Water & Its treatment Introduction

This chapter deals with

Specification of water,

Hardness of water,

Softening and its treatment.

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Water- Most important and basic requirement on earth

For existence of all living beings

(human, animals, plants)

For industrial processes and agricultural production

In thermal & nuclear power plants for steamgeneration & cooling purposes

Oceans contains- 97% of all the water on earth

Glaciers- 2%

1% available for ready use

• Hence it is urgently required to use the available watermost carefully and economically

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Sources of water

1. Rain Water

2. Ground Water Main Sources

3. Surface Water

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Rain Water: Caused due to evap. of surface water &

subsequent precip.

Most purest form of natural water

Dissolves Impurities (SPM, CO2, SO2, NO2) from atmosphere during pptation

Can be stored in underground reservoir tanks

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Ground Water: • Largest available source of fresh water

• Form of rain water falling on earth

• Generally pure because it undergoes natural filtration during the percolation through soil pores

• Less likely to be contaminated by BACTERIA but contains dissolved salts

• To obtain in large quantity tube wells are used

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Surface Water:The water that flows over the surface of earth & is Directly available

It includes

1. River water

2. Lake water

3. Sea water

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1. River water• Comes from melting of snow, rain and spring water

(coming from earth)

• Contains dissolved minerals/salts like chlorides,sulphates, bicarbonates of Na, Ca, Mg

• Also contains impurities of sand rocks & organicmatter

Surface Water:

2. Lake Water• Contains organic impurities due to decomposition of

plants and animals• Contains less amount of dissolved minerals• Chemical composition is constant

3. Sea Water• Most impure form of natural water• Dissolved salts are increased by impurities thrown by

rivers when they join sea• Contains 2000 times more dissolved salts than other

water• Very saline- can not be used in industries except for

cooling8

Surface Water:

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1. Dissolved Impurities2. Suspended Impurities3. Colloidal Impurities 4. Microorganism Impurities

IMPURITIES IN HARD WATER

Dissolved Impurities

a) Salts:

– Carbonates, Bicarbonates, Sulphates and chlorides of

Ca, Mg, Fe, Na, K.

b) Gases: CO2, O2, N2, H2S, NH3

Suspended impurities

Inorganic- Clay, sand

Organic- Vegetable & animal matter

Colloidal Impurities:Products from organic waste, finely divided silica and clay etc.

Microorganisms: Bacteria, Fungi, Algae10

HRDNESS OF WATER“The property that prevents lathering of soap”

Cause of Hardness:Presence of soluble salts of Ca, Mg or other heavymetals in water Hard water does not produce lather with soap.

SOAPSGenerally soaps consists of Na salts of higher fatty acidssuch as stearic acid, oleic acid, palmitic acid.

Soaps are highly soluble in water thus exert theircleansing action. 11

If Ca & Mg salts are present in water then thesesalts react with soap to form insoluble white scumas ppt. e.g.

2 C17H35COONa + CaSO4 → (C17H35COO)2Ca↓ + Na2SO4

Sod. Stearate From hard White ppt

(Soap) water

2 C17H35COONa + MgCl2 → (C17H35COO)2Mg↓ + 2NaCl

Sod. Stearate From hard White ppt

(Soap) water

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Lather is not produced till the hardness causingcations (Ca2+ Mg2+) are completely precipitated out inthe form of insoluble salts.

Thus a large quantity of soap is required to producelather with hard water.

HARD WATERHence the water that does not produce lather withsoap readily is called hard water.

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HARD WATER SOFT WATER1 Contains dissolved salts of Ca,

Mg or other heavy metalsDoes not containdissolved salts

2 Does not form lather withsoap

Forms lather with soap

3 Large quantity of soap isrequired during washing

Soap is not wasted

4 Due to presence of dissolvedsalts, B.P. of hard water iselevated. So more fuel isconsumed in cooking

Less fuel is required

DIFFERENCE BETWEEN HARD AND SOFT WATER

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TYPES OF HARDNESS Temporary & Permanent1. Temporary Harness:Cause: Due to the presence of bicarbonates of Ca & Mg

Also called carbonate hardness

Removal of Temp Hardness- by BoilingOn boiling, bicarbonates of Ca & Mg get decomposed to

give insoluble carbonates which are deposited as insoluble precipitates at the bottom of the vessel

∆Ca (HCO3)2 CaCO3 ↓ + CO2↑ + H20

∆Mg (HCO3)2 MgCO3 ↓ + CO2↑ + H20

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2. Permanent Harness:Cause: Due to the presence of sulfates and chlorides of

Ca & MgAlso called non-carbonate hardness

• Removal of perm. Hardness- is not possible by Boiling

• Special methods are used to remove permanent hardness

• Total Hardness = Temp. Hardness + Perm. Hardness

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DEGREE OF HARDNESSFor the sake of convenience,hardness is expressed in terms of equivalentamount of CaCO3

The use of CaCO3 as a standard reference is dueto two reasons:

1. CaCO3 is most insoluble salt that can beprecipitated in water treatment.

2. Mol. Wt of CaCO3 is 100, hence calculationsbecome easy

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