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Water Softening

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• 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.

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Types of Hardness

Temporary Permanent (Carbonate) (Non carbonate)Ca, Mg carbonate Ca, Mg –Sulphate, Chlorides

Ca HCO3-Mg ClFe SO4Mn

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Hardness Removal / Water SofteningI) Temporary hardness

A) By BoilingCa.(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

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Hardness RemovalII) Permanent hardness

A) Lime SodaB) Zeolite (Base/Cation Exchange)

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Water SofteningI) 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.

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I) Lime-Soda Method:Ca(HCO3)2 + Ca(OH)2 2CaCO3ꜜ +2 H2O Mg(HCO3)2 + Ca(OH)2 CaCO3ꜜ + MgCO3ꜜ + 2H2O Bicarbonate + Lime removal of temp. hardness-------------------------------------------------------------------------CaSO4 + Na2CO3 CaCO3ꜜ + Na2SO4

Soda Ash CaCl2 + Na2CO3 CaCO3ꜜ + 2NaCl Soda Ash Permanent hardness=============================MgSO4 + Ca(OH)2 Mg(OH)2ꜜ + CaSO4

MgCl2 + Ca(OH)2 Mg(OH)2ꜜ + CaCl2

Lime + Soda Ash

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Advantages• Economical• Augmentation is easy• Pre Addition: Less coagulant• Increases pH – Less corrosion• Kills pathogen upon prolonged exposure• Reduces mineral contentDisadvantages• High sludge quantity• Skilled workmanship• Recarbonation is necessary to avoid encrustation• Zero hardness not possible

I) Lime-Soda Method:

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Water SofteningII) Cation/Base Exchange: (Zeolite)Zeolite: Na2Al2O3. xSiO2. yH2OHard 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

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(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

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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

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• Charcoal is carbon. Activated charcoalis 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.

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PUR Water Filters

PUR Hiker Filter

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Demineralization / DesalinizationEvaporation & DistillationElectro dialysis Reverse Osmosis

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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.

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Solar distillation Still

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Small Solar Still

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Solar distillers

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Large Scale Solar Still

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Saudi Arabia desalinization plant.Water is heated by burning large quantities of fossil fuels – pollution is excessive.

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Reverse Osmosis

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Semipermeable membrane

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Hand-operated Desalinator

Used by military forces, voyagers, sea kayakers, and other adventurers. Kept in emergency life-rafts

Produces 4.5 liters per hourProduces 0.89 liters per hour

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Industrial Reverse Osmosis

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Ion Exchange

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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.

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Lab Cartridge