In which type of water demand, minimum average consumption of water takes place?
a) Domestic water demand
b) Industrial water demand
c) Institutional and commercial water demand
d) Fire demand
What is the minimum water pressure available at fire hydrants?
a) 80-100kN/m²
b) 100-150kN/m²
c) 40-60kN/m²
d) 150-200kN/m²
Water lost in theft and waste contributes to how much % of total consumption?
a) 5
b) 10
c) 15
d) 20
Which is the correct statement regarding per capita demand?
a) Daily water required by an individual
b) Water required for various purposes by a person
c) Water required by an individual in a year
d) Annual average amount of daily water required by one person
Which of the following statement is correct?
a) Rich class consumes less water
b) Intermittent water supplies leads to less water consumption
c) Loss of water is more if the pressure in the distribution system is less
d) Water consumption is less in flush system
What is the design period for the water treatment unit?
a) 10 years
b) 15 years
c) 20 years
d) 30 years
What is the design discharge for intake structures?
a) Maximum daily demand
b) Maximum hourly demand
c) Maximum weekly demand
d) Average daily demand
In which of the following units, design period is maximized?
a) Distribution system
b) Demand reservoir
c) Water treatment unit
d) Pipe mains
The size of suspended solids lies in the range of ________
a) 10-3 – 10-6 mm
b) 103 – 106 mm
c) 10-1 – 10-3 mm
d) 101 – 103 mm
Suspended solids are measured by which of the following?
a) Turbidity rod
b) Gravimetric test
c) Chromatography
d) Jackson’s turbidity meter
The maximum permissible limit for suspended solids is ____________
a) 10 mg/l
b) 20 mg/l
c) 30 mg/l
d) 40 mg/l
Identify the correct relation between the following?
a) Dissolved solid = Total solid + Suspended solid
b) Dissolved solid = Total solid – Suspended solid
c) Total solid = Dissolved solid / Suspended solid
d) Dissolved solid = Suspended solid – Total solid
Which method is used to measure the color of water?
a) Gravimetric analysis
b) Chromatography
c) Tintometer method
d) Hydrometer analysis
1 TCU (True Color Unit) is equivalent to _____
a) The color produced by 1 g of platinum cobalt
b) The color produced by 1 mg of platinum cobalt
c) The color produced by 1 mg of platinum cobalt in 1L of distilled water
d) The color produced by 1 mg of platinum cobalt in 1mL of distilled water
The range for threshold odour number is __________
a) 0-3
b) 1-5
c) 1-3
d) 0-5
One JTU is equivalent to turbidity produced by __________
a) 1mg of fine silica dissolved in 1L of distilled water
b) 1g of fine silica dissolved in 1L of distilled water
c) 1g of fine silica dissolved in 1ml of distilled water
d) 1mg of fine silica dissolved in 1ml of distilled water
If the PO value is 6, what does it imply?
a) No perceptible odour
b) Very faint odour
c) Very distinct odour
d) Extremely strong odour
The range of temperature of water that is required to do the temperature test is __________
a) 10-250C
b) 0-250C
c) 10-300C
d) 20-300C
Which of the following statement is wrong regarding turbidity?
a) It is an extent to which light is absorbed by particles in the water
b) It is expressed in ppm
c) It depends on the fineness of particle present in the water
d) Turbidity rod is a laboratory method to measure turbidity
The permissible limit of turbidity of domestic water is ____ ppm.
a) 5-10
b) 1-5
c) 10-50
d) 10-30
What is the full form of NTU in context with turbidity?
a) Number of transfer unit
b) Neurological turbidity unit
c) Nephelometric turbidity unit
d) Network terminal unit
When depth of insertion of turbidity rod increases, the reading in the turbidity rod ___
a) Decreases
b) Increases
c) First decrease, then increase
d) Remains constant
Chlorides are estimated by titration with a standard silver nitrate solution by using _______ as an indicator.
a) Potassium manganate
b) Potassium chloride
c) Potassium chromate
d) Potassium dichromate
Which of the following statement is wrong regarding permanent hardness?
a) It is also called carbonate hardness
b) It is due to the presence of sulfates, chlorides and nitrates of calcium and magnesium
c) It cannot be removed by boiling
d) It requires special methods of water softening to get removed
One degree of hardness is equivalent to ___ ppm.
a) 2
b) 1
c) 10
d) 100
a) Excessive hard water
b) Reasonably soft water
c) Very hard water
d) Hard water
In which method of determining total hardness of water is based on the premise that hardness producing substance react with soap and form insoluble compounds before lather is produced?
a) Clark’s method
b) Hehner’s method
c) Versenate method
d) EDTA method
What is the indicator used in EDTA method?
a) Potassium chromate
b) Potassium dichromate
c) Potassium chloride
d) Erio chrome, black T
The permissible limit of pH preferred for potable water is ___ ppm.
a) 6.5-9
b) 7-8.5
c) 10-14
d) 0-7
What is the concentration of H+ ions in moles/L in water if the pOH value is 6?
a) 10-6
b) 10-7
c) 10-8
d) 10-9
Which type of bacteria has a rod shaped structure?
a) Bacilli
b) Cocci
c) Spirilla
d) Vibrio
________ represents the bacterial density that is most likely to be present in water.
a) BOD
b) COD
c) MPN
d) Coliform index
Which of the following is a better test to identify Coliforms?
a) Coliform index
b) Multiple tube fermentation
c) MPN test
d) Membrane filter technique
What is the temperature at which MPN test is performed?
a) 35oC
b) 37 oC
c) 40oC
d) 45 oC
Which of the following statement is/are correct regarding coliform bacteria?
i. It is gram negative
ii. It is rod shaped bacteria
iii. It is a harmless aerobic microorganism
a) i, ii, iii
b) ii, iii
c) i, iii
d) i, ii
Which of the following is the disease caused by bacterial infections?
a) Amoebic dysentery
b) Infectious hepatitis
c) Typhoid fever
d) Poliomyelitis
The number of bacterial colonies by Agar plate count test should not exceed ____ per ml for potable water.
a) 1
b) 10
c) 100
d) 1000
If the acid and gas are formed in the multiple tube fermentation technique, the test is _____
a) Positive
b) Continued
c) Negative
d) Discarded
Which bacteria cause the reddish brown deposits in the tank?
a) Escherichia coli bacteria
b) Bacterium coli bacteria
c) Iron bacteria
d) Sulphur bacteria
Which bacteria results in the corrosion of iron and steel pipes embedded in soil?
a) Escherichia coli bacteria
b) Bacterium coli bacteria
c) Iron bacteria
d) Sulphur bacteria
What is the primary purpose of screening in water treatment?
a) To remove dissolved chemicals
b) To remove bulky, suspended, or floating matters
c) To disinfect water
d) To adjust water hardness
Which process involves retaining water in a quiescent basin so that heavy particles settle by gravity?
a) Filtration
b) Adsorption
c) Plain sedimentation
d) Coagulation
According to Stokes' law, the settling velocity (vₛ) of a small spherical particle is directly proportional to which of the following?
a) Its diameter
b) The square of its diameter
c) The cube of its diameter
d) The square root of its diameter
Why is retention time an essential factor in the design of a sedimentation tank?
a) It ensures that water temperature is maintained
b) It provides sufficient time for suspended solids to settle by gravity
c) It increases the water pH levels
d) It speeds up chemical reactions in the water
In the design of a sedimentation tank, the overall depth (D) is calculated as the sum of:
a) Freeboard and sludge zone depth only
b) Inlet depth and outlet depth only
c) Freeboard, sludge zone depth, and the effective depth of the settling zone
d) The effective depth of the settling zone alone
Sedimentation tanks are classified based on the direction of water flow. Which of the following is NOT a recognized classification based on flow direction?
a) Horizontal flow tanks
b) Vertical flow tanks
c) Diagonal flow tanks
d) Rectangular tanks with longitudinal flow
In sedimentation tank design, the Surface Overflow Rate (SOR) is defined as Q/(B∙I). What does SOR indicate?
a) The chemical dosage rate
b) The rate at which water exits the tank surface
c) The settling velocity of particles
d) The retention time of the sludge
According to design guidelines, what retention time is typically recommended for a closed continuous water treatment system (PS) using sedimentation?
a) 1–4 hours
b) 4–8 hours
c) 8–12 hours
d) 30–36 hours
Which of the following is not an objective of water treatment?
a) To remove objectionable colour and odor
b) To kill pathogens
c) To concentrate impurities
d) To reduce water hardness
Where is the screening operation typically located in a water treatment plant?
a) At the raw-water intake or pumping station
b) In the disinfection unit
c) At the filtration stage
d) In the final distribution system
What is the primary purpose of a coarse screen?
a) To remove fine sediment particles
b) To remove bulky suspended solids
c) To dissolve organic impurities
d) To adjust the water pH
Which process relies on gravity alone to remove heavy suspended particles without the use of chemicals?
a) Filtration
b) Plain sedimentation
c) Coagulation
d) Flocculation
Stokes’ law is used to determine which of the following for a spherical particle?
a) Its chemical composition
b) Its settling velocity
c) Its color intensity
d) Its temperature sensitivity
In Stokes’ law, which variable represents the dynamic viscosity of the water?
a) ρw
b) g
c) d
d) μ (mu)
In the design of a sedimentation tank, what does the detention time refer to?
a) The time taken to pump water through the system
b) The interval between cleaning cycles
c) The duration water is retained in the tank for settling
d) The time required for chemical reactions during coagulation
In sedimentation tank design, the overall depth (D) is calculated as the sum of which components?
a) Inlet zone depth and outlet zone depth
b) Freeboard, sludge zone depth, and effective settling depth
c) Only the effective settling depth
d) Sludge zone depth and the chemical dosing depth
Which of the following is a common construction material for sedimentation tanks?
a) Reinforced Cement Concrete (RCC)
b) Wood
c) Plastic
d) Glass
What is a major disadvantage of quiescent (fill and draw) sedimentation tanks?
a) They are too complex to operate
b) They require low retention times
c) They demand large volumes and long cycle times
d) They cannot remove coarse particles effectively
Which type of sedimentation tank processes water continuously without a fill and draw cycle?
a) Quiescent tank
b) Batch tank
c) Continuous flow tank
d) Static tank
In continuous flow sedimentation tanks, what does the Surface Overflow Rate (SOR) indicate?
a) The chemical dosing rate
b) The rate at which water flows over the surface of the settling zone
c) The rate of sludge removal
d) The sediment deposition velocity
What is the purpose of a hopper bottom in vertical flow sedimentation tanks?
a) To improve the aesthetics of the tank
b) To facilitate the collection and removal of settled sludge
c) To increase the freeboard of the tank
d) To reduce the inflow velocity
Under Stokes’ law for laminar flow, how does the settling velocity (vₛ) change with particle diameter (d)?
a) vₛ is independent of d
b) vₛ ∝ d
c) vₛ ∝ d²
d) vₛ ∝ d³
Which sedimentation tank design employs a central feed to produce a radial flow pattern?
a) Rectangular tank with longitudinal flow
b) Circular tank with central feed
c) Vertical flow tank
d) Diagonal flow tank
What is the role of freeboard (FB) in the design of a sedimentation tank?
a) To store extra water to prevent overflow
b) To increase the depth of the sludge zone
c) To accommodate fluctuations in water level and prevent overtopping
d) To regulate the incoming water velocity
Which term describes the process of allowing water to remain static in a settling zone so that solid particles can settle by gravity?
a) Coagulation
b) Flocculation
c) Sedimentation
d) Filtration
The overall length (L) of a sedimentation tank is calculated using the equation L = Lin + I + Lout. What does this sum represent?
a) The total effective flow length through the tank
b) The circumference of the tank
c) The effective depth of the settling zone
d) The total water storage volume
Which factor is least likely to affect the efficiency of plain sedimentation in a tank?
a) Detention time
b) Flow velocity
c) Colour of suspended particles
d) Particle density
In water treatment, what does the term "turbidity" refer to?
a) The concentration of dissolved gases
b) The clarity of the water
c) The presence of light-scattering suspended particles
d) The water’s pH level
For a discrete particle reaching point A in a sedimentation tank, what determines its actual movement?
a) Horizontal velocity only (Vh)
b) Settling velocity only (vs)
c) The vector sum of Vh and vs
d) The freeboard height
What does the Surface Overflow Rate (SOR) represent in the design of sedimentation tanks?
a) The ratio of flow velocity to detention time
b) The overflow rate or surface loading, defined as Q/(B∙I)
c) The difference between freeboard and sludge depth
d) The rate at which coagulants are added
For closed continuous water treatment systems (PS), what is the typical detention time in sedimentation tanks?
a) 1–4 hours
b) 4–8 hours
c) 8–12 hours
d) 12–16 hours
What is the typical effective depth (d) used in the design of sedimentation tanks?
a) 1–2 m
b) 2.5–5 m
c) 5–7 m
d) 7–10 m
In sedimentation tank design, which parameter is calculated as Q/(B∙I)?
a) Detention time
b) Surface Overflow Rate (SOR)
c) Flow velocity
d) Freeboard
In rectangular sedimentation tank design, what is the recommended range for the length-to-width ratio (l/B)?
a) 1 to 2
b) 2 to 3
c) 3 to 5
d) 5 to 7
Which unit in water treatment is responsible for removing bulky, suspended, or floating matters?
a) Screening
b) Clarification
c) Filtration
d) Sedimentation
What is the primary purpose of coagulation in water treatment?
a) To remove large debris
b) To form flocs from fine suspended/colloidal impurities
c) To disinfect water
d) To remove dissolved gases
Which coagulant is commonly used when water contains sufficient bicarbonate alkalinity?
a) Iron salts
b) Chlorinated copperas
c) Aluminum sulphate (alum)
d) Sodium aluminate
What is the effective pH range for using aluminum sulphate (alum) as a coagulant?
a) 4.5–6.0
b) 6.5–8.5
c) 8.5–10.0
d) 10.0–12.0
Which coagulant is often used in sewage treatment?
a) Aluminum sulphate (alum)
b) Iron salts
c) Chlorinated copperas
d) Sodium aluminate
After adding the coagulant in water treatment, which two processes follow to aid in particle removal?
a) Sedimentation and filtration
b) Coagulation and disinfection
c) Coagulation and flocculation
d) Screening and mixing
What is the main objective of the mixing step in the coagulation process?
a) To rapidly settle the particles
b) To fully disperse the coagulant throughout the water
c) To generate turbulence for sedimentation
d) To separate sludge from water
Which characteristic best describes the flocculation process in water treatment?
a) Rapid and vigorous mixing
b) Slow stirring that permits floc buildup
c) Immediate particle sedimentation
d) High-velocity flow in the flocculator
In a combined coagulation–sedimentation tank for smaller projects, what is the typical detention period for the sedimentation phase?
a) 15–40 minutes
b) 3–4 hours
c) 4–8 hours
d) 6–12 hours
Which design consideration is important in mixing basins used for coagulation?
a) End openings between baffles and basin wall should not exceed 0.6 m
b) Channel velocity must be above 1 m/s
c) Detention time must be less than 5 minutes
d) The basin should be free of any baffles
Which process typically follows sedimentation in a conventional water treatment plant?
a) Screening
b) Filtration
c) Coagulation
d) Disinfection
The effectiveness of a sedimentation tank is largely determined by which key parameter?
a) Freeboard
b) Surface Overflow Rate (SOR)
c) Mixing intensity
d) Chemical dosing rate
For a discrete particle in a sedimentation tank to be effectively removed, its settling velocity (vₛ) must be:
a) Less than Q/(B∙I)
b) Equal to Q/(B∙I)
c) Greater than or equal to Q/(B∙I)
d) Unrelated to Q/(B∙I)
The effective volume (V) of a rectangular sedimentation tank is given by:
a) V = l + B + d
b) V = l × B × d
c) V = Q/(B × d)
d) V = B/(l × d)
Which statement best describes circular sedimentation tanks?
a) They have a rectangular layout with fixed dimensions.
b) Their diameter typically ranges up to 30 m (or sometimes up to 60 m) with a bottom slope designed as a gradual slope (e.g., 1:12) from the periphery to the center.
c) They rely solely on chemical treatment for sedimentation.
d) They are not used in water treatment due to poor performance.
What is the primary purpose of free board in sedimentation tank design?
a) To store extra water for future use
b) To provide additional vertical space to accommodate water level fluctuations and wind effects
c) To increase the tank’s sediment capacity
d) To reduce the Surface Overflow Rate (SOR)
What is the typical depth range of the sludge zone in sedimentation tanks?
a) 0.1 to 0.3 m
b) 0.5 to 1 m
c) 1 to 2 m
d) 2 to 3 m
In rectangular sedimentation tanks, the typical inlet and outlet zone lengths are:
a) 0.05 to 0.1 m
b) 0.2 to 1 m
c) 1 to 2 m
d) 2 to 3 m
In the coagulation process, the primary objective is to:
a) Remove large debris from raw water
b) Form flocs from fine suspended and colloidal impurities
c) Adjust the water’s temperature
d) Remove dissolved gases
Which of the following is the effective pH range for using aluminum sulphate (alum) as a coagulant?
a) 4.0 to 5.5
b) 6.5 to 8.5
c) 8.5 to 10.0
d) 10.0 to 12.0
What is the typical velocity range in a mixing basin for the coagulation process?
a) 0.05 m/s to 0.1 m/s
b) 0.15 m/s to 0.45 m/s
c) 0.5 m/s to 1 m/s
d) 1 m/s to 1.5 m/s
Which design factor in the flocculation basin helps prevent floc breakage?
a) High chemical dosage
b) An outflow velocity maintained between 0.15 to 0.25 m/s
c) Increased free board
d) Very high turbulence levels
In a combined coagulation–sedimentation tank for small projects, the detention period for the floc chamber is typically:
a) 5–10 minutes
b) 15–40 minutes
c) 1–2 hours
d) 3–4 hours
During jar tests to determine optimum coagulant dosage, which water characteristic is most critical?
a) Water temperature
b) Bicarbonate alkalinity
c) Chlorine residual
d) Freeboard height
Which of the following coagulants is generally considered more cost-effective for public water supplies?
a) Sodium aluminate
b) Aluminum sulphate (alum)
c) Chlorinated copperas
d) Iron salts
The primary principle behind the flocculation process in water treatment is to:
a) Achieve high-speed mixing for rapid particle break-up
b) Utilize slow stirring to promote collisions and floc buildup
c) Initiate rapid sedimentation of dissolved substances
d) Adjust the water pH quickly
In a coagulation–sedimentation tank for small projects, the sedimentation phase typically has a detention period of:
a) 15–40 minutes
b) 1–2 hours
c) 3–4 hours
d) 6–8 hours
Which feature is commonly incorporated into mixing basins to ensure thorough dispersion of the coagulant?
a) A wide, open basin without partitions
b) The use of baffle walls
c) Increased depth of the sludge zone
d) A larger free board area
What is the typical detention period recommended for the flocculation process?
a) 1–5 minutes
b) 10–40 minutes
c) 1–2 hours
d) 2–3 hours
How does Brownian motion affect colloidal particles in water treatment?
a) It enhances their settling rate.
b) It keeps them in suspension, making removal more difficult.
c) It causes rapid aggregation into heavy flocs.
d) It increases the water’s density.