water PPT.pdf notes and detailed notes ppt

Engineering chemistry unit 2 water

1. WATERCHEMISTRY
1
Course: B.Tech
Subject: Engineering Chemistry
Unit:1

2. Water & Its treatment
1).Likeair,waterisoneofthefewbasicmaterialswhichisofprime
importanceforthepreservationoflifeonthisearth.
2).Allareawareoftheusesofwaterfordrinking,cooking,cooking,
bathing&forfarmingetc.
3).Butfewknowtheimportanceofwaterasanengineeringmatrial.
4).Asanengineeringmaterialwaterisusedforproducingsteam,in
boilerstogeneratehydro-electricpower,furnishingsteamfor
engines,forconstructionofconcretestructuresformanufacturing
purposes&asasolventinchemicalprocess.

3. Sources of Water
A) Surface Water
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/Sub-Surface Water
Spring/Well Water -Crystal clear but high dissolved
salts and high purity from organics
3

4. Sources of Water:
1).Rainwater:Rainwateristhepurestformofnaturalwater.
However,itdissolvesconsiderableamountofgases(CO
2–SO
2-NO–
NO
2etc)andsuspendedsolidparticlesfromatmosphere,duringits
journeythroughitandbecomespolluted.
2).Riverwater:Riverareformedbyrainandspringwaters.During
itsflowoverthesurfaceofland,itdissolvesmineralsofthesoilsuchas
chlorides,sulfates,bicarbonatesofsodium,calcium,magnesiumionsetc.
3).SpringorwellwaterorLakewater:Itcontainsconstant
chemicalcomposition.Themineralspresentinthelakewaterintheform
dissolvedformandhighquantityoforganicmatter.

5. 4).Seawater:Itisthemostimpureformofnaturalwater.Itcontains
largerpercentageofthedissolvedsalts(above3.5%)outofwhichabout
2.6%isNaCl.TheNaClwhichispresentinthedissolvedforminsea
waterwillcomeoutasNaClcrystalsduetoevaporationofseawater.
Theothersaltspresentinthesea-wateraresulphatesof
sodium,bicarbonatesofpotassium,magnesium,calcium,bromidesof
potassium,magnesiumetc.
Undergroundwater:Spring&wellwatersaretheunderground
watersources.Theyareingeneralclearerinappearanceduetothe
filteringactionofthesoil.
Theycontainmoreofthedissolvedsaltsgenerally,undergroundwater
isofhighorganicpurity.

6. Types of impurities in water
The impurities present in water are classified as:
1). Dissolved impurities: Dissolved impurities may organic or inorganic.
Inorganic impurities: The carbonates, bicarbonates, sulphates, chlorides
of calcium, magnesium, iron potassium and aluminium.
Organic impurities: Organic water products, amino acids, proteins, etc.
Gases:O
2 , CO
2 , CH
4,NH
3, Oxides of nitrogen and sulphur, H
2S etc.
2). Suspended impurities: It is of two types:
Inorganic -sand & clay;
Organic –vegetable and animal matter.
3) Biological Impurities: Micro-Organisms like Pathogenic bacteria,
fungi, algae etc

7. POTABLEWATER
Water : safe to drink,
Fit for human consumption, should satisfy the
following requirements:
1.Clear & odourless,
2.Pleasant in taste,
3.Perfectly cool,
4.Turbidity should not exceed 10ppm,
5.Free from objectionable dissolved gases
6.Objectionable minerals: lead,arsenic, Mn, Cr
7.pH:8.0
8.Reasonably soft,
9.Free from disease-producing microorganisms.
7

8. DISADVANTAGES OF HARDWATER / CAUSES OF HARDNESS :
The following are the disadvantages when hard water is used for
various purpose:
(i)DOMESTIC USE:
(a)Washing and Bathing : Hard water does not form lather easily
with soap is wasted
(b)Drinking: Hard water causes bad effects on our digestive system.
Sometimes, stone formation takes place in kidneys
(c)Cooking: The boiling point of water is increased due to the
presence of salts. Hence, more fuel and time are required for
cooking.

9. (ii) INDUSTRIAL USE:
(a)Textile Industry : Hard water causes wastage of soap. Precipitates
of calcium and magnesium soap adhere to the fabrics and cause
problem
(b)Paper Industry : Calcium and Magnesium salts in water may effect
the quality of paper.
(c)Sugar Industry : Water containing sulphates, carbonates, nitrates
affects the crystallisationof sugar.
(d)Pharmaceutical Industry : Hard water may form some undesirable
products while preparation of pharmaceutical products.

10. (iii) STEAM GENERATION IN BOILERS : For steam generation,
boilers are employed. If hard water is used in boilers, It may lead to the
following troubles
(a)Boiler Corrosion
(b)Scale and Sludge formation.
(c)Priming and Foaming
(d)Caustic embrittlementPharmaceutical industry

11. HARDNESSOFWATERORHARDWATER AND SOFT
WATER
11
• Hardness in Water is characteristic that prevents the ‘lathering
of soap’ thus water that 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.
Hard Water : Those water which does not produce lather (or) very little lather
with soap is called Hard Water
Soft Water : Soft water readily produce a lot of lather when mixed with little
soap.
The Hardness of water is caused by the presence of dissolved salts such as
Bicarbonates, Sulphates, Chlorides and Nitrates of bivalent metal ions like
Ca
+2
& Mg
+2

12. Soap is sodium/potassium salt of higher fatty acids like stearic, oleic and
palmeticacids.
When soap is mixed with soft water lather is produced due to stearic
acid and sodium stearate
Na –Stearate + H
2O NaOH + Stearic Acid [C
17H
35COOH]
Stearic Acid + Na-Stearate Formatioinof lather.
When soap comes in contact with HARD WATER,
Sodium stearate will react with dissolved calcium and magnesium salts
and produce calcium stearate or magnesium stearate which is white
precipitate
2Na –Stearate + Ca
+2
Ca –Stearate ↓ + 2Na
+
[2C
17H
35COONa] + Ca
+2
[(C
17H
35COO)
2Ca] ↓ + 2Na
+
(Soap) (Soluble) (Insoluble) (Soluble)
[2C
17H
35COONa] + Mg
+2
[(C
17H
35COO)
2Mg] ↓ + 2Na
+
(Soluble) (Soluble) (Insoluble) (Soluble)

13. Hardness Name OfWater
0-70 mg/litre
SoftWater
70-150 mg/litre
Moderate Hard Water
150-300 mg/litre
Hard Water
> 300 mg/litre
Very Hard Water
Different Type of Water have different degree of hardness .
The different types of water are commercially classified on the basis of
degree of hardness as follows:

14. TYPES OF HARDNESS
The hardness of water is of two types
(1)Temporary hardness(or) Carbonate hardness
(2)Permanent hardness (or) Non-Carbonate hardness

15. 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+ H
2O + CO
2
Calcium bicarbonate Calcium Carbonate
Mg(HCO
3)
2 Heat Mg(OH)
2+ 2CO
2
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.

16. PERMANENTHARDNESS
16
Non Carbonate Hardness is due to the presence of chlorides, sulfatesof
calcium, Magnesium, ironand other heavy metals. These salts are CaCl2,
CaSo4, Ca(NO3)2, MgCl2, MgSo4, Mg(No3)2
These Hardness cannot be removed easily by boiling. Hence it is called
“Permanent Hardness”. Only chemical treatment can remove this hardness.
2C
17H
35COONa + CaCl
2 (C
17H
35COO)
2Ca + 2NaCl
2C
17H
35COONa + MgSO
4 (C
17H
35COO)
2Mg + 2Na
2SO
4
Sodium stearate
(sodium soap)
Hardness Calcium stearate
(Insoluble)
Sodium stearate
(sodium soap)
Hardness
Magnesium stearate
(Insoluble)
Total Hardness Of Water = Temporary Hardness + Permanent Hardness

17. DEGREE OF HARDNESS:
•The Concentration of hardness as well as non-hardness constituting
ions are, usually expressed in the term of “Equivalent amount of
CaCo
3”
•Since this mode permits the multiplication and division
concentration, when required. The choice of CaCo3 in particular is
due to its molecular weight (m.wt) is “100” (Equivalent wt = 50),
and moreover, It is unsoluble salt that can be precipitated in water
treatment.

18. •Therefore 100 parts by weight of CaCo3 hardness must be
equivalent to
1 162 partsby weight of Ca(HCo
3)
2hardness
2
146 partsby weight of Mg(HCo
3)
2hardness
3
136 partsby weight of CaSo
4hardness
4
111 partsby weight of CaCl
2hardness
5
164 partsby weight of Ca(No
3)
2hardness
6 120 parts by weight of MgSo
4 hardness
7
146 partsby weight of MgCl
2hardness
8
136 partsby weight of Mg(No
3)
2 hardness

19. The method of calculating degree of hardness will be clear from the
following formula
•Hardness causing in salt in terms of CaCo
3
Amount of the hardness causing salt x 100
Molecular weight of hardness causing salt
UNITS OF HARDNESS:
These are 4 different units in which the hardness of water is expressed
as given below
(1)Parts per million (PPM): PPM is the number of parts of CaCo
3
equivalent hardness per 10
6
parts of water.
i.e., 1 PPM = 1 part of CaCo
3equivalent hardness in 10
6
parts of
water.

20. (2) Milligrams Per Litre(mg/litre): mg/L is the number of milligrams
of CaCo
3equivalent hardness present per litreof water.
i.e., 1 mg/L = 1 mg of CaCo
3equivalent hardness of 1 L of water.
But 1 L water weights = 1 kg of water
1 kg = 1000 gms
= 1000 x 1000 mg
= 10
6
mg
∴1 mg/L = 1 mg of CaCo
3 equivalent per 10
6
mg of water
= 1 part of CaCo
3 equivalent per 10
6
parts of water
∴1 mg/L = 1 ppm

21. Degree Of Clark (
o
cl) :
o
cl is number of grains (1/7000 lb) of CaCo
3equivalent hardness per
gallon (10 lb) of water.
(or)
It is defined as the number of parts of CaCo
3equivalent hardness per
70,000 parts of water.
∴1
o
cl = 1 grain of CaCo
3eq. hardness per gallon of water.
(or)
1
o
cl = 1 part of CaCo
3eq. hardness per 70,000 parts of water
∴1 ppm= 0.07
o
cl

22. Degree Of French (
o
Fr) :
o
Fris the number of parts of CaCo
3equivalent hardness per 10
5
parts
of water.
1
o
Fr = 1 part of CaCo
3equivalent hardness per 10
5
parts of water
Note: The hardness of water can be converted into all the four units by
making use of the following interconversionformula
1 ppm= 1mg/L = 0.07
o
cl = 0.1
o
Fr
1
o
cl = 1.43
o
Fr = 14.3 ppm= 14.3 mg/L
∴0.1
o
Fr = 1 ppm

23. Water Softening
Methods

24. Water Softening Methods
❖Soda Lime Process
❖Zeolite (Permutitprocess)
❖Ion-exchange
❖Mixed bed ion-exchange

25. Lime soda process
ItisaprocessinwhichLime(Ca(OH)
2)andsoda(Na
2CO
3)are
addedtothehardwatertoconvertthesolublecalciumand
magnesiumsaltstoinsolublecompoundsbyachemicalreaction.
TheCaCO
3andMg(OH)
2soprecipitatedarefilteredoffand
removedeasily.
It is further divided in to two types
1.Cold lime soda process
2.Hot lime soda process

26. 1. Cold lime soda process
InthisprocessacalculatedquantityofCa(OH)
2(lime)andNa
2CO
3
(soda)aremixedwithwateratroomtemperatureandaddedtothe
hardwater.Thefollowingreactionstakesplacedependingonthe
natureofhardness
If it is permanent hardness and due to calcium salt
Ca
2+
+ Na
2CO
3 CaCO
3+ 2Na
+
(soda)
slimy suspended precipitate
If it is due to Magnesium salt
Mg
2+
+ Ca(OH)
2 Mg(OH)
2+ Ca
2+
(lime)
slimy suspended precipitate
Ca
2+
+ Na
2CO
3 CaCO
3+ 2Na
+
(soda)
slimy suspended precipitate
Chemical reactions
Step 1

27. If it is Temporary hardness and due to calcium salt
Ca(HCO
3)
2+ Ca(OH)
2 2CaCO
3+ 2H
2O
slimy suspended precipitate
If it is due to Magnesium salt
Mg(HCO
3)
2+ 2Ca(OH)
2 2CaCO
3+ Mg(OH)
2+ 2H
2O
slimy suspended precipitates
Chemical reactions contd..
TheprecipitatesCaCO
3andMg(OH)
2areveryfineandformssludge
likeprecipitatesintheboilerwaterandaredifficulttoremove
becauseitdoesnotsettleeasilymakingitdifficulttofilterandthe
removalprocess.Finallyreducestheefficiencyoftheboiler.
Therefore,itisessentialtoaddsmallamountofcoagulant(suchas
Alum,Aluminiumsulfate,sodiumaluminateetc)whichhydrolysesto
flocculentprecipitateofAl(OH)
3whichentrapsthefineprecipitates.
Step 2

28. 28
8
Cold lime-soda process

29. When coagulants are added flocculation takes place followed by
the formation of flocculants.
NaAlO
2 + 2H
2O NaOH + Al(OH)
3
Coagulant
Flocculent-Gelatinous
precipitate which entraps the
fine precipitates of CaCO
3and
Mg(OH)
2
Al
2(SO
4)
3+ 3 Ca(HCO
3)
2 2Al(OH)
3+ CaSO
4+ CO
2
Aluminium
sulfate
Hard water
sample
Flocculent-Gelatinous
precipitate which entraps the
fine precipitates of CaCO
3and
Mg(OH)
2
TheAl(OH)
3formedbytheadditionofcoagulants
initiatestheprocessofflocculationandentrapsthe
fineprecipitatesandbecomesheavy.Theheavier
flocsthensettlesatthebottomandfilteredoffeasily.

30. Softening Procedure
Method:
•Raw water & calculated quantities of chemicals: from the
top in to the inner vertical circular chamber.
•There is a vigorous stirring & continuous mixing : softening
of water take place.
•Softened water comes into the outer co-axial chamber, it
rises upwards.
•Heavy sludge settles down & softened water reaches up.
•Softened water : passes through a filtering media to ensure
complete removal of sludge.
•Filtered soft water finally flows out continuously through
the outlet at the top.
•Sludge settling at the bottom of the outer chamber is drawn
off occasionally.
30

31. COLD-LIME-SODA PROCESS:

32. (ii) Hot lime-soda process:
Treating water with softening chemicals at a temp. of 80 to 150˚c.
Process : operated close to the boiling point.
consists three parts:
(a) Reaction tank: in which raw water, chemicals & steam are mixed,
(b) Conical sedimentation vessel: sludge settles down.
(c) Sand filter: complete removal of sludge from softened water.
32

33. 33
9
Hot lime-soda process

34. Advantages of hot lime-soda process:
•The precipitation reaction is almost complete,
•Reaction takes place faster,
•Sludge settles down rapidly;
•No coagulant is needed,
•Dissolved gases (which may cause corrosion) are
removed,
•Viscosity of soft water is lower, hence filtered
easily,
•Residual hardness is low compared to cold lime-
soda process.
34

35. Advantages & Disadvantages of Lime-soda process
Advantages:
•1.Economical
•2.Process incresespH value of the treated water, thereby
corrosion of the distribution pipes is reduced.
•3.Mineral content of water is reduced
•4.pH of water raises thus reducing content of pathogenic
bacteria
•5. iron & Mn: removed.
Disadvantages:
•1.Huge amount of sludge is formed and its disposal is difficult
•2.Due to residual hardness, water is not suitable for high
pressure boilers
35

36. In this method the lime & soda are mixed with hard water at room
temperature with constant stirring
Generally the precipitates formed by this process are finely divided and
in order to settle the precipitates, coagulants like alum, ferrous sulphate
etc are added
The hard water to be softened is mixed with calculated quantity of
chemicals (Lime + Soda + Coagulant) from the top into the inner
chamberonvigorous stirring. The chemical reactions takes place and
the hardness producing salts get converted into insoluble precipitates
The sludge is removed from the bottom of the outer chamber while the
softened water passes through a wood fibrefilter to ensure the complete
removal of any residual sludge particles
The clear softened water is withdrawn from the top of the outer
chamber. The softened water from this process contains a residual
hardness of 50-60ppm

37. HOT-LIME-SODA PROCESS:

38. This process is similar to the cold lime-soda process,
but no coagulant is needed.
Here the process is carried at a temperature of 80
o
to 150
o
c. Since the
reaction carried out at high temperature.
(a)The reaction takes place faster
(b)The sludge settles rapidly
(c)Viscosity of soft water is lower, hence filtered easily
(d)The dissolved gases such as CO2, air etc driven out of the water
(e)The residual hardness is low, compared to cold lime-soda process. Hot
lime soda process consists of three parts
“REACTION TANK” in which complete mixing of water, chemicals
and steam takes place and water gets softened.
“Conical Sedimentation Vessel” where the sludge settle down.

39. “SAND FILTER” where sludge is completely removed
The softened water from this process contains a residual hardness of
15-30 ppm
ADVANTAGES OF LIME -SODA PROCESS:
I.This process is economical
II.Mineral content of the water is reduced
III.The process increases the pH value of water, which reduces the content
of pathogenic bacteria
IV.Manganese and Iron salts are also removed by this process
V.The process improves the corrosion resistance of the water

40. DISADVANTAGES OF LIME -SODA PROCESS:
1)Due to residual hardness, water is not useful for high pressure boilers
2)Large amount of sludge is formed which create disposal problem

41. Permutit or Zeolite Process
oZeoliteishydratedsodiumaluminiumsilicatehavingageneralformula,
Na
2OAl
2O
3.xSiO
2.yH
2Owherex=2-10andy=2-6
oItexchangesNa
+
ionsforCa
2+
andMg
2+
ions.
oCommonZeoliteisNa
2OAl
2O
3.3SiO
2.2H
2Oknownasnatrolith.
oOthergluconites,greensand(ironpotassiumphyllosilicatewithcharacteristic
greencolour,amineralcontainingGlauconite)etc.areusedforwatersoftening.
oArtificialzeoliteusedforwatersofteningisPermutit.
oTheseareporous,glassyparticleshavinghighersofteningcapacitycomparedto
greensand.
oTheyarepreparedbyheatingchinaclay(hydratedaluminiumsilicate),feldspar
(KAlSi
3O
8-NaAlSi
3O
8–CaAl
2Si
2O
8)areagroupofrock-formingtectosilicate
mineralswhichmakeupasmuchas60%oftheearth’scrust)andsodaash
(Na
2CO
3)

42. Natural Zeolites:
1.Natrolite -Na
2O. Al
2O
34SiO
2.2H
2O
2.Laumontite -CaO. Al
2O
34SiO
2.4H
2O
3.Harmotome -(BaO.K
2O). Al
2O
35SiO
2.5H
2O
Synthetic zeolite:
Porous & possess gel structure.
-Capable of exchanging
its Na ions
Micro pores of Zeolite

43. Permutit or Zeolite Process
oMethod of softening:
Na
2Ze + Ca(HCO
3)
2 2 NaHCO
3+CaZe
Na
2Ze + Mg(HCO
3)
2 2 NaHCO
3+ MgZe
Na
2Ze + CaSO
4 2 Na
2SO
4+CaZe
Na
2Ze + CaCl
2 2 NaCl+CaZe
At this stage, the supply of hard water is stopped and exhausted zeolite is
reclaimed by treating the bed with concentrated NaCl solution.
oRegeneration of Zeolite:
CaZe(or) MgZe+ 2 NaCl Na
2Ze + CaCl
2or MgCl
2
Brine solution Reclaimed zeolite
To remove temporary
hardness
To remove permanent
hardness

45. Limitations of Zeolite process:
1.Turbidity: The turbidity causing particles clogs the pores of
the Zeolite and making it inactive
2.Colour/Colored ions: The ions such as Mn
2+
and Fe
2+
forms
stable complex Zeolite which can not be regenerated that
easily as both metal ions bind strongly and irreversibly to the
zeolite structure.
3.Acidic Nature: Any acid present in water (acidic water)
should be neutralized with soda before admitting the water to
the plant, since acid will hydrolyze SiO
2forming silicic acid
45

46. Limitations of process:
1.Ifthesupplyofwateristurbid,thesuspendedmattermustberemoved(by
coagulation,filtration,etc.),beforethewaterisadmittedtothezeolitebed;
otherwisetheturbiditywillclogtheporesofzeolitebed,therebymakingit
inactive.
2.IfwatercontainslargequantitiesofcolouredionssuchasMn
2+
andFe
2+
,theymust
beremovedfirst,becausetheseionsproducemaganeseandironzeolite,which
cannotbeeasilyregenerated.
3.Mineralacids,ifpresentinwater,destroythezeolitebedand,therefore,theymust
beneutralisedwithsoda,beforeadmittingthewatertothezeolitesofteningplant.

47. Zeolite Process
Advantages:
oResidualhardnessofwaterisabout10ppmonly
oEquipmentissmallandeasytohandle
oTimerequiredforsofteningofwaterissmall
oNosludgeformationandtheprocessisclean
oZeolitecanberegeneratedeasilyusingbrinesolution
oAnytypeofhardnesscanberemovedwithoutanymodificationstothe
process
Disadvantages:
oColouredwaterorwatercontainingsuspendedimpuritiescannotbe
usedwithoutfiltration
oWatercontainingacidicpHcannotbeusedforsofteningsinceacidwill
destroyzeolite.
oItreplacesonlyCa
2+
andMg
2+
withNa
+
butleavesalltheotherions
likeHCO
3
-
andCO
3
2-
inthesoftenedwater(thenitmayformNaHCO
3
andNa
2CO
3whichreleasesCO
2whenthewaterisboiledandcauses
corrosion)
oSoftwatercontainsmoresodiumsaltsthaninlimesodaprocess

48. Ion-Exchange Process
oIon-exchangeresinsarecrosslinkedlongchainpolymerswith
microporousstructure
oFunctionalgroupspresentareresponsibleforion-exchangeproperties
oAcidicfunctionalgroups(-COOH,-SO
3Hetc.)exchangeH
+
forcations
oBasicfunctionalgroups(-NH
2,=NHetc.)exchangeOH
-
foranions.
A. Cation-exchange Resins(RH
+
):
-Styrene divinyl benzene copolymers
-When sulphonated, capable of exchange H
+
48
Ionexchangeresinsareinsoluble,crosslinked,longchain
organicpolymerswithamicroporousstructure,andthe
functionalgroupsattachedtothechainisresponsibleforthe
“ion-exchange”properties.

49. Ion-Exchange Process
B. Anion-exchange resins (R’OH):
-Styrene divinyl benzene copolymers or amine formaldehyde copolymers with
NH
2, QN
+
, QP
+
, QS
+
, groups.
-On alkali treatment, capable of exchange of OH
-
49

50. 50

51. 51

52. Note: Hard water should be first passed through the cation exchanger and then
Anion exchanger to avoid hydroxides of Ca2+ and Mg2+ getting formed
52

53. 53

54. 54
Process or Ion-exchange mechanism involved in water softening
2 RH
+
+ Ca
2+
(hard water) R
2Ca
2+
+ 2 H
+
2 RH
+
+ Mg
2+
(hard water) R
2Mg
2+
+ 2 H
+
2 ROH
-
+ SO
4
2-
(hard water) R
2SO
4
2+
+ 2 OH
-
2 ROH
-
+ Cl
-
(hard water) R
2Cl
-
+ 2 OH
-
H
+
+ OH
-
H
2O
Reactions occurring at Cation exchange resin
Reactions occurring at Anion exchange resin
At the end of the process

55. 55
Regeneration of ion exchange resins
R
2Ca
2+
+ 2H
+
(dil. HCl (or) H
2SO
4) 2 RH
+
+ Ca
2+
(CaCl
2, washings)
R
2SO
4
2-
+ 2OH
-
(dil. NaOH) 2 ROH
-
+ SO
4
2-
(Na
2SO
4, 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
Regeneration of Cation exchange resin
Regeneration of Anion exchange resin

56. 56

57. Mixed Bed Deionizer
57

58. 58

59. Advantages & Disadvantages of
ion-exchange process
oAdvantages:
-Can be used for highly acid and highly alkaline water
-Residual hardness of water is as low as 2 ppm.
-Very good for treating water for high pressure boilers
oDisadvantages:
-Expensive equipment and chemicals
-Turbidity of water should be < 10 ppm. Otherwise output will
reduce; turbidity needs to be coagulated before treatment.
-Needs skilled labour
59

60. WATER FOR DOMESTIC USE &
TREATMENT OF WATER FOR MUNICIPAL SUPPLY :
The following are the specification of water drinking purpose:
This water should be clear, colourlessand odourless.
The water must be free from pathogenic bacteria and dissolved gases
like H
2S.
The optimum hardness of water must be 125 ppmand
p
H
must be 7.0 to 8.5
The turbidity in drinking water should not exceed 25ppm
The recommended maximum concentration of total dissolved solids in
potable water must not exceed 500ppm

61. TREATMENT OF WATER FOR MUNICIPAL SUPPLY :
The treatment of water for drinking purposes mainly includes the
removal of suspended impurities, colloidal impurities and harmful
pathogenic bacteria.
Various stages involved in purification of water for Municipal Supply:
Source Of Water Screening Aeration
Sedimentation
Filtration
Sterilisation
(or)
Disinfectation
Storage
and
Distribution

62. 1)SCREENING: The process of removing floating matter from water is
known as “Screening”
In this process, water is passed through a screen. The floating matter is
arrested by the screen and the water is free from the folatingmatter.
2) AERATION: The water is then subjected to aeration which
i)Helps in exchange of gases between water and air.
ii)Increases the oxygen content of water
iii)Removes the impurities like ‘Fe’ and ‘Mn’ by precipitating as their
hydroxides

63. 3) SEDIMENTATION :
i) Plain Sedimentation: The process of removing big sized suspended solid
particles from water is called ‘Plain Sedimentation’. In this process,
water is stored in big tanks for several hours.
70% of solid particles settle down due to the force of gravity
ii) Sedimentation By Coagulation:
This is the process of removing fine suspended and colloidal impurities
by adding coagulants like alum, ferrous sulpateand sodium aluminate.
When coagulant is added to water, “FlocFormation” takes place due to
hydroxide formation which can gather tiny particles together to form
bigger particles and settle down quickly

64. 4) FILTRATION: This process of passing a liquid containing suspended
impurities through a suitable porous materials so as to effectively
remove suspended impurities and some micro-organisms is called
“Filtration”.
It is mechanical process. When water flows through a filter bed, many
suspended particles are unable to pass through the gaps and settle in the
bed.

65. 5) DISINFECTION OR STERILISATION:
The process of killing pathogenic bacteria and other micro-organisms is
called ‘Disinfection or Sterilisation’. The water which is free from
pathogenic bacteria and safe for drinking is called Potable water. The
chemicals used for killing bacteria are called ‘DISINFECTANTS’.
a)By adding Bleaching Powder: Water is mixed with required amount of
bleaching powder, and the mixture is allowed o stand for several hours
CaOCl
2+ H
2O Ca(OH)
2+ Cl
2
Cl
2+ H
2O HOCl+ HCl(Hypo ChlorousAcid)
Germs + HOClGerms are killed
The disinfection action of bleaching powder is due to available chlorine
in it. It forms hypochlorousacid which act as a powerful germicide
(disinfectant)

66. b) CHLORINATION : Chlorine is mixed with water in a chlorinator, which
is a high tower having a number of baffle plates. Water and required
quantity of concentrated chlorine solutinare introduced from its top
during their passage through the tower. They get thoroughly mixed and
then sterilisedwater is taken out from the bottom.
ADVANTAGES:
i)Storage required less space
ii)Effective and economical
iii)Stable and does not deteriorate
iv)Produces no salts
v)Ideal disinfectant

67. DISADVANTAGES :
i)Excess of chlorine causes unpleasant taste and odour.
ii)More effective at below p
H
6.5 and less effective at higher p
H
values.
c) OZONATION: Ozone (O
3) is an excellent, disinfectant which can be
prepared by passing silent electric discharge through pure and dry
oxygen. Ozone is highly unstable and breaks down, liberating nascent
oxygen.
3O
22O
3
O
3O
2+ (O)
Nascent Oxygen
This nascent oxygen kills bacteria as well as oxidisesthe organic matter
present in water

68. ADVANTAGES:
Removes colour, odourand taste
DISADVANTAGES :
The method is costly.

69. PROBLEM
(5) Calculate the temporary & permanent hardness of water in
o
cl,
containing the following dissolved salts. CaCO
3=50 mg/L,
MgCl
2=9.5 Mg/L, CaCl
2=2.2 mg/L and MgSO
4=12 mg/L
Note: CaCO
3is an insoluble salt. It does not cause hardness. If CaCO
3is
given as H.C.S, It must be considered as Ca(HCO
3)
2whose hardness
is expressed in the term of CaCO
3equivalent
Sol:
Salt QuantityPresent (mg/L) M.Wt Eq. of CaCo3
CaCO
3 50 mg/L 100 50 mg/L
MgCl
2 9.5 mg/L 95 9.5x100= 10
95
MgSO
4 12 mg/L 120 12x100= 10
12
CaCl
2 22.2 mg/L 111 22.2x100= 20
111

70. Temporary Hardness Of Water = [Hardness Of CaCO
3]
= 50 ppm/50 mg/L
= 50 x 0.7 = 3.5
o
cl
Permanent Hardness Of Water = Hardness of MgCl
2+ MgSO
4+ CaCl
2
= 10 + 10 + 20
= 40 mg/L
= 40 x 0.7
= 2.8
o
cl

71. DETERMINATION OF HARDNESS OF WATER BY EDTA
METHOD:-
1.This is a Complexometricmethod where
EthleneDiamineTetra Acetic Acid (EDTA) is the reagent
2.EDTA forms complexes with different metal ions at different pH.
3.Calcium & Magnesium ions form complexes with EDTA at p
H
9-10.
To maintain the p
H
9-10 NH
4Cl, NH
4OH buffer solution is used.
4.An Alcoholic solution of EriochromeBlack-T (EBT) is used as an
indicator
5.The disodium salt of EDTA under the trade name Triplex-III is used
for complexation

72. EDTA
Disodium Salt Of EDTA
M-DETA COMPLEX

73. BASIC PRINCIPLE:
•When hardwatercomes in contact with EDTA, at p
H
9-10, the Ca
+2
&
Mg
+2
forms stable, colourlesscomplex with EDTA.
Ca
+2
++ EBT pH 9-10 Ca-EBT
Mg
+2
Mg-EBT (Complex)
(from hard water) (unstable, wine red colour)
•To the hard water sample the blue colouredindicator EBT is added
along with the NH
4Cl, NH
4OH buffer solution. EBT forms an
unstable, wineredcomplex with Ca
+2
& Mg
+2
Ca
+2
++ EDTA p
H
9-10 Ca-EDTA
Mg
+2
Mg-EDTA (Complex)
(from hard water)(stable, colourless)

74. •The wineredcoloured[Ca-EBT, Mg-EBT] complex is titrated with
EDTA replaces EBT from Ca-EBT complex and form stable
colourless
Mg-EBT
[Ca-EDTA] [Mg-EDTA] complex releasing the blue coloured
indicator EBT into H
2O
•Hence the colourchange at the end point is wineredto blue
colour
•The titration is carried out in the following steps
1.PREPARATION OF STANDARD HARD WATER :
Dissolve 1gm of pure, dry CaCO
3in minimum quantity of dilute
HCland evaporate the solution to dryness on a waterbath.

75. •Dissolve the residue in distilled water to make 1 litrein a standard flask
and shake well.
Molarityof standard hard water solution = wt. of CaCO
3
m.wt. of CaCO
3
= 1
100
= 0.01 M
(2) PREPARATION OF EDTA SOLUTION :
Dissolve 4 gmsof pure EDTA crystals along with 0.1 gm of MgCl
2in one
litreof distilled water.

76. (3) PREPARATION OF INDICATOR (EBT) :
Dissolve 0.5 gmsof ErichomeBlack-T in 100 ml of alcohol.
(4) PREPARATION OF BUFFER SOLUTION :
Add 67.5 gm of NH
4Cl to 570 ml of concentrated ammonia solution and
dilute with distilled water to one litre
(5) STANDARDISATION OF EDTA SOLUTION :
Pipette out 20 ml of standard hard water solution into a conical flask. Add
2-3 ml of buffer solution and 2-3 drops of EBT indicator.
Titrate the wine red colouredcomplex with EDTA taken in a burette after
rinsing it with EDTA solution till the wine red colourchanges to clear
blue.

77. Not the burette reading and let the volume be “x”-ml. Repeat the titration to
get concurrent values.
(6) STANDARDISATION OF HARD WATER SAMPLE :
Pipette out 20 ml of the water sample into a 250ml conical flask, add 2-3 ml
of buffer solution and 2-3 drops of EBT indicator.
•Titrate the wine red colouredsolution with EDTA taken in the burette
till a clear blue colouredendpoint is obtained
•Let the volume of EDTA be “y” ml. Repeat the titration to get
concurrent values

78. (7) STANDARDISATION FOR PERMANENT HARDNESS :
Pipette out 100 ml of hard water sample in a beaker and boil till the volume
reduces to 20 ml. All the bicarbonates of Ca
++
and Mg
++
decomposes to
CaCO
3and Mg(OH)
2
•Cool the solution and filter the water into a flask, wash the beaker and
precipitate with distilled water and add the washing to conical flask
•Add 2-3 ml of buffer solution and 2-3 drops of EBT indicator and titrate
with EDTA solution taken in the burette till a clear blue colourend
point is obtained.
•Note the burette reading. Let the volume be “z” ml

79. CALCULATIONS :
Molarityof standard hard water solution = 0.01 M.
(Calculated in the preparation of standard hard water)
•Molarityof EDTA solution (M
2):
V
1M
1= V
2M
2
n
1 n
2
•n
1& n
2are no. of moles of Ca
+2
and EDTA = 1 each
i.e., n
1=1, n
2=1

80. V
1= volume of standard hard water
M
1= Molarityof standard hard water
V
2= volume of EDTA
M
2= molarityof EDTA
M
2= V
1M
1= 20x 0.01
V
2 titrevalue (xml)

81. •Molarityof hard water sample (M
3):
V
2M
2= V
3M
3
n
2 n
3
V
2= volume of EDTA
M
2= molarityof EDTA
V
3= volume of standard hard water
M
3= Molarityof standard hard water
M
3= V
2M
2= titrevalue (4 ml) x M2
V
3 20

82. •Total Hardness Of Water = M
3x 100 gms/1 litre
= M
3X 100 X1000 mg/L or ppm
•Permanent Hardness Of Water:
V2= volume of EDTA
M2= molarityof EDTA
V4 = volume of water sample containing permanent hardness (100 ml)
M4= Molarityof water sample containing permanent hardness
M
3= V
2M
2= V
4M
4
n
2 n
4

83. •Permanent Hardness Of The Water Sample = M
4 x 100 x 1000 ppm
•Temporary Hardness Of The Water Sample
= (Total Hardness –Permanent Hardness)
= (M3 x 100 x1000 –M4 x 100 x1000) ppm

84. •1 gm of CaCO
3was dissolved in HCland the solution was made upto
one litrewith distilled water. 50 ml of the above solution required 30 ml
of EDTA solution on titration. 50 ml of hard water sample required 40
ml of the same solution of EDTA for titration. 50 ml of the hard water
after boiling, filtering etc. required 30 ml of the same EDTA solution for
titration.
Calculate the temporary hardness of the water
Soln: Molarityof CaCO
3solution (M
3) = 1/100 = 0.01 M
Molarityof EDTA solution (M
2) = V
1M
1
V
2
V
1= volume of CaCO
3solution = 50 ml
M
1= Molarityof CaCO
3solution = 0.01 M
V
2= volume of EDTA = 30 ml
M
2= V
4M
4= 50 x 0.01= 0.016 M
n
2 30

85. •Molarityof Hard Water Solution (M
3) = V
2M
2
V
3
V
2= volume of EDTA = 40 ml
M
2= Molarityof EDTA = 0.016 M
V
3= volume of hard water = 50 ml
M
3= 40 x 0.016= 0.0128 M
50
Total Hardness of water = 0.0128 x 100 x 1000
= 1280 ppm
Permanent hardness of water: = V
4M
4= V
2M
2
n
4 n
2
M
4= V
2M
2
V
4

86. n
4=1; V
2= volume of EDTA = 30 ml
n
2=1; M
2= molarityof EDTA = 0.016
V
4= volume of permanent hardness containing water = 50
M
4= 30 x 0.016= 0.0096 M
50
Permanent hardness of water = 0.0096 x 100 x 1000
= 930 ppm
Temporary hardness = Total hardness –Permanent hardness
= 1280 –960
= 320 ppm

87. 0.5 g of CaCO
3was dissolved in dil. HCl& diluted to 1000 ml. 50 ml of
this solution required 48 ml of EDTA solution for titration. 50 ml of
hard water sample required 15 ml of EDTA solution for titration. 50 ml
of same water sample on boiling, filtering etc required 10 ml of EDTA
solution.
Calculate the different kind of hardness in ppm
Soln:
Volume of EDTA consumed for 50 ml of standard hardwater(V
1) = 48 ml,
Volume of EDTA consumed for 50 ml of given sample (V
2) = 15 ml
Volume of EDTA consumed for 50 ml of boiled water (V
3) = 10 ml

88. •Total Hardness = V
2x 1000 mg/L
V
1
= 15x 1000 = 312.5 mg/L
48
•Permanent Hardness = V
3x 1000 ml
V
1
= 10x 1000
48
= 208.3 mg/L
•Temporary Hardness = Total Hardness –Permanent Hardness
= 312.5 –208.3
= 104.2 mg/L