very informative and helpful too.

1. Water & Its treatment Introduction
This chapter deals with
Specification of water,
Hardness of water,
Softening and its treatment.
1

2. Water- Most important and basic requirement on earth
 For existence of all living beings
(human, animals, plants)
 For industrial processes and agricultural production
 In thermal & nuclear power plants for steam
generation & cooling purposes
Oceans contains- 97% of all the water on earth
Glaciers- 2%
1% available for ready use
• Hence it is urgently required to use the available water
most carefully and economically
2

3. Sources of water
1. Rain Water
2. Ground Water Main Sources
3. Surface Water
3

4. Rain Water:
 Caused due to evap. of surface water &
subsequent precip.
 Most purest form of natural water
 Dissolves Impurities (SPM, CO2, SO2, NO2)
from atmosphere during pptation
 Can be stored in underground reservoir tanks
4

5. Ground Water:
• Largest available source of fresh water
• Form of rain water falling on earth
• Generally pure because it undergoes natural
filtration during the percolation through soil
pores
• Less likely to be contaminated by BACTERIA
but contains dissolved salts
• To obtain in large quantity tube wells are used
5

6. Surface Water:
The water that flows over the surface of earth & is Directly
available
It includes
1. River water
2. Lake water
3. Sea water
6

7. 7
1. River water
• Comes from melting of snow, rain and spring water
(coming from earth)
• Contains dissolved minerals/salts like chlorides,
sulphates, bicarbonates of Na, Ca, Mg
• Also contains impurities of sand rocks & organic
matter
Surface Water:

8. 2. Lake Water
• Contains organic impurities due to decomposition of
plants and animals
• Contains less amount of dissolved minerals
• Chemical composition is constant
3. Sea Water
• Most impure form of natural water
• Dissolved salts are increased by impurities thrown by
rivers when they join sea
• Contains 2000 times more dissolved salts than other
water
• Very saline- can not be used in industries except for
cooling 8
Surface Water:

9. 9
1. Dissolved Impurities
2. Suspended Impurities
3. Colloidal Impurities
4. Microorganism Impurities
IMPURITIES IN HARD WATER

10. Dissolved Impurities
a) Salts:
– Carbonates, Bicarbonates, Sulphates and chlorides of
Ca, Mg, Fe, Na, K.
b) Gases: CO2, O2, N2, H2S, NH3
Suspended impurities
Inorganic- Clay, sand
Organic- Vegetable & animal matter
Colloidal Impurities:
Products from organic waste, finely divided silica and clay etc.
Microorganisms: Bacteria, Fungi, Algae
10

11. HRDNESS OF WATER
“The property that prevents lathering of soap”
Cause of Hardness:
Presence of soluble salts of Ca, Mg or other heavy
metals in water
 Hard water does not produce lather with soap.
SOAPS
Generally soaps consists of Na salts of higher fatty acids
such as stearic acid, oleic acid, palmitic acid.
Soaps are highly soluble in water thus exert their
cleansing action. 11

12. If Ca & Mg salts are present in water then these
salts react with soap to form insoluble white scum
as ppt. e.g.
2 C17H35COONa + CaSO4 → (C17H35COO)2Ca↓ + Na2SO4
Sod. Stearate From hard White ppt
(Soap) water
2 C17H35COONa + MgCl2 → (C17H35COO)2Mg↓ + 2NaCl
Sod. Stearate From hard White ppt
(Soap) water
12

13. Lather is not produced till the hardness causing
cations (Ca2+ Mg2+)are completely precipitated out in
the form of insoluble salts.
Thus a large quantity of soap is required to produce
lather with hard water.
HARD WATER
Hence the water that does not produce lather with
soap readily is called hard water.
13

14. HARD WATER SOFT WATER
1
Contains dissolved salts of Ca,
Mg or other heavy metals
Does not contain
dissolved salts
2
Does not form lather with
soap
Forms lather with soap
3
Large quantity of soap is
required during washing
Soap is not wasted
4
Due to presence of dissolved
salts, B.P. of hard water is
elevated. So more fuel is
consumed in cooking
Less fuel is required
DIFFERENCE BETWEEN HARD AND SOFT WATER
14

15. TYPES OF HARDNESS Temporary & Permanent
1. Temporary Harness:
Cause: Due to the presence of bicarbonates of Ca & Mg
Also called carbonate hardness
Removal of Temp Hardness- by Boiling
On boiling, bicarbonates of Ca & Mg get decomposed to
give insoluble carbonates which are deposited as
insoluble precipitates at the bottom of the vessel
∆
Ca (HCO3)2 CaCO3 ↓ + CO2↑ + H20
∆
Mg (HCO3)2 MgCO3 ↓ + CO2↑ + H20
15

16. 2. Permanent Harness:
Cause: Due to the presence of sulfates and chlorides of
Ca & Mg
Also called non-carbonate hardness
• Removal of perm. Hardness- is not possible by Boiling
• Special methods are used to remove permanent
hardness
• Total Hardness = Temp. Hardness + Perm. Hardness
16

17. DEGREE OF HARDNESS
For the sake of convenience,
hardness is expressed in terms of equivalent
amount of CaCO3
The use of CaCO3 as a standard reference is due
to two reasons:
1. CaCO3 is most insoluble salt that can be
precipitated in water treatment.
2. Mol. Wt of CaCO3 is 100, hence calculations
become easy
17