This document discusses various impurities found in water and their removal methods. It describes suspended, colloidal, dissolved, and biological impurities and filtration, coagulation, chemical treatment, and sterilization methods. It also discusses hardness in water, including temporary and permanent hardness and their removal by boiling or other chemical methods. EDTA titration and alkalinity determination methods are outlined. Issues caused by hard water in boilers like corrosion, priming, foaming, sludge, scale, and caustic embrittlement are summarized along with their prevention.

1. Water Technology

2. IMPURITIES IN WATER:
Impurities
Properties Removal methods
Suspended
Impurities
particles like soil,
sand, organic waste,
size of particles
greater than 1000Ao
and visible
simple filtration or the sedimentation or
settlement
Colloidal
Impurities
organic or inorganic
matter of the colloidal
particle size 10 to
1000Ao makes water
turbid.
coagulation followed by sedimentation or
filtration.
The coagulants are like FeSO4,alums,puls floors,
sodium acuminate ,aluminum sulphate.
Dissolved
Impurities
Dissolved salts/ions
Ca+2,Mg+2,Fe+2,Mn+2,
Cl-, NO3
-,HCO3
-,SO4
2-
& dissolved gases O2,
SO2, NH3,
chemical treatment, mechanical deaeration
method for gases.
Biological
Impurities
includes bacteria,
algae,fugi, and other
small size aquatic
Sterilization, use of chem. eg. bleaching powder,
sodium hypochlorite, chlorine, chloramines,
Ozone , UV light

3. Hardness of water:
Temporary Hardness/Carbonate Hardness:
The hardness comes in water due to presence of carbonates &
bicarbonates of heavy metal salts. This hardness is called
temporary Hardness/Carbonate Hardness. e.g.
CaCO3,MgCO3,Ca(HCO3)2,Mg(HCO3)2,FeCO3 etc
• This hardness can be removed by boiling the water i.e. CO2 is
removed.
• Mg(HCO3)2 boiling Mg(OH)2 +2CO2
• Ca(HCO3)2 boiling CaCO3 +CO2+H2O
• MgCO3 boiling Mg(OH)2 +CO2

4. 2.Permanent/Non carbonate Hardness:
• The hardness comes in water due to presence of dissolved salts other than
carbonates & bicarbonates. This hardness is called as permanent/Non
carbonate Hardness.
• Such salts are CaCl2,MgCl2,CaSO4,MgSO4 etc.
• Total hardness = Temporary Hardness +Permanent Hardness
• Units of hardness:
• Quantity in terms of mg CaCO3
= mg of chemical x 50/Equi. Wt. of chemical
• 1. mg CaCO3 equivalent per litre
• 2.ppm CaCO3 equivalent
• 3.ppb CaCO3 equivalent

5. Hardness of water by EDTA method
1. Complexometric titration.
2. Buffer solution of pH about 10.
3. Disodium EDTA reacts quickly with the hardness causing metal
ions in water, even in very low conc. of salts.
4. Indicators- Erichrome black-T (EBT), Calcon

6. • Principle:
• The hardness causing ions like Ca ++ & Mg++ present in water form unstable
complexes (M-EBT) with indicator EBT, having pink red colour. EDTA then
reacts with all hardness causing metal ion present in water to form stable
complexes. (EDTA – metal complex).
Part-A: Standardization of Na2EDTA by MgSO4
Part-B: Determination of total hardness
Part-c: Determination of permanent hardness
Part-D: Determination of temporary hardness

7. • Reactions:
• i) M++ + EBT ↔ M-EBT + 2H+
• Pink red
ii) M++ + EDTA → M-EDTA + 2H+
colorless
• iii) M-EBT + EDTA → M-EDTA + EBT
• colourless blue
• Calculations:
• Total hardness of water sample = (Y x Z x100 x 1000) / V ppm CaCO3
equivalent.
• Permanent hardness = (Y x Z x100 x 1000) / V) ppm CaCO3 equivalent.
• Temporary hardness = Total hardness - permanent hardness

8. Alkalinity of water sample:
• Theroy:
• When an alkaline water is titrated with strong acid, first all OH – get neutralized,
then all the CO3
2- ions are half neutralized to HCO-
3.
• Till this stage PH of mixture decreases to about 8.2 & completion of this stage is
indicating by change in colour of phenolphthalein.
• On continued addition of acid during titration ,all the HCO3
- in the titration
mixture get neutralized & completion of this stage ,is indicated by methyl
orange colour change at 4 to 5 pH.
• Reactions:
• -O H + H+ → H2O
• CO3
-2 + H+ → HCO-
3
• HCO-
3 + H+ → H2O + CO2

9. • Calculations:
• Phenolphthalein alkalinity (P):
P = (V1 × Z × 50 × 1000) / V ppm of CaCO3 equivalents.
• Methyl orange alkalinity OR Total alkalinity
(M): = (V2 × Z × 50 × 1000) / V ppm of CaCO3 equi.

10. • Types of alkalinities:
i)Only -OH ii) Only CO3
-2
iii)Only HCO3
- iv) -OH & CO3
-2 together
v) CO3
-2 & HCO3- together.
• Types of alkalinities:
Alkalinity Quantity of HO- Quantity of CO3
-- Quantity of HCO3
-
P=0 O 0 M
P = ½ M 0 2P 0
P =M P 0 0
P < ½ M 0 2P M-2P
P > ½ M (2P-M) 2(M-P) 0

11. • Ill effect of hard water in boiler.
A) Boiler Corrosion
B) Priming & foaming
C) Sludge & scale formation
D) Caustic embrittlement

12. A) Boiler Corrosion:
• Disadvantages of corrosion:
1.Reducing the life of boiler
2.Leakage of joints and rivets
3.Increased cost of repairs & maintence.
• Causes:
• a)Dissolved oxygen:
• 2Fe + 2H2O + O2 Heat 2Fe(OH)2 +1/2O2 +Fe2O3.2H2O
• (Rust)
• Removal of oxygen:
• i)The dissolved oxygen is removed by adding some quantity of
Na2SO3(Sodium Sulphite) or hydrazine(N2H4)
• Na2SO3 +1/2O2 Na2SO4
• N2H4+ O2 N2+ 2H2O

13. • b)Dissolved CO2
• i)If boiler feed water contains dissolved CO2,then it forms
carbonic acid (H2CO3)hence corrosion takes place.
• CO2+H2O H2CO3
• Removal of CO2:
• CO2 can remove by adding suitable amount of NH3
• CO2+ 2NH3+H2O (NH4)2CO3
• To avoid corrosion due to ammonia, its conc. is maintained
to 10 ppm.
• ii)Dissolved CO2 can be removed by mechanical deaerator.

14. c) Hydrolysis of salts:
If water contains weak base- strong acid salts like
MgCl2,CaSO4 etc, then they are hydrolysed at high temp. &
form strong acid .This acid corrodes boiler metal
• MgCl2 +2H2O 2Mg(OH)2 +2HCl
• Fe +2HCl FeCl2 +H2 +2HCl
• FeCl2+2H2O 2Fe(OH)2 +2HCl
• To prevent corrosion due to acid formation in boiler ‘the pH of
water is adjusted to 8.5-9.0.
d)Galvanic Cells: use Sacrificial anode to minimize corrosion
due to galvanic cell formation

15. BOILER CORROSION

16. • Priming and Foaming:
• Priming: “When a boiler produces steam rapidly, some
water droplets are carried along with steam. This process
of “Wet” steam formation is called priming.”
• Causes:
1. Very high level of boiler feed water
2. Presence of excessive foam
3. High speed of steam generation.
4. Faulty boiler design.

17. • Foaming: “It is the formation of continuous foam or bubbles on the surface
of water.”
• Causes:
• High conc. of dissolved salts in boiler feed water.
• Presence of oil droplets and alkalies.
• Presence of Finely dispersed suspended material
• Violent agitation of boiler feed water
• Disadvantages of priming and foaming:
• Because of foaming actual height of water column cannot be judged well.
• Because of priming, the salts present in the droplets enter in the part of
machineries where steam is being used, thereby decreasing life of
machineries.
• The dissolved salts in droplet of wet steam get deposited on evaporation of
water, which reduces efficiency of machine parts.
• Foaming causes wet steam formation.

18. • Prevention of Priming and foaming:
• Foaming can be prevented by adding antifoaming agents like
castor oil or by adding chemical like sodium aluminate and
followed by blow down operation.
• Priming can be prevented by use of well softened and filtered
water
• Maintaining low water level in boiler prevent priming
• Rapid changes in steam rate should be avoided.
• Steam purifier can be used.

19. C) SLUDGE & SCALE
FORMATION

20. • Sludge formation:
Definition:
In boiler water evaporate continuously & the concentration of salt
left behind, that slimy and loose deposit of precipitated salts in boiler
tube, depositing at the bends and valves, affecting free flow of water, is
known as sludge.
• Disadvantages:-
• They waste some portion of heat.
• It disturbs working of boiler and sometimes may choke up the pipe
• It reduces the flow rate of water in boiler.
• Prevention:-
• Use of water containing very low quantity of total dissolved solids.
• Frequently making blow down operation.

21. Scale formation:-
• Def: The hard and strong coating formed inside boiler tube by chemical
reactions, which is bad conductor of heat, is known as scale.
• Causes-
i) Decomposition of bicarbonates
ii) Hydrolysis of magnesium salts
iii) Presence of silica
iv) Decreased solubilities of CaSO4
• Disadvantage of Scales:
• Wastage of Fuel: Scales are bad conductors of heat & result in the reduction of
heat transfer to the boil.
• Over heating of boiler: Scale reduces transfer of heat from boiler to boiler
water, hence overheating is required to keep the required steam pressure.
• Boiler safety:
• Danger of explosion:

22. • Prevention & Removal of scales:
• Use of softened water.
• Adding sodium phosphate to the water. (Phosphate conditioning).
• Frequent blow down operations to remove the sludge & precipitate rich
water from boiler.
• Adding sodium aluminates, which can trap the scale forming particles.
• Adding organic chemicals like tannin which forms coating on the scale
forming particles. This matter becomes easily removable by blow down
operation.
• Removal of scales:
• 1.Use of chemicals.
• 2.Use of Scraper or wire brush.
• 3. Use of hammer & chisel for thick scales.
• 4.Thermal shocks technique.

23. • D)Caustic embrittlement:
• It is the phenomenon during which the boiler material becomes brittle due to the
accumulation of caustic substances.
• Definition: It is the fast corrosion of boiler caused by highly alkaline condition of water,
during steam generation, especially in those boilers which generate high pressure steam.
• Na2CO3 + H2O 2NaOH + CO2
Disadvantages:
i)Decreases strength of boiler metal.
ii) Galvanic cell.
iii) Concentration cell.
Prevention:
• Use Sodium phosphate for water softening instead of Na2CO3.
• Add some Tannin or Lignin to boiler water which blocks the cracks.
• Adjust pH 8-9 of boiler water.
• Add Na2SO4 to boiler water to keep the ratio of Na2SO4 to NaOH as 1:1, 2:1, 3:1 at
pressure 10,20 and above 20 Kg /cm2 respectively.

24. Internal treatment of boiler scale.
• Principle: - “Chemicals added for internal treatment either does
not allow the scale formation to take place or they attack on the
previously formed scales to convert them into sludge. Or
dissolve the scales.”
A. Calgon conditioning:
• Calgon is sodium hexametaphosphate (NaPO3)6 or
Na2[Na4P6O18). This substance forms highly soluble
coordination complexes with Ca++ Mg++, Fe++ and thus scale
formation is prevented. The optimum pH required for complex
formation is 9.0 to 10.5
• Na2[Na4P6O18) 2Na+ + [Na4P6O18)
• Ca++ + [Na4P6O18]-2 2Na+ + [CaNa2P6O18]-2
(Soluble complex)

25. B. Phosphate Conditioning:
• Principle: Hard adherent scales are converted into their phosphate by
treatment with sodium phosphate and are removed as sludge by blow
down operation.
• Chemical in scale Sludge
• Reactions:
• Sodium orthophosphate can attack scales to convert them to sludge’s.
When scale is formed in boiler proper quantity of sodium phosphate is
added in feed water.
• Orthophosphates:
• NaH2PO4 = Sodium dihydrogen phosphate (acidic)
• Na2HPO4 = DiSodium hydrogen phosphate (weakly alkaline)
• Na3PO4 = Trisodium phosphate (alkaline)
• Na4 P2O7 = Sodium pyrophosphate
• NaPO3 = Sodium metaphosphate

26. • 3CaCo3 + 2NaH2PO4 Ca3(PO4)2 + Na2CO3 + 2H2O + 2CO2
• 3 Mg(OH)2 + 2 Na3PO4 Mg3 (PO4)2 + 6 NaOH
• 3 CaSO4 + 2 Na3PO4 Ca3 (PO4)2 + 3 Na2SO4
• Depending upon the quality of feed water choice of particular
orthophosphate is made.
C. Colloidal conditioning:
• In low pressure boilers, scale formation can be avoided by
adding organic substances like tanin, agar-agar gel etc. These
substances coated on scale & convert in to sludge. Sludge can
be removed by blow down operation.

27. • Zeolite process:
• Principle : Sodium Zeolite has the property of capturing the heavy
metal ions from water & in exchange released the Na+ due to
removal of heavy water ions ( Ca ++, Mg++ ,etc ) from water ,the hard
water is converted into soft water ,by Zeolite.
• Zeolite structure Representation: Na2O.Al2O3.xSiO2.yH2O
• Process reactions:
• Na2Ze + Mg++ → MgZe + 2 Na+
• Na2 Ze + Ca ++ → CaZe +2 Na+
• Regeneration reactions:
• MgZe + 2 NaCl → Na2 Ze + MgCl2
• CaZe + 2 NaCl → Na2 Ze + CaCl2

29. • Advantages:
• Easy process to operate.
• Low cost operating process.
• Process adjusts with water of any hardness & there is no need to analyse water
before softening
• The zeolite bed is whether active or exhausted, a be easily tested with soap
solution.
• The softener occupies small space.
• Limitations:
• Warm water should not be softened as it may decompose sodium zeolite slowly.
• Mn++,Fe+2 like ions get permanently captured by Zeolite bed .
• The output water has almost zero hardness but contains equivalent quantities of
sodium salts.

30. • Demineralization process :
• Principle :
• When water containing cation & anions ,is passed through the resins, cation exchange resin
captures all cation & anion exchanger resin captures all anions ,to give pure & all ions free
water .
• Process reactions :
Cation exchanger:
• H2+ Na+ → Na2 R + 2H+
• H2 R + Ca ++ → Ca R + 2 H+
• Anion Exchanger:
• R’ (OH) 2 + 2 Cl- → R’ Cl2 + 2-OH
• R’ ( OH )2 + SO4
-2→ R’SO4 + 2 -OH

32. • Regeneration:
• The exhausted cation exchanger is regenerated by washing with dil. HCl
solution.
• Na2R + 2 HCl → H2R + 2 Na+
• Ca R + 2 HCl → H2 R + CaCl2
• ii) Cation exhausted anion exchanger resin is generated by washing with
NaOH solution.
• R’ Cl2 + 2 NaOH → R ‘(OH)
• R’ SO4 + 2 NaOH → R’ (OH)2 + 2Na2So4

33. • Advantages:
• The method gives water of zero hardness & no ionic impurities .
• If the output water is passed throw degassifier, then the gaseous impurities
like O2 , CO2 also get expelled, to get water of ‘
• Equipment occupies small space.
• Process is easy to operate, with negligible running cost.

34. Desalination of brackish water:
• The water contains high concentration of dissolved salts is called
brackish water.
• Desalination is the process of removing common salts (mostly
NaCl) from water
• There are two methods of desalination
• 1) Electrodialysis
• 2) Reverse osmosis
• Electro dialysis:-
The process of removing ionic pollutants from water using
membranes and electric field is known as Electro dialysis.

35. • Diagram
• Applications:-
• Removal of ionic pollutants (Toxic, salts, ionic dyes, etc. ) from treated
industrial waste.
• Removal of salt from tree water, to get pure water.
• Removal of limited quantity of salts from sea water to get drinking (mineral
) water.

36. • Reverse Osmosis:
Membrane technique selectively separate the solutes or
impurities on the basis of pore size.
• Membrane technique involves ;
a) Reverse osmosis
b) Hyper filtration
c) Ultra filtration
Reverse osmosis is commonly used.
• Principle:
“The flow of solvent from higher concentration to lower
concentration solution through semipermeable membrane by
applying slightly higher external pressure than osmotic pressure of
higher conc. Solution.”

37. • Semi permeable membrane made up from polymeric materials like acrylics,
polyamides, aramids .
• Advantages:
• Ionic, colloidal, non-ionic impurities remove from water.
• Pure water for high pressure boiler can be obtained.
• It is used to obtain drinking mineral water.
• Simple to operate.
• Low cost process.