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SRM University. 1 st SEM Applied Chemistry. Technology Of Water. Water: Water is a chemical substance with the chemical formula H2O. Existance on Earth 1. Solid state-ice, 2. Gaseous state (water vapor or steam) 3. Liquid

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SRM University

1st SEM Applied Chemistry


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Technology Of Water

Water:

Water is a chemical substance with the chemical formula H2O.

  • Existance on Earth

    1. Solid state-ice,

    2. Gaseous state (water vapor or steam)

    3. Liquid

  • Water is not only universal solvent but also an essential material for engineering applications.

  • Prime factor in development

  • Water on Earth moves continually through a cycle of evaporation or transpiration (evapotranspiration),


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Evotranspiration Process


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  • Evapotranspiration (ET) is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere.

  • Evaporation :-

    The movement of water to the air from sources such as the soil, canopy interception, and water bodies.

  • Transpiration :-

    The movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.

  • An element (such as a tree) that contributes to evapotranspiration can be called an evapotranspirator.


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Sources of Water

  • The source of water are listed under two categories

    1. Surface Water

    2. Underground Water

  • Surface Waters:

    1. Rain Water

    2. River Water

    3. Lake Water

    4. Sea water

    B. Underground Water:

    1. Spring

    2. Well water


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Types Of Impurities

1. Dissolved Impurities:

a) Inorganic salts e.g

sulphates and chlorides of calcium, Magnesium, Iron

b) gases like carbon dioxide, nitrogen , oxygen, hydrogen sulphides

c) organic salts

2. Suspended Impurities:

a) Clay

b) mud

c) Vegetable and animal matters


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3. Colloidal Impurities:

a) fine size like silica and alumina, organic wastes etc.

  • These are soluble materials, other than gases

  • cannot be removed by conventional filters

  • referred as TDS which stands for total dissolved solids.

    4. Bacterial Impurities:

    a) Bacteria, Germs, Pathogens, Microbes, Viruses, Parasites

  • include

    - algae, beneficial bacteria that decompose wastes

    - harmful bacteria such as those that cause cholera.


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  • Effects of Impurities:

    a) colour of surface water- dissolved organic matters

    b) Taste and Odour- formation of compounds

    c) Turbidity- suspended Impurities

    d) Pathogenicity- micro organisms

    Hardness of Water

  • Characteristics of water which prevent the Leather Formation.

  • due to presence of:- salts like bicarbonates, sulphates,

    chlorides of mg and other metals

  • Units of Hardness:

    1) ppm 2) mg/l 3) ̊Cl 4) ̊Fr

  • Relation - 1ppm = 1mg/l = 0.07 ̊Cl = 0.1 ̊Fr


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  • Types of Hardness

    1) Temporary:- 0r Carbonate Hardness

    Water that contains bicarbonate of calcium and magnesium or of both

  • removed by boiling

    Ca(HCO3)2  → CaCO3 ↓ + CO2 ↑+ H2O

    Mg(HCO3)2 → Mg (OH) 2 ↓ + 2CO2 ↑

  • Permanent :- or Non- Carbonate Hardness

    Contains chlorides or sulphates of calcium or magnesium or of both

  • Can not be removed by boiling

    CaCl2 →  Ca+2 + 2Cl-1

    MgSO4 →   Mg+2 + SO4-2


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Disadvantages of Hard Water

(A) Domestic Uses:

  • Washing 2. Bathing 3. Drinking 4. Cooking

    C17 H35 COO Na + H2O→ C17 H35 COOH + NAOH

    C17 H35 COOH + C17 H35 COO Na → Lather

    C17 H35 COO Na + CaSO4 → (C17 H35 COO) 2 Ca ↓ + Na2SO2

    (in water) (White Scum)

    (B) Industrial Uses:

    1. Boiler Feed: should not contain nitrates- scale and sludges

    2. Paper Mill: should not contain iron and lime- destroy resin of soap

    3. Sugar industries: Sulphates and Alkaline carbonates- Deliquescent

    4. Dyeing Industries: should not contain iron and hardness

    5. Laundries: should be soft


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Estimation Of Hardness

1. EDTA Method 2. O.Herner’s Method

  • EDTA Method:

    Ethylene Diamine Tetra Acetic Acid

    -OOOCH2 CH2COO-

    NCH2.CH2N

    -OOOCH2 CH2COO-

  • Estimation is by titration method at pH 10

  • Using Indicator Eriochrome Black-T

    Method:

  • Take 50 ml water in coinical flask

  • Add buffer and few drops of EBT-T

  • Titrate against EDTA

  • Red colour change to steel blue/violet


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O.Herner’s Method (0r) Alkali Titration Method

  • Bicarbonates of Ca and Mg makes water alkaline and can react with HCl

    Ca(HCO3)2  + 2HCl → CaCl2 + 2CO2 ↑+ 2H2O

    Mg(HCO3)2  + 2HCl → MgCl2 + 2CO2 ↑+ 2H2O

  • Ca(HCO3)2 and Mg(HCO3)2 decomposes into insoluble carbonates on boiling the water.

    For Temporary Hardness:

  • 50ml sample water in conical flask

  • 2-3 drops of methyl orange indicator

  • Titrated against N/50 HCl

  • Change colour from yellow to orange

  • Take 100 ml of same sample of water

  • Boil until 1/5th volume

  • Make them again 100 ml Distilled water

  • Take 50ml and perform again the above steps


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For Permanent Hardness

  • Caused by Chlorides and Sulphates of Calcium and Magnesium

  • Can be determined by using Na2CO3 and HCl.

    CaCl2+Na2CO3→CaCO3 ↓+ 2NaCl

    CaSO4+Na2CO3→CaCO3 ↓+ 2NaSO4

    Method:

  • 50 ml hard water + 50 ml Na2CO3 solution

  • Boiled and Evaporated to dryness.

  • Chlorides of Ca and Mg ppt. as carbonates of Ca and Mg.

  • Extract residue with distilled water

  • Add few drops of methyl orange as indicator

  • Titrate against N/50 HCl

  • End point changes colour from yellow to orange.


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Determination of Alkalinity in water

  • It is due to 1) OH- and CO3-2 2) HCO3-

  • Titrate against phenolphthalein and methyl orange

    Method

  • 100 ml sample water in conical flask

  • Add 2-3 drops of phenolphthalein indicator

  • Titrate against N/50 H2SO4

  • Continue till pink colour disappear

  • To the same solution add 2-3 drops of methyl orange

  • Titrate till yellow colour changes to red

    Reaction Involved:

    OH-+H+ → H2O (using phenolphthalein)

    CO3-2+ H+→ HCO3- (using phenolphthalein)

    HCO3-+H+ → H2O+ CO2 (using methyl orange)


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Scale and Sludge

  • Troubles met in boiler which are used in steam production.

    Scale:

    When water is evaporated in boilers to produce steam continuously

    the concentration of the slats present in the water increases progressely

    As the concentration reaches a saturation point the salts are thrown

    over the inner surface of the boiler.

    Sludge:

    During boiling salts form precipitate of loose slimy form.

    Magnesium Chloride

    Decomposes to form hydroxide and hydrochloric acids. The former will produce hard scale and the later lowers the pH.

    MgCl2 + 2H2O  2HCl + Mg(OH)2

    Magnesium Sulphate

    Forms a hard scale on the heating surfaces


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Calcium Sulphate

Forms a hard scale on the heating surfaces

Calcium Bi-carbonate

Decomposes at a low temperature when CO2 is liberated. Remaining Calcium carbonate deposits on the heating surface as a soft scale.

Ca(HCO3)2 CaCO3 + CO2 + H2O


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Disadvantages of Scale Formation

1. Wastage of fuel 2. Decreases in Efficiency

3. Lowering of boiler safety 4. Danger of Explosion

5. Corrosion

Removal of Scales

  • By scrapping 2. Giving thermal shocks

    3. Dissolving by using chemicals e.gCaCO3 by 5-10% HCl

    4. Adding complexing agents e.gCaSO4 by EDTA

    5. Blow down Process

    Disadvantages of Sludge Formation

  • Chocking of pipes

  • Low supply of heat

  • Wastage of fuel

  • Get entrapped in scales


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Prevention of Sludge Formation

  • Blow down Process: Withdrawing portion of sludge containing water and replacing with fresh water

  • Softening of water

    Method of Preventing Scale Formation

  • External Treatment:

    Treatment of water before entering into boiler

    - Removal of Ca, Mg and Silica

    2. Internal Treatment:

    Addition of chemicals directly to water in boiler.

  • Scale forming substances produces loose precipitate

  • Blow down process

  • Adding complexing agents: to form soluble complex


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Caustic embrittlement :

It is the phenomenon in which the material of

a boiler becomes brittle due to the accumulation of caustic substances.

  • Sodium carbonate is used in softening of water by lime soda process, due to this some sodium carbonate maybe left behind in the water.

    Na2CO3 + H2O → 2NaOH + CO2

  • As Conc. of NaOH increases, water flows into minute hair cracks.

  • Water get evaporated and NaOH increases further and react with iron of boiler, hence cause Embrittlement.

    Prevention:

  • Addition of sodium sulphate or sodium phosphate. Which will block hair-cracks.

  • Addition of tannin and lignin- blocks the cracks.

  • Excess of Na2SO4 is avoided else it will form CaSO4


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Priming and Foaming

Priming:- Carry over of varying amounts of water in the steam e.g.

(Foam, mist)

  • Leads to deposits of salt crystals

  • Lowers the energy efficiency

    Causes:-

  • Presence of suspended impurities and dissolved salts

  • High steam velocity and sudden boiling

  • High water levels

  • Faulty boiler design

    Preventions:

  • Good boiler design

  • Avoid rapid changes in temp.

  • Maintaining low water level

  • Fitting mechanical steam purifier

Normal Bubble

Carry Over


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Foaming: Formation of small bubbles and forth on the surface of water

  • Caused by high conc. of any solids in water

    Causes:

  • Difference b/w conc. of solute and suspended matters.

  • Surface tension lowering substances

  • Oil and grease

    Prevention:

  • Adding antifoaming agents e.g. castor oil

  • Removing oily particles using silicic acid and sodium alluminate.

    Boiler Corrosion: Decay of material by chemically or electrochemically

    Causes:

  • Presence of dissolved gases e.g. O2 , CO2

  • Caustic Embrittlement

  • Acid formation due to Hydrolysis

  • Presence of free acids.


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Treatment Methods of Water

A. Internal Treatment

B. External Treatment

Internal Treatment Method

  • Phosphate Conditioning:

    - Small amount of phosphate ions are added to precipitate Ca ions.

    - Chosen depending on the pH conditions of boiler.

    2. Colloidal Conditioning:

  • Using kerosine, tannin, starch etc

  • Get coated over the scale forming particles

  • Removed by Blow down Process

    3. Carbonate conditioning:

  • Na2CO3 is added to precipitate Ca salts as CaCO3

  • Removed by Blow down Process

  • Used in low pressure boilers


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  • Calgon Conditioning:

  • Scale forming salts are converted into soluble complexes.

  • E.g. Sodium Hexameta Phosphate (Na2PO3)6 is added…reacts with Ca and forms Calcium Hexameta Phosphate (Ca2PO3)6

  • Prevents Scale formation

  • Radioactive conditioning:

  • Adding radioactive tablets

  • Emits radiation energy which prevents Scale formation

  • Electrical Conditioning:

  • Mercury bulbs placed in boiler

  • Emits electrical discharge

  • Prevents Scale formation


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External Treatment Method (or) Water softening Method

  • Removal of hardness causing substances from water

    Methods:

  • Zeolite process

  • Ion Exchange Process

  • Mixed Bed deionization

    Zeolite (or Permutit) Process: are Hydrated sodium alumino Silicate

    Na2O. Al2O3XSiO2Y H 2O (X= 2-10, Y= 2-6 )

    Natural Zeolites:

  • Natrolite - Na2O. Al2O3 4SiO2 .2H 2O

  • Laumontite - CaO. Al2O3 4SiO2 .4H 2O

  • Harmotome - (BaO.K2O). Al2O3 5SiO2 .5H 2O

    - Capable of exchanging its Na ions.


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A. Natural Zeolite:-

Derived from green sand by washing, Heating, treating with NaOH.

  • Non porous in nature.

    B. Synthetic Zeolite: -

    Prepared from solution of Sodium Silicate and AlOH

  • Higher exchange capacity and porous in Nature.

    Process:


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  • Consist of Steel Tank

  • Having Thick Layer of Zeolite

  • When water pass through it hardness causing ions (Ca, Mg) are retained by Zeolite.

    Chemical Reaction:

    Ca(HCO3) 2 + Na2 Ze → CaZe + 2 NaHCO3

    CaSO4 + Na2Ze → CaZe + Na2SO4

    MgCl 2 + Na2Ze → MgZe + 2NaCl

    Mg (NO3)2 + Na2Ze → MgZe + 2NaNO3

  • Exchange of Na ions continues until Na ions are exhausted

    Regeneration:

    CaZe + 2NaCl → Na2Ze + CaCl 2

    MgZe + 2NaCl → Na2Ze + MgCl 2

  • CaCl 2 and MgCl 2 led to drain and Na2Ze can be reused.


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Advantages

  • Hardness can be completely removed

  • Process can be made automatically

  • Easy operation. No experts required

  • Less time and sludge

  • Small area requires

    Disadvantages

  • Only Ca+ and Mg+ ions can be removed

  • Large amount of Na ions present in treated water.

  • Leaves other acids which causes corrosion

  • Fe 2+ and Mn 2+ containing water can not be treated because Fe and Mn Zeolite can not be regenerated

  • Water should be free from suspended impurities to prevent clogging on Zeolite beds.

  • Treated water contains more dissolved solids.


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B. Ion Exchange (or) Demineralization (or) Deionization Process.

  •  mineral ions are removed

  • physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water.


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Advantage:

  • Produces soft water

  • Can treat highly acidic or alkaline water

  • Regeneration of ion resins are possible

  • Maintenance cost is low

    Disadvantage:

  • Cost of equipment is high

  • Highly turbid water can not be treated

  • Expensive chemicals are required.


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3. Mixed Bed Deionization

  • This equipment consist of single column which contain mixture of cation and anion exchangers.

  • When water pass through bed, it comes in contact several times with both exchangers

  • Resultant water contain lesser amount of salt.

    Regeneration: by back wash

    a) anions with dil. NaOH

    b) cations with dil. H2SO4

    Advantages:

  • More convenient and more effective

    Disadvantages:

  • Regeneration cost is more

  • Equipment cost is high


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Desalination

  • Processes that remove some amount of salt and other minerals from

    Water.

  • Brackish Water: contain 3.5 % salts & salty taste. Unfit for drinking

  • Separation of salts from water by evaporation followed by condensation.

  • Freezing method can also be employed

  • Commonly used methods:

  • Electrodialysis

  • Reverse Osmosis


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A. Electrodialysis:

  • Method of separation of ions from salt water by passing electric current.

  • Semi permeable membranes are placed

  • Consist of three compartments containing

    1. Sea Water 2. Pair of electrodes 3. Semi permeable membrane


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  • As current applied Na ions moves towards cathode and Cl moves towards anode

  • As result brine concentration decreases in the middle compartment.

  • Pure water is removed from the central compartment.

  • Conc. Brines are replaced by fresh brine water.

  • Much more effective separation Ion selective membranes are used


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Reverse Osmosis (or) Super Filtration (or) Hyper Filtration

  • Movement of solvent molecule from concentrated side to diluted side.

  • If only pressure higher than that of osmotic pressure

    Membranes:

    Cellulose Acetate, Polymide,

    Polymethylmethaacrylate

    Thickness:

    0.0005 to 0.0000002 µm

  • Advantages:

  • Removes both ionic and non ionic and colloidal matters

  • Maintenance cost is low

  • Membrane replacement can be done with in few minutes.


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Domestic Treatment of Water

  • Removal of Suspended Impurities

  • Removal of Micro organisms

    Removal of Suspended Impurities

  • Screening:

    Floating matters are removed by passing through screens.

    2. Sedimentation:

  • Big tanks are used

  • Left undisturbed

  • Water settle down due to gravity.

  • Supernatent water is drawn with the help of pump

  • Takes 2-6 hours

    3. Filtration:

    Sand Filters are used.


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4. Sedimentation with Coagulation:

  • Addition of Chemicals (Coagulants) to water. E.g. Alum (Potash Alum or Ferric Alum), Sodium Aluminate (NaAlO2) ,Ferrous Sulphate (FeSO4)

  • On addition they form an insoluble gelatinous, flocculent precipitate which absorbs very fine particles and form bigger flocs.

  • Due to this tiny particles which have no charge also come closers.


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B. Removal of Micro Organisms

  • Boiling

  • Adding Bleaching Powder:

  • 1 kg for 1000 KL

  • Mixed and Allowed to stand several hours

    CaOCl2 + H2O → Ca (OH)2 + Cl2

    Cl2 + HO → HOCl (Hypochlorous Acid) + HCl

    HOCl + Germs → Germs Killed

    HOCl → HCl+ [O] (Nascent Oxygen)

    [O] + Germs → Germs Killed

    Disadvantages:

  • Excess addition give bad odour and taste.

  • Introduces Ca into water and makes it hard

  • Disintegrates on storing


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3. By Chlorination:

  • Chlorine produces Hypochlorous Acid.

  • Hypochlorous acid is strong Germicide.

    Cl2 + HO → HOCl (Hypochlorous Acid) + HCl

    HOCl + Germs → Germs Killed

  • Cl may be used in Gaseous or Concentrated Form.

  • Filtered water with 0.3-0.5 ppm Cl is sufficient.

  • Lower pH is favourable (5-6.5)

    Advantages:

  • Effective and Economical

  • Stable and does not deteriorate on storage

  • No impurities such as salts are introduced.

  • Can be used at high as well as low temp.


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Disadvantages

  • Excess chlorination produces unpleasant taste. (0.1-0.2 ppm only)

  • More effective at low pH.

    Breakpoint Chlorination:

  • The addition of chlorine in such amount that it Oxidizes the organic matter, reducing matters and free ammonia in raw water. And leaves free residual Cl which disinfect Water.

    Advantages

  • Oxidizes organic compounds, reducing substances and ammonia.

  • Removes colour and taste.

  • Kill germs.

    - Excess of Declorination can be done by

  • Filtering through bed of molecular carbon

  • Addition of SO2 and Na2SO3

    SO2 + Cl2 + 2H 2O → H 2SO4+ 2HCl

    Na2SO3 + Cl2 + H 2O → Na2SO4 + 2HCl


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4. By chloramine:

- Using 2 : 3 ratio of Cl3 and NH3

ClNH2+ H2O → HOCl + NH3

HOCl + Germs → Germs Killed

5. By Ozonization:

  • Ozone and raw water are allowed to come in contact with each other

  • 10 – 15 min. in 2-8 ppm

    3O2 → 2O3 (Highly Unstable)

    O3 → O2 + [O]

    [O] + Germs → Germs Killed

    Advantage: 1. Leaves no residue. Because of unstability

    2. Removes odour, colour, Taste.

    Disadvantage: Very Expensive

    6. By Ultraviolet Radiation:

    - Using Electric mercury vapour lamp


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International Standards for water

  • Depends on purpose

  • Standards Set By:

  • WHO- World Health Organization

  • USPHD- United States Health Service

  • ICMR- Indian Council of Medical Research

    Water should be free from

  • Turbidity, Colour

  • Taste, Odour

  • Microbes

  • Toxicity (Organic and Inorganic Metals)


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