Water

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Slide 1: 

WATER Treatment

Slide 2: 

Hardness Hardness is the property of water which prevents the lather formation with soap. Hardness in water is due to bicarbonates,chlorides and sulphates of calcium,magnesium and other heavy metals.Soaps are generally sodium and potassium salts of oleic acid,palmitic acid stearic acid.Ca2+and Mg2+ions present in hard water react with soap and form insoluble salts.So lather is not produced until all cations are consumed.So hardness is also defined as soap consuming capacity of water.Other metal ions like Al3+,Mn3+,Fe2+ etc. also react with soap, but they are present in traces.

Slide 3: 

2C17H35COONa + Ca2+ (C17H35COO)2Ca + 2Na Soap From hard water Insoluble (Sodium Stearate) Calcium stearate 2C17H35COONa + Mg2+ (C17H35COO)2Mg + 2Na Soap From hard water Insoluble (Sodium Stearate) Magnesium stearate Types of hardness: 1.Temporary hardness of water is due to bicarbonayes of calcium and magnesium,which can be removed by boiling.

Slide 4: 

Ca(HCO3)2 ∆ CaCO3+ H2O + CO2 Calcium bicarbonate Calcium carbonate insoluble Mg(HCO3)2 ∆ CaCO3+ H2O + CO2 Magnesium bicarbonate Magnesium carbonate insoluble 2.Permanent hardness is due to the presence of chlorides and sulphates of calcium,magnesium , iron and other heavy metals.Permanent hardness can not be removed by boiling.It can be removed by :- (i) Zeolite process (ii) Lime Soda process (iii) Ion exchange process

Slide 5: 

3.Alkaline hardnessis due to hydroxides,bicarbonats and carbonates of the hardness producing cations. Units of hardness Parts per million ppm :- Parts of CaCO3 equivalent hardness per million parts of water. Milligram per litre:-Milligrams of CaCO3 equivalent hardness present in one litre of water. Degree French:- Parts of CaCO3 equivalent hardness per 105 parts of water. Carke’s degree:- Parts of CaCO3 equivalent hardness per 70,000 parts of w 1 ppm=1 mg/litre=0.1o Fr=0.07o Cl

Slide 6: 

Calcium Carbonate equivalent The hardness of water is expressed in terms of CaCO3 equivalent hardness because:- The molecular weight of CaCO3 is 100, which makes calculations easy. It is the most insoluble salt that can be precipitated in water treatment Hardness of water= Mass of hardness producing [Chemical equivalent of CaCO3 ] x2 Substance in mg/litre x [Chemical equivalent of hardness producing substance] x 2

Slide 7: 

= Mass of hardness 100 producing substance x 2 x chemical equivalent of hardness producing substance Hardness of water Mass of hardness ( multiplication in terms of CaCO = producing substance x factor) mg/litre or Equivalent in mg/litre or ppm ppm e.g. Salts Molar mass Chemical Multiplication equivalent Factor Ca(HCO3)2 162 81 100/162 Mg(HCO3)2 146 73 100/146

Slide 8: 

Determination of hardness EDTA Method EDTA is Ethylene diamine tetra acetic acid Because of limited solubility of EDTA its disodium salt is used. CH2COONa CH2COOH N – CH2– CH2– N CH2COOH CH2COONa Disodium salt of EDTA

Slide 9: 

EDTA is a hexadentate ligand which on reacting with Ca and Mg ion forms a stable colourless complex.Therfore this method of determination of hardness is known as Complexometric titration. O = C – O O = C – O M H2C – N N – CH2 -OOCCH2 CH2 CH2 CH2COO- Where M is Ca+2 ,Mg+2 etc. or MY-2

Slide 10: 

Theory: Mg+2 NH4CL+NH4OH Mg+2 + EBT pH=10 EBT Ca+2 Ca+2 From hard water Wine red coloured unstable Complex Mg+2 EBT + EDTA Ca+2 Blue Stable complex Indicator free colourless

Slide 11: 

Preparation of solutions:- (i) Preparation of standard hard water:Dissolve 1 gm. of CaCO3 in minimum quantity of dil. HCl and then evaporate it to dryness.Now dissolve the residue in distilled water and make up the solution upto 1 litre. (ii) EDTA solution:Dissolve 3.7 gm. Of disodium salt of EDTA in 1 litre of distilled water. (iii) EBT solution: Dissolve 0.5 gm. Of EBT in 100 ml of alcohol. (iv) Buffer solution:-Dissolve 67.5 gm. of NH4 Cl in 570 ml of concentrated ammonia solution and then make up the solution up to 1 litre with distilled water.

Slide 12: 

Procedure:- Step 1. Standardisation of EDTA solution :Take 20 ml of Standard hard water in conical flask.Add 2-3 drops of EBT.The solution turns wine red.Titrate it with EDTA solution till the solution turns blue.let v1 ml is the volume of EDTA used. Step 2. Titration with hard water sample:Repeat the titration with hard water as in step 1.let the volume of EDTA used is v2 ml. Step 3. Titration with Permanent hard water:-Boil 250 ml of hard water till its volume becomes 50 ml.Filter and wash the ppt.make up the filtrate upto 250 ml with distilled water.Titrate it in the same way as in step 1.let the volume of EDTA used is v3 ml.

Slide 13: 

Calculations: 1 litre of SHW = 1 gm. Of CaCO3 1 ml of SHW = 1 mg. of CaCO3 v1ml of EDTA = 20 ml SHW 1 ml of EDTA = 20/v1ml SHW 1 ml of EDTA = 20/v1mg CaCO3 20 ml of hard water = v2ml of EDTA solution 1 ml of hard water = v2/20 ml EDTA solution = v2/20 x 20/v1mg. CaCO3 1000 ml hard water = v2/v1x 1000 ppm Total hardness = v2/v1x 1000 ppm

Slide 14: 

20 ml boiled hard water = v3ml EDTA solution 1 ml boiled water = v3/20 ml EDTA solution = v3/20 x 20/v1 mg. CaCO3 1000 ml boiled water = v3/ v1x 1000 mg. CaCO3 Permanent hardness = v3/ v1 x 1000 ppm Temporary hardness = Total hardness- permanent hardness Temporary hardness = v2– v3 x 1000 ppm v1

Slide 15: 

Alkalinity of water may be defined as its capacity to neutralise acids. The alkalinity of water may be due to the presence of :- OH- ions CO3-2 ions HCO3- ions When these ions react with acids following reactions occur:- OH- + H+ H2O P CO3-2 + H+ HCO3- M HCO3- + H+ H2O + CO2

Slide 16: 

The titration of water sample with standard acid upto phenolphthalein end point (P) marks the completion of reactions (i) and (ii) only.While the titration of water sample with standard acid upto methyl orange end point (M) marks the completion of reactions (i),(ii) and (iii) So, P = OH-+ ½ CO3-2 M= OH- + CO3-2 + HCO3- The alkalinity of water may be due to the presence of :- OH- only CO3-2 only HCO3- only

Slide 17: 

(iv) OH- and CO3-2 both (v) CO3-2 and HCO3- both But it can never be due to the presence of OH- and HCO3- together because they combine to form CO3-2 and H2O. OH-+ HCO3- CO3-2 + H2O Procedure:- Step 1. Take 10 ml of water sample in a conical flask.Add to it 2 drops of Phenolphthalein.The colour becomes pink.Titrate it with N/50 H2SO4 solution,till the pink colour is discharged. .let the volume of acid used is A ml.

Slide 18: 

Step 2. To the same solution add 2 drops of Methyl orange.The colour becomes yellow.titrate it with N/50 H2SO4 till it becomes pink in colour.Let the total volume is B ml. Phenolphthalein Alkalinity i.e P Water vs Acid N1V1= N2V2 N1 x 10 = N/50 x A N1 = N/50 x A/10 Phenolphthalein alkalinity(P)=A/500 x 50 x 1000 ppm

Slide 19: 

Methyl Orange Alkalinity (M) Water vs Acid N1V1 = N2V2 N1 x 10 = N/50 x B N1 = N/50 x B/10 Methyl Orange alkalinity(M)= B/500 x 50 x 1000 ppm

Slide 20: 

Nature of alkalinity

Slide 21: 

Boiler Troubles Sludge is soft, loose precipitate that floats over the surface of water.Salts like MgCl2,MgCO3 ,CaCl2 ,MgSO4 are responsible for formation of sludge. Disadvantages of sludge formation:- Sludges are bad conductors of heat,so wastage of fuel occurs. Sludge cause choking of pipes. Removal of sludge:- It can be removed by blow down operation i.e. is removal of concentrated water and filling the boiler with fresh water.

Slide 22: 

2.Scales are the hard deposits sticking to the inner walls of the boiler.They may be formed due to following reasons:- Hydrolysis of magnesium salts: MgCl2 + 2H2O Mg(OH)2 +2HCl (ii) Decomposition of calcium bicarbonate: Ca(HCO3)2 CaCO3+ CO2+ H2O (iii) On continuous heating CaSO4 present in hard water gets precipitated asnscalec. (iv) If silica is present in hard water then it forms calcium and magnesium silicates(CaSiO3 and MgSiO3 which deposit on the walls as scales.

Slide 23: 

Disadvantages of scales: Wastage of fuel Decrease in efficiency Lowering of boiler safety due to overheating Danger of explosion Removal of scales: Scales can be removed by thermal shocks i.e. by heating the boiler and suddenly cooling it. Silicates and calcium sulphats are removed by dissolving them with EDTA solution. CaCO3 can be removed by dissolving in 10% HCl. Loose scale can be removed by scratching with a knife and frequent blow down operation.

Slide 24: 

Prevention of scale formation can be done by two methods ; 1.External treatment:in external treatment the water is softened by either lime soda process or Zeolite process or by Ion exchange resin process and then fed in the boiler. 2. Internal treatment:The treatment of water is done inside the boiler by any of the following proces:- (i) Phosphate conditioning:In this method sodium phosphate is added to the water inside the boiler which reacts with Ca and Mg salts and form precipitate which can be removed by blow down operation.

Slide 25: 

3MgCl2+2NA3PO4 Mg3(PO4)2 + 6NaCl 3CaCl2+ 2Na3PO4 Ca3(PO4)2+ 6NaCl (ii) Calgon Conditioning:Calgon is sodium hexametaphosphate Na2[Na4(PO3)6] which reacts with CaSO4 to form soluble complex. 2CaSO4+ Na2[Na4(PO3)6] Na2[Ca2(PO3)6] +2Na2SO4 Boiler Corrosion is loss of boiler body or its useful properties by chemical or electrochemical interaction with its environment. It may be due to following reasons:- (i) Dissolved carbondioxide in water which is formed by decomposition of bicarbonates forms carbonic acid which corrodes boiler.

Slide 26: 

Ca(HCO3)2 ∆ CaCO3+ H2O + CO2 Calcium bicarbonate Calcium carbonate insoluble Mg(HCO3)2 ∆ MgCO3+ H2O + CO2 Magnesium bicarbonate Magnesium carbonate insoluble CO2 + H2O H2CO3 Carbonic acid Removal: (a) It can be removed by adding ammonium hydroxide. CO2 + 2 NH4OH (NH4)2CO3 + H2O (b) By mechanical deaeration.

Slide 27: 

(ii) Dissolved oxygen present in water attacks the boiler material and forms iron rust. [Fe Fe+2 +2e ] x 2 at anode O2 +2H2O +4e 4OH- at cathode 2Fe + O2 + 2H2O 2Fe+2 + 4OH- 2Fe(OH)2 4Fe(OH)2 + 2H2O +O2 4Fe(OH)3 Fe2O3.xH2O Rust Removal: (a) O2 is removed by adding Na2SO3 ,Hydrazine etc.

Slide 28: 

2Na2SO3 +O2 2Na2SO4 N2H4 + O2 N2 + 2H2O (b) It is also removed by mechanical deaeration. (iii) By acids: MgCl2 on hydrolysis forms acid which corrodes the boiler material. MgCl2 + 2H2O Mg(OH)2 +2HCl Fe +2HCl FeCl2 + H2 FeCl2 + 2H2O Fe(OH)2 +2HCl Removal: It can be removed by neutralising the acid with alkali.

Slide 29: 

Caustic embrittlement is that type of corrosion due to which boiler matrial becomes brittle in presence of high concentration of caustic and static tensile stress.Durin softening by lime soda process ,some sodium carbonate is present in soft water,which form sodium hydroxide at high pressure. Na2CO3 + H2O 2NaOH + CO2 This caustic water into the hair line cracks .gradually its concentration increases which reacts with iron and forms iron ferrate.A concentration cell forms. Iron at stressed part Conc.NaOH Dilute NaOH Iron at unstressed Anode solution solution part cathode

Slide 30: 

Prevention: (i) Using sodium phosphate as softening agent instead of soda lime. (ii) By adding sodium sulphate to boiler water which clogs the hair cracks. (iii) Tanin or lignin is added to boiler water which blocks the hair cracks. Priming is the process of formation of wet steam.It is formed due to: Suspended impurities Sudden boiling High steam velocity Faulty boiler design.

Slide 31: 

Priming can be prevented by; Proper designing Maintaining low water levels Controlled rate of steam velocity Efficient softening Foaming is the process of formation of persistent bubbles which do not break easily.It is caused due to the presence of clay,organic matter,oil,grease.It can be prevented by removing oil,grease,organic matter from water and addition of castor oil to boiler water.

Slide 32: 

Water Softening

Zeolite process : 

Zeolite process Zeolites are hydrated sodium alumino silicates capable of exchanging its sodium ions with hardness producing cations in water. Na2O Al2O3.xSiO2.yH2O , where x=2 to 10 and y= 2 to 6 There are two types of Zeolites:- (i) Natural Zeolites:- Are amorphous and non porous in nature.They are derived from green sand,by washing,heating and treating with NaOH.

Slide 34: 

e.g. Natrolite- Na2O Al2O3.4SiO2.2H2O (ii) Synthetic zeolites are porous and are prepared by heating together solutions of sodium silicate,sodium aluminate and aluminium sulphate. Principle: Zeolites can be represented as Na2Z,from which Na can easily be replaced by Ca and Mg ions present in hard water. Ca(HCO3)2+ Na2Z CaZ + 2NaHCO3 Mg(HCO3)2+ Na2Z MgZ +2NaHCO3

Slide 35: 

CaCl2+ Na2Z CaZ + 2NaCl MgCl2+Na2Z MgZ + 2NaCl CaSO4 +Na2Z CaZ + Na2SO4 MgSO4 +Na2Z MgZ + Na2SO4 Regeneration:- After sometime, sodium Zeolites are completely converted into Calcium and Magnesium Zeolites i.e. get exhausted.The process by which exhausted Zeolite is converted into sodium Zeolite again by treating with 10% brine solution is known as Regeneration.

Slide 36: 

CaZ + 2 NaCl Na2Z + CaCl2 MgZ + 2 NaCl Na2Z + MgCl2 Process:- Hard water is percolated through Zeolite bed in a cylindrical tank.Sodium ions are replaced by Ca2+ and Mg2+ ions to form CaZ and MgZ.After sometimes the bed gets exhausted.At this stage supply of water is stopped and regeneration is carried out,by passing 10% brine solution. Advantages of Zeolite process:- 1. Water of about 15 ppm hardness is obtained.

Slide 37: 

2. The equipment is compact and occupies less space. 3. It requires less time for softening. 4. There is no danger of sludge formation because impurities are not precipitated. Disadvantages of zeolite process:- Only cations are removed and not anions. If water is turbid it clogs the pores of zeolite bed and makes it inactive.So the suspended impurities must be removed from hard water by coagulation and filtration first, before the water is fed to the zeolite bed.

Slide 38: 

3. Mineral acids destroy the zeolite bed,so they must be neutralised befor hand. 4. Acid radicals which are not removed during softening cause caustic embrittlement and boiler corrosion. NaHCO3 NaOH + CO2 CO2 + H2O H2CO3 5. If large quantities of Fe2+ and Mn2+ are present in water ,the zeolite is converted into iron and manganese zeolite which can not be regenerated.

Slide 40: 

Lime Soda process Lime soda process is based upon the precipitation of soluble calcium and magnesium salts by addition of Lime and Soda.Calcium ions are precipitated as CaCO3 and magnesium ion as Mg(OH)2 . Lime soda process is of two types:- Cold lime soda process:-In this process softening of water is carried out at room temperature by adding lime and soda.A small amount of coagulant like alum is added to precipitate finely divided Precipitates of CaCO3 and Mg(OH)2

Slide 41: 

(ii) Hot lime Soda process:-In this process water is treated with lime and soda at temperature of 80-150o C.No coagulant is needed in this process. Two main types of process will be discussed here. Continuous cold Lime-soda process:- The raw water and calculated amount of Lime and soda are continuously fed from the top into an inner chamber provided with paddle stirrer at room temperature,when softening of water takes place and sludge settles down and soft water goes up in the outer chamber, where it passes through wood filter.Filtered water comes out through the outlet.

Slide 43: 

Batch Process (Intermittent type cold lime-soda process) It consists of a pair of tanks which are used in turn for softening of water.Raw water is passed from one side and lime and soda from another side and stirring is continued.Coagulant is also added.After sometime ,stirring is stopped,sludge settles down and soft water is sent to filtering unit from where filtration occurs and softened water is obtained.

Slide 44: 

Continuous type hot soda process consists of (i) Reaction tank:-Raw water and chemicals are added .Superheated steam is also passed. (ii)Sedimentation tank:-The sedimentation of sludge takes place here. (iii) Sand filter :- Here sludge is removed by sand filters.

Slide 46: 

Advantages of lime-soda process: It is very economical. Lesser amount of coagulants are required. Iron and manganese are also removed . Soft water obtained by this method is alkaline and so less corrosion. The alkaline water reduces the amount of pathogens. Disadvantage of lime-soda process: Disposal of large amount of sludge is a problem. Soft water is of 15 ppm hardness, not ideal for boilers. Skilled supervision is required.

Slide 47: 

Ion exchange process Ion exchange resins are high molecular mass insoluble cross linked organic polymers which are capable of exchanging cations and anions from hard water.They are of two types:- 1. Cation Exchange Resins contain functional groups like –COOH,-SO3H etc. which are capable of exchanging their H ions with the cations.They are denoted as RH.They are mainly carboxylate or sulphonated styrene and divinyl benzene copolymers.e.g. Zeocarb,Amberlite IR-120,Dowex-50,Duolite etc.

Slide 49: 

2. Anion Exchange Resins contain basic functional group like –NH2 ,=NH etc. as hydrochloride or hydroxide which are capable of exchanging their OH- ion with anions present in hard water.They are represented as ROH.They are mainly styrene divinyl benzene or amine-formaldehyde copolymers.e.g. Amberlite-400,Dowex-3.

Slide 51: 

Principle:-When hard water is passed through cation exchange column H+ ion are replace by cations present in hard water. 2RH+ + Ca2+ R2Ca + 2H+ 2RH+ + Mg2+ R2Mg + 2H+ Then water is passed through anion exchange column,where anions are removed from water. 2R’OH + SO42- R’2SO4 +2OH- R’OH + Cl- R’Cl + OH- R’OH + HCO3- RHCO3 + OH- The H+ and OH- ions released will combine to form water.

Slide 52: 

Regeneration:-As the cation and anion exchangers are used continuously they loose their ion exchanging cpacity and become exhausted.They are treated with dil.HCl/ dil.H2SO4and dil. NaOH. R2Ca +2H+ 2 RH + Ca2+ R2SO4 + 2OH- 2 ROH + SO42- Mixed bed deioniser/demineraliser:It consists of cation exchanger and anion exchanger in a single unit.The hard water is passed through it .Soft water obtained by this method is free from both cations and anions.

Slide 54: 

Advantages of ion Exchange Process:- Soft water of 0-2 ppm hardness is produced Both cations and anions are removed by this method. Osmosis :- Definitions Osmosis: The flow of solvent from a region of low concentration to region of high concentration , when two solutions of different concentrations are separated by a semipermeable membrane is known as osmosis.

Slide 55: 

Osmotic pressure is the hydrostatic pressure which must be applied to the solution of higher concentration, in order to just prevent osmosis. Reverse osmosis:-if a hydrostatic pressure in excess of osmotic pressure is applied to the high concentration side , the flow of solvent gets reversed and this process is called Reverse osmosis.

Slide 57: 

Potable water is the water which is safe to drink.It should have following characteristics:- 1.It should be colourless,odourless and clear. 2. It should have pleasant taste. 3. It should be free from objectionable gases (CO2 ,NH3 ,H2S) and minerals like Pb,Mn,Cr,As etc 4. pH should be about 8.0 5. It should be soft water. 6. Turbidity should be less than 10 ppm.Free chlorine should be less than 0.1-.2 ppm. 7.It should be free from pathogens.

Slide 58: 

Polished water :- The extremely pure water used for washing in the manufacture of delicate electronic equipments like TV tubes,calculators,watches,transistors etc.It is prepared by passing water through column of cation and anion exchangers and then through bed of mixed exchange resins.