Category: WASTE WATER Engineering Objective Questions

250+ TOP MCQs on Oxidation Ditch and Answers

Waste Water Engineering Multiple Choice Questions on “Oxidation Ditch”.

1. Oxidation ditch is an extended activated sludge process.
a) True
b) False
Answer: a
Clarification: Oxidation ditch is an extended aeration activated sludge process. An oxidation ditch is a large holding tank in a continuous ditch with an oval shape similar to that of a racetrack. The ditch is built on the surface of the ground and is lined with an impermeable lining.

2. What is the shape of the oxidation ditch?
a) Square
b) Rectangular
c) Circular
d) Oval
Answer: d
Clarification: An oxidation ditch is a large holding tank in a continuous ditch with an oval shape similar to that of a racetrack. The ditch is built on the surface of the ground and is lined with an impermeable lining.

3. The ditch is lined by _______ layer.
a) Brick
b) Cement
c) Permeable
d) Impermeable
Answer: d
Clarification: The ditch is built on the surface of the ground and is lined with an impermeable lining. This allows the waste water to have plenty of exposure to the open air for the diffusion of oxygen.

4. What is the range of liquid depth in oxidation ditches?
a) 0.2-0.3 m
b) 0.3-0.5 m
c) 0.5-0.9 m
d) 0.9-1.5 m
Answer: d
Clarification: The liquid depth in the ditches is very shallow, 0.9 to 1.5 m, which helps to prevent anaerobic conditions from occurring at the bottom of the ditch.

5. Anaerobic conditions occur at the bottom of the ditches.
a) True
b) False
Answer: b
Clarification: The liquid depth in the ditches is very shallow, 0.9 to 1.5 m, which helps to prevent anaerobic conditions from occurring at the bottom of the ditch.

6. What is the range of MLSS concentration in oxidation ditch?
a) 500-1000 mg/L
b) 1000-2000 mg/L
c) 2000-4000 mg/L
d) 3000-5000 mg/L
Answer: d
Clarification: The MLSS concentration in the oxidation ditch generally ranges from 3,000 mg/L to 5,000 mg/L. This is dependent upon the surface area provided for sedimentation, the rate of sludge return and the aeration process.

7. Which of the following is MLSS concentration not dependant upon?
a) Surface area of sedimentation
b) Rate of return sludge
c) Aeration process
d) Number of bar screens
Answer: d
Clarification: The surface area provided for sedimentation, the rate of sludge return and the aeration process affects MLSS concentration. The MLSS concentration in the oxidation ditch generally ranges from 3,000 mg/L to 5,000 mg/L.

8. Oxidation ditch uses ______ to remove biodegradable organics.
a) Long SRTs
b) Short SRTs
c) pH
d) chemicals
Answer: a
Clarification: Long solids retention times (SRTs) are used by oxidation ditch to remove biodegradable organics. The typical oxidation ditch is equipped with aeration rotors or brushes that provide aeration and circulation.

9. What is the velocity of wastewater within the ditch?
a) 0.5 ft/s
b) 0.7 ft/s
c) 5 ft/s
d) 2 ft/s
Answer: d
Clarification: The velocity of the wastewater within the ditch is 1 to 2ft/s. This process may be adaptable to the fluctuations in flows and loadings associated with recreation area wastewater production.

10. Which of the following process is not adopted in oxidation ditches?
a) Adsorption
b) Desorption
c) Oxidation
d) Decomposition
Answer: b
Clarification: An oxidation ditch is a large circular basin equipped with aerators that are used to remove organic matter and pollutants from sewage through the processes of adsorption, oxidation and decomposition.

250+ TOP MCQs on Suspended Solids Removal & Dissolved Air Floatation – 2 and Answers

Waste Water Engineering Questions and Answers for Campus interviews on “Suspended Solids Removal & Dissolved Air Floatation – 2”.

1. What does the performance of a Dissolved air floatation depend on?
a) Air to solid ratio
b) Air to oil ratio
c) Air to flow rate of water
d) Air to the grease ratio
Answer: a
Clarification: Dissolved air floatation performance depends on air to solid ratio. This ratio will vary with different type of suspension. This floatation process is dependent on the surface area of the materials.

2. What are the typical A/S ratios encountered in a Dissolved air floatation method?
a) 0.25-0.5
b) 0.005-0.06
c) 0.5-2
d) 3-5
Answer: b
Clarification: The typical A/S ratios encountered in a Dissolved air floatation method is 0.005-0.06. Floatation depends on solid loading rate and particle rise velocity. It also depends on the concentration of particulate matter and the quantity of air used.

3. Which of these pollutants is removed by Dissolved air floatation?
a) Free oil
b) Emulsified oil
c) Both free and emulsified oil
d) Only grease
Answer: b
Clarification: The Dissolved air floatation removes emulsified oil. This process is similar to froth floatation. This process is widely used to treat effluent from the oil industry, petrochemical etc.

4. What portion of the Dissolved air floatation effluent is recycled?
a) 70-80%
b) 80-90%
c) 30-50%
d) 15-20%
Answer: d
Clarification: Around 15-20% of Dissolved air floatation effluent is recycled. The recycled flow is mixed with unpressurized main stream prior to letting it inside the floatation tank. This process is mainly used to treat industrial wastes.

5. What is dispersed air floatation used to remove?
a) Emulsified oil and suspended solids
b) Free oil and suspended solids
c) Emulsified oil
d) Free oil
Answer: a
Clarification: Dispersed air floatation used to remove suspended solids. It is also used to remove emulsified oil. It doesn’t however remove free oil.

6. What is the pressure supplied for a dissolved air flotation process?
a) 1-2 bar
b) 5-7 bar
c) 2.75-3.75 bar
d) 9.75-12.75 bar
Answer: c
Clarification: The pressure supplied for a dissolved air flotation process is the 2.75-3.75 bar. This is around 275-375 kPa. The entire flow for a dissolved air flotation is held under pressure in a retention tank for several minutes.

7. Which of these chemicals is not used during Dissolved air floatation?
a) Aluminium Salts
b) Ferric salts
c) Activated silica
d) Magnesium salts
Answer: d
Clarification: Aluminium and Iron salts are used in dissolved air flotation in order to bind particulate matter. Activated silica is also used for the same purpose. Only magnesium salts are not used in dissolved air flotation process.

8. What is the hydraulic loading rate considered for a conventional dissolved air flotation?
a) 4 m/h
b) 5-15 m/h
c) 25-30 m/h
d) 35-40 m/h
Answer: b
Clarification: The hydraulic loading rate considered for a conventional dissolved air floatation is 5-15 m/h. The mixing intensity is considered as 50-100 sec-1. Usually, the basin depth is considered 2.0-3 m.

9. What is the hydraulic loading rate considered for a high rate dissolved air flotation?
a) 10-30 m/h
b) 30-35 m/h
c) 40-55 m/h
d) 60-80 m/h
Answer: a
Clarification: The hydraulic loading rate considered for a high rate of dissolved air floatation is 10-30 m/h. The mixing intensity is considered as 50-100 sec-1. Usually, the basin depth is considered 2.5-4.5 m.

10. What is the separation zone loading rate for a conventional dissolved air floatation process considered?
a) 10-30 m/h
b) 30-35 m/h
c) 4-9 m/h
d) 6-18 m/h
Answer: d
Clarification: The separation zone loading rate for a conventional dissolved air floatation process considered is 6-18 m/h. In case of high rate dissolved air floatation process it is considered as 20-40 m/h. It is higher in case of high rate air floatation process.

11. What is the contact zone loading rate for a conventional dissolved air floatation process considered?
a) 100-200 m/h
b) 300-350 m/h
c) 40-90 m/h
d) 60-180 m/h
Answer: a
Clarification: The contact zone loading rate for a conventional dissolved air floatation process considered is 100-200 m/h. The detention time considered while designing this is 10-20 mins. The contact zone loading rate is little higher in case of high rate floatation process.

12. What is the contact zone loading rate for a conventional dissolved air floatation process considered?
a) 120-300 m/h
b) 300-350 m/h
c) 40-90 m/h
d) 60-180 m/h
Answer: a
Clarification: The contact zone loading rate for a conventional dissolved air floatation process considered is 120-300 m/h. The detention time considered while designing this is 10-15 mins. The contact zone loading rate is little higher in case of high rate floatation process.

13. What is the recycle ratio considered while designing the dissolved air floatation process?
a) 10-30
b) 1-4
c) 4-9
d) 6-12
Answer: d
Clarification: The recycle ratio considered while designing the dissolved air floatation process is 6-12. This holds good for conventional type dissolved air floatation process. This is also true in case of high rate dissolved air floatation process.

14. What is the detention time considered for the contact zone while designing the conventional dissolved air floatation process?
a) 1-2.5 mins
b) 2.5-4 mins
c) 4-9 mins
d) 9-15 mins
Answer: a
Clarification: The detention time considered for the contact zone while designing the conventional dissolved air floatation process is 1-2.5 mins. In case of high rate dissolved air floatation it is a little lesser. It is considered as 1-2 mins.

15. DAF separates _______ in water.
a) Suspended particles
b) Dissolved particles
c) Floating particles
d) Settleable solids
Answer: a
Clarification: A dissolved air flotation (DAF) clarifier separates suspended solids in wastewater. DAF clarifiers can be round or rectangular tanks.

Waste Water Engineering for Campus Interviews,

250+ TOP MCQs on Total Dissolved Solids – 2 and Answers

Basic Waste Water Engineering Questions and Answers on “Total Dissolved Solids – 2”.

1. What is the process by which Total dissolved solids are removed?
a) Reverse Osmosis
b) Ultrafiltration
c) Adsorption
d) Clarification
Answer: a
Clarification: The total dissolved solids are removed by reverse osmosis. Water passing through a semi permeable membrane is subjected to pressure greater than osmotic pressure. In this process, the ions are removed.

2. What is the limit of total dissolved solids in treated water which is to be used for the gardening purpose?
a) 1200 mg/L
b) 1100 mg/L
c) 1000 mg/L
d) 500 mg/L
Answer: a
Clarification: The limit of total dissolved solids in treated water is 1200 mg/L. This holds good for surface water. According to the applications, the limit of total dissolved solids is fixed.

3. What is the percentage of TDS removed by the reverse osmosis membrane?
a) 97-99%
b) 50-60%
c) 60-70%
d) 70-90%
Answer: a
Clarification: The amount of TDS removed is around 97-99%. This depends on the membrane used. This depends on the salt rejection of the membrane.

4. What is the flux assumed while designing the reverse osmosis system to treat surface water?
a) 3-10 LMH
b) 14-28 LMH
c) 28-32 LMH
d) 32-40 LMH
Answer: b
Clarification: The flux assumed while designing the reverse osmosis system to treat surface water is 14-28 LMH. This depends on the influent TDS. Also, this also depends on the required TDS in the treated effluent.

5. What is the flux assumed while designing the reverse osmosis system to treat well water?
a) 3-10 LMH
b) 13-23 LMH
c) 24-30 LMH
d) 30-35 LMH
Answer: c
Clarification: The flux assumed while designing the reverse osmosis system to treat well water is 24-30 LMH. This depends on the influent TDS. Also, this also depends on the required TDS in the treated effluent.

6. What is the flux assumed while designing the reverse osmosis system to treat RO permeate?
a) 3-10 LMH
b) 13-20 LMH
c) 23-30 LMH
d) 34-50 LMH
Answer: d
Clarification: The flux assumed while designing the reverse osmosis system to treat RO permeate is 34-50 LMH. This depends on the influent TDS. Also, this also depends on the required TDS in the treated effluent.

7. What is the % flux decline per year assumed while designing the reverse osmosis system for treating surface water?
a) 7.3-9.9
b) 9.9-11.2
c) 11.2-14
d) 14-16
Answer: a
Clarification: The % flux decline per year assumed while designing the reverse osmosis system for treating surface water is 7.3-9.9. The SDI considered is between 2-4. This is a very important factor while designing a reverse osmosis system.

8. What is the % flux decline per year assumed while designing the reverse osmosis system for treating well water?
a) 4.4-7.3
b) 8.5-11.5
c) 12-15
d) 15-18
Answer: a
Clarification: The % flux decline per year assumed while designing the reverse osmosis system for treating surface water is 4.4-7.3. The SDI considered is between 2-4. This is a very important factor while designing a reverse osmosis system.

9. What is the % flux decline per year assumed while designing the reverse osmosis system for treating RO permeate water?
a) 2.3-4.4
b) 4.4-7.3
c) 7.3-9.9
d) 12-16
Answer: a
Clarification: The % flux decline per year assumed while designing the reverse osmosis system for treating surface water is 2.3-4.4. The SDI considered is between <2. This is a very important factor while designing a reverse osmosis system.

10. What is the limit of LSI assumed while designing the reverse osmosis system without a scale inhibitor?
a) <0.2
b) 0.5-1
c) 1-2
d) 2-4
Answer: a
Clarification: The LSI is <0.2 assumed without scale inhibitor while designing the reverse osmosis system. With organic scale inhibitor, the value assumed is different. It is assumed <1.8.

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250+ TOP MCQs on Advanced Oxidation Process – Ozonators and Answers

Waste Water Engineering Multiple Choice Questions on “Advanced Oxidation Process – Ozonators”.

1. How many oxygen atoms are present in the ozone?
a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: Ozonation is a chemical water treatment technique based on the infusion of ozone into water. Ozone is a gas composed of three oxygen atoms, which is one of the most powerful oxidants.

2. Ozone is one of the powerful oxidants.
a) True
b) False
Answer: a
Clarification: Ozone is a gas composed of three oxygen atoms, which is one of the most powerful oxidants. Ozonation is a type of advanced oxidation process, involving the production of very reactive oxygen species.

3. _______ is produced by subjecting oxygen to high electric voltage.
a) Carbon-monoxide
b) Carbon-dioxide
c) Pure oxygen
d) Ozone
Answer: d
Clarification: Ozone is produced with the use of energy by subjecting oxygen or high electric voltage or to UV radiation. The required amounts of ozone can be produced at the point of use but the production requires a lot of energy and is therefore costly.

4. Which of the following can be inactivated using ozone?
a) Algae
b) Fungi
c) Protozoa
d) All microbes
Answer: c
Clarification: Ozone is excellent and can even be used to inactivate microorganisms such as protozoa, which are very resistant to conventional disinfectants.

5. Ozone is an unstable gas.
a) True
b) False
Answer: a
Clarification: Ozone is an unstable gas. Under suitable conditions, it splits into O2 and O. Ozonation helps in removing colour, odour and taste of the water.

6. Which of these is not an advantage of Ozonation?
a) Reaction with bacteria
b) Organics degradation
c) Equipment costs
d) Chemicals
Answer: c
Clarification: The advantages of Ozonation is that it rapidly reacts with bacteria, viruses and protozoa over a wide pH range, no chemicals are added to water and also efficient for organics degradation and inorganics removal.

7. Which of the following is not a disadvantage of Ozonation?
a) Chemicals
b) Costs
c) Energy
d) Fire hazard
Answer: a
Clarification: There are various disadvantages of Ozonation such as the equipment costs are really high, requires large amounts of energy, no residual effect, etc.

8. Which of the following is not removed by Ozonation?
a) Iron
b) Manganese
c) Magnesium
d) Bacteria
Answer: c
Clarification: Ozone is a colourless gas that has an odour similar to the smell of the air after a major thunderstorm.

9. What is the maximum time required for ozone degradation?
a) 15 minutes
b) 30 minutes
c) 45 minutes
d) 60 minutes
Answer: b
Clarification: Organic particles and chemicals will be eliminated through either coagulation or chemical oxidation. Ozone is unstable, and it will degrade over a time frame ranging from a few seconds to 30 minutes. The rate of degradation is a function of water chemistry, pH and water temperature.

10. What is the average ozone concentration created during Ozonation?
a) 1000 mg/l
b) 5000 mg/l
c) 10000 mg/l
d) 15000 mg/l
Answer: c
Clarification: In general, an ozonation system includes passing dry, clean air through a high voltage electric discharge, i.e., corona discharge, which creates and ozone concentration of approximately 1% or 10,000 mg/L.

11. Which of the following is not correct regarding Ozonation?
a) Does not requires chemicals
b) Eliminates bad taste
c) Eliminates odour
d) Operational costs are low
Answer: d
Clarification: The process of Ozonation does not require chemicals, it eliminates bad taste and odour and the operational costs of ozonation are really high.

12. What is the colour of ozone?
a) Violet
b) White
c) Grey
d) Colourless
Answer: d
Clarification: Ozone (O3) or trioxide is a colourless odourless gas made of oxygen. It is sometimes called the activated oxygen. It contains three atoms of oxygen rather than the two atoms we normally breathe.

13. Ozone is formed by the interaction of _______
a) UV or O2
b) O and O2
c) O and UV
d) O2 and CO
Answer: a
Clarification: Stratospheric ozone is formed naturally through the interaction of solar ultraviolet (UV) radiation with molecular oxygen (O2). The stratospheric “ozone layer” extends from approximately six to thirty miles above the earth’s surface and reduces the amount of harmful UV radiation reaching the Earth’s surface.

14. In which year was the structure of ozone determined?
a) 1865
b) 1875
c) 1885
d) 1895
Answer: a
Clarification: Ozone’s odour is sharp, reminiscent of chlorine and detectable by many people at concentrations of as little as 100 ppb in air. Ozone’s O3 structure was determined in 1865.

15. In which year was the ozone named?
a) 1829
b) 1839
c) 1849
d) 1859
Answer: b
Clarification: In1839, he succeeded in isolating the gaseous chemical and named it “ozone”, from the Greek word ozein meaning “to smell”. For this reason, Schoenbein is generally credited with the discovery of ozone.

16. At what pH ozonation is carried out?
a) 8
b) 9
c) 11
d) 7
Answer: a
Clarification: At pH 8, ozonation is carried out using UV rays. This produces free OH radical. These OH radical oxidizes the organic content present in the waste water.

17. Photo catalysis uses which of the following methods to produce free radicals?
a) UV rays
b) UV + TiO2
c) Ozone + UV
d) TiO2
Answer: b
Clarification: Photocatalysis utilizes TiO2 and UV to produce free radical OH. This method doesn’t involve ozone directly in order to produce OH radicals. This is a non- ozone based method to produce OH radicals.

18. How is the electrical requirement for the ozonation process expressed mathematically?
a) EE/O =EEt/ Vlog(Ci-Cf)
b) EE/O =EEt/ (Ci-Cf)
c) EE/O =EEt Vlog(Ci-Cf)
d) EE/O =EEt(Ci-Cf)
Answer: a
Clarification: EE/O =EEt/ Vlog(Ci-Cf) is the mathematical representation of the electrical requirement for the ozonation process. Here EE/O is electrical requirement for the ozonation process. V is the volume of the liquid to be treated.

19. What are the byproducts of the breakdown of the organic compounds by UV rays?
a) CO
b) CO2 + H2O
c) H2CO3 and water
d) CO + H2O
Answer: b
Clarification: The byproducts of the breakdown of these organic compounds is H2O and CO2. In most cases, it is broken down into aldehydes. In certain cases, it is broken down into carboxylic acids also.

20. In what range is the EE/O present in order to reduce one log of reduction?
a) 0-20 KWH
b) 20-265 KWH
c) 265-365 KWH
d) 365-650 KWH
Answer: b
Clarification: The EE/O is present in between 20-265 KWH in order to reduce one log reduction. This requires around 5-6 ppm of H2O2. In some cases the H2O2 is also not necessary.

250+ TOP MCQs on Construction & Planning of Sewer System and Answers

Waste Water Engineering Multiple Choice Questions on “Construction & Planning of Sewer System”.

1. The process that involves connecting pipelines and sewer appurtenances to transport waste to sewage treatment centres is called?
a) Connecting pipelines
b) Pipelines construction
c) Sewer construction
d) Sewage construction
Answer: c
Clarification: Sewers are the pipelines to carry sanitary sewage and storm water to treatment plants or centres. The process of connecting pipelines and sewer appurtenances to transport waste to sewage treatment plants is called sewage construction.

2. Pipeline networks are designed by engineers and installed by sewer contractors in accordance with federal and state regulations.
a) True
b) False
Answer: a
Clarification: To construct sewer systems certain rules and regulations have to be followed based on the quality of pipes chosen, alignment and so on. Pipeline networks are designed by engineers based on city and installed by sewer contractors.

3. Sewer systems can also be referred as _________
a) Sewage
b) Sewerage
c) Storm
d) Wastewater
Answer: b
Clarification: Sewer systems are also referred to as sewerage and can be comprised of storm sewers, sanitary sewers, or a combination of both. Sewerage starts at the building’s drainage system and is transported through sewer pipeline until it reaches a sewage treatment plant.

4. On which of the factors mentioned below, the type of the sewer installed does not depend on?
a) Usage pattern
b) Terrain
c) location
d) storm water
Answer: d
Clarification: Storm water does not act as a distinctive factor for the installation of sewer systems. The type of sewer installed depends upon the terrain, where it is placed and the uses. Sanitary sewers are the most common type of system used to transport wastewater and industrial waste.

5. __________ is required to transport storm water runoff from roofs, parking lots, streets, and highways to a point of discharge.
a) Sanitary sewers
b) Storm sewers
c) Wastewater sewers
d) Water sewers
Answer: b
Clarification: There are different types of sewers used based on a type of flow it is designed to carry. Storm sewers are required to transport storm water runoff from roofs, parking lots, streets, and highways to a point of discharge. Storm drainage system helps to minimize flooding and soil erosion.

6. Combined sewer systems are no longer installed due to the water pollution problems they present.
a) True
b) False
Answer: a
Clarification: As combined sewer systems carry both sanitary sewage and storm water, they overflow when storm water rate is high during rainy season. This causes water pollution. However, these sewer systems are still used by older cities located primarily in the Northwest, Northeast, and Great Lakes regions.

7. Which of the following factors mentioned below marks essential for planning sewer systems for a community?
a) Usage pattern
b) Terrain
c) Location
d) Wastewater flow
Answer: d
Clarification: Planning is needed when designing sewer networks. Calculating the wastewater flow for the community is the most essential factor. The calculation of wastewater flow shows the size of the sewer to be considered.

8. The abbreviation of SUE is?
a) Subsurface utility engineering
b) Surface utility engineering
c) Storm usage engineering
d) Storm utility engineering
Answer: a
Clarification: SUE stands for subsurface utility engineering. Before SUE, a survey is carried out. It helps contractors locate pipelines and subsurface utilities using a variety of detection tools such as ground penetrating radar and evacuation pipe.

9. Which of these is the most common pipeline installation method?
a) Trench sewer construction
b) Storm sewer construction
c) Pipeline construction
d) Tunnel construction
Answer: a
Clarification: Trench sewer construction is the most common pipeline installation method. At grade level, sewers can be installed and protected by an embankment or a wall, or placed inside tunnel walls.

10. The type of wastewater treatment process for treating wastewater or industrial wastewater using aeration and biological flocs is called?
a) Active sludge process
b) Aeration
c) Biological aeration
d) Anaerobic digestion
Answer: a
Clarification: One of the sewer wastewater treatment processes is a biological treatment known as activated-sludge process. Wastewater is agitated and aerated to remove solids and oxidation methods are introduced to activate decomposition.

11. What is the abbreviation of SSMP?
a) Storm and Sewage Management Plan
b) Sewer System Management Plan
c) Soil and Storm Management Plan
d) Storm System Management Plan
Answer: b
Clarification: SSMP stands for Sewer System Management Plan. This is a document that any agency uses to manage the wastewater collection system effectively. It helps in improving the condition of the collection system infrastructure.

12. For which of the following reason SSMP is not used?
a) Minimizing sanitary sewer overflows
b) Minimizing infiltration/ inflow
c) Reducing sewer size
d) Maintaining the condition of a collection system
Answer: c
Clarification: Sewer System Management plan is mainly used to maintain and improve the condition of the collection system infrastructure in order to provide reliable service for the future. Reducing the size of the sewers may lead to overflow conditions during the periods of high storm.

13. SSMPs are used to minimize the number and impact of sanitary sewer overflows that occur.
a) True
b) False
Answer: a
Clarification: SSMP is a document used to manage wastewater systems effectively. Hence one of the goals of Sewage System Management Plan is to minimize the number and impact of sanitary sewer overflows that occur in few regions.

14. The legal entity that is responsible for the wastewater collection system is called ___________
a) Collection system agency
b) Sewer system agency
c) Water collection agency
d) Storm collection agency
Answer: b
Clarification: The legal entity that is responsible for the wastewater collection system is the Wastewater Collection System Agency. It is also called Sewer System Agency.

15. SORP stands for?
a) Storm Overflow Response Plan
b) Sewer Overflow Response Plan
c) Sanitary Overflow Response Plan
d) Sewage Overflow Response Plan
Answer: b
Clarification: SORP stands for Sewer Overflow Response Plan. It is the fourth revised version posted in the Public Document Repository on May 9, 2011, by Waterworks and sanitary sewer board.

250+ TOP MCQs on Different Types of Reactors in Water Treatment – 1 and Answers

Waste Water Engineering Multiple Choice Questions on “Different Types of Reactors in Water Treatment – 1”.

1. In which of the following systems no flow is added or allowed to leave during the design detention time?
a) Arbitrary flow reactor
b) Fluidized bed reactor
c) Mixed batch reactor
d) Packed bed reactor
Answer: c
Clarification: Arbitrary reactor is any degree of partial mixing between plug-flow and complete-mix. Where no flow is added or allowed to leave during the design detention time is called mixed batch reactor.

2. In __________ reactor the bed is filled with a packing material that expands when wastewater moves upwards.
a) Fluidized bed reactor
b) Packed bed reactor
c) Plug flow reactor
d) Mix batch reactor
Answer: a
Clarification: Fluid particles pass through the tank and are discharged in the same sequence in which they enter in plug flow reactor. The packing material that expands and gets fluidized when wastewater moves upward in the reactor is provided in fluidized bed reactor.

3. What is the aspect ratio of a stirred tank bioreactor?
a) 1-2
b) 2-3
c) 2-4
d) 3-5
Answer: d
Clarification: The aspect ratio of a stirred tank bioreactor is usually between 3-5. However, for animal cell culture applications, the aspect ratio is less than 2. The number of impellers depends on the size of the bioreactor and is variable.

4. The diameter of the impeller is usually 1/3 rd of the vessel diameter.
a) True
b) False
Answer: a
Clarification: The diameter of the impeller is usually 1/3 rd of the vessel diameter. The distance between two impellers is approximately 1.2 impeller diameter. Different types of impellers (Rustom disc, concave bladed, marine propeller etc.) are in use.

5. In bubble column bioreactor, the flow rate of air/ gas influences the performance of oxygen transfer.
a) True
b) False
Answer: a
Clarification: The air or gas is introduced at the base of the column through perforated pipes or plates, or metal micro porous sparger is in the bubble column bioreactor. The flow rate of the air/gas influences the performance factors —O2 transfer, mixing.

6. The vessel used for bubble column bioreactors is _______
a) Square
b) Rectangular
c) Cylindrical
d) Circular
Answer: c
Clarification: The bubble column bioreactors may be fitted with perforated plates to improve performance. The vessel used is usually cylindrical with an aspect ratio of 4-6 (i.e., height to diameter ratio).

7. In which of the following bioreactors is the vessel divided into two interconnected zones?
a) Bubble column bioreactors
b) Airlift bioreactors
c) Continuous stirred tank bioreactors
d) Packed bed bioreactors
Answer: b
Clarification: In the airlift bioreactors, the medium of the vessel is divided into two interconnected zones by means of a baffle or draft tube. Air is pumped in one of two zones. The other zone that receives no gas is the down comer.

8. Which of the following reactors is comparable to bubble column bioreactor?
a) Fluidized bed bioreactor
b) Packed bed bioreactors
c) Airlift bioreactors
d) Continuous stirred tank bioreactors
Answer: a
Clarification: Fluidized bed bioreactor is comparable to bubble column bioreactor except the top position is expanded to reduce the velocity of the fluid. The design of the fluidized bioreactors is such that the solids are retained in the reactor while the liquid flows out.

9. Which of the following bioreactor consists of biocatalysts on or within the matrix of solids?
a) Photo-bioreactors
b) Packed bed bioreactors
c) Airlift bioreactors
d) Fluidized bed bioreactor
Answer: b
Clarification: A bed of solid particles, with biocatalysts on or within the matrix of solids, packed in a column constitutes a packed bed bioreactor. The solids used may be porous or non-porous gels, and they may be compressible or rigid in nature.

10. Which bioreactor is designed for fermentation?
a) Photo bioreactors
b) Continuous stirred tank bioreactors
c) Fluidized bed bioreactor
d) Airlift bioreactors
Answer: a
Clarification: The bioreactors designed for fermentation that can be carried out either by exposing to artificial illumination or sunlight is called Photo bioreactors.

11. The array of tubes or flat panels constitutes ________ in photo bioreactors.
a) Light receiving systems
b) Heating systems
c) Cooling systems
d) Radiation emitting systems
Answer: a
Clarification: Glass or more commonly transparent plastic is used to make photo bioreactors. The array of tubes or flat panels constitutes light receiving systems (solar receivers).

12. Hydrolysis of chlorine in water has a rate constant of 11 s-1. What does this imply?
a) It is a slow reaction.
b) It is a moderate reaction
c) It is a fast reaction
d) It is a very slow reaction
Answer: c
Clarification: Hydrolysis of chlorine in water is a first order reaction. Any first order reactions with rate constant > 1s-1 is considered as a fast reaction. Hence the above reaction is a fast reaction.