Water TreatmentWater Treatment

Sources of waterSources of water1.Surface water- rivers, lakes, reservoirs etc.1.Surface water- rivers, lakes, reservoirs etc.

2.Underground water – wells and springs2.Underground water – wells and springs

3.Rain water 3.Rain water

4. Sea water4. Sea water

Surface waterSurface water

River water – dissolved mineralsRiver water – dissolved minerals

ClCl--, SO, SO442-2-, HCO, HCO33

-- of of

Na+, MgNa+, Mg2+2+, Ca, Ca2+2+ and Fe and Fe2+2+

suspended impurities- Organic matter, suspended impurities- Organic matter,

sand, rock sand, rock

composition is NOT constant – dep on the contact composition is NOT constant – dep on the contact with soil.with soil.

Lake water: High in organic and less in minerals.Lake water: High in organic and less in minerals.

composition is constant.composition is constant.

Rain waterRain water – pure form – pure form

dissolved organic and inorganic dissolved organic and inorganic particles and dissolved industrial gases COparticles and dissolved industrial gases CO22, , NONO22,SO,SO22 etc etc

Underground waterUnderground water-- free from organic free from organic impurities due to filtering action of the soilimpurities due to filtering action of the soil

Sea waterSea water – very impure; too saline for – very impure; too saline for industrial use except coolingindustrial use except cooling

Impurities in waterImpurities in water

Suspended impuritiesSuspended impurities

inorganic (clay, sand) organic (oil,plant, inorganic (clay, sand) organic (oil,plant, and animal matter)and animal matter)

Colloidal impurities- finely divided silica and Colloidal impurities- finely divided silica and clayclay

Dissolved impurities – salts and gasesDissolved impurities – salts and gases Microorganisms – bacteria, fungi and algaeMicroorganisms – bacteria, fungi and algae

Hardness of waterHardness of water

Hardness prevents the lathering of soap.Hardness prevents the lathering of soap.due to the presence of salts of Ca, Mg, Al, Fe and due to the presence of salts of Ca, Mg, Al, Fe and Mn dissolved in it.Mn dissolved in it.

Soap – Na or K salts of long chain fatty acids Soap – Na or K salts of long chain fatty acids CC1717HH3535COOHCOOH

2C2C1717HH3535COONa + CaClCOONa + CaCl22 → (C→ (C1717HH3535COO)COO)22Ca↓ + 2NaClCa↓ + 2NaCl

2C2C1717HH3535COONa + MgSOCOONa + MgSO44 → (C→ (C1717HH3535COO)COO)22Mg↓ + NaMg↓ + Na22SOSO44

The Cleansing Action of Soap

12.8

Hard WaterHard WaterDoes not produce lather with Does not produce lather with

soapsoap

Contains Ca and Mg saltsContains Ca and Mg salts

Soap is wasted and cleaning Soap is wasted and cleaning quality is depressedquality is depressed

Boiling point elevated, more Boiling point elevated, more time and fuel for cookingtime and fuel for cooking

Soft WaterSoft WaterProduces lather easily with Produces lather easily with

soapsoap

Does not contain dissolved Does not contain dissolved Ca and Mg saltsCa and Mg salts

Cleaning quality of soap not Cleaning quality of soap not depressed.depressed.

Less fuel and time required Less fuel and time required for cookingfor cooking

Hard WaterHard WaterDoes not produce lather with Does not produce lather with

soapsoap

Contains Ca and Mg saltsContains Ca and Mg salts

Soap is wasted and cleaning Soap is wasted and cleaning quality is depressedquality is depressed

Boiling point elevated, more Boiling point elevated, more time and fuel for cookingtime and fuel for cooking

Soft WaterSoft WaterProduces lather easily with Produces lather easily with

soapsoap

Does not contain dissolved Does not contain dissolved Ca and Mg saltsCa and Mg salts

Cleaning quality of soap not Cleaning quality of soap not depressed.depressed.

Less fuel and time required Less fuel and time required for cookingfor cooking

Types of HardnessTypes of Hardness

Temporary Hardness-Temporary Hardness- caused by caused by dissolved bicarbonates of Ca and Mgdissolved bicarbonates of Ca and Mg

Also known as ‘alkaline or carbonate Also known as ‘alkaline or carbonate hardness’hardness’

Permanent HardnessPermanent Hardness – dissolved Cl- and – dissolved Cl- and SOSO44

2-2- of Ca, Mg, Fe and Al etc of Ca, Mg, Fe and Al etc

Temporary HardnessTemporary Hardness

caused by dissolved bicarbonates of Ca and Mgcaused by dissolved bicarbonates of Ca and MgTemporary hardness can be removed by boiling of Temporary hardness can be removed by boiling of waterwater

Ca(HCOCa(HCO33))22 → CaCO→ CaCO33↓ + H↓ + H22O + COO + CO22↑↑

Mg(HCOMg(HCO33))22 → Mg(OH)→ Mg(OH)22↓ + 2 CO↓ + 2 CO22↑↑

Also known as ‘alkaline or carbonate hardness’Also known as ‘alkaline or carbonate hardness’Determined by titration with HCl using methyl orange Determined by titration with HCl using methyl orange

as indicatoras indicator

Permanent HardnessPermanent Hardness

CaClCaCl22, MgCl, MgCl22, CaSO, CaSO44, MgSO, MgSO44, FeSO, FeSO44, Al, Al22(SO(SO44))33

Cannot be destroyed on boiling the waterCannot be destroyed on boiling the water

Also known as Also known as non-carbonatenon-carbonate or or non alkalinenon alkaline hardness hardness

non alkalinenon alkaline hardness = Total hardness – alkaline hardness = Total hardness – alkaline

hardnesshardness

Hard WaterHard Water

AdvantagesAdvantages

Tastes betterTastes better

Ca in water helps produce Ca in water helps produce strong teeth and bonesstrong teeth and bones

Hard water coats lead pipes Hard water coats lead pipes with layer of insoluble with layer of insoluble CaCOCaCO33, preventing any , preventing any

poisonous lead dissolving poisonous lead dissolving in drinking waterin drinking water

DisadvantagesDisadvantages

no taste, produces scum no taste, produces scum with soapwith soap

Boiler feed water should be Boiler feed water should be free from hardness or even free from hardness or even explosions can occurexplosions can occur

Degree of HardnessDegree of Hardness

Hardness is expressed as equivalent amount Hardness is expressed as equivalent amount ((equivalentsequivalents) of CaCO) of CaCO33

Reason: Molar mass is exactly 100, and is the most insoluble salt that can be Reason: Molar mass is exactly 100, and is the most insoluble salt that can be

precipitated in water treatment.precipitated in water treatment.

Equvalents of Equvalents of CaCOCaCO3 = 3 =

( mass of hardness producing substance in mg/L) x100 / (eq.wt of ( mass of hardness producing substance in mg/L) x100 / (eq.wt of

substancex2)substancex2)

units – mg/L = ppmunits – mg/L = ppm

parts of CaCO3 equivalents in hardness in 10parts of CaCO3 equivalents in hardness in 1066 parts of water parts of water

Equivalent weightEquivalent weight

Eq. wt = Molar mass/ no of charge on ionEq. wt = Molar mass/ no of charge on ion

CaCOCaCO33 MM/2 MM/2

NaClNaCl MM/1MM/1

AlClAlCl33 MM/3MM/3

AlAl22(SO(SO44))33 MM/6MM/6

Example 1:Example 1:

A water sample contains 408 mg of CaSOA water sample contains 408 mg of CaSO44

per liter. Calculate the hardness in terms of per liter. Calculate the hardness in terms of CaCOCaCO33 equivalents equivalents

Hardness = mg/L of CaSOHardness = mg/L of CaSO44 x 100/MM(CaSO x 100/MM(CaSO44 ) )

= 408 mg/L x 100/136= 408 mg/L x 100/136

= 300 mg/L = 300 ppm= 300 mg/L = 300 ppm

Example 2Example 2

How many grams of MgCOHow many grams of MgCO33 dissolved per dissolved per

liter gives 84 ppm of hardness?liter gives 84 ppm of hardness?

Hardness = mg/L of MgCOHardness = mg/L of MgCO33 x 100/MM(MgCO x 100/MM(MgCO33))

84 ppm = ppm of MgCO84 ppm = ppm of MgCO33 x 100/84 x 100/84

ppm of MgCOppm of MgCO33 = 84 ppm x (84/100) = 84 ppm x (84/100)

= 70.56 ppm= 70.56 ppm

= 71 mg/L= 71 mg/L

Calculation of hardness caused by each ion.Calculation of hardness caused by each ion. Na+ - 20 mg/LNa+ - 20 mg/L Ca Ca2+2+ - 15 mg/L - 15 mg/L

MgMg2+2+ - 10 mg/L - 10 mg/L Sr Sr2+2+ - 2 mg/L - 2 mg/LAlAl3+3+ - 0.3 mg/L - 0.3 mg/L

Equvalents of Equvalents of CaCOCaCO3 = 3 =

( mass of hardness producing substance in mg/L) x100 / (eq.wt of ( mass of hardness producing substance in mg/L) x100 / (eq.wt of

substancex2)substancex2)

CationCation Eq.wtEq.wt HardnessHardness CaCa2+2+ 40.0/240.0/2 37.537.5 MgMg2+2+ 24.4/224.4/2 41.041.0 SrSr2+2+ 87.6/287.6/2 2.3 2.3 AlAl3+3+ 27.0/327.0/3 1.7 1.7

Total hardness = 82.5 ppmTotal hardness = 82.5 ppm

Potable Water (Drinking water)Potable Water (Drinking water)

Colorless and odorless; good in tasteColorless and odorless; good in taste Turbidity should be less than 10 ppmTurbidity should be less than 10 ppm No objectionable dissolved gases like HNo objectionable dissolved gases like H22SS

or minerals such as Pb, As , Cr, Mn salts.or minerals such as Pb, As , Cr, Mn salts. Alkalinity should not be high; pH 7.0 – 8.5Alkalinity should not be high; pH 7.0 – 8.5 Total hardness less than 500 ppmTotal hardness less than 500 ppm Free of harmful microorganisms.Free of harmful microorganisms. Cl-, F-, and SOCl-, F-, and SO44

2–2– less than 250, 15 and less than 250, 15 and

250 ppm, respectively250 ppm, respectively

Methods of disinfection of waterMethods of disinfection of water

1. Bleaching powder (CaOCl1. Bleaching powder (CaOCl22))

CaOClCaOCl22+H+H22O O → Ca(OH)→ Ca(OH)22 + HCl + HOCl + HCl + HOCl

Enzymes of microorganism get deactivated by HOClEnzymes of microorganism get deactivated by HOCl Excess imparts bad taste and smellExcess imparts bad taste and smell Not stable during storageNot stable during storage Introduces Ca to water and thus increases Introduces Ca to water and thus increases

hardnesshardness

2. Chlorination2. Chlorination

Commonly used disinfectant in waterCommonly used disinfectant in water

used directly as a gas or conc. solution.used directly as a gas or conc. solution.

It produces HOCl, a powerful germicide. It produces HOCl, a powerful germicide.

0.3 0.5 ppm chlorine is sufficient0.3 0.5 ppm chlorine is sufficient

3. Disinfection by ozone3. Disinfection by ozone

OO33 → O→ O22 + O + O

oxygen atom is a oxygen atom is a powerful oxidizing powerful oxidizing agent.agent.

2 – 3 ppm is injected2 – 3 ppm is injected10 – 15 min contact time10 – 15 min contact time

Expensive methodExpensive method

AlkalinityAlkalinity

The capacity of water accept H+ is called alkalinityThe capacity of water accept H+ is called alkalinity The basic species responsible areThe basic species responsible are

1.1. HCOHCO33- - + H + H++ → H→ H22OO

2.2. COCO332-2- + H + H++ → HCO → HCO33

--

3.3. OH- + H+ → HOH- + H+ → H22OO

Different from basicity; high pHDifferent from basicity; high pHpH is an intensity factorpH is an intensity factor

alkalinity is a capacity factoralkalinity is a capacity factor1.00x101.00x10-3-3 M NaOH - pH=11;neutralize 1.00x10 M NaOH - pH=11;neutralize 1.00x10-3-3 mole acid mole acid

0.100 M NaHCO0.100 M NaHCO33 - pH = 8.34, 0.100 mole acid - pH = 8.34, 0.100 mole acid

Alkalinity of water is attributed to presence ofAlkalinity of water is attributed to presence of

i. caustic alkalinity (due to OHi. caustic alkalinity (due to OH-- and CO and CO332-2- ions) ions)

ii. Temporary hardness (due to HCOii. Temporary hardness (due to HCO33-- ions) ions)

i. [OH-] + [H+] i. [OH-] + [H+] → H→ H22O -P -MO -P -M

ii. [ii. [COCO332-2-] + [H+] ] + [H+] → [→ [HCOHCO33

-- ] -P -M ] -P -M

iii. [HCOiii. [HCO33-- ] + [H+] ] + [H+] → H→ H22O + COO + CO2 2 -M-M

P = OH- + ½ P = OH- + ½ COCO332- 2-

M = OH- + COM = OH- + CO332- 2- + HCO+ HCO33

--

Biological oxygen demand (BOD)Biological oxygen demand (BOD)

BOD is the quantity of dissolved OBOD is the quantity of dissolved O22 required required by aerobic bacteria for oxidation of organic by aerobic bacteria for oxidation of organic matter under aerobic conditions.matter under aerobic conditions.source of effluentsource of effluent BOD(ppm)BOD(ppm)

Domestic sewageDomestic sewage 320 320Cow shed sewageCow shed sewage 3010 3010Paper millPaper mill 8190 8190

BOD indicator of organic pollutantsBOD indicator of organic pollutants

Chemical oxygen demand (COD)Chemical oxygen demand (COD)

Defined as the oxygen consumed in the Defined as the oxygen consumed in the oxidation of organic and oxidizable inorganic oxidation of organic and oxidizable inorganic matter.matter.

Use a strong oxidizing agent like KUse a strong oxidizing agent like K22CrCr22OO77

COD COD > BOD (> BOD (O2 is a weak oxidizing agent)O2 is a weak oxidizing agent)

COD test does not differentiate between bio-inert COD test does not differentiate between bio-inert and bio degradable materialsand bio degradable materials