1. Engineering Chemistry
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2. Sources of Water Impurities in Water
Oceans and seas contain 96.5% water, and snow and groundwater hold 1.74% and 1.7%, respectively.
Impurities in Water
Biological impurities: Microorganisms
Suspended impurities: Organic matter
Colloidal impurities: Metal hydroxides, oil globules
Dissolved impurities: Dissolved gases and salts
Engineering Chemistry
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3. To know “How hard water prevents the formation of lather with soap?”
Hardness of water:
Presence of Ca+2 and Mg+2 ions in water water prevents the formation of lather with soap.
To know “How hard water prevents the formation of lather with soap?”
First we have to know how soap work?
Engineering Chemistry
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4. How soap works?
Soaps are sodium or potassium fatty acids (Palmitic acid Stearic acid Oleic acid) salts. Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with a carboxylate 'head'. In water, the sodium or potassium ions float free, leaving a negatively-charged head.
Na Salt of Stearic acid

5. The organic part of a natural soap is a negatively-charged, polar molecule. Its hydrophilic (water-loving) carboxylate group (-CO2) interacts with water molecules via ion-dipole interactions and hydrogen bonding. The hydrophobic (water-fearing) part of a soap molecule, its long, nonpolar hydrocarbon chain, does not interact with water molecules. The hydrocarbon chains are attracted to each other by dispersion forces and cluster together, forming structures called micelles.

6. In hard water the Ca+2 and Mg+2 ions replaces the Na+ ion from fatty acid salt (in the soap) and make water insoluble fatty acid salt, thus prevent the formation of foam.
From soap
From hard water
Water soluble
Water insoluble

7. Types of Hardness
Temporary hardness: due to presence of bicarbonates and carbonate of calcium and magnesium; can be Removed by boiling.
Permanent hardness: due to presence of chlorides and sulphates of calcium and Magnesium; cannot be removed by boiling; removed by softening agents.
Engineering Chemistry
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8. In ppm or mg/l Degree of hardness:
Expressed in terms of CaCO3 equivalent (in mg/l)
In ppm or mg/l
Degree Clarke ( 0 Cl) = It’s number of equivalent of CaCO3 present in 70,000 parts of water
Degree Feench (0F) = It’s number of equivalent of CaCO3 present in parts of water
1 ppm = 1 mg/l = 0.10F = 0.070Cl
Engineering Chemistry
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9. What is the temporary , permanent and total hardness of a 1L of water sample containing mg of Ca(HCO3)2 and 5.6 mg of MgSO4 ?
Temporary hardness:
= 7.53 mg/l
Permanent hardness:
= 4.67 mg/l
Total hardness = Temporary hardness+ Permanent hardness =
= 12.2 mg/l

10. Determination of Hardness of Water
Soap Solution Method
Hard water does not produce lather until all the ions causing hardness have precipitated.
Complexometric Ttration Method:
EDTA reacts with calcium and magnesium ions which cause hardness and forms complex compounds.
Engineering Chemistry
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11. Complexometric Ttration Method using EDTA:
When indicator is added to hard water it combines with free metal ions present in water.
HIn M → MIn H {M = Mg or Ca}
(Wine red)
When EDTA solution is added to the titration flask it combines with the free metal ions giving metal EDTA complex, which is stable and colorless.
H2Y M → MY H+
When all the free metal ions are exhausted, next drop of EDTA removes the metal ion engaged with indicator and the original blue color is restored.
H2Y MIn → MY-2 + HIn+2 + H+

12. Hardness calculation using EDTA
(1)
Normality of sample is calculated by titrating it against EDTA.
By applying normality equation:
Nsample × V sample = NEDTA × VEDTA
………………….(2)
Substitute Eq. (2) in Eq. (1)

13. Hardness calculation using EDTA
If molarity of EDTA solution is given

14. 100 ml of water sample required 13. 5 ml of 0. 02 M EDTA
100 ml of water sample required 13.5 ml of 0.02 M EDTA. What is the total hardness?

15. Alkalinity of water
Its ability of water to neutralize acid.
Types of Alkalinity
carbon dioxide
carbon dioxide and bicarbonate
bicarbonate and carbonate
hydroxyl groups
Alkalinity is estimated by titration of water with a standard acid solution using phenolphthalein and methyl orange as indicators.

16. General Considerations
Its capacity to neutralize acids or its buffering capacity.
3 major classes of materials
A. Bicarbonates, HCO3- - pH 4.0 ≤ pH 8.3
B. Carbonates, CO3- - >pH 8.3 < pH 9.6
C. Hydroxide, OH- - > pH 9.6

17. Method of Analysis Phenolphthalein Alkalinity
Phenolphthalein indicator
pH 8.3 endpoint of titration
Indicates neutralization of hydoxide ions and half of the Carbonates
Total Alkalinity
Methyl Orange indicator
pH 4.5 endpoint of titration
Indicates neutralization of hydoxide ions, carbonate and bicarbonate

18. **It’s practically impossible for the
OH- and HCO3- to exist together
as they will react within to give
CO3-2

19. Alkalinity calculation by titrating water sample against acid
(1)
Normality of sample is calculated by titrating it against Acid
By applying normality equation:
Nsample × V sample = NAcid × VAcid
………………….(2)
Substitute Eq. (2) in Eq. (1)

20. Alkalinity Relationships

21. 100 ml water sample required 25 ml of 0
100 ml water sample required 25 ml of 0.05N acid for phenlopthaline end point and another 10 ml for methyl orange end point. Determine alkalinity.
P = 25 ml M = 35 ml

22. Types of Hardness * Carbonate and Noncarbonate Hardness
* Calcium and Magnesium Hardness
* Total Hardness – Calcium Hardness = Magnesium Hardness
* Carbonate and Noncarbonate Hardness
When alkalinity < Total Hardness,
then CO3 Hardness = T. Alkalinity
When alkalinity ≥ Total hardness,
Then CO3 Hardness = Total Hardness
* CO3 hardness removed by boiling or lime (Temporary Hardness)
* Noncarbonate Hardness (permanent) = T. Hardness – CO3 Hardness
* Pseudo-Hardness
* Associated with Na+ which causes soap consumption but not
considered part of hardness.

23. Techniques for Water Softening
External Treatment for Softening Water
Lime soda process
Engineering Chemistry
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24. Removal of Carbonate Hardness
***
CaCO3 is precipitated out of the water (sludge) and it’s filtered off.
Removal of Noncarbonate Hardness
Lime is used to remove temporary hardness + Mg-permanent hardness, Soda Ash is used mainly to remove permanent hardness.

25. Before solving numerical problems –take a look

26. Lime-Soda Softening method
Batch Softening ( Lime and soda
Both are mixed together with hard water tank. After completing of reaction, the sludge is filtered off)
Continuous Softening ( Lime and soda
are added to hard water into different compartment.)
Advantage: It not only reduce hardness but also reduce the TDS, alkalinity.
It also reduces total dissolved CO2
Disadvantage: It cannot remove the water hardness completely.
The feed water quality may change from source to source, which makes adjusting the amount of lime and soda difficult

27. Internal Treatment for Softening Water: (Carried out inside boiler)
Complexation
Calgon (Sodium Hexametaphosphate) Treatment
Carbonate Treatment
Engineering Chemistry
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28. Calculate the lime and soda required for softening 50,000 l of water containing the following salts: Ca(HCO3)2 = 8.1 mg/l, Mg(HCO3)2 = 7.5 mg/l and CaSO4 = 13.6 mg/l, MgSO4 = 12 mg/l, MgCl = 2 mg/l
Ca(HCO3)2 = 8.1 mg/l = 8.1 × 100/ 162 = 5 mg/ l CaCO3.
Mg(HCO3)2 = 7.5 mg/l = 7.5 × 100/146 = 5.13 mg/l of CaCO3
Similarly CaSO4= 10 mg/l, MgSO4 = 10 mg/l, MgCl2 = 2.1 mg/l of CaCO3 equivalent.
So lime required = 74 (MW of Lime)/ 100 (MW of CaCO3)[5+2× ] = mg/l.

29. So soda required = 106(MW of soda)/ 100 [ 10 +10 +2.1] = 23.43 mg/l
Now calculate it for 50,000 L.

30. Reverse Osmosis Process
Water flows from
High conc. of water
To low conc. of water

31. It results in conc. Of all solutes
In one compartment and all pure
Water in another compartment

32. Boiler Feed Water Boiler Troubles/Problems
Should be such that the impurities can be concentrated a reasonable number of times without exceeding the tolerance limits.
Boiler Troubles/Problems
Scale (hard deposits) and sludge (suspended solids) formation
Engineering Chemistry
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33. Priming (outlet steam containing large drops of water) and Foaming (bubble formation on surface of boiler water)
Caustic Embrittlement (material becomes brittle due to exposure to caustic solutions at high temperature and pressure)
Boiler Corrosion (degradation of boiler surface by feed water containing dissolved oxygen and carbon dioxide)
Engineering Chemistry
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41. Chlorination
Water chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water that has been treated with chlorine is effective in preventing the spread of waterborne disease.
chlorine is a highly efficient disinfectant, and is added to public water supplies to kill disease-causing pathogens, such as bacteria, viruses and protozoans
The chlorination process involves adding chlorine to water, but the chlorinating product does not necessarily have to be pure chlorine. Chlorination can also be carried out using chlorine-containing substances. Depending on the pH conditions required and the available storage options, different chlorine-containing substances can be used. The three most common types of chlorine used in water treatment are: chlorine gas, sodium hypochlorite, and calcium hypochlorite.

42. Cl2 + H2O HOCl + H+ + OCl- OCl- = Cl- + O
How does chlorine disinfection work?
Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells. When enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are replaced by chlorine. This causes the entire molecule to change shape or fall apart. When enzymes do not function properly, a cell or bacterium will die.
OCl- = Cl- + O
This O is also disinfectant.

43. HOCl, which is electrically neutral and hypochlorite ions (OCl-, electrically negative) will form free chlorine when bound together. This results in disinfection. Both substances have very distinctive behaviour. HOCl acid is more reactive and is a stronger disinfectant than hypochlorite. HOCl acid is split into hydrochloric acid (HCl) and oxygen (O). The oxygen atom is a powerful disinfectant. The disinfecting properties of chlorine in water are based on the oxidising power of the free oxygen atoms and on chlorine substitution reactions.

44. Water Drainage
Drainage means the removal of excess water from a given place.
Two types of drainage can be identified:
i) Land Drainage: This is large scale drainage where the objective is to drain surplus water from a large area by such means as excavating large open drains, and levees and pumping. Such schemes are necessary in low lying areas and are mainly Civil Engineering work.

45. ii) Field Drainage:
This is the drainage that concerns us in agriculture. It is the removal of excess water from the root zone of crops.

47. Water in Soil After Heavy Rain

48. The main aims of Field drainage include:
i) To bring soil moisture down from saturation to field capacity. At field capacity, air is available to the soil and most soils are mesophites ie. like to grow at moisture less than saturation.
ii) Drainage helps improve hydraulic conductivity: Soil structure can collapse under very wet conditions and so also engineering structures.
iii) In some areas with salt disposition, especially in arid regions, drainage is used to leach excess salt.

49. The main aims of Field drainage Contd.
iv) In irrigated areas, drainage is needed due to poor application efficiency which means that a lot of water is applied.
v) Drainage can shorten the number of occasions when cultivation is held up waiting for soil to dry out.

50. Two types of drainage exist: Surface and Sub-surface drainage.
4.2 DESIGN OF SURFACE DRAINAGE SYSTEMS:
Surface drainage involves the removal of excess water from the surface of the soil.
This is done by removing low spots where water accumulates by land forming or by excavating ditches or a combination of the two.

51. Surface Drainage

52. DESIGN OF SUB-SURFACE DRAINAGE SYSTEMS
Sub-surface drainage is the removal of excess groundwater below the soil surface.
It aims at increasing the rate at which water will drain from the soil, and so lowering the water table, thus increasing the depth of drier soil above the water table.
Sub-surface drainage can be done by open ditches or buried drains.

53. Sub-Surface Drainage Using Ditches

67. Treatment of Sewage It consists of three steps: 1. Primary treatment
2. Secondary treatment
3. Tertiary treatment

68. Primary Treatment
The first step consists of screens, grit removal, oil and grease trap and primary sedimentation.
Screens: The influent sewage water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic packets etc. carried in the sewage stream
Grit removal: It includes a sand or grit channel or chamber, where the velocity of the incoming sewage is adjusted to allow the settlement of sand, grit, stones, and broken glass. These particles are removed because they may damage pumps and other equipment.
Oil & grease trap: Removal of oil and grease.
Primary Sedimentation: Gravitational settlement of suspended and colloidal particles denser than water.

69. Secondary Treatment
The sludge is further treated in 'sludge digesters': large heated tanks in which its chemical decomposition is catalysed by microorganisms. The sludge is largely converted to 'biogas', a mixture of CH4 and CO2, which is used to generate electricity for the plant.
It consists of biological treatment for the removal of organic matter. Use microorganism to decompose organic waste. After several hours bacteria are allowed to settle down as secondary sludge.

71. Sewage Treatment Secondary Treatment (Microbial Process)
Supernatant or primary effluent contains high levels of dissolved organic load (Biological Oxygen Demand)
Aeration to stimulate aerobic degradation
activated sludge reactor
trickling filter reactor
bacteria degrade organic
carbon to CO2

73. trickling filter

74. Activated sludge mixed community of microorganisms
Both aerobic and anaerobic bacteria may exist
The water is mixed with biological agents and then aerated. The increased oxygen promotes the growth of the beneficial biological material. That material will consume unwanted waste products held in the water. Finally, the beneficial material will grow due to the increased oxygen and food, which makes it easier to filter from the clean water.

76. Treatment stages – Tertiary treatment
remove disease-causing organisms from wastewater
3 different disinfection process
Chlorination
UV light radiation
Ozonation

77. Chlorination Most common Advantages: low cost & effective
Disadvantages: chlorine residue could be harmful to environment

78. UV light radiation
Damage the genetic structure of bacteria, viruses and other pathogens.
Advantages: no chemicals are used
water taste more natural
Disadvantages: high maintenance of the UV-lamp

79. Ozonation Oxidized most pathogenic microorganisms
Advantages: safer than chlorination
fewer disinfection by-product
Disadvantage: high cost

80. Analysis of Water
Determination of various ions is carried out as follows:
Chloride by argentometric method
Fluoride by SPADNS method
Nitrate by phenol disulphonic method
Sulphate by gravimetric method
Dissolved oxygen by Winkler’s method
Engineering Chemistry
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81. Disadvantages of Hard Water
Hard water is neither fit for domestic purposes nor for industrial purposes.
Domestic Purposes
Laundering
Bathing
Dishwashing
Industrial Purposes
Sugar industry
Concrete industry
Pharmaceutical industry
Textile industry
Dyeing industry
Water boilers and pipes
Engineering Chemistry
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82. Potable Water
Water is made fit for domestic use by the following treatments:
Pretreatment
Removal of suspended impurities by:
Screening
Flocculation
Sedimentation
Filtration
Engineering Chemistry
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83. Disinfection of Water Physical methods: UV light, gamma radiation
Chemical methods: chlorine, chlorine dioxide, hypochlorite, ozone, hydrogen peroxide, potassium permanganate, halogens
Chlorination
2. Ozonization
Engineering Chemistry
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84. Desalination of Brackish Water
Reverse Osmosis
Engineering Chemistry
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85. Electrodialysis Engineering Chemistry
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86. Sewage Characteristics of waste water:
Biological oxygen demand (BOD): amount of dissolved oxygen needed by aerobic microorganisms in a water body to breakdown organic matter.
Chemical oxygen demand (COD): amount of oxygen consumed to oxidize organic and oxidizable inorganic material.
Engineering Chemistry
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87. Sewage treatment Engineering Chemistry
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88. Primary Waste Treatment
Filter through screens and sedimentation
Secondary Waste Treatment
Trickling Filter
Engineering Chemistry
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89. Rotating biological reactor
Activated sludge process
Engineering Chemistry
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90. Sand filter/ Activated carbon filter
Tertiary Waste Treatment
Sand filter/ Activated carbon filter
Lagoons
Denitrification
Disinfection
Engineering Chemistry
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91. Specification of drinking water
S.No.
Parameter
ISI (BIS) standards mg/L
WHO standards mg/L 1
Color, odor and taste
Colorless, odorless and tasteless 2 pH
6.9 3
Total dissolved solids -
1500ppm 4
Dissolved oxygen
3.0 5
Chloride
600
250 6
Sulphate
1000
400 7
Nitrate 45 8
Cyanide
0.01
0.2 9
Fluoride
1.5 10
Chromium
0.05 11
Lead
0.1 12
Arsenic 13
Mercury
0.001
0.006
Indian Standards Institute (Bureau of Indian Standards)