water technology-1

7/30/2019 water technology-1

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Water is most abundant, useful & misused one

It is universal solvent


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Surface water :1. Rain Water : Purest one among all the sources May consists industrial gases like COx , NOx , SOx,

2. River Water : It is flow water This dissolves minerals of soil Contains SO4

-2, NO-3 , of Fe+2, Ca+2 & Mg+2

3. Lake Water : Has more const. Chemical compositions Contains lesser amount of dissolved salts high % of

organic matter.


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4. Sea Water :It is most impure formContinuous evaporation increases concentration of

impurities.Average of impurities in sea waterDissolved salts = 3.5 %NaCl = 2.6 %Others K, HCO3

-, Mg, CaSurface water, generally contains suspended particlesWhich may often contains the disease producing

bacteria.It is not suitable for human consumption.

Under Ground Water :Part of rain water,Reaches the earth, percolates into the earth.It comes in constant with a no of minerals


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EFFECT OF WATER ON ROCKS AND

MINERALS

NaCl Dissolves in water (Na+ + Cl-)

CaSO4.2H2O Ca+2

+ SO4-2

+ H2O

1. Dissolution :

2. Hydration :Anhydrite minerals undergo hydration to form products of

increased volume.

CaSO4 + 2H2O CaSO4 . 2H2OGypsum (of 33% more volume)

Mg2SiO4 + xH2O Mg2SiO4 . x H2O.


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3. Action of dissolved oxygen :

2Fe2O4 + O2 2Fe2O3Magnetite

3 Fe2O3 + 2H2O 3Fe2O3 2H2O Limonite.

2FeS2 + 2H2O + 7O2 2FeSO4 + 2H2SO4


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4. Action of dissolved Carbon dioxide :

Converts insoluble carbonates of Ca, Mg and Fe intosoluble bicarbonates.

Converts rock forming silicates to carbonates.


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TYPES OF IMPURITIES IN WATER Natural water contaminated by different types of

impurities.

The quality of water depends on the following heads: I) Physical impurities:

a) Color: Color in water is caused by metallicsubstances like salts of Fe, Mn, algae, Protozoa &

Industrial effluents. b)Turbidity: Is due to the colloidal, inorganic &

organic, micro organisms etc,.


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c) Taste: is usually inter linked directly with odour. Ex:Bitter taste can be due to the presence of Fe, Al, Mn,Sulphate or excess of Lime.

d) Odour: Disagreeable odour is water may be caused bythe presence of living organisms, algae , bacteria & fungi etc,. II)Chemical impurities in water: Inorganic and organic

chemicals released from dyes,paints, drugs, textile

industries etc. a)Acidity: Acidity is caused by the presence of Free CO2,Mineral acids(H2SO4) & weakly dissociated acids.


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b) Gases

c) Mineral matters

III) Biological impurities: Algae, fungi, viruses etc,.


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HARDNESS OF WATER Characteristic of water which prevents lathering of soap,

Due to the presence of salts of Ca, Mg & other heavymetals.

Hard water does not produce lather, form white scum or

precipitate

Precipitate forms due to the formation insoluble soaps(Calcium stearate & magnesium stearate)

C17H35COONa + Ca+2 (C17 H35COO)2 Ca + Na

+

C17H35COONa + Mg+2 (C17 H35COO)2 Mg + Na+


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Types :1. Temporary (carbonate) Hardness

2. Permanent ( Non carbonate ) Hardness

Temporary Hardness : (Carbonate)

Caused due to the presence of dissolved bicarbonates ofCa, Mg, Na, K.

Destroyed by boiling.

Ca(HCO3)2 CaCO3 +CO2 + H2O

Mg(HCO3)2 Mg(OH)2 + CO2


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Permanent (Non Carbonate) : Caused due to the presence of Chloride, Sulphates,

Nitrates of Ca, Mg, and other metals.

Cant be removed by boiling.Calcium Carbonate Equivalence : Hardness is expressed in calcium carbonate equivalence. M.Wt. of CaCO3 = 100

Most insoluble


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Units :

1 ppm = 1 part of CaCO3 present in 106 parts of water

1 mg/lit. = 1 mg of CaCO3 present in 1L of water

10C1 = 1 part of CaCO3 present in70,000 L of water (1Gallon)

10 Fr = 1 part of CaCO3 present in 105 parts of water

cesubsproducinghardnessofweightEquivalentChemical

CaCOofweightequivalentchemicalcesubsproducinghardnessofMass

tan

tan 3

1 ppm = 1mg/lit = 0.07 0C1 = 0.1 0Fr


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EDTA method : (Complexometric method)EDTA = Elthylene diamine tetra acetic acid

It exists as its di sodium salt

H+N

N+H

-OOC

+Na-OOC

COO-

COO-Na+

H2C

CH2


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Principle :Equivalent point (end point ) is determined by

eriochrome black T indicator (alcoholic solution ofblue dye.)

Indicator is effective at pH 10

Buffer used is (NH4OH NH4Cl) to maintain pHM+2 +EBT [M(EBT)]Hard water Wine red(Unstable)

[M(EBT) [M(EDTA)] + EBT

(blue)

Colour change wine-red to blue


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Procedure :1. Preparation of standard Hard water :

1 Grm of dry CaCO3

Heat -CO2

Min. Quantity of dil. HCL

Dissolve in distilled water

Make the vol. 1 L

Its concentration is 1000 ppm or 1 mg / 1ml

2. Standardization of EDTA

3. Estimation of total Hardness

4. Estimation of permanent Hardness


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Advantages :

Great accuracy

Convenience rapid procedure


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Disadvantages of Hard Water :1. Domestic

Washing :

does not lather with soap

Produces sticky ppt of Ca, Mg soaps.This continues till all the Ca & Mg present in water are

predicated.

This causes wastage of soap.

Bathing :Produces sticky scum on bath tub & body.


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Cooking :

Due to presence of salts boiling point of water is elevated.Moe fuel and time is required for cookingGives unpleasant smell.Drinking :

Effects the digestive system.Industries :Textile Industry :Much of soap go as waste because hard water cannot

produce good quality of lather.Sugar Industry :Difficult in crystallization


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Dye Industry :

Yields impure shades & gives spots.

Pharmaceuticals :

Produce undesirable products as it consists of Ca & Mgsalts.

Steam Generation boilers :

Scale & sludge formation

Corrosion

Priming & foaming

Caustic embrittlement


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POTABLE WATER Municipalities have to supply potable water ,i.e. water

which is safe to drink.

Drinking or potable water ,fit for human consumption,Should satisfy the following essential requirements:

1) It should be sparking clear & odour less.

2) It should be pleasant in taste.

3) Its turbidity should not exceed 10 ppm. 4)Its alkalinity should not be high, its pH should be

about 8.0.


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5)Its total dissolved solids should be less than 500ppm.

6) It should be free from disease producing microorganisms.

7) It should be free from objectionable minerals suchas Pb, As, Cr & Mn salts Etc.


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TREATMENT OF WATER FOR

DOMESTIC PURPOSE Natural water from rivers canals etc., not suitable

for human consumption the impurities may beremoved by the following processes.

Removal of Suspended impurities:

Screening:

Raw water is passed through screens having largenumber of holes.

With this process floating matter is removed


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Sedimentation:It is a process of allowing water to stand

undisturbed in big tanks about 5 m deep.

The clear supernatant water is then drawn fromtanks with the help of pump.

Coagulation:Coagulants like alum or ferrous sulphate provide

Al+3 or Fe+3 ions, which neutralize the negativecharge on the colloidal clay particles.With the help of Coagulants colloidal particles

also settle down


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With alum2

64

3

.)(

min3)(2

)2

.(2)

3(

)(342

COCaSO

pptFlocculanthydroxide

iumAlu

OHAl

OHinpresent

eBicarbonatCal

HCOCa

coagulant

SOAl

With Sodium Aluminate:

NaAlO2+2H2O

Al (OH)3 +NaOH


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Filtration :

It is the process of removing colloidal matter andmost of the bacterias micro-organisms by passingthrough a bed of fine sand and other proper-sizedgranular materials.


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Removal of micro-organisms :Water after passing through sedimentation,coagulation and filtration still contains a small

percentage of disease causing bacterias.The process of destroying such bacterias from thewater and making it safe for use is called disinfection.This may be carried out in different ways

By boiling :Water is boiled for 10-15 minutes, all thedisease producing bactrias are killed.

By adding bleaching powder :In Small water worksabout 1 kg of bleaching powder for 1000 kL of water ismixed and is allowed to stand for several hours.


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CaOCl2 + H2O Ca (OH)2 + Cl2 Cl2+H2OHCl + HOCl

Germs +HOCl

Germs are killed.Drawbacks:It makes water hardIt deterioratesOnly calculated quantity should be added


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By Chlorination :

Chlorine produces hypochlorous acid which ispowerful germicide.

Mechanism of action: HOCl H+ + OCl-

Due to liberation of nascent oxygen bacteria arekilled.Chemical reaction of hypochlorous acid with the

enzymes in the cell of the organisms, death ofmicroorganisms causes.


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Factors affecting efficiency of chlorine :

Time of Contact

Temperature of water

pH of water


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Advantages of chlorine:

Most effective and economical

Requires very little space for storage.It is stable (does not decompose)

Most ideal disinfectant.

Disadvantages :Excess chlorine causes unpleasant taste and odour.

It is effective below 6.5 pH.


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Break-point Chlorination (Free residual chlorination):It involves in addition of sufficient amount of chlorine to

oxidize

a)Organic matter b) Reducing substancesc) Free ammonia

The dosage of applied chlorine and the free Chlorine can be

depicted graphically in which appearance of following fourstages occurs:


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The addition of chlorine at the dip or break is calledbreak point chlorination.

All tastes odors disappear at break-point, resultingin appearance of water free from bad taste andothers.

Because of the highly persistent and powerful

disinfection possessed by available free chlorineand type of pathogenic are destroyed.


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Dechlorination carried out by the following reactionsSO2+Cl2 +2 H2O H2SO4 + 2HClNa2SO3 + Cl2 + H2ONa2SO4 + 2HCl

By Ozone:Ozone is an excellent disinfectant, which is produced

by passing silent electric discharge through cold anddry oxygen.

It is highly unstable and breaks down. Liberatingnascent oxygen.3O2 2O3O3O2 + [O]


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Reverse Osmosis:

When two solutions of unequal concentrations areseparated by a *SPM, flow of solvent takes placefrom dilute to concentrated sides, due to osmosis.If a hydrostatic pressure in excess of osmotic

pressure is applied on the concentrated side thesolvent flow reverses.The membrane filtration is also called as Super-

filtration or Hyper-filtration.In this method 15-40 Kg/Cm2 is applied.


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Advantages:

It removes ionic, non-ionic, colloidal substances etc.

Cost is on the replacement of SPM (life time 2years)

Converts sea water into drinking water and obtaining waterfor very high pressure boilers.

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water technology-1