2. 2
• Hardness: Water that contains dissolved Mg+2, Ca+2, Fe+2, and
Mn+2 salts is called hard water.
• Soap reacts with these ions to form soap scum.
• Hard water also causes scale to form on the walls of water heaters,
hot water pipes, and steam irons.
• The scale reduces efficiency and plugs-up pipes.
3. 3
Types of Hardness
Temporary Permanent
(Carbonate) (Non carbonate)
Ca, Mg carbonate Ca, Mg –Sulphate, Chlorides
Ca HCO3-
Mg Cl
Fe SO4
Mn
4. Hardness Removal / Water Softening
I) Temporary hardness
A) By Boiling
Ca.(HCO3)2 Heat CaCO3ꜜ + H2O +CO2ꜛ
Mg.(HCO3)2 Heat CaCO3ꜜ + H2O +CO2ꜛ
B) By Addition of Lime [Ca(OH)2 ]
Ca(HCO3)2 + Ca(OH)2 2CaCO3ꜜ +2 H2O
Mg(HCO3)2 + Ca(OH)2 CaCO3ꜜ + MgCO3ꜜ + 2H2O 4
6. 6
Water Softening
I) Lime-Soda Method:
Ca+2 and Mg+2 ions are precipitated from
hard water by adding lime and sodium
carbonate
The insoluble solids are removed by
sedimentation or commercially by filtration.
8. Advantages
• Economical
• Augmentation is easy
• Pre Addition: Less coagulant
• Increases pH – Less corrosion
• Kills pathogen upon prolonged exposure
• Reduces mineral content
Disadvantages
• High sludge quantity
• Skilled workmanship
• Recarbonation is necessary to avoid encrustation
• Zero hardness not possible
8
I) Lime-Soda Method:
9. 9
Water Softening
II) Cation/Base Exchange: (Zeolite)
Zeolite: Na2Al2O3. xSiO2. yH2O
Hard ions are passed through a tank of zeolite. The
process replaces the hard ions with sodium ions.
Na2Zeolite + Ca+2 CaZeolite + 2 Na+
Operation : Gravity/ Pressure type
10. 10
(1) Negatively charged sites are occupied by
Na+ ions.
(2) Hard water replaces Na+ ions with Ca+2 ,
Fe+2 , and Mg+2 ions.
(3) Eventually the resin becomes saturated with
the hard ions and is no longer effective.
Zeolite
11. Zeolite/Base Exchange/
Advantage
• Zero hardness (Good for Industrial use)
• Compact, automatic, easy to operate
• No sludge
• O & M cost is less
Disadvantage
• Not suitable for turbid water
• Sodium carbonate left in water causes foaming
• Zero hardness
11
12. 12
• Charcoal is carbon.
Activated charcoal
is charcoal that has been treated with oxygen
to open up millions of tiny pores between
the carbon atoms. This results in highly
porous charcoals that have surface areas of
300-2,000 square meters per gram. These
so-called active, or activated, charcoals are
widely used to adsorb odorous or colored
substances from gases or liquids.
15. 15
A simple distillation setup
to separate water from
seawater. The seawater is
boiled in the flask. The
rising vapor is channeled
into a downward-slanting
tube kept cool by cold
water flowing across its
outer surface. The water
vapor inside the cool tube
condenses and collects in
the flask on the right.
23. 23
Hand-operated Desalinator
Used by military forces, voyagers, sea kayakers,
and other adventurers. Kept in emergency life-rafts
Produces 4.5 liters per hour
Produces 0.89 liters per hour
26. 26
Two-stage Ion-Exchange System
• This process removes both cations and anions.
• Special synthetic organic resins are used in the
beds.
• In the first stage cations are replaced by H+ ions.
• In the second stage anions are replaced by OH–
ions.
• The H+ and OH– ions react to form mineral-free
water.