1. Associate Professor (H & S)
WATER
UNIT IV
Dr.JYOTSNA CHERUKURI
Associate Professor (H & S)

2. CONTENTS
Sources and impurities of water
Hard and soft water
Units for expressing hardness
Types of hardness
Estimation of hardness
Disadvantages of usage of hard water
Boiler troubles
Softening of water
Treatment of water used for municipal
supply

3. Sources of water Surface water Rain water River water Lake water and
sea water
Underground water
Spring water and
Well water

4. Impurities present in water
Suspended impurities
Mainly present in river water
Inorganic matter like clay and sand,
Organic matter like animal and vegetable matter
Suspended matter is responsible for turbidity of water.
Dissolved impurities
These include inorganic salts like carbonates, chlorides, sulphates of calcium and magnesium, salts of sodium and potassium, other salts like iron, manganese,silica and alumina.
Salts of calcium and magnesium cause
hardness to water.

5. Also dissolved gases like CO2, N2, O2,and H2S.
Dissolved gases causes corrosion in boilers.
Colloidal impurities
Very finely divided silica, clay, aluminium hydroxide.
Micro-organisms include protozoa and
some forms of vegetable life.

6. Hard water and soft water
Hard water is one which does not
produce lather with soap solution readily, but forms a curdy precipitate.
Hard water contains dissolved calcium and magnesium salts.
Soft water gives lather easily on
shaking it with soap solution.
Dissolved salts are not present
in soft water.

7. Units of hardness Hardness is expressed as Parts per million (ppm)
Milligrams per liter (mg/l)
Clarke’s degree (oCl)
Degree French (oFr)
1ppm = 1 mg/l = 0.1oFr = 0.07 oCl
1mg/l = 1 ppm = 0.1oFr = 0.07 oCl
1 oCl = 1.433oFr = 14.3 ppm = 14.3 mg/l
1 oFr = 10 ppm = 10 mg/l = 0.7 oCl

8. Types of hardness Hardness is of two types Temporary hardness
Permanent hardness
Total hardness = temporary hardness + permanent hardness
Caused by the presence of dissolved bicarbonates of calcium, magnesium and heavy metals.
Can be removed by mere boiling of
water

9. Permanent hardness
Caused by the presence of dissolved chlorides, sulphates and nitrates of calcium, magnesium and heavy metals.
Cannot be removed by mere boiling of
water
Chemical treatment processes like lime-soda, zeolite and ion exchange process can remove this hardness

10. Estimation of hardness
Three methods of estimation
Soap titration method
O.Hehner’s alkalimetric
method
EDTA method

11. Soap titration method (Clark’s method)
Principle:
The hardness is estimated by adding a soap solution of a definite strength to a known volume of a water sample until a permanent lather is formed on shaking.
O.Hehner’s alkalimetric method
The basic principle is finding the alkalinity of water before boiling and that left after
boiling.

12. EDTA method (Complexometric method) Principle:
When hard water comes in contact with EDTA at pH
9-10 (NH4Cl + NH4OH), the calcium and magnesium ions
forms stable, colorless complex with EDTA.
Ca 2+ or Mg 2+ + EBT Ca-EBT or Mg-EBT
(blue) (wine red complex)
Ca-EBT or Mg-EBT + EDTA Ca-EDTA
or Mg-EDTA
(colorless complex)
+ EBT
(blue)

13. Disadvantages of usage of hard water
Water finds great use in a number of industries. Hard water if is used leads to:
Paper industry: paper with smooth and glossy finish is not obtained
Dyeing industry: incorrect shade and spots on fabric
Sugar industry: sugar does not crystallize and is deliquescent
Steam production: Boiler troubles

14. Boiler troubles
Carry over: priming & foaming
Boiler corrosion
Caustic embrittlement
Scale and Sludge formation
Carry over
The phenomenon of carrying water along with impurities by steam is called carry over which is caused by
priming & foaming

15. Priming and foaming Priming
Process of wet steam formation is called priming. This is caused by
Presence of large amounts of dissolved salts
High steam velocities
Improper boiler design
Sudden boiling
High level of water in boilers
Avoiding all the above factors in the
boilers will prevent priming

16. Foaming
Production of persistent foam or bubbles in boilers leads to foaming. This is due to the presence of substances like oils and alkalies in the boiler feed water.
Foaming decreases the life time and efficiency of the machinery
It can be prevented by:
Adding antifoaming agents
Removing oils from boiler water by adding
alum or sodium aluminate
By blow down operation

17. Boiler corrosion
This is due to the decay or deterioration of the boiler material by direct or electrochemical attack of its environment.
It is caused by the presence of
Dissolved oxygen
Dissolved carbon dioxide and
Presence of acids or acidic salts
It results in shortening the boiler life,
leakage from joints, increased cost
of repairs and maintenance.

18. Boiler corrosion can be prevented by mechanical deaeration,preheating and chemical treatment.
Caustic embrittlement
Develops if water of high alkalinity is used in boilers operating at high pressures.
It can be prevented by
Maintaining the pH of water
Using sodium phosphate as softening agent instead of sodium carbonate
Adding colloidal agents like tannin or
lignin, agar-agar etc.

19. Scale and sludge formation
Scales are:
Hard deposits
Stick firmly to the inner surfaces of boilers
Difficult to be removed
Formed at heated portions of the boiler
Formed by substances like CaSO4,Mg(OH)2etc.
Decrease the efficiency of the boiler
and chances of explosion are possible

20. Sludges are:
Sludges are soft loose and slimy precipitates
Non-adherent deposits
Can be removed easily with a wire brush
Formed at cooler portions of the boiler
Formed by substances like CaCl2,MgCl2,MgSO4 etc.
Decrease the efficiency of the boiler
and less chances of explosion

21. Prevention of sludge formation
Using water free from dissolved salts
By frequent blow-down operation
Removal of sludge from time to time
Prevention of scale formation
This involves 2 types of treatment:
Internal treatment
External treatment

22. Internal treatment
This involves addition of proper chemicals to the boiler water to precipitate scale forming impurities in the form of sludge, which can be removed by blow down operation. It can be done by the following methods:
Colloidal conditioning
Phosphate conditioning
Carbonate conditioning
Calgon conditioning
Treatment with sodium aluminate
Electrical conditioning
Radioactive conditioning.

23. Colloidal conditioning: addition of kerosene
Colloidal conditioning: addition of kerosene. tannin, agar-agar etc to avoid scale formation in low pressure boilers.
Phosphate conditioning: complexation of calcium salts with sodium phosphate in boilers operating at high pressures.
Carbonate conditioning: strong and adherent scales formed due to CaSO4 are avoided by adding sodium carbonate.
Calgon conditioning: sodium hexameta phosphate (calgon) forms soluble
complex compounds with CaSO4(stong
scale)

24. Treatment with sodium aluminate: sodium aluminate functions as a coagulant and removes scale forming salts as loose precipitates.
Electrical conditioning: electrical discharges prevent scale forming particles from sticking to the walls of the boiler.
Radioactive conditioning: radiation emitted from radioactive salts in the form of tablets prevent scale formation.

25. External treatment This is accomplished by removing
hardness producing constituents from water.
The techniques employed are:
Lime-Soda process
Zeolite process and
Ion-exchange process
This treatment is done before the water is
fed into the boilers.

26. Lime-Soda process
Principle: conversion of salts of calcium and Magnesium into insoluble substances which settle down as sludges and can be easily removed.
This conversion is brought about by adding lime and sodium carbonate (soda). The process is of two types:
Cold lime-soda process (carried at room temperature)
Hot lime-soda process (carried at
temperatures of oC)

27. Advantages:
Process is economical
Removes hardness causing salts and also iron and manganese salts
Pathogenic bacteria is reduced due to alkaline nature of water rendered by adding lime & soda.
Disadvantages:
Skilled supervision is necessary
Disposal of large quantities of sludge
Water still contains residual hardness
of 15-50ppm.

28. Zeolite or Permutit process
Zeolites are hydrated sodium aluminium silicates,Na2O.Al2O3.xSiO2.yH2O.
Principle: The hardness causing salts are retained by the zeolites as CaZe and MgZe and an equivalent amount of sodium salts are introduced into water.
Limitations:
Raw water should not contain turbidity,
colored ions and mineral acids, as all these
interfere in effective softening of
water

29. Advantages: Requires less skilled assistance
No sludge disposal problems
Residual hardness in the water is 10 ppm
Disadvantages:
Treated water contains more amounts of sodium salts
Results in caustic embrittlement
Replaces only Ca and Mg ions only
Zeolite bed is regenerated by treating
with 10% brine solution (NaCl)

30. Ion-Exchange Process
Principle: The exchange of the cations and anions of the dissolved salts with H+ & OH- ions of the ion-exchangers which are insoluble, cross linked long chain organic polymers with micro-porous structure.
Exchangers are of two types:
Cation Exchangers (capable of exchanging H+ ions)
Anion Exchangers (capable of exchanging
OH- ions)

31. Advantages:
Highly acidic or alkaline water can be treated
Residual hardness of treated water is 2 ppm
Disadvantages:
Ion exchange resins are very expensive
Turbidity more than 10 ppm interferes with the process
Always the water should be passed first
through the cation exchanger and then
only through the anion exchanger……
Regeneration: cation exchanger with dilute
acids (HCl or H2SO4) and anion
exchanger with NaOH.

33. Desalination of brackish water
Sea water containing excess salts cannot be used for industrial purposes and hence subjected to desalination, which is done by:
Electrodialysis
Reverse osmosis
Electrodialysis Principle:
Ions present in saline water migrate towards their respective electrodes through ion selective membranes under
the influence of applied emf.

34. Reverse Osmosis Principle:
When two solutions of unequal concentrations are separated by a semi permeable membrane usually the solvent flow takes place from dilute to concentrated side. But if a pressure is applied the reverse happens i.e. the solvent flows from concentrated side to the diluted side.
This is the process of reverse osmosis and is also termed as hyper-filtration or
super-filtration of water.

35. Reverse Osmosis

36. Treatment of water for municipal supply
The various stages involved in treatment are:
Screening: to remove floating matter
Aeration: increase the oxygen content of water
Sedimentation with coagulation: to remove the suspended and colloidal matter
Filtration: removal of colloidal and suspended impurities not removed by sedimentation, by using rapid and slow
sand filters

37. Screening
Boiling

38. Sterilization & Disinfection: This is done by:
Boiling
Passing ozone
Chlorination using chloramines and bleaching powder
The amount of chlorine required to kill bacteria and to remove organic matter is called break point chlorination.
Over chlorination after break point is removed by dechlorination by addition
of SO2 and sodium thiosulphate.

39. Thank u