SRM University

1st SEM Applied Chemistry

Technology Of WaterWater: 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),

Evotranspiration Process

• 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.

Sources of Water• The source of water are listed under two categories 1. Surface Water 2. Underground Water

A. Surface Waters: 1. Rain Water 2. River Water 3. Lake Water 4. Sea water

B. Underground Water: 1. Spring 2. Well water

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

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.

• 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 ̊� ̊�

Hardness TableWater Classification Hardness, mg/L Hardness.

Grains/GalSodium Added mg/L

Soft 0 to 49 0 to 2.9 0 to 22.5

Medium Hard 50 to 149 2.9 to 8.7 23 to 68.5

Hard 150 to 249 8.7 to 14.6 69 to 115

Very Hard 250 to 299 14.6 to 173 115 to 138

Extremely Hard 300 and up 17.5 and up 138 and up

mg/L = milligrams/Liter

• 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 ↑

2) 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

Disadvantages of Hard Water(A) Domestic Uses: 1. 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

Estimation Of Hardness 1. EDTA Method 2. O.Herner’s Method1. 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: 1. Take 50 ml water in coinical flask2. Add buffer and few drops of EBT-T3. Titrate against EDTA4. Red colour change to steel blue/violet

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:

1) 50ml sample water in conical flask2) 2-3 drops of methyl orange indicator3) Titrated against N/50 HCl 4) Change colour from yellow to orange5) Take 100 ml of same sample of water 6) Boil until 1/5th volume7) Make them again 100 ml Distilled water8) Take 50ml and perform again the above steps

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:1. 50 ml hard water + 50 ml Na2CO3 solution

2. Boiled and Evaporated to dryness.3. Chlorides of Ca and Mg ppt. as carbonates of Ca and Mg.4. Extract residue with distilled water5. Add few drops of methyl orange as indicator6. Titrate against N/50 HCl7. End point changes colour from yellow to orange.

Determination of Alkalinity in water• It is due to 1) OH- and CO3

-2 2) HCO3-

• Titrate against phenolphthalein and methyl orange Method

1. 100 ml sample water in conical flask2. Add 2-3 drops of phenolphthalein indicator3. Titrate against N/50 H2SO4

4. Continue till pink colour disappear5. To the same solution add 2-3 drops of methyl orange6. 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)

Scale and Sludge• Troubles met in boiler which are used in steam production.Scale: When water is evaporated in boilers to produce steam continuouslythe concentration of the slats present in the water increases

progresselyAs the concentration reaches a saturation point the salts are thrownover the inner surface of the boiler.Sludge: During boiling salts form precipitate of loose slimy form.Magnesium ChlorideDecomposes 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 SulphateForms a hard scale on the heating surfaces

Calcium SulphateForms a hard scale on the heating surfaces

Calcium Bi-carbonateDecomposes 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

Disadvantages of Scale Formation1. Wastage of fuel 2. Decreases in Efficiency3. Lowering of boiler safety 4. Danger of Explosion5. Corrosion Removal of Scales1. By scrapping 2. Giving thermal shocks3. Dissolving by using chemicals e.g CaCO3 by 5-10% HCl

4. Adding complexing agents e.g CaSO4 by EDTA

5. Blow down Process Disadvantages of Sludge Formation1. Chocking of pipes2. Low supply of heat3. Wastage of fuel4. Get entrapped in scales

Prevention of Sludge Formation1. Blow down Process: Withdrawing portion of sludge containing water

and replacing with fresh water2. Softening of water Method of Preventing Scale Formation1. External Treatment: Treatment of water before entering into boiler- Removal of Ca, Mg and Silica2. 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

Caustic embrittlement : It is the phenomenon in which the material ofa 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:1. Addition of sodium sulphate or sodium phosphate. Which will block

hair-cracks.2. Addition of tannin and lignin- blocks the cracks.3. Excess of Na2SO4 is avoided else it will form CaSO4

Priming and FoamingPriming:- 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:- a) Presence of suspended impurities and dissolved saltsb) High steam velocity and sudden boiling c) High water levelsd) Faulty boiler design

Preventions:a) Good boiler designb) Avoid rapid changes in temp.c) Maintaining low water leveld) Fitting mechanical steam purifier

Normal Bubble

Carry Over

Foaming: Formation of small bubbles and forth on the surface of water- Caused by high conc. of any solids in water

Causes: a) Difference b/w conc. of solute and suspended matters.b) Surface tension lowering substancesc) Oil and grease

Prevention:a) Adding antifoaming agents e.g. castor oilb) Removing oily particles using silicic acid and sodium alluminate.Boiler Corrosion: Decay of material by chemically or electrochemically

Causes:a) Presence of dissolved gases e.g. O2 , CO2

b) Caustic Embrittlementc) Acid formation due to Hydrolysisd) Presence of free acids.

Treatment Methods of WaterA. Internal TreatmentB. External Treatment

Internal Treatment Method1. 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 Process3. Carbonate conditioning:- Na2CO3 is added to precipitate Ca salts as CaCO3

- Removed by Blow down Process- Used in low pressure boilers

• 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

External Treatment Method (or) Water softening Method• Removal of hardness causing substances from waterMethods:1. Zeolite process2. Ion Exchange Process3. Mixed Bed deionization

Zeolite (or Permutit) Process: are Hydrated sodium alumino Silicate Na2O. Al2O3 X SiO2 Y H 2O (X= 2-10, Y= 2-6 )

Natural Zeolites:1. Natrolite - Na2O. Al2O3 4SiO2 .2H 2O

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

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

- Capable of exchanging its Na ions.

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:

• 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.

Advantages1. Hardness can be completely removed2. Process can be made automatically3. Easy operation. No experts required4. Less time and sludge5. Small area requires

Disadvantages1. Only Ca+ and Mg+ ions can be removed2. Large amount of Na ions present in treated water.3. Leaves other acids which causes corrosion4. Fe 2+ and Mn 2+ containing water can not be treated because Fe and

Mn Zeolite can not be regenerated5. Water should be free from suspended impurities to prevent clogging

on Zeolite beds.6. Treated water contains more dissolved solids.

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.

Advantage:1. Produces soft water2. Can treat highly acidic or alkaline water3. Regeneration of ion resins are possible4. Maintenance cost is lowDisadvantage:1. Cost of equipment is high2. Highly turbid water can not be treated 3. Expensive chemicals are required.

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. NaOHb) cations with dil. H2SO4

Advantages:• More convenient and more effective

Disadvantages:• Regeneration cost is more• Equipment cost is high

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:1. Electrodialysis2. Reverse Osmosis

A. Electrodialysis: • Method of separation of ions from salt water by passing electric

current.• Semi permeable membranes are placed

• Consist of three compartments containing1. Sea Water 2. Pair of electrodes 3. Semi permeable membrane

• 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

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:1. Removes both ionic and non ionic and colloidal matters2. Maintenance cost is low3. Membrane replacement can be done with in few minutes.

Domestic Treatment of WaterA. Removal of Suspended ImpuritiesB. Removal of Micro organisms

Removal of Suspended Impurities1. 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 hours3. Filtration: Sand Filters are used.

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.

B. Removal of Micro Organisms1. Boiling 2. 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

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:1. Effective and Economical2. Stable and does not deteriorate on storage3. No impurities such as salts are introduced.4. Can be used at high as well as low temp.

Disadvantages1. Excess chlorination produces unpleasant taste. (0.1-0.2 ppm only)2. 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.

Advantages1. Oxidizes organic compounds, reducing substances and ammonia.2. Removes colour and taste.3. Kill germs.- Excess of Declorination can be done by1. Filtering through bed of molecular carbon2. Addition of SO2 and Na2SO3

SO2 + Cl2 + 2H 2O → H 2SO4+ 2HCl

Na2SO3 + Cl2 + H 2O → Na2SO4 + 2HCl

4. By chloramine:- Using 2 : 3 ratio of Cl3 and NH3

ClNH2+ H2O → HOCl + NH3

HOCl + Germs → Germs Killed5. 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 KilledAdvantage: 1. Leaves no residue. Because of unstability 2. Removes odour, colour, Taste. Disadvantage: Very Expensive6. By Ultraviolet Radiation:- Using Electric mercury vapour lamp

International Standards for water- Depends on purpose- Standards Set By:1. WHO- World Health Organization 2. USPHD- United States Health Service 3. ICMR- Indian Council of Medical Research

Water should be free from1. Turbidity, Colour 2. Taste, Odour3. Microbes4. Toxicity (Organic and Inorganic Metals)