lecture Water technology

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Unit-1

Water Technology

The process of removing all types of impurities from water of
impurities from water and making fit for domestic (or)industrial
purpose is called water technology.
Types of impurities in water:
The impurities present in water may be broadly classified into three
types
(i)Physical impurities
(a) Suspended impurities
(b) Colloidal impurities
(ii) Chemical impurities
(a) Dissolved salts
(b)Dissolved gases
(iii) Bacterial impurities
Boiler feed water
The water fed into the boiler for the production of steam is called boiler
feed water.
Requirements
Boiler feed water should be free from turbidity, oil, dissolved gases,
alkali and hardness causing substances.
Hard water:
Which does not produce lather with soap soln,but produce white
ppt(scum) is called hard watetr.
2C17H35COONa +Ca ++ →

(C17H35COO)2Ca + 2Na+

Soft water:

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Which produce lather readily with soap soln is called soft water.
Absence of Ca&Mg salts.
Types of hardness:
1.Temporary hardness
2.permanent hardness
Units of hardnss:
Parts per million(ppm)
It is defined as the no.of parts of CaCo3 eqivalent hardness per
10 parts of water.
6

Milligram per litre(mg/lit)
It is defined as the no.of milligrams of CaCO3
hardness per 1 litre of water.

equivalent

Clarke’s degree( Cl)
It is defined as the no.of parts of CaCO3 equivalent hardness
per 10 5 parts of water.
French degree( Fr)
It is defined as the no.of parts of CaCO3 equivalent hardness per

10 5 part of water.
1ppm=1mg/lit=0.10Fr=0.070cl

Alkalinity determination:

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PRINCIPLE
Alkalinity in water is due to the presence of soluble hydroxides,
bicarbonates and carbonates. Alkalinity can be determined by
Potentiometric methods
Using pH meter
Titrimetry using different indicators
Determination of various types and amounts of alkalinity is easily
carried out by titration with standard HCl employing the indicators
phenolphthalein and methyl orange independently or in succession.
The following reactions occur when different types of alkalinity are
neutralized with acid.
OH- + H+  H2O

CO32- + H+

HCO3- + H+
4.2-5.5---(3)

completed at pH 8.2-9.0 ----------- (1)

 HCO3-

-------------- (2)

 (H2CO3)  H2O + CO2 , completed

at pH

Neutralisation (1) & (2) will be notified by phenolphthalein endpoint while all the three will be accounted by methyl orange endpoint. Bicarbonate in eqn (3) may be due to the existence of soluble
free bicarbonate salts or bicarbonates resulting from half

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neutralization of soluble carbonates (eqn. (2))Various steps to be
followed:
A known volume of water sample is titrated against std. HCl using first
phenolphthalein indicator till end-point (P) and the titration is
continued without break using methyl orange indicator till the
equivalence end-point (M).
From the magnitudes of the P & M, the nature of alkalinity can be
arrived as follows:
(i) P = M

=>

Presence of only OH-

(ii) 2P = M

=>

Presence of only CO32-

(iii) P =0, M#0 =>

Presence of only HCO3-

(iv) 2P > M

=>

Presence of OH- & CO32-

(v) 2P < M

=>

Presence of HCO3- & CO32-

(Mixture of OH- & HCO3-are not listed since they do not exist
together and are considered equivalent to CO32-).

PROCEDURE

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TITRATION – I
STANDARDISATION OF HCl
Exactly 20 ml of the given standard NaOH solution is pipetted out into
a clean conical flask and 2 drops of phenolphthalein indicator is added.
The solution is titrated against the given HCl taken in the burette. The
pink colour of the solution in the conical flask disappears at the endpoint. The titre value is noted down from the burette and the titration
is repeated to get concordant value.
TITRATION – II
ESTIMATION OF ALKALINITY IN WATER SAMPLE
Exactly 20 ml of water sample is pipetted out into a clean conical
flask. Few drops of phenolphthalein indicator are added and titrated
against the standardized HCl taken in the burette. The end-point is the
disappearance of pink colour, which is noted as P. Into the same
solution few drops of methyl orange indicator is added. The solution
changes to yellow. The titration is continued further by adding same
HCl without break till the end-point is reached. The end point is the
colour change from yellow to reddish orange. The titre value is noted
as M.
The experiment is repeated to get concordant values. From the
magnitudes of P & M values, the type of alkalinity present in the
water sample is inferred and the individual amounts are calculated
and reported.

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Estimation of hardness by EDTA method:
EDTA:ethylene diammine tetra acetic acid
(CH2COOH )2N-CH2-CH2-N(CH2COOH)2
Principle:

Hadness causing ions (Ca2+,mg2+)estimatimated by titrating the
water sample against EDTA.
Indicator: eriochrome –black –T
Buffer soln: (NH4Cl-NH4OH):PH:8-10

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*Ca2+,Mg2+++EBT→*Ca,Mg EBT+ complex(wine red
coloured weak complex)
*Ca ,Mg EBT+Complex +EDTA→*Ca Mg EDTD++EBT(Steel
blue)
The estimation is based on the complexometric titration.

(i) Total hardness of water is estimated by titrating it
against EDTA using EBT indicator.

EBT+Mn+ [EBT-M] (complex)

EBT-M (unstable complex) +EDTA  [EDTA-M] (stable complex)
+EBT
(Wine red)

(Steel blue)

EBT indicator forms wine red coloured complex with hardness
causing metal ions present in water. On addition of EDTA, metal ions
preferably form complexes with EDTA and steel blue EBT indicator
is set free. Therefore change of colour from wine red to steel blue
denotes the end point.

(iii) Temporary hardness is removed by boiling the water.

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Ca (HCO3)2  CaCO3 ↓+CO2 +H2O

Mg (HCO3)2  Mg(OH)2 ↓ +2CO2

The precipitate is filtered and the remaining permanent
hardness is estimated using EDTA.

Pipette out 20ml of standard CaCl2 into a 250ml conical flask.
(Standard hard water is prepared by dissolving 1 g of calcium
carbonate in one litre of distilled water) . Add 5ml of buffer solution
and 3 drops of eriochrome black T indictor. Titrate the solution with
EDTA from the burette until the colour changes from wine red to
steel blue at the end point. Repeat the titration for concordant
values. Let the titre value be V1ml.

TITRATION – II
(ii) DETERMINATION OF TOTAL HARDNESS

Pipette out 20ml of sample hard water into a clean conical flask.
Add 5ml of buffer solution and 4 -5 drop of eriochrome black T
indicator. Titrate the wine red coloured solution with EDTA from the

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burette until the colour steel blue appears at the end point. Repeat
the titration for concordant values. Let the titre value be V2ml.

TITRATION – III
(iii)DETERMINATIONOF PERMANENT HARDNESS

Take 250ml of hard water sample in a 250ml beaker and boil gently
for about 20 minutes. Cool, filter it into a 250ml standard flask and
make the volume upto the mark. Take 20ml of this solution and
proceed it in the same way as in titration (I). The volume of EDTA
consumed corresponds to the permanent hardness of the water
sample. Let the titre value be V3ml. Temporary hardness is
calculated by subtracting permanent hardness from total hardness.

Step 1- Arriving at standard equation,

1ml of Std CaCl 2 = 1 mg of CaCO3

( given)

V1 ml of EDTA

= 20 ml of Std. CaCl 2

1 ml of EDTA

= (20 / V1) ml of Std. CaCl 2

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Therefore, ml of EDTA = (20 / V1) mg of CaCO3
equation.)

(standard

Step 2.- Calculation of total hardness.

Volume of EDTA consumed (V2)

=-------- ml

20ml of sample hard water

= V2 ml of EDTA

1000 ml of sample hard water

=V2X(1000/20) ml of EDTA

As per standard equation,100ml of given hard water
= V2 X (1000/20) X (20 / V1) mg of CaCO3

=1000 x (V2 / V1 ) mg of CaCO3

Therefore, total hardness

= ----------ppm

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Step 3.- Calculation of permanent hardness.

Volume of EDTA consumed (V3) =-------- ml

20ml of boiled water

= V3 ml of EDTA

1000 ml of boiled water =V3 X (1000/20) ml of EDTA

As per standard equation,
1000ml of given hard water= V3 X

/V1) mg of CaCO3

(1000/20) X (20

= 1000 x (V3 / V1 ) mg of CaCO3

Therefore, permanent hardness

= ----------ppm

Step 4 – Calculation of temporary hardness

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Temporary hardness of the given sample of water = Total hardness –
Permanent hardness

=ppm
Treatment of water for domestic supply :

Screening:
It is a process of removing the fioating material like
leaves,woodpieces,etc.from water.
Aeration:
The process of mixing water with air is known as aeration.
To remove gases like CO2,H2S

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Sedimentation:
It is a process of removing suspended impurities by allowing
the water to stand un disturbed for 2-6 hours in a big tank.
Coagulation:
In this method certain chemicals called coagulats,like alum,
Al2(SO4)3+6H2O→Al(OH)3↓+3H2SO4
Filtration :
It is the process of removing
bacteria,colour,taste,odour.passing water through filter beds.

Sterilization(or)disinfection:
The process of destroying the harmful bacteria is known as
sterilization.
By boiling:

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Water boiled for 10-15minitues all the harmful bacteria are
killed and the water becomes safe for use.
By ozonation
O3→O2+[O]
Ozone is a powerful disinfectant and is readily absorbed by water,

By using UV radiation
Using for sterlisizing water in swimming pool.
Cl2+H2O→HCl+HOCl
Cl2+NH3→ClNH2+HCl
ClNH2+H2O→HOCl+NH3
CaOCl2+H2O→Ca(OH)2+Cl2
Cl2+H2O→HCl+HOCl
HOCl+Bacteria→bacterias are killed
Break point chlorination:
Water contains following impurities:
1.bacterias
2.organic impurities
3.redusing substances(Fe2+,H2S etc)

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4.Free ammonia
Boiler feed water:
The water feed into the boiler fo the production of steam is called
boiler feed water
Boiler troubles: 1.scale&sludge formation
2.priming&foaming
3.caustic embrittlement
4.boiler corrosion
Sludge: if the ppt is loose and slimy it is called sludge .sludge are
formed by substances like mgcl2,mgso4,cacl2
Scale: if the ppt forms hard&adherent coating on the inner walls of

the boiler like Mg(OH)2,caso4
S.NO
1

sludge

scale

sludge is a loose ,slimy and non

scale is a hard,adherent coating.

adherent precipitate.
2

The main sludge forming

The main scale forming substances

substance are MgCO3,CaCl2 etc.

areca(HCO3)2,Mg(OH)2

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3

Disadvantages:sludge are poor

Disadvantages: scales act as a thermal

conductors of heat.excess of

insulators.it decreases the efficiency of

sludge formation decreases the

the boiler.

efficiency of boiler.
4

sludge formation can be

scale formation can be prevented by

prevented by using softened

dissolving using acids like HCl,H2SO4

water.

scale formation can also be removed by

Sludge can also be removed by

external,internal treatment.

using blow down operation.

Priming&foaming:
Priming is the process of production of wet steam .priming is casued by

1.high steam velocity
2.very poor boiler design .

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Foaming (the formation of stable bubbles above the surface of
water is called foaming.
Foaming is caused by presence of oil.&grease.presence of finely
divided particle.
Caustic embrittlement:
It means intercrystaline cracking .boiler water containsNa2co3
Na2co3+H2O→2NaOH+CO2
Fe+2NaOH→Na2Feo2+H2↑
Boiler corrosion:
Corrosion in boilers is due to the presence of →→
1.Dissolved o2
2.Dissolved CO2
3.Dissolved salts
4Fe+6H2O+3O2→4Fe(OH)3
2Na2SO3+O2→2Na2SO4
N2H4+O2→N2+2H2O

Mechanical de-aeration method:
The high temperature &low pressure produced inside the tower
dissolved oxygen content of the water.

CO2+H2O→H2CO3

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2NH4OH+CO2→ (NH4)2CO3+H2O
MgCl2+2H2O→Mg(OH)2+2HCl
Fe+2HCl→FeCl2+H2↑
Softening(or)conditioning method:
The process of removing hardness producing salts from
water is known as softening(or)conditioning of water.
This method can be done in 2 methods
1.External conditioning
2.Internal conditioning
External conditioning:
Ion exchange (or)demineralization process.
Cation exchanger:
Resins contains acidic functional groups (COOH,SO3H) cation
exchange resin is presented as RH2
ex:

1.sulphonated coals.
2.sulphonated polystyrene RSO3H

Anion exchanger
Resin contain basic functional groups (NH2,OH)Anion exchange
resin is representated as R(OH)2
RH2+CaCl2→RCa+2HCl

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RH2+mgso4→Rmg+H2SO4
RH+NaCl→RNa+HCl
Regeneration:
RCa+2HCl→RH2+CaCL2
RNa+HCl→RH+NaCl
R’Cl2+2NaOH→R’(OH)2+2NaCl
Carbonate conditioning: scale formation can be avoided by adding
Na2CO3 to the boiler water.
CaSO4+Na2CO3→CaCO3+Na2SO4
Phosphate conditioning:
sodium phosphate.

scale formation can be avoided by adding

3CaSO4+2Na3po4→Ca3(po4)2
Trisodiumphospate Na3po4(Weaklyalkaline) used for too acidic water.
Disodium hydrogen phosphate-Na2HPO4(weakly alkaline) used for alka
weakly acdic water.
Sodium dihydrogen phosphate-NaH2PO4(acidic) used for alkaline
water.

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Calogen conditioning
Calogen is sodium hexa meta phosphateNa2[Na4(PO3)6]
2Caso4+Na2[Na4(po3)6+→Na2[Ca2(PO3)6]+2Na2SO4
The complex Na2[Na4(po3)6] is soluble in water and ther is no problem
of sludge disposal. So calogen conditioning is better than phosphate
conditioning.
Zeolite process:
Hard water contains Ca2+&Mg2+ ions this ions form hard soap
(in soluble)with soap which does not produce lather with soap soln.
Hard water is softened by passing it through a column packed with
sodium cation exchange resin (called sodium zeolite )

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Na2Ze+Ca2+→CaZe+2Na+

Synthetic zeolite is represented by Na2Ze. The sodium ions which are
loosely held in Na2Ze are replaced by Ca2+ and Mg 2+ ions present in the
water.
Process:
Sodium ions with Ca2+ and Mg 2+ ions present in the water to form Ca

and Mg ions present in the water.
Ca(HCO3)+Na2Ze→ CaZe+2NaHCO3
Mg (HCO3)+Na2Ze→ MgZe+2NaHCO3
CaSO4+ Na2Ze→ CaZe+Na2SO4

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Mg SO4+ Na2Ze→ Mg Ze+Na2SO4
CaCl2 +Na2Ze→ CaZe+2NaCl
Mg Cl2 +Na2Ze→ Mg Ze+2NaCl
Regeneration:
CaZe+2Na+Cl-→Na2Ze+CaCi2
Desalination of brackish water:
The process of removing common salt from the water is
known as desalination.
1.Fresh water -<1000ppm of dissolved solids
2.Brackish water-contains >1000ppm but <35000ppm of dissolved
solids .
3.sea water –contains>35000ppm of dissolved solids.
Reverse osmosis(RO)
Two solns of different concentrations are separated by a semi
permeable membarane.
Flows from a region of lower concentration to higher concentration.
This process is called osmosis .

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Solvent flows from higher concentration to lower
concentration.this is called reverse osmosis.

Advantages:
1.The life of the membarane is high ,and it can be replaced with in
few minutes.
2.It removes ionic as well as non –ionic ,colloidal impurities
3.Due to low capital cost,simplicity.

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Unit-I
Part A
1. Define hardness of water.
2. What are the salts responsible for carbonate and non-carbonate hardness of
water?
3. What is meant by soft water and hard water?
4. Distinguish hard and soft water.
5. How the hardness of water is expressed?
6. Give the significance of calcium carbonate equivalent.
7. How does EBT indicator function as an indicator in EDTA titration?
8. What is meant by permanent hardness of water?
9. Define alkalinity?
10. How is alkalinity classified?

11. How is alkalinity determined?
12. Why water is softened before using in boilers?
13. What are scales and sludges?
14. What is meant by priming and foaming?
15. How the caustic embrittlement is prevented?
16. Indicate the reasons for boiler corrosions.
17. Define softening of water. How it is carried out?
18. Soft water is demineralised water (DM) where as DM water is a soft water.
Justify.
19. What is sodium Zeolite?
20 (a). What is aeration of water/Mention it’s uses?
(b). What is calgon conditioning?

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(c). Explain the term break point chlorination.
(d). What is desalination?
(e). What is blow down operation?.
(f). How hardness of water is removed in zeolite process?
Part-B
1. Describe the principle and method involved in the determination of different
types and amount of alkalinity of water.
2. Explain the EDTA method of estimation of hardness of water.
3. What are boiler troubles? How are they caused? Suggest steps to minimize the
boiler troubles.
4. What is potable water? What are the steps taken to obtain pure drinking
water?

5. How is internal treatment of boiler water carried out?
6. What is desalination? Name the different methods of desalination. Explain the
reverse osmosis in detail.
7. Discuss the chlorination, ozonation and UV methods of disinfection.
8. Explain Zeolite process in detail.
9. Explain the process of sterilization of domestic water supply?
10.(a) 100ml of a water sample requires 20ml of EDTA solution for titration. 1ml
of EDTA solution is equivalent to 1.1mgs of CaCO3. Calculate the hardness in ppm.
(b).In an estimation of hardness of water by EDTA titration 250 ml of a sample
water require 15ml of 0.025M EDTA solution to get the end point. Calculate the
hardness of water.

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