer: b
Clarification: Dynamic precipitator is used in ceramics, woodworking industries. It uses centrifugal force to remove gaseous matter.

2. Wet scrubbers are classified into ____ types.
a) 2
b) 3
c) 5
d) 6
Answer: b
Clarification: Web scrubbers are used to remove air pollutants and are classified into Spray towers, Wet cyclonic scrubber and Venturi scrubber.

3. The centrifugal collectors are classified into how many types?
a) 3
b) 4
c) 5
d) 2
Answer: d
Clarification: The Centrifugal collectors are classified into the Cyclone collector and Dynamic precipitator.

4. Which of the following air pollution control device has maximum efficiency?
a) Electrostatic precipitator
b) Dynamic precipitator
c) Spray tower
d) Wet cyclonic scrubber
Answer: a
Clarification: Electrostatic precipitator has the maximum efficiency among the rest with a value of 99%.

5. Which of the following fluid is used in web scrubbers?
a) Lime
b) MgSO₄
c) NaCl
d) K₂Cr₂O₇
Answer: a
Clarification: Apart from lime, K₂CO₃, a slurry of MnO and MgO and water can be used in Web scrubber.

6. Which of the following is incorrect regarding the fabric filter?
a) They can remove very small particle
b) They are liable to chemical attack
c) They have low efficiency in comparison to venturi scrubber
d) They can handle large volume of gas at relatively high speed
Answer: c
Clarification: The efficiency of Electrostatic precipitator is <99%, whereas the efficiency of Fabric filter is >99%.

7. Which of the following removes both gaseous and particulate contaminants?
a) Venturi scrubber
b) Gravitational settling chamber
c) Dynamic precipitator
d) Wet scrubber
Answer: a
Clarification: Venturi scrubber removes both gaseous and particulate contaminants. The minimum particle size removal is 0.5μm and its efficiency is < 99%.

8. Identify the correct statement regarding the Electrostatic precipitator.
a) Minimum particle size removal is <0.5μm
b) They can be operated at high temperature
c) It has a low maintenance cost
d) It does not cause any freezing problem
Answer: b
Clarification: Electrostatic precipitator can be operated at a high temperature between 3000C to 4500C, has a high maintenance cost, can cause a freezing problem and minimum particle size removal is < 1μm.