Category: WASTE WATER Engineering Objective Questions

250+ TOP MCQs on Total Dissolved Solids – 1 and Answers

Waste Water Engineering Multiple Choice Questions on “Total Dissolved Solids – 1”.

1. Cations with ______ increase corrosivity.
a) Bromide
b) Chloride
c) Iodide
d) Sulphide
Answer: b
Clarification: Cations combined with carbonates can lead to an increase in the scale formation and bitter taste. Cations combined with chloride can lead to an increase in the corrosivity.

2. _______ is the universal solvent.
a) Organic solvents
b) Inorganic solvents
c) Water
d) Acid
Answer: c
Clarification: Water is a good solvent and picks up impurities easily. Pure water is tasteless, colourless and odourless and is often called the universal solvent.

3. Total dissolved solids consist of cations only.
a) True
b) False
Answer: b
Clarification: The total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.

4. _______ is used as an indicator test to determine the general quality of the water.
a) Oxidation test
b) Reduction test
c) Total dissolved solids test
d) Organic test
Answer: c
Clarification: The total dissolved solids test is used as an indicator test to determine the general quality of the water. The sources of total dissolved solids can include all of the dissolved cations and anions.

5. TDS decreases the efficiency of hot water heaters.
a) True
b) False
Answer: a
Clarification: The concentration of the dissolved ions may cause the water to be corrosive, salty or brackish taste, result in scale formation and interfere and decrease the efficiency of hot water heaters.

6. At what temperature is the filtrate dried in a TDS laboratory test?
a) 100˚C
b) 102˚C
c) 103˚C
d) 105˚C
Answer: c
Clarification: In a laboratory setting, the total dissolved solids are determined by filtering a measured volume of sample through a standard glass fiber filter. The filtrate (i.e., filtered liquid) is then added to a preweighed ceramic dish that is placed in a drying oven at a temperature of 103˚C.

7. What is the temperature required to remove occluded water?
a) 170˚C
b) 180˚C
c) 190˚C
d) 200˚C
Answer: b
Clarification: After the sample dries, the temperature is increased to 180˚C to remove occluded water i.e., water molecules trapped in the mineral matrix.

8. What is the standard for TDS for aesthetic considerations?
a) 250 mg/l
b) 500 mg/l
c) 750 mg/l
d) 1000 mg/l
Answer: b
Clarification: High total dissolved solids may affect the aesthetic quality of the water; interfere with washing clothes and corrode plumbing fixtures. For aesthetic reasons, a limit of 500 mg/l (milligrams per litre) has been established as part of the Secondary Drinking Water Standards.

9. On which of the factors does the relationship between TDS and conductivity does not depend on?
a) Type of ions
b) Nature of ions
c) Nature of suspended solids
d) Type of microbes
Answer: d
Clarification: There are various factors on which the relationship between TDS and conductivity depends on and they are a type of ions, their nature and also the nature of suspended solids.

10. The primary dissolved solids are assumed to be _________
a) KI
b) KCl
c) MnCl
d) AlCl
Answer: b
Clarification: Total Dissolved Solids can be measured in the field using an electronic pen and it then calculates the total dissolved solids assuming that the primary dissolved minerals are either a combination of NaCl or KCl.

11. What is the secondary standard for TDS?
a) 400 mg/l
b) 500 mg/l
c) 600 mg/l
d) 700 mg/l
Answer: b
Clarification: Primary Standards are based on health considerations and Secondary Standards are based on taste, odour, colour, corrosivity, foaming and staining properties of water.

12. The treatment options for an elevated total dissolved solid depends on _______
a) Quantity of water
b) Nature of ions
c) Nature of suspended solids
d) Type of microbes
Answer: b
Clarification: The treatment options for elevated total dissolved solids really depend on the nature of the cations and anions. It is possible to remove these solids using a water softener.

250+ TOP MCQs on Chlorinators and Answers

Waste Water Engineering Multiple Choice Questions on “Chlorinators”.

1. Which of the following is not true about gas chlorination systems?
a) Disinfection of swimming pools
b) Improves taste
c) Increases algae
d) Controls slime
Answer: c
Clarification: Gas chlorination systems can be used for the disinfection of swimming pools, improving taste, safety and odour of drinking water and for algae and slime control.

2. Which of the following methods are suggested for a water flow of less than 200 Lpm?
a) Hypochlorinators
b) Vacuum chlorinators
c) Direct feed chlorinators
d) Chlorine cylinders
Answer: a
Clarification: The simplest method of continuous chlorination of water supply systems for a water flow of less than 200 Lpm is by the use of a hypochlorinator. Hypochlorinators are motor driven pumps which are used to add hypochlorite solutions to water.

3. In hypochlorinators, the hypochlorite solution is fed into the water by means of _________
a) Pumps
b) Injectors
c) Manual methods
d) Tanks
Answer: a
Clarification: The pump pulls the hypochlorite solution out of a holding chamber and pumps it into the water to be treated. The venturi effect creates a small vacuum and pulls the chlorine solution into the water.

4. How is the amount of chlorine adjusted in hypochlorinators?
a) Increasing feed water
b) Decreasing chlorine amount
c) Varying stroke length
d) Increasing treatment time
Answer: c
Clarification: In hypo chlorinators, the amount of chlorine fed into the water is adjusted either by varying the stroke length or machine speed.

5. _______ used to perform continuous chlorination in smaller systems.
a) Vacuum chlorinators
b) Chlorine cylinders
c) Direct feed chlorinators
d) Hypochlorinators
Answer: d
Clarification: The amount of chlorine added can be adjusted by changing the strength of the hypochlorite solution. Hypochlorinators are usually used to perform continuous chlorination in smaller systems.

6. ______ are used when the supply source is greater than 200 Lpm.
a) Chlorinators
b) Vacuum chlorinators
c) Direct feed chlorinators
d) Hypochlorinators
Answer: a
Clarification: When the supply source is greater than 200 Lpm, chlorinators are more economical. To introduce chlorine solution to water, devices called chlorinators are used.

7. NaCl is hydrolysed to chlorine and ______
a) Na
b) NaOH
c) NaI
d) NaNO3
Answer: b
Clarification: Chlorinators are devices which introduce chlorine solution to water. NaCl is hydrolysed to chlorine (Cl) and NaOH.

8. What is the minimum pressure required to convert chlorine gas to liquid?
a) 3 Ksc
b) 4 Ksc
c) 5 Ksc
d) 6 Ksc
Answer: b
Clarification: NaCl is hydrolysed to chlorine (Cl) and NaOH. By pressurizing the Cl gas at 4 to 7 Ksc pressure, Cl gas is converted into liquid and the liquefied chlorine gas is filled and stored in the cylinders of 48.4-kg and 68-kg capacity or in 907-kg (one-ton) container.

9. What is the maximum weight of chlorine cylinders?
a) 807 Kg
b) 907 Kg
c) 957 Kg
d) 997 Kg
Answer: b
Clarification: By pressurizing the Cl gas at 4 to 7 Ksc pressure, Cl gas is converted into liquid and the liquefied chlorine gas is filled and stored in the cylinders of 48.4-kg and 68-kg capacity or in 907-kg (one-ton) container.

10. The liquid expands back into a gas as it leaves the cylinder.
a) True
b) False
Answer: a
Clarification: The liquid expands back into a gas as it leaves the cylinder. Whenever a substance changes state from a liquid form to a gaseous form, heat is required. The heat which is absorbed by the chlorine as it changes state in the cylinder comes from the surrounding air.

11. If chlorine is drawn off from a cylinder too quickly, the temperature of the air surrounding the tank will increase.
a) True
b) False
Answer: b
Clarification: If chlorine is drawn off from a cylinder too quickly, the temperature of the air surrounding the tank will drop and will cause frosting and lower gas flow.

12. What is the maximum draw off rate of chlorine to prevent frosting?
a) 110 Kg
b) 120 Kg
c) 140 Kg
d) 150 Kg
Answer: d
Clarification: The draw off rate should be not greater than 150 kg of gas per day from each cylinder to minimize frosting. Cylinders are joined together so that chlorine gas is drawn from several cylinders at a time.

13. What is the instrument used to measure the chlorine feed rate?
a) pH meter
b) Thermometer
c) Rotameter
d) Spectrometer
Answer: c
Clarification: Once the gas has entered the chlorinator, the chlorine feed rate is measured using an indicator known as a rotameter.

14. Injector of chlorine feed is also called as _____
a) Rotameter
b) Ejector
c) Feeder
d) Disinfector
Answer: b
Clarification: The chlorine gas is pulled into the injector, also known as an ejector. The injector consists of a pipe filled with flowing water.

15. What is the other name for vacuum chlorinators?
a) Disinfector
b) Solution feeder
c) Hypochlorinators
d) Chlorinators
Answer: b
Clarification: Vacuum chlorinator is also known as a solution feeder since the chlorine gas is dissolved into a small amount of source water, which is then piped into the main line of water to be chlorinated.

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.

250+ TOP MCQs on Sewage Filters and Answers

Waste Water Engineering Multiple Choice Questions on “Sewage Filters”.

1. Rapid filtration is used as the _______ clarifying step in municipal water treatment plants.
a) First
b) Second
c) Intermediate
d) Final
Answer: d
Clarification: Rapid filtration is used as the final clarifying step in municipal water treatment plants. Flocculation and sedimentation are provided as pre-treatment units to the rapid filter if the raw water has turbidity in excess of 10-20 NTU for an efficient process.

2. Biological action takes place in a rapid filtration unit.
a) Tue
b) False
Answer: b
Clarification: There is practically no biological action in rapid filtration although some nitrification occurs where the filtration velocity is relatively slow, where the oxygen content is adequate, and where the nitrifying bacteria finds favourable nutrients in the water.

3. How many hours does it take for filters to attain turbidity breakthrough?
a) 12-16 hours
b) 18-22 hours
c) 23-36 hours
d) 38-42 hours
Answer: c
Clarification: The filter operates usually 24-36 hours before attaining turbidity breakthrough. The influent water passes through the filter medium, the supporting layer and the underdrain where it experiences an energy loss due to frictional resistance referred to as head loss.

4. What is the maximum head loss at which the filter should be cleaned?
a) 1.5 m
b) 2 m
c) 2.5 m
d) 3 m
Answer: c
Clarification: When the head loss becomes excessive and beyond 1.5-2.5 m, the filter should be cleaned. During cleaning, the water above the filter is drained until the water lies a few centimetres above the top of the bed when air from a compressed air unit is blown in reverse to the normal flow direction at a rate of about 1-1.5 m3 free air/m2 of bed area, at a pressure of 20-35 kN/m2, for about 2-3 minutes.

5. Air is blown in the reverse direction during cleaning of filter beds.
a) True
b) False
Answer: a
Clarification: During cleaning, the water above the filter is drained until the water lies a few centimetres above the top of the bed when air from a compressed air unit is blown in reverse to the normal flow direction at a rate of about 1-1.5 m3 free air/m2 of bed area.

6. At what pressure is the air blown during cleaning?
a) 5-10 KN/m2
b) 10-15 KN/m2
c) 15-30 KN/m2
d) 20-35 KN/m2
Answer: d
Clarification: Air from a compressed air unit is blown in reverse to the normal flow direction at a rate of about 1-1.5 m3 free air/m2 of bed area, at a pressure of 20-35 kN/m2, for about 2-3 minutes.

7. What is the specified minimum time for backwash of rapid filters?
a) 2 minutes
b) 5 minutes
c) 10 minutes
d) 3 minutes
Answer: b
Clarification: The entire process of backwashing the filters and restarting the water supply takes about 15 minutes. The specified minimum backwash time for a rapid filter is 5 minutes.

8. What is the rate of backwash water?
a) 0.3-1 m/min
b) 1-1.5 m/min
c) 0.03-0.3 m/min
d) 15-3 m/min
Answer: a
Clarification: The wash water required for a rapid filter may vary from 3-6% of the total amount of water filtered. Upward wash water rates are usually of the order of 0.3-1.0 m/min.

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.