Water Technology Ppt

Water Technology Introduction: Composed of hydrogen and oxygen Occupies a unique position in industries. Most important use is in the steam generation. Water is also used as coolant in power and chemical plants. Inadditionitiswidelyusedinotherfieldssuchas production of steel, rayon, paper, atomic energy, textiles etc. CHARACTERISTICS IMPARTED BY IMPURITIES IN WATER: The natural water is usually contaminated by different types of impurities.Physical impurities Color Turbidity and sediment Taste and odour Bacterial impurities Microorganisms(algae,pathogenicbacteria,fungi,viruses,pathogens, parasites worms etc.) Suspended impurities Dust particles, clay and sand Organic suspended impurities Silica aluminium hydroxide, ferric hydroxide colouring matter Radioactive Substances Chemical impurities in water: Inorganicandorganicchemicalsreleasedfromdyes,paints, drugs, pesticides, textiles, tanneries etc . Acidity from industrial wastage like acid, mine, drainage, etc. UsuallyacidityiscausedbythepresenceoffreeCO2,mineral acid and weakly dissociated acids. Dissolved gases (O2, CO2, NH3) Mineral matters have origin from rocks and industrial effluents.Theseincludemineralacids,Ca2+,Mg2+,Na+,K+,Fe2+,Cl-, NO3-,F-, SiO2 etc. Contaminant Potential Health Effects from Ingestion of Water Sources of Contaminant in Drinking Water AntimonyIncrease in blood cholesterol; decrease in blood sugar Discharge from petroleum refineries; fire retardants; ceramics; electronics; solder ArsenicSkin damage or problems with circulatory systems, and may have increased risk of getting cancer Erosion of natural deposits; runoff from orchards, runoff from glass & electronics production wastes Asbestos (fiber >10 micrometers) Increased risk of developing benign intestinal polyps Decay of asbestos cement in water mains; erosion of natural deposits BariumIncrease in blood pressureDischarge of drilling wastes; discharge from metal refineries; erosion of natural deposits BerylliumIntestinal lesions Discharge from metal refineries and coal-burning factories; discharge from electrical, aerospace, and defense industries Cadmium Kidney damage Corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints Chromium (total) Allergic dermatitisDischarge from steel and pulp mills; erosion of natural deposits Copper Short term exposure: Gastrointestinal distressLong term exposure: Liver or kidney damagePeople with Wilson's Disease should consult their personal doctor if the amount of copper in their water exceeds the action levelCorrosion of household plumbing systems; erosion of natural deposits Cyanide (as free cyanide) Nerve damage or thyroid problemsDischarge from steel/metal factories; discharge from plastic and fertilizer factories ParametersUnitsWHO standard BIS Standard pH6.5-9.26.5-8.5 TDS (Total dissolved salts) mg/l 500500 Sulphatemg/l 200200 Chloridemg/l250200 Cyanidesmg/l0.050.05 Fluridemg/l1.50.6-1.2 Aluminiummg/l0.2 Arsenicmg/l0.010.01 Drinking water standards comparative table ParametersUnitsWHO standard BIS Standard Cadmiummg/l0.0030.01 Leadmg/l0.010.05 Mercurymg/l0.0010.001 Sodiummg/l200 Zincmg/l35 Drinking water standards comparative table WHO- World Health Organization BIS - Bureau of Indian standardsHard water Has high mineral content (in contrast with soft water). Hardness in water is defined as the presence of multivalent cations. It can cause water to form scales and a resistance to soap. It can also be defined as water that does not produce lather with soap solutions, but produces white precipitate (scum). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Types of hardness: i) Temporary hardness ii) Permanent hardness Temporary hardness: Combination of calcium ions and bicarbonate ions in the water. Itcan be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate. The following is the equilibrium reaction when calcium carbonate (CaCO3) is dissolved in water: CaCO3(s) + CO2(aq) + H2O Ca2+(aq) + 2HCO3-(aq) Permanent hardness: Usuallycausedbythepresenceinthewaterofcalciumand magnesiumsulfatesand/orchlorideswhichbecomemore soluble as the temperature rises. Permanent hardness can be removed using a water softener or ionexchangecolumn,wherethecalciumandmagnesiumions are exchanged with the sodium ions in the column. Inindustrialsettings,waterhardnessmustbeconstantly monitored to avoid costly breakdowns in boilers, cooling towers and other equipment that comes in contact with water. Hardnessiscontrolledbytheadditionofchemicalsandby large-scale softening with zeolite(Na2Al2Si2O8.xH2O) and ion exchange resins. Unit of hardness: Hardnessisexpressedintermsofequivalentofcalcium carbonate. [It is the most insoluble salt that can be precipitated in water treatment.] Hardness in Terms of Calcium Carbonate Equivalents:ItiscustomarytoexpresshardnessintermsofequivalentsofCaCO3.The reasonforchoosingCaCO3asthestandardforcalculatinghardnessof water is due to: 1. Itsmolecularweightisexactly100,whichmakesmathematical calculations easier. 2. Itisthemostinsolublesalt,thuscanbeeasilyprecipitatedinwater treatmentprocesses.TheCaCO3equivalentsforvarioussaltsareas follows: 100g of CaCO3 111g of CaCl2 136 g of CaSO4 95 g of MgCl2 120 g of MgSO4 162g of Ca(HCO3)2 146 g of Mg(HCO3)2 164 g ofCa(NO3)2 44 g of CO2 148 g of Mg(NO3)2 If x g of CaCl2 s present in a water sample, then amount of CaCl2 present on terms of its equivalent will be: 1 g mole of CaCl2 1 g mole of CaCO3 111 g of CaCl2 100 g of CaCO3 55.5 g of CaCl2 50 g of CaCO3x g of CaCl2=50/55.5*x g of CaCO3 In general calcium carbonate equivalent of hardness is given by

Wt. of the substance producing hardness X Eq.wt. of CaCO3

= ----------------------------------------------------------------------------Eq.wt.of substance

Various units used to express hardness of water are as under Parts per million (ppm): calcium carbonate equivalent per 106 parts of water Milligramsperliter(mg/L):numberofcalciumcarbonateequivalenthardness present per liter of water DegreeFrench(oFr):1partofcalciumcarbonateequivalenthardnessper70,000 parts ClarkesDegree(oCl):1partofcalciumcarbonateequivalenthardnessper105parts of water 1ppm=1mg/L=0.1 oFr=0.07oCl Very Soft water0-70ppm of CaCO3

Softwater 70-140 ppm of CaCO3 Slightly hard water140-210 ppm of CaCO3 Moderately hard210-320 ppm of CaCO3 Hard water 320-530 ppm of CaCO3 Very hard water 530ppm of CaCO3 Determination of total hardness of water: EDTA method EDTA is a weak acid and has a structure as shown below.

CH2CH2N NCH2COO-CH2COO-O-OCH2CO-OCH2CCH2CH2N NCH2COOHCH2COOHHOOCH2CHOOCH2C1.a1.b 1.a. The structure of EDTA

1.b.Thestructureof tetracarboxylate[EDTA]4-ion formedbythedissociationof EDTA Tetracarboxylate ion(1.b) is electron rich having six bonding sites. The four carboxylate groups and the two nitrogen atoms. Each site has an electron pair available for bonding. The [EDTA]4- anion wraps itselfaround a Ca2+ or Mg2+ ion so that all sixelectronspairsaresharedwiththemetalionasshowninthe figure. In this manner [EDTA]4- forms strong 1:1 complexes known as chelates with metal ions like Ca2+ and Mg 2+. Structure of [Ca-EDTA]2- chelate Structure of [Mg-EDTA]2- chelate In an aqueous solution buffered at pH 10, Erio T also dissociate forming [H-Erio T ]2- ion a blue ion that bonds witheitherMg2+orCa 2+iontoformawineredcomplex.The reaction of [H-Erio T]2- ion with Ca2+ and Mg2+ ions are reversible. Mg 2+(aq)+ [ H-Erio T]2-(aq,blue)+ H2O[Mg-Erio T]-(aq,wine red)+ H3O (aq) Ca 2+(aq) + [ H-Erio T]2-(aq,blue) + H2O[Ca-Erio T]-(aq,wine red) + H3O (aq) When the end point is reached [EDTA]4- anion breaks up the wine red [Mg-Erio T]- and [Ca-Erio T]- complexes releasing the [ H-Erio T]2- ion and hencethe solution changes from wine red to permanent blue color. [Ca-Erio T]-(aq,wine red) +H3O(aq)+[EDTA]4-[Ca-EDTA] aq +[ H-Erio T]2(aq,blue)+ H2O

[Mg-Erio T]-(aq,wine red)+H3O(aq) +[EDTA]4- [Mg-EDTA] aq+[ H-Erio T]2-(aq,blue) + H2O

Procedure: Total hardness:Pipette out 50 ml of the sample of water into a clean titration flask, add 1 ml of NH3-NH4Cl buffer solution and 3-4 drops of indicator. TitrateagainststandardEDTAtillthecolorchangesfromwineredtoclear blue without any reddish tinge. Let the volume of EDTA required be v1 ml. Permanent hardness: Transfer50mlofthesampleofwaterintoaclean500mlbeakerandboil gently for 20-30minutes. Cool and filter it directly into a 250 ml conical flask.Add 1 ml of buffer solution followed by 3-4 drops of indicator. Titrate against standard EDTA as described above. Let the volume of EDTA required be v2 ml. Calculation : 1000ml of 1 M EDTA = 100g CaCO3( Mol.weight of CaCO3 =100g) 1ml ofZ M EDTA = 100/ 1000 g of CaCO3 V1 ml of 0.01 M EDTA = V1 X Z X 100 -------------------------- g of CaCO3 1000 50 ml of water sample contains = V1 X Z X 100 -------------------------- g of CaCO3 1000 106 ( 1 million ) ml of water sample contains = V1 X Z X 100 X 106 ----------------------- g of CaCO3 1000 X 50 SimilarlyPermanent hardness = V2 X Z X 100 X 106 ----------------------------- g of CaCO3 1000 X 50 Softening of water: Ion exchange or deionization or demineralization process Ion-exchange resins are widely used in different separation,purification,anddecontaminationprocesses.Themost common examples are water softening and water purification. Anion-exchangeresinorion-exchangepolymerisan insolublematrix(orsupportstructure)normallyintheformof small(12 mm diameter) beads. Insoluble cross linked long chain organic polymer and thefunctional groups attached to the chains are responsible for the ion exchange properties.

Materialhashighlydevelopedstructureofporesonthe surface ofwhich is sites with easily trapped and released ions. Thetrappingofionstakesplaceonlywithsimultaneous releasingof other ions; thus the process is called ion-exchange Resins containing acidic functional groups are capable ofexchanging their H+ ions with other cationsResins containing basic functional groups are capable ofexchanging their anions with other anions. The ion exchange resin may be classified as Acidic or cationic exchange resin Basic or anion exchange resinCation exchange resins(RH+) They are mainly styrene-divinyl benzne copolymers which on sulphonationorcarboxylationbecomecapabletoexchange their hydrogen ions with the cations in the water. Acidic or cationic exchange resin (Sulphonate form) Anion exchange resins: Theyarestyrenedivinylbenzeneoramine-formaldehyde copolymerizationwhichcontainsquaternaryammoniumorquaternary phosphonium or tertiary tertiary sulphoniumgroups as an integral part of theresinmatrix.TheseaftertreatedwithdilNaOHbecomescapableof exchanging their OH- ions with anions of water. Basic or anion exchange resin (hydroxide form) Ion exchange or deionization or demineralization process The hard water is passed first through cation exchange column: 2RH++ Ca2+R2Ca2++2H+

2RH++ Mg2+R2Mg2++ 2H+

After cation exchange column the hard water is passed through anion exchange resin column : ROH-+ Cl- RCl-+OH- 2ROH-+ SO42- R2SO42-+ 2OH- H ++ OH- H2O Thus water coming out from the exchange is free from cations as well as anions. Ion free water is known as deionized or demineralised water. Regeneration: Cation exchange column is regenerated by passing a solution of dil HCl or dil H2SO4. The regeneration can be represented asR2Ca2++ 2H+2RH + Ca2+ Exhausted anion exchange column is regenerated by passing a solution of dil. NaOH. The regeneration can be represented as R2SO42- + 2OH- 2ROH + SO42- Advantages: Can be used to soften highly acidic or alkalinewaters. It produces water of very low hardness. Disadvantages: The equipment is costlyExpensive chemicals are needed. Output of the process is reduced if watercontains turbidity.(turbidity must be below10ppm) Mixed bed deionizer: Consistsofasinglecylindercontaininganintimatemixtureof hydrogen exchanger and strongly basic anion exchanger. Water passed through this bedcomes in contact with two kind of the resin alternatively. Theneteffectofthisexchangerisequivalenttopassingwater through a series of several cation and anion exchangers. The outgoing water from this mixed bed exchanger contains less than 1ppm of dissolved salts. Regeneration : The mixed bed is back washedLighter anion exchanger gets displaced Forms an upper layer above the heavier cation exchanger. RegenerationofAnionexchanger-Passingcausticsodafromthe top and then rinsed.Regeneration of Cation exchanger Passing H2SO4 solution. PP Boiler feed Water(Scales and Sludges) In boilers, water evaporates continuously concentrations of the dissolved salts increases whenconcentrationsofdissolvedsaltsreachsaturationpoint, theyform precipitates on the inner walls of the boiler. SludgeScale Loose slimy precipitateAhard, adhering crust/coating on the inner walls of the boiler, Scale and sludge in Boilers Disadvantages of sludge formation Sludges are poor conductor of heat. Tend to waste a portion of heat generated. Sludges get entrapped in the scale and bothget deposited as scales. Disturbs the working of the boiler. Prevention of sludge formation: By using well softened water By frequently blow-down operation, i.e., drawing off a portion of the concentrated water. (In high-pressure boilers) Formation of scales may be due to (1) Decomposition of calcium bicarbonate: Ca (HCO3)2 CaCO3 + H2O + CO2 CaCO3 + H2O Ca (OH) 2 (soluble) + CO2 (In low-pressure boilers) (2) Deposition of Calcium Sulphate:Solubilityofcalciumsulphateinwaterdecreasewithriseof temperature.HenceCaSO4getsprecipitatedashardscaleontheheated portions of the boiler. Dissolved Mg salts undergo hydrolysis forming magnesium hydroxide precipitate, which forms a soft type of scale (3) Hydrolysis of magnesium salts:

MgCl2 +2H2O Mg(OH)2+ 2HCl (Scale)

(4) Presence of silica:SiO2,present deposits as calcium silicate (CaSiO3) and / ormagnesium silicate (MgSiO3).These deposits stick on the inner side of the boiler surface.Difficult to remove.

Lowering of boiler safety Due to scale formation, over heating of boiler is done.Causes distortion of boiler tube.High pressure boiler is unsafe to bear the pressure of the steam. Decrease in efficiencyScales maydeposit in the valve and condensers of the boiler and choke them partially.

Danger of explosion When thick scales crack, the water comes suddenly in contact with over-heated iron plates.

Disadvantages of scale formation Wastage of fuelScales have a low thermal conductivity Rate of heat transfer from boiler to inside water is greatly decreased.

Removal of scales With the help of scraper or piece of wood or wire brush. By giving thermal shocks, if they are brittle. By dissolving them by adding chemicals, (5-10% HCl, EDTA) if they are adherent and hard. By frequent blow -down operation, if the scales are loosely adhering. Prevention of scales formation

(1)ExternalTreatment:Includesefficientsofteningofwater (i.e., removing hardness-producing constituents of water)

(2) Internal Treatment: Accomplished by adding a proper chemical to the boiler water either:(a) to precipitate the scale forming impurities in the form of sludges,which can be removed by blow-down operation, or(b)toconvertthemintocompounds,whichwillstayindissolved form in water and thus do not cause any harm. Priming and Foaming: Priming: Whenaboilerissteamingsomeparticlesoftheliquidwaterare carried along-with steam. Priming is caused by: the presence of large amount of dissolved solids high steam velocities sudden boiling improper boiler design and sudden increase in steam- production rate. FoamingProduction of persistent foam or bubbles in boilers. Isduetopresenceofsubstances(oils)whichreducethe surface tension of water. Priming and foaming usually occur together. They are objectionable because (i)Efficiencyreducesasdissolvedsaltsinboilerwaterget depositedonsuper-heaterandturbineblades,aswater evaporates. (ii) Life of the machinery may decrease as dissolved salts may enter the parts of other machinery. (iii)Maintenanceoftheboilerpressurebecomesdifficult,as actualheightofthewatercolumncannotbejudgedproperly.

Priming can be avoided byFitting mechanical steam purifiers. Avoiding rapid change in steaming rate. Maintaining low water levels in boilers. Efficient softening and filtration of the boiler-feed water. Foaming can be avoided by Adding anti-foaming chemicals like castor oil. Removing oil from boiler water by adding compounds like sodiumaluminate.