Drinking Water Treatment: Important 25 MCQs

COMPETITIVE EXAM MCQs SERIES of ENVIRONMENTAL SCIENCE for UGC-NET/JRF, SLET, ARS, GATE, and other entrance tests – Environmental Pollution and Control – Drinking Water Treatment.

Syllabus Outline

1. Major water pollutants and associated health impact on human health.
2. Drinking water standards and the need for water treatment facilities.
3. Unit operation of water treatment plant (e.g. coagulation, flocculation, sedimentation, filtration, and disinfection: chlorination, ozonation, UV irradiation).
4. Membrane filtration (microfiltration, ultrafiltration, nanofiltration, reverse osmosis), adsorption, and ion exchange.
5. Principles, mechanisms, design considerations, operation, and maintenance of each treatment process.

This quiz contains the concept-based most frequently asked 25 MCQs of “Environmental Pollution and Control – Drinking Water Treatment“. Each question has a single correct/most appropriate answer.

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1. Which of the following processes/unit operations of conventional wastewater treatment is the correct order starting from the inflow?

a) Coagulation & Flocculation – Sedimentation – Filtration – Disinfection

b) Sedimentation – Coagulation & Flocculation – Filtration – Disinfection

c) Preliminary treatment, Primary clarifier – Aeration – Secondary clarifier – Filtration – Disinfection

d) Preliminary treatment, Aeration – Primary clarifier – Activated sludge process – Secondary clarifier – Filtration – Disinfection

2. Choose the correct order with an increasing dose of coagulants

I – Restabilization or charge reversal

II – No destabilization

III – Destabilization by sweep floc

IV – Destabilization by charge neutralization

a) I, II, III, IV

b) IV, II, I, III

c) II, IV, I, III

d) III, I, IV, II

3. The magnitude of the buoyant force acting on a particle in water depends on which factors?

a) Weight and shape of the particle

b) The density of the water and mass of the particle

c) The density of the water and volume of the particle

d) The density, weight, and shape of the particle

4. What is the key mechanism by which inter-particle contact occurs in a simple coagulation and flocculation process?

a) Brownian motion, stirring and precipitation

b) Thermal motion, Centrifugal and Gravitational affect

c) Gravitational, solvation and drag force

d) Thermal motion, bulk fluid motion and particle settling

5. Inactivation of microorganisms/pathogens in water distribution systems is classified as:

a) Primary disinfection

b) Secondary disinfection

c) Tertiary disinfection

d) Quaternary disinfection

6. At which zone of coagulation and flocculation turbidity is efficiently removed?

a) Restabilization or charge reversal

b) No destabilization

c) Destabilization by charge neutralization

d) Destabilization by sweep floc

7. Various species are formed in coagulation and flocculation with alum due to hydrolysis of alum salt such as Al³⁺, Al(OH)₂⁺, Al(OH)₂⁺, Al(OH)₃(s), Al(OH)₄^–, Al(OH)₅^-2. Which species is predominant at pH above 8?

a) Al₃⁺

b) Al(OH)₂⁺

c) Al(OH)₃(s)

d) Al(OH)₄^–

8. Which of the following is not a limitation of natural coagulants such as crude Moringa oleifera (drumstick) seed extract?

a) It increases colloidal particles

b) It increases organic matter and chlorine demand

c) It causes colour, taste & odour problems by long periods of water storage

d) Unable to coagulate orthophosphate & nitrates

9. Flotation is a physical process used in water treatment to remove

a) Particles that are denser than water

b) Pertinacious material from the water

c) Colloidal particles including clay and bacteria

d) Particles that are lighter than water

10. Which species is more potent in the disinfection process?

a) HOCl

b) OCl^–

c) Cl2 (g)

d) Cl2 (aq)

11. Perikinetic flocculation is controlled by:

a) Brownian motion

b) Both Brownian motion and Intrinsic properties of the system

c) Intrinsic Properties of the system

d) Mechanical mixing

12. The majority of the suspended impurities get removed in a slow sand filter by:

a) Absorption

b) Adsorption

c) Coagulation

d) Filtration

13. In the sedimentation tank, the drag force on a particle is directly proportional to:

a) Density of the liquid

b) Velocity of the particle

c) Volume of the particle

d) Projected area of the particle

14. Flotation is a physical process used in wastewater treatment to remove

a) Particles that are denser than water

b) Pertinacious material from the water

c) Colloidal particles including clay and bacteria

d) Particles that are lighter than water

15. Sedimentation is a physical process used in wastewater treatment to remove

a) Particles that are denser than water

b) Particles that are less dense than water

c) Pertinacious material from the water

d) Colloidal particles including clay and bacteria

16. Chlorination of water and wastewater may result in the formation of:

a) Chlorox

b) Chloramines

c) Hypochlorites

d) Chlorinated hydrocarbons

17. Control of the disinfection process is usually based on maintaining total residual chlorine of at least ______for a contact time of at least 30 minutes at design flow.

a) 10 mg/L

b) 0.1 mg/L

c) 2.5 mg/L

d) 1.0 mg/L

18. Extract of Seeds of Moringa Oleifera (drumstick) has the potential to replace chemical coagulant since it contains about 36% natural coagulative______________.

a) Protein

b) Carbohydrate

c) Lipid

d) Glycolipids

19. Bone char filters are effective for the removal of:

a) Organic matter and decreased chlorine demand

b) Heavy metals such as arsenic and also fluoride

c) Pathogenic microorganisms such as bacteria and viruses

d) Colloidal particles and colour-causing molecules

20. Chemical coagulant can be used to reduce______ between colloidal particles.

a) Electrostatic attraction

b) Intermolecular or Van der Waals force of attraction

c) Gravitational force of attraction

d) Electrostatic repulsion

21. The enmeshment of colloidal particles in a hydrolyzed chemical coagulant precipitate is known as:

a) Perikinetic floc

b) Orthokinetic floc

c) Sedimentation

d) Sweep floc

22. The random motion imparted to the particle by collisions between the molecules of the fluid surrounding the particle and the particle is known as:

a) Floatation

b) Sedimentation

c) Brownian motion

d) Sedimentation coefficient

23. Laboratory studies using the _____ are adequate to select the optimum coagulant dose for water treatment.

a) Column test

b) Hydraulic flocculation test

c) Gravimetric test

d) Jar test

24. The rate of aggregation of destabilized colloidal particles in a simple coagulation and flocculation is dependent upon:

a) Size of the particles

b) Charges on the particles

c) Amount of bulk fluid and density of particles

d) The rate at which collision occurs between particles

25. The resultant force (F_net) responsible for floating particles in a fluid can be theoretically estimated using the following formula (F_g = gravitational force, F_b = buoyant force and F_d = Drag force).

a) F_net = F_g – F_b – F_d

b) F_net = F_g + F_b – F_d

c) F_net = F_g – F_b + F_d

d) F_net = F_b – F_g – F_d

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References

1. American Water Works Association (2017) Water Treatment Plant Design, McGraw-Hill Education, 5th edition.
2. Sharma, S. K. (2019) Water Pollution and Its Management, Khanna Publishers, 1st edition.
3. Rao, N. N. (2006) Water Pollution, Tata McGraw-Hill Education, 2nd edition.