1. Water is essential for human survival but is often contaminated. 2. Water sources include surface water and groundwater, with varying levels of physical, chemical, and biological impurities depending on the source. 3. Hard water contains high levels of calcium and magnesium ions which can cause soap scum, clog pipes and boilers, and is classified as temporary or permanent hardness. Preventing scale formation in boilers is important to improve efficiency and avoid accidents.

1. UNIT - I
WATER TECHNOLOGY
Dr. RupamSingh
CY101 ENGG. CHEM.
1

2. “Without food, human can survive for number of
days, but water is such an essential that without it
one cannot survive”.
“Although water is nature’s most wonderful,
abundant and useful compound yet is also the
most misused one”.
2

3. Distribution of water
3

4. Sources of Water
A) Surface Waters
Rain Water - Pure but contaminated with gases
River Water - High dissolved salts moderate organics
Lake Water - Const. composition but high organics
Sea Water - High salinity, pathogens, organics
B) Underground Waters
Spring/Well Water - Crystal clear but high dissolved
salts and high purity from organics
4

5. Classification of Impurities in water
 Physical Impurities - Dissolved Solids/Salts
 Chemical Impurities - Inorganic & Organic Chemicals
 Biological Impurities - Pathogens, algae, fungi,viruses...
1) Acidity (pH)
2) Gases (CO2-
1) Colour
2) Turbidity O2, NH3) 1) Microorganism
3) Taste 3) Minerals 2) Water Bodies
4) Odour 4) pH
5) Conductivity 5) Salinity
6) Alkalinity 5
7) Hardness

6. Colour
• Colour in water is due to metallic salts of Fe, Mn and due to organic
substances like humus, peat, algae, weed …
• Industrial activities such as textile, paper & pulp, dyeing, tanneries
• Colour intensities of water sample can be measured using
tintometer using Platinum cobalt standard colour complex
Turbidity
• It is due to colloidal, extremely fine suspension such as clay, slit,
finely divided matters, sometimes microorganisms…
• It reflects the optical properties of water in terms of light scattering
ability instead of transmitting in straight lines.
Conductivity
• The ability of water to conduct electricity, indicates the amount
of dissolved minerals and gases in water.
• Conductivity measured in micro mhos/cm or MicroSiemns/cm3
6

7. Taste
• Presence of dissolved salts and gases imparts bitter, soapy, brackish
and palatable taste which normally co-related with odour but it is
not applicable always the case
• Bitter (Fe, Al, Mn, SO4, Ca(OH)2)
• Soapy (NaHCO3)
• Brackish (High salt content - NaCl)
• Palatable (CO2 and NO3)
Odour
• Domestic and industries activities cause undesirable odour to water
• Industrial effluent of organics, sewage discharge, presence of N, S
and P contains compounds, metal ion pollution like Fe
• Substances like algae, peat, bacterias
• Grassy odour, peaty odour, offensive odour, tarry and faint odour
7

8. pH
• pH a measure of hydrogen ion activity is used to
express the intensity of acidic or alkaline condition of a
solution.
• The pH scale runs to 0 from 14 with 0 representing
maximum acidity and 14 maximum basicity
pH = -log [H+]
8

9. Acidity of Water
Acidity is a measure of the effects of combination of
compounds and conditions in water.
It is the power of water to neutralize hydroxyl ions and
is expressed in ppm interms of CaCO3 equivalence.
• Acidity - - - - Free Mineral Acidity
- - - - CO2 Acidity
9

10. MAJOR IMPURITIES OF WATER
Ionic and dissolved
Cationic Anionic Nonionic and undissolved Gases
Alkalinity
Calcium Bicarbonate Turbidity, silt, mud, dirt and CO2
Magnesium Carbonate other suspended matter H 2S
Hydroxide NH3
Sodium Color, Plankton CH4
Potassium Sulfate Organic matter, O2
Ammonium Chloride Colloidal silica,
Iron Nitrate Microorganisms,
Manganese Phosphate Bacteria
10

11. Hard Water
What’s hard water?
Practically speaking, measurement of:
•Calcium (Ca) ions
•Magnesium (Mg) ions
Hardness as calcium carbonate
mg/L (ppm)
Soft 0-17
Moderately hard (Medium) 60-120
Hard 120-180
Very hard 180 & over
11

12. Why be concerned about Hard Water?
• Originally, water hardness was defined as the measure of
the capacity of the water to precipitate soap
• Hard water does cause soap scum, clogs pipes and clogs
boilers as lime scale
12

13. Hardness of Water
• Hardness in Water is characteristic that prevents the
‘lathering of soap’ thus water which does not produce lather
with soap solution readily, but forms a white curd is called
hard water.
• Type of Hardness
– Temporary or Carbonate Hardness
– Permanent Hardness or non-carbonate Hardness.
13

14. Temporary Hardness
– Temporary Hardness is caused by the presence of dissolved bicarbonate
of calcium, magnesium and other heavy metals and the carbonate of iron.
It is mostly destroyed by more boiling of water, when bicarbonates are
decomposed yielding insoluble carbonates.
Ca(HCO 3 ) 2 Heat CaCO 3 + H2O + CO2
Calcium bicarbonate Calcium Carbonate
Mg(HCO 3 ) 2 Heat Mg(OH) 2 + 2CO2
Magnesium Bicarbonate Magnesium hydroxide
– Calcium/Magnesium Carbonates thus formed being almost insoluble, are
deposited as a scale at the bottom of vessel, while carbon dioxide escapes
out.
14

15. Permanent Hardness
Non Carbonate Hardness is due to the presence of
chlorides, sulfates of calcium, Magnesium, iron and other
heavy metals
2C17H35COONa + CaCl2 (C17H35COO)2Ca + 2NaCl
Sodium Hardness Calcium stearate
stearate
(Insoluble)
(sodium soap)
2C17H35COONa + MgSO4 (C17H35COO)2Mg + 2Na2SO4
Sodium Hardness Magnesium stearate
stearate
(Insoluble)
(sodium soap)
15

16. Units of Hardness
Most Commonly used
• Parts per million (ppm)
1ppm=1 part of CaCO3 equivalence hardness causing substance present in 10 6
parts of water
• Milligrams per liter (mg/litre)
1mg/L=1mg of CaCO3 equivalence hardness causing substance present in one
liter of water
1mg/L=1ppm
Relationship; 1L water = 1Kg = 1000 g = 1000 X 1000 mg = 106 mg
1mg/L = 1mg of CaCO3 eq per 106 mg of water
= 1 part of CaCO3 eq per 106 parts of water = 1ppm
• Clare's Degree(oCl)
1o Clarke= 1part of CaCO3 equivalent hardness in 70000 parts of water
• Degrees French (oFr) 16
1o Fr = 1 part of CaCO3 eq per 105 parts of water

17. CaCO3 equivalent hardness
Mass of hardness Molecular weight
producing
X of CaCO 3
Calcium carbonate equivalent = substance
Molecular weight of hardness producing
substances
Problem 1
Calculate the calcium carbonate equivalent hardness of a water sample
containing 204mg of CaSO4 per litre
Solution
: 204 X 100
Calcium carbonate equivalent hardness = = 150 mg of
136 CaCO 3 /L
= 150 ppm
Note : Mol. Weight of CaCO 3 = 100
Mol. Weight of CaSO 4 =
136
17

18. Calcium carbonate equivalence conversion during
hardness calculation
Hardness Molecular Multiplication factor
producing weight (in terms of CaCO3
substance equivalence)
Ca(HCO3)2 162 100/162 or 50/81
Mg(HCO3)2 146 100/146 or 50/73
CaSO4 136 100/136 or 50/68
CaCl2 111 100/111 or 50/55.5
120 100/120 or 50/60
MgSO4
95 100/95 or 50/47.5
MgCl2
100 100/100 or 50/50
CaCO3 84 100/84 or 50/42
MgCO3 44 100/44 or 50/22
CO2 61 100/61 or 50/61
HCO-3 17 100/17 or 50/17
OH- 60 100/60 or 50/30
CO32-
18

19. Problems
1. A water sample from an industry in Bombay had the following data
Mg(HCO3)2 = 16.8mg/L, MgCl2 = 19 mg/L, CaCO3 = 20 ppm, MgSO4 =24.0mg/L
and KOH = 1 ppm. Calculate the temporary, permanent and total hardness of
the water sample.
Solution
Step 1 conversion in to CaCO 3
equivalent
Constituent quantity Conversion Hardness
present factor
Mg(HCO3)2 16.8 mg/L 100/146 16.8 *100/146 = 11.5ppm
19.0 mg/L 100/95 19.0*100/95 = 20ppm
MgCl2
20.0*100/100 = 20 ppm
CaCO3 20 ppm 100/100
24.0*100/120 = 20 ppm
MgSO4 24.0 mg/L 100/120
Calculatio
n
Temp. Hardness = 31.5 ppm P. Hardness = 40 ppm
Tot. Hardness =71.5 ppm
19

20. Draw backs (or) Disadvantages of Hard Water
Domestic Use Industrial Use
1. Washing 1. Textile Industry
2. Bathing 2. Sugar Industry
3. Drinking 3. Dyeing Industry
4. Cooking 4. Paper Industry
5. Pharmaceutical Industry
The sticky precipitate adheres
on the fabric/cloth and gives
spots and streaks. Fe salts stain 6. In Steam generation in
the cloths. Boilers
Produces sticky scum on the
bath tub and the body
Bad to the digestive system
and calcium oxalate formation
is possible in urinary tracts
Requires more fuel and time.
Certains food don’t cook soft
and also gives unpleasant
taste 20

21. Boiler troubles due to Hard Water
1. Scale and 1.
Sludge Sludge Slimy loose precipitate
called sludge
2. Caustic suspended in water
embitterment
3. Priming and
Foaming
4. Boiler water
corrosion
Boiler
wall
Sludge is a soft, loose and slimy precipitate formed within the
boiler. It can be easily scrapped off with a wire brush.
It is formed at comparatively colder portions of the boiler and
collects in areas of the system, where the flow rate is slow or at
bends.
It is formed by substances which have greater solubility's in hot
water than in cold water, e.g. MgCO 3 , MgCl 2 , CaCl 2 , MgSO 4 etc.,
21
Remedy: Sludges can be removed using wire brush or mild acid

22. 1. Scale
Hard adherent coating
on inner walls of boiler
water
Boiler
wall
Scales are hard substances which sticks very firmly to the
inner surfaces of the boiler wall.
Scales are difficult to remove even with the help of a hammer
and chisel.
Examples: CaSO 4 , CaCO 3 , Mg(OH) 2 22

23. 23

24. Reasons for formation of scale
1. Presence of Ca(HCO 3 ) 2 in low pressure boilers
Ca(HCO 3 ) 2 CaCO 3 + H2O + CO2 Low pressure boilers but in high
pressure boilers it is soluble by
Calcium bicarbonate Calcium Carbonate (scale) forming Ca(OH) 2
2. Presence of CaSO 4 in high pressure boilers
T oC Solubility of CaSO 4
4. Presence of SiO 2
15 3200 ppm
230 15 ppm It forms insoluble hard adherent
320 27 ppm CaSiO 3 and MgSiO 3 as scales
Cold water soluble
Super heated water Insoluble
(scale)
3. Presence of MgCl 2 in high temperature boilers
MgCl 2 + 2 H 2 O Mg (OH)2 + 2HCl
Magnesium chloride scale
Mg(OH) 2 can also be generated by thermally decomposing Mg(HCO 3 ) 2
24

25. Disadvantages of scale formation
1. Fuel wastage – scales have low thermal conductivity
2. Degradation of boiler material and increases of risk of
accident
3. Reduces the efficiency of the boiler and- deposit on the valves
and condensers
4. The boiler may explode – if crack occurs in scale
Remedies: Removal of scale
1. Using scrapper, wire brush often
2. By thermal shock- heating and cooling suddenly with cold water
3. Using chemicals – 5-10% HCl and by adding EDTA
25

26. Prevention of scale
formation
Scale formation can be prevented by two methods
1. Internal conditioning or Internal Treatment
2. External conditioning or External treatment- will be discussed later
1. Internal conditioning methods - of boiler water to prevent scale formation
1. Phosphate conditioning – addition of phosphate compound
2. Carbonate conditioning – addition of carbonate compound
3. Calgon conditioning – addition of sodium hexa meta phosphate
4. Colloidal conditioning – spreading of organic compounds like tannin, agar
gel
5. Sodium Aluminate – removes oil and silica
6. Complexometric method – using EDTA (refer expt. 1 chemistry lab manual)
1. Phosphate conditioning
Scale formation can be prevented by adding sodium phosphate to the boiler water which
reacts with the hardness producing ions and forms easily removable phosphate salts of
respective ions
3CaCl 2 (Boiler water) + 2 Na 3 PO 4 Ca 3 (PO 4 ) 2 + 6 NaCl
Calcium Sodium calcium phosphate
chloride phosphat (non adherent and
e can be removed by 26
blow down method)

27. Selection of Phosphate compound
Calcium can not be precipitated below a pH = 9.5, hence the selection of
phosphate has to be based on the pH of the boiler feed water.
NaH 2 PO 4 (acidic in nature) ,
Na 2 HPO 4 (weakly alkaline in
nature),
Na 3 PO 4 (Alkaline in nature)
2. Carbonate conditioning
CaSO 4 (Boiler water) + Na 2 CO 3 CaCO 3 +
Na 2 SO 4
Calcium Sodium calcium carbonate
sulfate carbonate
(non adherent loose
sludge and can be
removed by blow
down method)
Caution: Excess Na 2 CO 3 can result in caustic embrittlement
27

28. 3. Calgon conditioning
Na 2 [Na 4 (PO 3 ) 6 2Na+ +
[Na 4 P 6 O 18 ] 2-
Calgon – sodium
hexa meta
phosphate
2CaSO 4 (Boiler water) + [Na 4 P 6 O 18 ] 2- [Ca 2 P 6 O 18 ] 2- + 2Na 2 SO 4
Calcium
Soluble complex ion
sulfate
of calcium - can be
removed easily
Calgon tablets are used in the cleaning of washing machine
drums
28

29. II. Caustic embitterment
 Excess sodium carbonate used up for removing hardness can also
result in the formation of NaOH in high pressure boilers.
NaOH has better mobility and can percolate into fine cracks present
in boiler walls.
Na2CO3 + H2O → 2 NaOH + CO2
 NaOH gets concentrated in the fine cracks present in the boiler
walls.
 A concentration cell corrosion is established between the conc.
NaOH and dilute NaOH solution in contact with boiler walls.
 Concentrated NaOH region behaves as anode thus resulting in
corrosion of boiler leading to the formation of sodium ferroate.
Remedies: (i) Use phosphate salts instead of sodium carbonate
(ii) use Na 2 SO 4 or agar-agar gel compounds to fill the fine cracks.
29

30. III. Priming and foaming
Foaming
It is the production of continuous foam
or hard bubblers in boilers. Foaming is
due to the presence of substance like
oil in boiling water.
Priming
Foamin It is the process in which some
g Normal bubble particles in water are carried along
with the steam. The resulting process
is called as wet steam or carry over.
The process of formation of wet steam
in boilers is called as priming.
Causes of Priming,
1. Presence of dissolved salts
Priming 2. High velocity steam due to sudden
Carry over boiling
bubble
3. Improper boiler design
Disadvantages of Priming and
foaming – refer Jain and Jain Text 30
book

31. IV. Boiler
corrosion
Degradation or destruction of boiler materials (Fe) due to the
chemical or electrochemical attack of dissolved gases or salts is
called boiler corrosion
Boiler corrosion is of three types
1. Corrosion due to dissolved O 2
2. Corrosion due to dissolved CO 2
3. Corrosion due to acids formed by dissolved
salts
1. Corrosion due to dissolved oxygen
(DO)
2 Fe + 2 H2O + O2 2 Fe(OH)2
4 Fe(OH)2 + O2 2 [Fe2O3.2H2O]
Ferrous Rust
hydroxide
31

32. Removal of Dissolved Oxygen (DO)
1. By the addition of chemicals
The dissolved oxygen present in the boiler feed water can be removed by the
addition of sodium sulphite or hydrazine and the reactions can be written as below
2 Na2SO3 + O2 2 Na2SO4
Sodium DO Sodium
sulphite sulphate Water feed
Na2S + 2O2 Na2SO4
N2H4 + O2 N2 + 2H2O
O2 To vacuum
Hydrazine Nitrogen
Steam jacket
2. By mechanical deaeration
It comprises of a tall stainless tower with different
layers capped with baffles to facilitate multiple Perforated
plate
equilibration.
The entire chamber is vacuumized and also maintained
at high tempt using perforated heating plates on the
walls. Deaerate 32
d water

33. 2. Corrosion due to dissolved
CO 2
Presence of bicarbonate salts of either magnesium or calcium also causes the release
of CO 2 inside the boiler apart from the dissolved CO 2
Mg(HCO 3 ) 2 MgCO 3 + H 2 O +
CO 2
CO 2 + H 2 O H 2 CO 3 (causes slow
corrosion)
Removal
1. It can be removed by the addition of ammonia
2 NH 4 OH + CO 2 (NH 4 ) 2 CO 3 +
H 2O
3. Corrosion due to dissolved
salts
MgCl2 + 2 H2O Mg(OH)2 + 2HCl
Fe + 2 HCl FeCl2 + H2
FeCl2 + 2 H2O Fe(OH)2 + 2HCl
33

34. Softening of hard water –
External treatment
Attn: Part B Question
34

35. II External treatment of water – External Conditioning of water
Softening of hard water can be done by the following
methods
1. Lime soda process
2. Zeolite methods
3. Ion exchange resin method
4. Mixed bed deionizer method
1. Lime soda process
It is a process in which Lime (Ca(OH) 2 ) and soda (Na 2 CO 3 ) are added to the hard
water to convert the soluble calcium and magnesium salts to insoluble compounds
by a chemical reaction. The CaCO 3 and Mg(OH) 2 so precipitated are filtered off
and removed easily.
It is further divided in to two types
1. Cold lime soda process
2. Hot lime soda process
35

36. 1. Cold lime soda process
Step 1
In this process a calculated quantity of Ca(OH)2 (lime) and Na2CO3 (soda) are
mixed with water at room temperature and added to the hard water. The following
reactions takes place depending on the nature of hardness
Chemical reactions
If it is permanent hardness and due to calcium salt
Ca2+ + Na2CO3 CaCO3 + 2Na+ (soda)
slimy suspended precipitate
If it is due to Magnesium salt
Mg2+ + Ca(OH)2 Mg(OH)2 + Ca2+ (lime)
slimy suspended precipitate
Ca2+ + Na2CO3 CaCO3 + 2Na+ (soda)
slimy suspended precipitate
36

37. Chemical reactions contd..
If it is Temporary hardness and due to calcium salt
Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O
slimy suspended precipitate
If it is due to Magnesium salt
Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O
slimy suspended precipitates
Step 2
The precipitates CaCO3 and Mg(OH)2 are very fine and forms sludge like
precipitates in the boiler water and are difficult to remove because it does not
settle easily making it difficult to filter and the removal process. Finally reduces
the efficiency of the boiler.
Therefore, it is essential to add small amount of coagulant (such as Alum,
Aluminium sulfate, sodium aluminate etc) which hydrolyses to flocculent
precipitate of Al(OH)3 which entraps the fine precipitates.
NOTE: Particles finer than 0.1 µm (10-7m) in water remain continuously in motion due to electrostatic charge
(often negative) which causes them to repel each other. Once their electrostatic charge is neutralized by the use of
coagulant chemical, the finer particles start to collide and agglomerate (combine together) under the influence of
37
Van der Waals's forces. These larger and heavier particles are called flocs.

38. When coagulants are added flocculation takes place followed by the
formation of flocculants.
NaAlO2 + 2H2O NaOH + Al(OH)3
Coagulant Flocculent- Gelatinous
precipitate which
entraps the fine
precipitates of CaCO3
and Mg(OH)2
Al2(SO4)3 + 3 Ca(HCO3)2 2Al(OH)3 + CaSO4 + CO2
Aluminium Hard water
sulfate sample Flocculent- Gelatinous
precipitate which
entraps the fine
precipitates of CaCO3
and Mg(OH)2
The Al(OH)3 formed by the addition of coagulants initiates the process of
flocculation and entraps the fine precipitates and becomes heavy. The
heavier flocs then settles at the bottom and filtered off easily.
38

39. Continuous cold lime soda softener
Chemicals
Hard water
(soda+lime
feed
+coagulant)
feed
Softened
water
Wood fiber
filter
Stirrer
paddles
Sedimented sludge (CaCO3,
Mg(OH)2
39

40. 2. Hot lime soda Process
In this process a calculated quantity of Ca(OH)2 (lime) and Na2CO3 (soda) are
mixed with hot water at a temperature range of 80 to 150oC and added to the hard
water. The following reactions takes place depending on the nature of hardness
Advantages of Hot Lime Soda Process
1. The reaction between hardness producing substance and lime soda proceeds at a faster
rate
2. The precipitates and sludges formed are settled at the bottom easily and hence No
coagulants are required
3. The dissolved gases such as CO2 escapes and the water becomes free from dissolved
gases
4. It produces soft water with the residual hardness of 15-30ppm in contrast to the cold lime
soda process which produces soft water with 50-60ppm of residual hardness
Hot lime soda Plant consists of three parts
1. Reaction tank: water, chemicals and steam are mixed
2. Conical sedimentation tank : sludge settles down
3. Sand filter : complete removal of sludge from the soft water is ensured 40

41. Continuous Hot Lime soda Process
Hard water feed
Super heated steam
Chemicals feed (lime
and soda)
Reaction tank
Soft water
r
dl aye
Conical sedimentation san
Fine yer
tank
a nd la
r se s
Coa
n
Precipitated sludge a tio Gravellayer
(CaCO3, Mg(OH)2 ltr
Sludge
Fi nk
ta
outlet
Filtered soft
water
41

42. Advantages of Lime soda process
1. It is very economical compared to other methods
2. Iron and manganese salts are also removed by this process
3. It increases the pH of the softened water hence corrosion is minimized
also pathogenic bacteria
Disadvantages of Lime soda process
1. Disposal of large amount of sludge (insoluble precipitates) poses a
problem
2. This can remove hardness to the extent of 15ppm which is not good for
boilers
42

43. Calculation of lime and soda required for the softening of hard water by
the lime soda process
Hardness producing Chemical reaction with lime and soda Need
substance
Permanent Hardness
Ca Salts CaCl2 + Na2CO3 CaCO3 + 2NaCl S
Mg salts MgSO4 + Ca(OH)2 Mg(OH)2 + CaSO4 L+S
CaSO4 + Na2CO3 CaCO3 +Na2SO4
Temp. Hardness
Ca(HCO3)2 Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O L
Mg(HCO3)2 2L
Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O
Acids
HCl L+S
2H+ + Ca(OH)2 Ca2+ + 2H2O
H2SO4
Ca2+ + Na2CO3 CaCO3 + 2Na+
L-S
HCO3-
HCO3- + Ca(OH)2 CaCO3 + H2O + CO32-
L+S
FeSO4
Fe2+ + Ca(OH)2 Fe(OH)2 + Ca2+
Ca2+ + Na2CO3 CaCO3 + 2Na+ L/2
43
NaAlO2
NaAlO2 + H2O Al(OH)3 + NaOH

44. Rules
1. If Ca(HCO3)2 and Mg(HCO3)2 are considered as ions (Ca2+ + 2HCO3-) and (Mg2+ + 2HCO3-)
respectively then the calculation result will be the same based on the ability of the ions to
take up bicarbonate ions
2. If treated water found to contain excess of OH - and CO32- ions these are formed from excess
equivalent each of Ca(OH)2 and Na2CO3 and hence these excess amounts should be added
to the calculation (in temp. hardness and perm. hardness)
3. When the impurities are given as CaCO3 and MgCO3 present in water it should be
considered as due to bicarbonates of calcium and magnesium respectively
4. Substances like NaCl, KCl, Na2SO4, SiO2, Fe2O3 etc do not contribute to hardness and
therefore, they do not consume any soda or lime and hence if these present need not be
taken in to consideration during calculation.
5. Soda (Na2CO3) neutralizes only permanent hardness
Molecular weight of lime = 74
Molecular weight of soda = 106
Molecular weight of CaCO3 = 100
Therefore, 100 parts by mass of CaCO3 are equivalent to
(i) 74 parts by mass of Ca(OH)2
44
(ii) 106 parts by mass of Na2CO3

45. Therefore, Lime requirement for softenening
= 74 T.H of Ca2++ 2 x T.H of Mg2+ + P.H of (Mg2+ + Fe2+ + Al3+) + CO2 + H+ +
100 HCO3- - NaAlO2/2
X Vol .of water (L)
T.H = temporary hardness
P.H = Permanent Hardness
llIly, Soda requirement for softenening
= 106 P.H of (Ca2+ + Mg2+ + Fe2+ + Al3+) + H+ - HCO3- X Vol .of water (L)
100
Problem 1
Calculate the amount of lime required for softening 5,000 litres of hard water
containing 72 ppm of MgSO4 (mol wt = 120) Ans = 222g
45

46. Solution
Step 1 List out the given data
Given data : Hardness 72 ppm due to MgSO4; water qty = 5000 litres; mol. wt. MgSO4 = 120
Step 2 calculate the CaCO3 equivalent
Hardness producing Quantity (ppm) Multiplication factor CaCO3 equivalent
substance hardness (ppm or
mg/L)
MgSO4 72 100/120 72 X (100/120) = 60
Step 3 calculation of lime requirement
Lime required = 74/100 (hardness due to MgSO4) x vol. of water
= 74/100 (60 mg/L) x 5000 L
= 222,000 mg
= 222 g
46

47. Problem 2
Calculate the amount of lime and soda required for softening 50,000 litres of hard water containing:
Mg(HCO3)2 = 144 ppm, CaCO3 = 25 ppm, MgCl2 = 95ppm, CaCl2 = 111ppm, Fe2O3 = 25ppm and
Na2SO4 = 15ppm
Solution
Step 1 List out the given data
Given data : MgCO3 = 144 ppm, CaCO3 = 25 ppm, MgCl2 = 95ppm, CaCl2 = 111ppm, Fe2O3 =
25ppm and Na2SO4 = 15ppm
Step 2 calculate the CaCO3 equivalent
Hardness producing Quantity (ppm) Multiplication factor CaCO3 equivalent
substance hardness (ppm or
mg/L)
Mg(HCO3)2 144 100/84 144 x(100/84) = 171.4
CaCO3 025 100/100 25 x (100/100) = 25.0
MgCl2 095 100/95 95 x (100/95) = 100.0
CaCl2 111 100/111 111 x (100/111) = 100.0
025 (does not cause hardness)
Fe2O3
015 (does not cause hardness)
Na2SO4
Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O; Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O
MgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2 ; CaCl2 + Na2CO3 CaCO3 + Na2SO4
47
What happens when lime is treated with CaCl 2?

48. Step 3 calculation of lime requirement
Lime required = 74/100 ( {2 x MgHCO3} + CaCO3 + MgCl2 in terms of CaCO3 eq) x vol. of water
= 74/100 (2 x 171.4 + 25.0 +100.0) mg/L x 50,000 L
= 74/100 (467.8) mg x 50,000
= 17, 309,000 mg
Answer = 17. 31 kg
Step 4 calculation of soda requirement
soda required = 106/100 ( MgCl 2 + CaCl2 in terms of CaCO3 eq) x vol. of water
= 106/100 (100 +100.0) mg/L x 50,000 L
= 106/100 (200) mg x 50,000
= 10, 6,00,000 mg
Answer = 10. 6 kg
48

49. II. Zeolite (Permutit) method of Softening of water
Zeolite is a Hydrated Sodium Alumino Silicate (HSAS),
capable of exchanging reversibly its sodium ions for
hardness producing ions in water.
The general chemical structure of zeolite is given
below Na2O.Al2O3.xSiO2.yH2O (x = 2-10 and y = 2-6)
Why synthetic zeolite is better than natural zeolite for the
softening of water? Ans: Natural zeolites are non-porous
Micro pores of Zeolite Porous Structure of zeolite
 Porosity or cavity size of synthetic zeolite structures can be
controlled by varying the Si/Al ratio
 Ion-exchange process of zeolite structure is associated with sodium
49
ions

50. Zeolite softener
Hard water in
Hard water spray
Zeolite bed
Gravel
Injector
Softened water
NaCl storage To
sink
50

51. Process of softening by Zeolite method
For the purification of water by the zeolite softener, hard water is passed through the zeolite
bed at a specified rate. The hardness causing ions such as Ca 2+, Mg2+ are retained by the zeolite
bed as CaZe and MgZe respectively; while the outgoing water contains sodium salts. The
following reactions takes place during softening process
To remove temporary hardness
Na2Ze + Ca(HCO3)2 CaZe + 2NaHCO3 Scale formation
Hardness
Na2Ze + Mg(HCO3)2 MgZe + 2NaHCO3
To remove permanent hardness water
Na2Ze + CaCl2 CaZe + 2NaCl
Na2Ze + MgSO4 MgZe + Na2SO4
Regeneration of Zeolite Bed
CaZe (or) MgZe + 2NaCl Na2Ze + CaCl2 (MgSO4)
Used 10% brine Regenerated Washings
Zeolite solution Zeolite drained
51

52. Limitations of Zeolite process
1. If the water is turbid ---- then the turbidity causing particles clogs the pores of the Zeolite
and making it inactive
2. The ions such as Mn2+ and Fe2+ forms stable complex Zeolite which can not be regenerated
that easily as both metal ions bind strongly and irreversibly to the zeolite structure.
3. Any acid present in water (acidic water) should be neutralized with soda before admitting
the water to the plant, since acid will hydrolyze SiO 2 forming silicic acid
Advantages of Zeolite process
1. Soft water of 10-15 ppm can be produced by this method
2. The equipment occupies less space
3. No impurities are precipitated, hence no danger of sludge formation in the treated water
4. It does not require more time and more skill
Disadvantages of Zeolite process
1. Soft water contains more sodium salts than in lime soda process
2. It replaces only Ca2+ and Mg2+ with Na+ but leaves all the other ions like HCO3- and CO32-
in the softened water (then it may form NaHCO 3 and Na2CO3 which releases CO2 when
the water is boiled and causes corrosion)
3. It also causes caustic embitterment when sodium carbonate hydrolyses to give NaOH 52

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53

54. III. Ion-Exchange resin (or) deionization (or) demineralization process
Ion exchange resin
Ion exchange resins are insoluble, cross linked,
long chain organic polymers with a microporous
structure, and the functional groups attached to
the chain is responsible for the “ion-exchange”
properties.
Cation Resin after
exchange Resin treatment 54

55. In general the resins containing acidic functional groups (-COOH, -SO 3H etc) are capable of
exchanging their H+ ions with other cations, which comes in their contact; whereas those
containing basic functional groups ( -NH 2, =NH as hydrochlorides) are capable of exchanging
their anions with other ions, which comes in their contact.
Based on the above fact the resins are classified into two types
1. Cation exchange resin (RH+) –
Strongly acidic (SO3-H+) and weakly acidic (COO-H+) cation exchange resins
2. Anion Exchange resin (ROH-) –
Strongly basic (R4N+OH-) and weakly basic (RNH2+OH-) anion exchange resins
Continued… next slide
55

56. Structure of Cation and Anoin exchange resins
Cation exchange resin Anion exchange resin
R = CH3
56

57. Ion exchange purifier or softener
Hard
water
Gravel
Cation exchange Resin Anion exchange Resin bed
Injector
Injector
Acid
solution for Wastages to
regeneratio sink Alkaline solution for
n of resin Wastages to
regeneration of resin
sink
pump
57
Soft water

58. Process or Ion-exchange mechanism
involved in water softening
Reactions occurring at Cation exchange resin
2 RH+ + Ca2+ (hard water) R2Ca2+ + 2 H+
2 RH+ + Mg2+ (hard water) R2Mg2+ + 2 H+
Reactions occurring at Anion exchange resin
2 ROH- + SO42- (hard water) R2SO42+ + 2 OH-
2 ROH- + Cl- (hard water) R 2Cl- + 2 OH-
At the end of the process
H+ + OH- H 2O
58

59. Regeneration of ion exchange resins
Regeneration of Cation exchange resin
R2Ca2+ + 2H+ (dil. HCl (or) H2SO4) 2 RH+ + Ca2+ (CaCl2, washings)
Regeneration of Anion exchange resin
R2SO42- + 2OH- (dil. NaOH) 2 ROH- + SO42- (Na2SO4, washings)
Advantages
1. The process can be used to soften highly acidic or alkaline waters
2. It produces water of very low hardness of 1-2ppm. So the treated
waters by this method can be used in high pressure boilers
Disadvantages
1. The setup is costly and it uses costly chemicals
2. The water should not be turbid and the turbidity level should not be
more than 10ppm 59

60. IV. Softening of water by Mixed Bed deioniser
Description and process of mixed bed deionizer
1. It is a single cylindrical chamber containing a mixture of anion and cation exchange
resins bed
2. When the hard water is passed through this bed slowly the cations and anioins of the
hard water comes in to contact with the two kind of resins many number of times
3. Hence, it is equivalent to passing the hard water many number of times through a series
of cation and anion exchange resins.
4. The soft water from this method contains less than 1ppm of dissolved salts and hence
more suitable for boilers
Hard water
c a c a Anion exchange
resin
c Mixed bed Mixed
a deionizer a resin bed
a
c a cc Cation exchange
resin
Demineralised
water
60

61. Regeneration of mixed bed deionizer
1. When the bed (resins) are exhausted or cease to soften the water, the mixed bed is back washed
by forcing the water from the bottom in the upward direction
2. Then the light weight anion exchanger move to the top and forms a upper layer above the
heavier cation exchanger
3. Then the anion exchanger is regenerated by passing caustic soda solution (NaOH) from the top
and then rinsed with pure water
4. The lower cation exchanger bed is then washed with dil.H 2SO4 solution and then rinsed.
5. The two beds are then mixed again by forcing compressed air to mix both and the resins are now
ready for use
Low
NaOH
density
resin
c a c a c a c a c aa c
aa a a a a cRegenerated a
c Mixed bed c Exhausted a
H2
Back washed
a deionizer a a Mixed bed a
Mixed bed
SO
a
4
deionizer
a a ccccc c
c a cc c a cc c a c c
Back Compressed
wash High air 61
water density
resin

62. Treatment of Municipal Drinking Water
• Screening – to remove floating matters
• Aeration – to remove dissolved gas and
improve taste of water
• Sedimentation & Coagulation – this is done
after chemical treatment (L-S)
• Filtration – Gravity (or) Pressure sand filters
• Sterilization and disinfection
• Storage and distribution
Attn: Part B Question 62

63. 63

64. Desalination of seawater
• Desalination, refers to any process that
removes some amount of salt and
other minerals from water.
Technologies for desalination process
• Reverse Osmosis (Pressure membrane process)
• Electrodialysis membrane process
Attn: Part B Question 64

65. Pressure Membrane
Processes
• Microfiltration (MF), which can remove particles ranging in size
from 10-100 μm. It is operated in the pressure range of 10 psig.
• Ultrafiltration (UF), which can remove particles ranging in size
from 0.01 to 10 μm. It is operated in the pressure range of 15 psig.
• Nanofiltration (NF), which can remove particles size from 0.001
μm to 0.01 μm. It is operated in the pressure range of 75-250 psig.
• Reverse osmosis (RO), which can remove particles in the size
range of 0.1-1.0 nm. It operates in the pressure range of 200-1200
psig.
65

66. Principle - Reverse osmosis
 When two solutions of unequal concentration are separated by a
semi-permeable membrane, flow of solvent takes place from
dilute to concentration side, due to increase in osmostic pressure,
which is termed as osmosis.
 However, when a hydrostatic pressure in excess of osmotic
pressure is applied on the concentrated side, the solvent flow is
reversed from concentrated side to dilute side, across the
membrane. This principle is termed as reverse osmosis.
 The semi-permeable membrane (in reverse osmosis) is selective
in not permitting the passage of dissolved solute particles such as
molecules, ions, etc.) It permits only the flow of water molecules
(solvent) from the concentrated to dilute side.
 Cellulose acetate, polyamide, etc., are used as membrane
 Reverse osmosis process requires only mechanical force to
generate the required hydrostatic pressure.
 Hydrostatic pressure generated is in the order of 15-40 Kg m-266

67. Reverse Osmosis
67

68. Principle -Electrodialysis
 Electrodialysis is an electrochemical process whereby electrically charged
particles, ions, are transported from a raw solution (retentate, diluate) into a
more concentrated solution (permeate, concentrate) through ion-selective
membranes by applying an electric field.
68

69. Theory of Electrodialysis
• Electrodialysis chamber comprises of sheet like barriers made
out of high-capacity, highly cross-linked ion exchange resins that
allow passage of ions but not of water.
• There are two types : (a) Cation exchange and (b) Anion
exchange membranes
• Cation exchange membranes consists of an insoluble matrix and
mobile cation reside in the pore space that allows the pass
through of only cations.
• Anion exchange membranes consists of an insoluble matrix and
mobile anion reside in the pore space that allows the pass
through of only anions.
• Cation- and Anion- exchange membranes are installed
alternatively in the tank.
• By impressing electricity on the electrodes, the positive anode
attracts negative ions in solution, while the negative cathode
attracts positive ions in the solution. 69