Two Marks Questions with Answers

TWO MARK QUESTION AND ANSWERS

 

1. What are the main objectives of treating water?

(i) To remove colour, dissolved gases and murkiness of water

(ii) To remove objectionable tastes and odour.

(iii) To remove the disease producing micro-organism so that water is safe for drinking purposes

(iv) To remove hardness of water

 (v) To make water suitable for industrial purposes such as brewing, dyeing and steam generation

 

2. Differentiate between unit operations and unit process in context of water treatment?

Unit Operations

Unit operations are primary treatment of water which uses physical or mechanical forces to create the desirable changes

Unit operations are mixing, agitating, aeration, absorption, membrane separation, distillation, sedimentation and filtration

Unit Processi

Unit processes are secondary treatment of water which uses chemicals or biological processes to get desirable changes during water treatment

Unit processes es are oxidation, coagulation, chlorination disinfection

 

3. What are the various unit operations and unit processes used in the treatment of water?

Screening, Plain Sedimentation, Sedimentation with coagulation, Filtration, Disinfection, Aeration, Water Softening etc.

 

4. What are the factors influencing the settling of a particle?

• Horizontal flow velocity of water

• Viscosity of water

• Size and shape of particle

• Specific gravity of the particle

• Temperature of water

• Short circuiting of flow

• Scour velocity

 

5. State stokes equation for finding settling velocity of particles?

V1 = settling velocity of particle

g = acceleration due to gravity

d = diameter of the particle

G = specific gravity of the particle

v = kinematic viscosity of particle

 

6. Differentiate between Plain Sedimentation and Sedimentation with coagulation

Plain Sedimentation: When water is detained in a tank, the large discrete suspende yot particles settle under gravity which is known as plain sedimentation. This require ($10 only a sedimentation tank.

Sedimentation with coagulation: The colloidal particles do not settle under gravity As such, coagulants such as alum, ferric chloride, chlorinated copperas etc are adde to water to make the colloidal particles to settle in a sedimentation tank. Thi process requires a flash mixer, flocculator and a sedimentation tank.

 

7. On what factors does the dose of coagulants depend?

Temperature, turbidity, pH, alkalinity, nature of coagulant, intensity and duratio br of mixing.

 

8. What are the common coagulants used in water treatment?

• Alum or aluminium sulphate

• Chlorinated copperas

• Iron salts - ferrous sulphate, ferric chloride, ferric sulphate no.

• Sodium aluminate

9. What is the significance of velocity gradient in flash mixer?

Velocity gradient (G) determines the mixing efficiency and power consumption a flash mixer. It also controls the floc formation in flocculators.

 

10. Define: Detention time and surface over flow rate for a sedimentation tank?

Detention time is theoretical time taken by a particle of water to pass betwee entry and exit of the settling tank. t = volume of tank / rate of flow

Surface loading rate or surface over flow rate

The quantity of water passing per hour per unit horizontal area is known as the ove flow rate or surface loading.

SOR or SLR = Discharge/Surface Area

 

11. What is coagulation?

The process of addition and mixing of chemicals (coagulants) in water to aid in th settling of colloidal and fine suspended particles is called coagulation.

 

12. Define Flocculation.

The process of floc formation by the aggregation of chemical precipitate and colloid is known as flocculation.

 

13. Define filtration. What are the different types of filters?

The process of passing the water through the beds of granular materials is known a filtration.

Types: Slow sand filters, Rapid sand filters, Pressure filters etc

 

14. What is schmutzdecke layer or dirty skin?

After few weeks of commissioning the sand filters, a layer of algae, bacteria protozoa, suspended particles and partly decomposed organic matter is formed o the surface of sand, which is called the dirty skin or schmutzdecke layer. This laye helps in further absorbing organic matter from water.

 

15. What is the theory of filtration?

• Mechanical straining

• Sedimentation

• Biological metabolism

• Electrolytic changes

 

16. List out advantages of rapid sand filter?

• High filtration rate 3000 to 6000 litres/m2/hr

• Occupies less area

• Less initial cost

•  Donoldo boilggs

 

17. What are the operational problems in sand filters?

Formation of mud balls: Mud from atmosphere may accumulate on the sand surface. It is broken by mechanical rakes or by washing with water under pressure.

Cracking or clogging of filters: The fine sand in the top layers may shrink causing ow shrinkage cracks.

Air binding: The dissolved air and gases from water, occupy the void space of filter media. This can be controlled by preventing any algal growth on filters and by Tavo preventing super-saturation of water.

 

18. What are the advantages and disadvantages of pressure filters?

Advantages: Compact, automatic operation, requires small area for installation, very high rate of filtration 6000 to 15000 litres per hour per square meter.

Disadvantages: Treatment cost is high, efficiency of bacteria removal is low.

 

19. Differentiate between sterilisation and disinfection?

 

20. List the different methods of disinfection. Enumerate the mechanism o disinfection process?

Mechanism of disinfection may be chemical or physical which are tabulated below

Physical: Boiling, Ultra-violet radiation.

Chemical: Chlorination, Bromine and Iodine, Potassium permanganate, Ozon Excess Lime.

 

21. What is break point chlorination?

The chlorine added to water is utilized in the oxidation of organic matter and killin of bacteria. It reacts with the ammonia to form chloramines. During the initi phase of chorine addition, the residual chlorine or free chlorine will be less than the applied chlorine. But further dosage of cholorine beyond a certain value. Will equally appear as free  residual chlorine. This dosage of chlorine is called as break point chlorination. Residual chlorine limit is 0.2 to 0.3 mg/l

 

22. What are the advantages of chlorine as disinfectant?

• Kills germs and disease causing bacteria effectively

• Cheap and easily available

• Can be stored for long periods

• Prevention of algal growths

• Taste and odour control

 

23. What are the tests to be done to find the residual chlorine in water?

• Orthotolidine test

• D.P.D test

• Chlorotex test

• Starch Iodide test

 

24. How to manage the residue in water treatment plant?

Land filling, horticulture use, disposal to waste water injection, regeneration of coagulants, incineration.

 

25. Define aeration.

Aeration is the process of gas transfer between water and air.

 

26. State the objectives of aeration process in water treatment?

• To remove dissolved gases, such as carbon dioxide, hydrogen sulfide

• To remove iron and manganese.

• To remove taste and odour.

• To increase the DO of water.

 

27. Mention the types of aerators used in water treatment?

(a) Spray nozzles

(b) Cascade aerators

 (c) Air diffusers

(d) Trickling bed aerators

 

28. List the pollutants that get removed in an aerator?

Carbon dioxide, Hydrogen sulfide (rotten-egg odour), Methane (flammable), Iron (stains clothes and fixtures), Manganese (black stains), Volatile organic chemicals, taste and odour

 

29. How do you remove iron and manganese from water?

List out the unit process applied to remove iron and manganese from water?

Iron and manganese from water can be removed by the following methods:

(a) Aeration

(b) Manganeze Zeolite

Addition of lime, chlorine and potassium permanganate

 

30. Define hardness of water? What are the types of hardness present in water?

It is a property of water, which prevents the lathering of soap. Hardness is of two types: Temporary Hardness and Permanent Hardness

 

31. Differentiate between Temporary Hardness and Permanent Hardness?

Temporary Hardness

This is due to the presence of carbonate and bicarbonate of Calcium and

This is also called as Carbonate This is also called as Non-Carbonate Hardness

 It can be removed easily by boiling and adding lime

Permanent Hardness

This is due to the presence of sulphates, chlorides and nitrates of Calcium and Magnesium

This is also called as Non- Carbonate Hardness

 Its removal requires special treatment like zeolite or lime-soda process.

 

32. Describe about the term water softening?

Reduction or removal of hardness from water is known as water softening. Temporary hardness is removed by boiling and addition of lime.

Permanent hardness is removed by: Lime-soda process, base exchange or zeolite process, and demineralization process.

 

33. List out any four effects of hardness in water?

• Causes more consumption of soap in laundry work.

• Affects dyeing of textiles

• Causes difficulties in paper, canning, ice and rayon industry

• Causes choking and clogging of pipes

• Causes scaling in boilers and heaters

• Makes food tasteless, tough or rubbery

34. What are the methods of removing hardness?

• Boiling

• Addition of lime.

• Lime-soda process

•Base exchange or Zeolite process

 

35. What is Zeolite process?

Silicates of aluminium and sodium compounds, which exchange calcium and magnesium ions for sodium ions is known as zeolite process. Zeolites are used in the water softening process to remove permanent hardness from water.

 

36. What are the advantages of Zeolite process?

No sludge is formed, hence problem of sludge disposal does not arise.

It can be operated easily and no skilled supervision is required.

Hardness of water reduces to zero and hence used for boiler and textile industries. Economical process

 

37. What is demineralization?

It is the removal or reduction of minerals in water to make it suitable for industrial and domestic purposes. It involves cation exchange process followed by anion exchange process.

38. How do you regenerate softener?

Water softeners can be regenerated by treating with 5-10% solution chloride (Brine solution)

CaZ + 2NaCl = Na₂Z + CaCl₂

Mg + 2NaCl = Na₂Z + MgCl₂

 

39. Define Fluoridation?

If the fluoride concentration in water is less than 1 mg/l, excess fluoride is added to water which is called as fluoridation.

 

40. Name the methods of deflouridation?

• Prashanthi technique using adsorption by activated alumina

• Ion exchange adsorption method

• Nalgonda technique

• Reverse osmosis process

 

41. What is the maximum permissible limit of fluoride in drinking water?

Acceptable limit of flouride in drinking water is 1 mg/l

 

42. Define the term fluorosis.

Disease caused by intake of excess fluoride affecting the bone and teeth is known as fluorosis.

 

43. Water Supply and Waste Water Engineering

Dental fluorosis: discolouration and pitting of teeth

Skeletal fluorosis: severe bone deformation

Non-skeletal fluorosis: gastrointestinal problems, neurological problems

 

44. Distinguish between physical a dsorption and chemical adsorption?

 

45. Write down the principle of desalination of water?

Desalination is the process of removing dissolved salts from water, thus producin fresh water from seawater or brackish water. Salts are present in water as Na+ catio and Cl- anion. These ions are separated either by oppositely charged electrodes o ion selective membranes.

 

46. Mention any four methods of desalination process?

a. Evaporation and Distillation

b. Electrodialysis

c. Reverse osmosis

d. Freezing process

e. Solar distillation method

 

47. What is Reverse Osmosis?

The natural osmotic pressure is opposed by exerting an external pressure on t side containing the salt solution which forces pure water from the salt solution [S10 move across a semi-permeable membrane towards the side containing water. Th process is called as reverse osmosis.