Unit1 Water treatment and its industrial application Water
- Slides: 87
Unit-1 Water treatment and its industrial application
Water Treatment Water is an wonderful & useful compound of the living being without food human can survive for a number of days but without it one cannot be survive
Sources of Water Sources of water is devised into four categories 1. Surface water. 2. Underground water. 3. Rain water. 4. Estravive & sea water. On the basis of industrial used water is devided into three classes
(i). Moorland water (a). Fairly constant composition. (b). Clear and brown colored. (c). Slight acetic due to resoles. (d). Hardness is low.
(ii). Lowland Surface Draimage (a). Widely vary in composition. (b) It is not colored. (c). Hardness is high. (d). Serious scale formation in boiler is produced by this water.
(iii). Deep Well Water (a). Fairly constant in composition. (b). Colorless and clear. (c). It contains no alkali hardness. (d). Serious scale formation in boiler.
Impurities The impurities present in water may be divided into following Dissolved impurities Suspended impurities Colloidal impurities Bacterial impurities
Classes (i). Dissolved impurities. (A). Inorganic salt: - (a) Cations: - Ca+2, Mg+2, Na+, K+, (b). Anions: - Cl -, SO 4 - -, NO 3 -, HCO 3 -, F-. (B). Gases: - CO 2, NH 3, H 2 S. (C). Inorganic salt (ii). Suspended impurities: (a). Clay and sand (b). Organic e. g. oil globles, etable and animal matter (iii). Colloidal impurities: - Al(OH)3, Fe(OH)3, coloring matter. (iv). Bacterial impurities: - Micro organisms, animal & vegetable life
Hardness of Water Hardness of the water is that characteristic, which present the lathering of soap. The hardness of water is due to the presence of salt of Ca & Mg. when the hardness water is treatment with soap. It does not produce lather but it forms a white scum or PPT. Typical reaction of soap is take place with hard water. 2 C 17 H 35 Coo. Na + Ca. Cl 2 ---> (C 17 H 35 Coo)2 Ca + 2 Na. Cl The water which does not produce lather with soap solution but forms white curd called hard water. The water which produce lather with soap solution is called soft water.
Hardness is mainly two types (i). Temporary Hardness or carbonate hard: -It is due the presence of bicarbonates of Ca, Mg. The temporary hardness is mostly destroyed by boiling of water. Ca(HCO 3)2 Ca. CO 3 + H 2 O + CO 2 Mg (HCO 3)2 Mg. CO 2 + H 2 O + CO 2 (ii). Permanent or non carbonate hardness: - It is due to the presence of chlorite hardness is not destroyed on boiling.
Unit of Hardness (i). Part per million (PPM): - The part of calcium carbonate equivalent hardness per 106 part of water. 1 PPM= 1 part of Ca. CO 3 ea. Hardness in 106 part of water. (ii). Milligrams per liter (mg/l): - The number of milligrams of Ca. CO 3 equivalent Hardness present per liter of water. 1 mg/l= 1 mg of Ca. CO 3 ea. Hardness in 1 liter of water. But 1 L of water weight= 1 kg =1000 gr= 1000 x 1000=10 6 mg. 1 mg/l= 1 mg of Ca. CO 3 ea per 106 mg of water. = 1 part of Ca. CO 3 ea. Per 106 parts of water= 1 ppm.
(iii). Clarke’s degree: - (. Cl) It is parts of Ca. CO 3 equivalent Hardness per 70, 000 parts of water 1 Clarke= 1 gram of Ca. CO 3 ea hardness per gallon of water. 1 Clarke= 1 part of Ca. CO 3 ea. Hardness per 70, 000 part of water. (iv). Degree French: - ( 0 Fr) is the part of each ea. Hardness per 105 parts of water 10 Fr= 1 part of Ca. CO 3 hardness ea. Per 105 part of water
Relationship between various unit of hardness 1 ppm= 1 mgl. L=. 10 Fr=. 070 Cl 1 mgl. L= 1 ppm=. 10 Fr=. 070 Cl 10 Cl= 1. 430 Fr= 14. 3 ppm= 14. 3 mgl. L 10 Fr= 10 ppm= 10 mgl. L=. 70 Cl
Water Softening Method Lime soda process Cold lime Hot lime Zeolite process In exchange process
(1). Cold lime soda softener: It is mainly four types. (a). The intermittent type (batch process). (b). The conventional type. (c). The catalyst (d). The sludge blanket type.
(1). The Intermittent type: - This process consist of two sets of tanks which are used in turn for softening of water each tank consist of outlets for raw water & chemicals for sludge and softened water and a mechanical stirrer, raw water and calculated quantities of chemicals are slow added into tank simultaneously with the help of stirrer some sludge from previous operation is added in it which forms nucleus for fresh precipitation , stirring is stopped and the sludge formed is allowed to settle.
(2). Conventional type: - In this process the raw water & chemicals fed from the top into an inner chamber of vertical circular tank provided with a paddle stirrer. Due to continuo's stirring softening reaction is take place, sludge sattle at bottom from where it is remove & the softened water passes through fiber filter.
(3). The catalyst or spiral Reactor type: - It is conical tank consist of 2/3 of finely divided granular catalyst. The raw material & water enter spiral upwards through the suspended catalyst bed. The retention time is 8 to 10 min. The sludge formed during reaction deposited on catalyst grains. The softened water rises to the top from where it is drawn off.
Hot lime soda process: (1). Elevated temp. not only accelerate the actul chemical reaction but also reduce the viscosity of the water and increase the rate of aaregation of the particals (2). Thus both the settling rates and filtrations rates are in creased so. (3). The softing capacity of the hot lime soda process will be several times higher than the cold process since. (4). The sludge formed settles down rapidly there is no need of adding any coagulants. (5). Dissolved gases are driven out and the softing water having relatively lower residual hardness, the unit of hot lime soda water consist of settling tank and a filter. If the water is alkaline filtration through sand gravel beds. If the precipitation in complete in the softing tank occurs in pires, storage tanks and even in boiler.
treatment by lime soda process: 1. One equivalent of calcium required one equivalent of lime Ca(HCO 3)2 + Ca(OH)2 2 Ca. CO 3 + 2 H 2 O 2. One equivalent of magnesium temporary hardness requires two equivalents of lime Mg(HO 3)2 + 2 Ca(OH)2 Mg(OH)2 + 2 Ca. CO 3 + 2 H 2 O 3. One equivalent of magnesium temporary hardness requires one equivalent of soda Ca. SO 4 + Na. CO 3 Ca. CO 3 + Na 2 SO 4 4. One Equivalent of magnesium permanent hardness requires on equivalent of lime and on equivalent of soda Mg. SO 4 + Ca(OH)2 + Na. CO 3 Mg(OH)2 + Ca. CO 3 + Na 2 SO 4
Advantage of soda lime process 1. It is very economical 2. If this process is combined with sedimentation with coagulation lesser amount of coagulants shall be needed. 3. The PH value of the treated water is increaser so, the corrosion of the distribution pipes is redo. 4. To, certain extent, iron and manganese are also removed. 5. Due to alkaline nature of the water pathogenic bacteria's is reduced.
Disadvantage of soda lime process 1. Careful operation and skilled supervision is required. 2. Disposal of large amounts of sludge causes a problem. 3. This can remove hardness only upto 15 ppm, which is not good for boilers.
Zeolite or permutit process Zeolite is hydrated sodium alumina silicate, capable of exchanging reversible its sodium ions for hardness producing ions in water. The chemical structure of sodium zeolite may be Na 2 O. Al 2 O 3, x. Sio 2, y. H 2 O, where x= 2 -10 and y= 2 -6 Zeolite are also known as permutits Zeolite are of mainly two types. 1. Natural zeolite or no porous: - Example: - natrolite, Na 2 O, Al 2 O 3. 4 Si. O 2, 2 H 2 O 2. Synthetic Zeolite: - Are porous and possess gel structure. They are prepared by heating together chenaclay, faldspar, and soda-ash
Process For softening water by Zeolite process hard water is percolated at a specified rate through a bed of zeolite kept in a cylinder. The hardness – causing ions are retained by the zeolite as white the outgoing water contains sodium after reactions taking place during the softening process are. Na 2 Ze + Ca(HCO 3)2 Ca. Ze + 2 Na. HCO 3 Na 2 Ze + Mg(HCO 3)2 Mg. Ze + 2 Na. HCO 3 Na 2 Ze + Mg. Cl 2 Mg. Ze + 2 Na. Cl
Regeneration After some time, the zeolite is completely converted into Ca & Mg zeolite. At this stage, the supply of hard water is stopped in the exhausted, zeolite is reclained by treating the bed with a concentrated brine solution. Cage or Mg. Ze + 2 Na. Cl Na 2 Ze + Ca. Cl 2
Diagram of zeolite softener
Limitation of zeolite process If the supplied water is turbid it will clog the pores of zeolite bed & marking it inactiue 2. If water contain Fe++ & Mn++ it produce maganese and iron zeolite which cannot be regenerated, so it must be remove first. 3. If minral aids are present, it destroyed the zeolite bed. So it must be neutralized with soda, before admitting the water to zeolite. 1.
Advantages of zeolite process 1. If removed the hardness completely 2. The equipment used is compact & occupying a small space. 3. No, impurities are ppt, so there is no danger of sludge formation. 4. The process is automatically adjusted itself for variation in hardness of incoming water. 5. It is quite clean. 6. If required less time for softening.
Disadvantages of zeolite process Treated water contains more sodium salt than soda lime process. 2. This method olny replaces Ca++ & Mg++ by sodium but leaves acidic ions which causes corrosion and caustic emprittrment. 3. High turbidity water cannot be treated efficiently by this method. 1.
The Comparision between lime soda process & zeolite process Zeolite process 1. Water of 10 -15 ppm residual hardness is obtained. 2. Treated water contained large amount of Na-salt. 3. Cost of plant and material is higher. 4. Operation expanses are lower. 5. It cannot be used for treating acidic water. Lime soda process 1. Water of 10 -15 ppm hardness is obtained. 2. It contain lesser amount of sodium salt. 3. Capital cost is lower. 4. Operation expanses are higher. 5. There are no such limitation.
6. Plant occupies less space. 7. The raw watch to be softened must be free from suspended matter. 8. It can operated under pressure. 9. It involves no problems of setting, coaqulation, kilt ration and removal of sludge. 6. Plant occupies more space 7. It. There are no such limitation. 8. It cannot operated under pressure. 9. It involves difficulties in setting, co-agulation, filtration, eet.
Ion exchange or deionization or demineralization process Ion exchange resins are insoluble & having functional If which is responsible for Ion exchanging properties. The Ion exchange resins may be clasified as 1. Cation exchange resions: -(RH+): - There are mainly styrene divinely bengene co poly mers which on sulphonation or carborelation, becomes capable to exchange their hydrogen ions with the cations in water.
Anion exchange resins (R’-OH-) These are styrene – divinely benzene or amine formaldehide co-polymers, which contains amino or quaternary ammonium as an internal part of the resin matrix.
Process 1. 2. The hard water is passed first through cation exchange column which all the cations like Ca 2+, Mg 2+ etc from it, and equivalent amount of H+ ions released from this column to water. 2 RH+ + Ca 2+ R 2 Ca 2+ + 2 H+ 2 RH+ + Mg 2+ R 2 Mg 2+ + 2 H+ After cation exchange column, the hard water is passed through anion exchange column which removes all the anions like SO 4 -2, Cl-, etc present in water. R’-OH+ + Cl- R’Cl- + OH 2 R’OH + SO 4 -2 R 2’ SO 4 -2 + 2 OH- 3. H+ and OH- ions released from cation exchange columns get combined to produce water molecule H+ + OH- H 2 O The water coming out from the exchange is free from cation as well as anions ion free water is know as demineralised water
Regeneration When capacities of cation and anions exchanger are last. The exhausted cation exchange column is regenerated by passing a solution of dil HCl or dil H 2 SO 4. The regeneration can be represented as R 2 Ca 2+ + 2 H+ 2 RH+ + Ca 2+
Advantages The process can be used to soften highly acidic or alkaline water. 2. It producer water of very low hardness. 1.
Disadvantages The equipment is costly and more expensive chemicals are needed. 2. If water contains turbidity, than the output of the process is reduced 1.
demineralization or deionization In this method water is passed through “mixed – bed” consisting of anion and cation exchange resin. When water is passed through this bed. It comes in contact, a number of times with two kinds of exchanger. The outgoing water from the mixed bed contains less than 1 ppm of salt.
Disadvantages 1. It is very costly process 2. Turbidity of the water reduce the efficiency of the process 3. This process is only used for high pressure boilers.
Boiler - troubles The major boiler troubles caused by the use of unsuitable water are 1. Carry over : -priming & foaming. 2. Scale & sludge formation. 3. Corrosion. 4. Caustic embrittlement.
1. Carry over The phenomenon of carrying of water by steam along with the impurities is called “carry – over” This is mainly due to priming and foaming. priming: - Priming is very rapid boiling of water occurring in the boiler in such a way that some particles are carried a way along with the steam in the form of spay in to the steam outlet.
Priming may be caused by 1. 2. 3. 4. 5. High velocity of steam. High water laud in boiler. Presence of excessive foam on surface of water. Sudden steam demand. Faulty boiler design.
Priming can be minimized by 1. Good boiler design. 2. Maintaining low water level. 3. Avoiding sudden steam demand. 4. Minimizing foaming.
Foaming is the formation of small but persistent bubbles at the water surface. Foaming may causes by soluble salts in water, clay or organic matter, oil or grease in water, finely divided particles of sludge. Foaming can be prevented by removed of the foaming and stabilizing agents, clay and other suspended solids as well as droplets of oil and grease. It can also be controlled by adding anti foaming agents. For avoiding priming and foaming the following limits on total diss.
Solids are usually suggested Type of boiler Water Lancashire Vertical - T. d. s. (ppm) - 2000 to 5000 - 1000 to 1500 - ≤ 3500
Scale and sludge formation in boiler In boiler, water evaporated continuously and the concentration of the dissolve salts increase progressively. When their concentration reach saturation point, they are thrown out of on the inner wall of the boiler. If the precipitation takes place in the form of louse and slimy precipitate, it is called “sludge”. When it is in the forms of adhering crust on the inner walls of the boiler called “scale”.
Sludge 1. 2. 3. 4. It is soft, loose, slimy precipitate It can be scrapped off with wire brush. It is formed at comparatively colder part of boiler. The substance which more soluble in cold water form sludge.
Disadvantages of sludge formation 1. They waste the heat (power conductor) 2. If sludge are formed along with scales then former gets entrapped in the latter and both get deposited as scales. 3. It disturb the working of the boiler.
Prevention of sludge formation 1. By using well soften water. 2. By frequently “blow – down” operation.
Scales are hard deposits, which stick the inner surface of boiler formation of scales may be due to: 1. Decomposition of calcium bicarbonate: Ca(HCO 3)2 Ca. CO 3 + H 2 O + CO 3 2. Decomposition of calcium sulphate: - it is ppt as hard scale on the heated portion of the boiler. 3. Hydrolysis of magnesium salts: Mg. Cl 2 + 2 H 2 O Mg(OH)2 + 2 HCl 4. Presence of silica: - magnesium silicate deposits stick very firmly on the inner side of the boiler surface and are very difficult to remove
Disadvantage of scale formation Wastage of fuel: - sales have low thermal conductivity, so the rate of heat transfer from boiler to inside water decreased & the consumption of fuel increaser. 2. Lowering of boiler safety: - due to scale formation, over heating of boiler is done is causes distortion of boiler tube and makes the boiler unsafe to bear. 3. Decrease in efficiency: - scale may deposit in the values and condensers of the boiler and choke them partially, it decrease in efficiency of the boiler. 4. Danger of explosion: - when thick scales creak suddenly in water contact with our heated iron. Plates form large amount of steam suddenly, causes explosion of the boiler. 1.
Removal of scales 1. With scraper or wire brush it remove if they are loosely adhering. 2. By dissolving them adding chemicals. 3. By frequently blow – down operations, if the scales are loosely adhering.
Prevention of scale formation (A) External treatment: - This involutes removal of hardness causing impurities which are already discussed earlier. (B) Internal treatment: - An internal treatment is consists of adding appropriate reagent to the boiler water itself either. (a). To, ppt. the scale forming impurities in the form of sludge which can be removed by blow- down operation. (b). To, convert them into compounds which will stay in “dissolved form” in water and thus do not cause any harm.
Important internal treatment methods are Colloidal conditioning: - in this method colloidal conditioning agents like agar-agar tannic are mixed which get coated by scale forming ppt, they yielding non-sticky and louse deposits. Which can easily removed. 2. Phosphate conditioning: - in this method scale formation can avoided by sodium phosphate, which react with hardness of water forming non-adherent and easily removable, soft sludge of calcium and magnesium 3 Ca. Cl 2 + 2 Na 3 PO 4 Ca 3(PO 4)2 + 6 Na. Cl The main phosphate employed are: (a)Na. H 2 PO 4: -sodium dihydrogen phosphate(acidic) (b)Na 2 HPO 4: -disodium hydrgen phosphate(weak acid) (c)Na 3 PO 4: -trisodium phosphate(alkaline) 1.
3. Carbonate conditioning: - In low pressure boiler scale formation can be avoided by adding sodium carbonate in water, when Ca. CO 3 is converted into calcium carbonate in ea. CO 3 + Na 2 CO 3 Ca. CO 3 + Na 2 SO 4 Ca. CO 3 is precipitated as loose sludge of Ca. CO 3 which can removed by blow-down method. 4. Calgon conditioning: - scale formation can be avoided by adding Calgon [sodium hexa meta phosphate(Na. PO 3)6] to boiler water. It form complex compound with Ca. SO 4. Na 2[Na 4(PO 3)6]↔ 2 Na+ + [Na 4 P 6 O 18]22 Ca. SO 4 +[Na 4 P 6 O 18]2 - ↔[Ca 2 P 6 O 18]2 - + 2 Na 2 SO 4 5. Treatment with sodium aluminate: -sodium aluminate gets hydrolysed yisid and form Na. OH & Al(OH)3 getatinous. Na. Al. O 2 + 2 H 2 O Na. OH + Al(OH)3 The sodium hydroxide, so formed, ppt. some of the Mg as Mg(OH) 2 Mg. Cl 2 + 2 Na. OH Mg(OH)2 + 2 Na. Cl The ppt. of Mg & Al entraps finaly suspended and colloidal impurities. 6. Electrical conditioning: 7. Radio active conditioning: -
Caustic embrittlement In during softening process small amount of Na. CO 3 is present which react with water and form sodium hydroxide it makes the boiler water caustic, this water form minute haircracks in the inner side of boiler Na. CO 3 + H 2 O 2 Na. OH + CO 2 This causes embrittlement of boiler part, particularly bends, joints & failure the boiler. This dissolving the iron of boiler as sodium feroat.
Caustic embrittlement can be avoided 1. By using sodium phosphate as softening reagent 2. By adding tannin or lianin to boiler water, since these blocks the hair cracks. 3. By adding sodium sulphate to boiler water: Na 2 SO 4 blocks hair cracks, if Na 2 SO 4 is added to boiler water , so that the radio [Na. SO 4 concentration] [Na. OH concentration] Is kept 1: 1, 2: 1, 3: 1 in boiler working resp. at pressure up to 10, 20 and above atm.
Boiler corrosion is decay of boiler material by chemical attack of its environment. Main reasons for boiler corrosion are: 1. Dissolved oxygen: -Dissolved oxygen in water, in present of prevailing high temp, attacks boiler material. 2 Fe + 2 H 2 O + O 2 2 Fe(OH)2 4 Fe(OH)2 + O 2 2(Fe 2 O 3. 2 H 2 O)
1. Removal of dissolved oxygen 1. By adding sodium sulphite or sodium suphite. 2 Na 2 SO 3 + O 2 2 Na 2 SO 4 N 2 H 4 + O 2 N 2 + 2 H 2 O Na 2 S + 2 O 2 Na 2 SO 4 Hydrazine reaction with O 2 & forming N 2 and water which is harmless & hydrazine remove oxizen without increasing the concentration of dissolved solid. 2. By mechanical dearation: - spraying water in a perforated plate fitted tower, hated from sides and connected to vacuum pump. High tump, low pressure to large exposed surface, reduced the dissolved oxygen in water.
2. Dissolved carbon dioxide CO 2 react with water and form carbonic acid which has slow corrosive abbect on boiler materail. CO 2 + H 2 O H 2 CO 3 Removal of CO 2: (i)by adding calculated quantity of ammonia. thus 2 NH 4 OH + CO 2 (NH 4)2 CO 3 + H 2 O (ii)Mechanical dearation of water: -
3. Acid from dissolved salts water containing dissolved Mg salt liberated acid on hydrolysis. Mg. Cl 2 + 2 H 2 O Mg(OH)3 + 2 HCl This acid react with iron in chain – like reactions producing HCl again. Fe + 2 HCl Fe. Cl 2 + H 2 Fe. Cl 2 + 2 H 2 O Fe(OH)2 + 2 HCl
water for domestic and industrial purpose Water supplied by municipalities for domestic purpose must be free from pathogen’s, it should be clear, colorless, and pleasant to taste. the treatment of water involves removal of suspended impurities, removal of colloidal impurities followed by sterilization sedimentation, coagulation, filtration. 1. sedimentation: - sedimentation is a process of removing suspended impurities by allowing water to remain undisturbed in big tanks. Most of the particles settle down at the bottom of the tank. Due to gravitational force. The detention period in the sedimentation is 2 To 8 hours. The clear supernatant water is them drawn out from the tank. 2. coagulation: -To remove the impurities from (which are not removed by sedimentation) water certain chemicals are added this chemicals are known as coagulants. This coagulants produce ions of right electrical charge that neutralize the oppositely charged
Aluminum sulphate is the most common coagulating agent. When it added to neutral water hydrolyed to form colloidal aluminium hydroxide. Al 2(SO 4)3 + 6 H 2 O 2 Al(OH)3 + 3 H 2 SO 4 aluminum hydroxide ramous the finely divided colloidal impurities by other mechanisms. coagulation and setting equipment should be so designed that quick and through mixing of the coagulant and raw water should be achieved. modern types of coagulation and setting equipment include the 1. floc-former type. 2. Sludge – blanket type. 1. floc-former type: - this equipment consists of (i) A flace mixer where coagulant is quickly efficiently mixed with raw water. (ii) Rolling mix chamber where gentle mixing of ppt and formation of large particle take place. (iii) Settling basins where the bloc is allowed to settle & sludge is remoued. 2. Sludge – blanket type: - This type of equipment is used for coagulation , setting , as well as softening of water by soda lime process it filter all the coagulation water.
3. Filtration: - filtration is the process of clarification of water by passing the water through a porous material. The porous material used is called the filtrtion is takes place by three types of filtration 1. Slow sand filtration. 2. Rapid gravity filtration. 3. Rapid pressure filtration. 1. Slow sand filtration: - A sand filtration consists of a thick top layer of fine sand placed over sand layer and qravels. It is consist of an inlet for water and an underdrain channels get clossed, due to impurities , it replaced with clean sand the filter iss reused.
2. Rapid gravity filtration: - It consist of graded quarts sand the advantage of rapid gravity filtation. (i)The quality of the filtrate can easily inspected. (ii)The filter is unaffected by pressure variations. (iii)Very low cost.
Rapid pressure filtration In rapid pressure filtration water from an elevated source can be passed through the filter and delivered in storage these filter consists of cylindrical steal shell felted with dashed heads, containing a layer of a granular filter medium supported by graded gravel equipped with required accessories.
Sterilization of water Elimination of bacteria's can be achieved by sterilization. The chemicals which are added to water for killing the bacteria's & etc are known as disinfectants. (1)By adding bleaching powder: -bleaching powder is mixed with water a allowed to stand for several hours. . B. P. react with water and produce Cl 2. which again react with water and form hypochlorous acid it react as powerful germicide. Ca. OCl 2 + H 2 O Ca(OH)2 + Cl 2 + H 2 O HCl + HOCl Germs are killed Draw backs: - (i)bleaching powder introduce Ca- in water. (ii)Only calculated quantity of bleaching powder is used because it gives a bad taste and samll to treated water. (2)By chlorination: -chlorine react with water and form hydrochlorine acid and hyprochrorous acid, hypochlorous acid is powerful germicide. Cl 2 + H 2 O HOCl + HCl HOCl + Bacterias bacterias are killed
Mechanism of action The death of the microorganism, bacteria's, results from chemical reaction of hypochlorous acid with enzymes in the cells of the organisms and enzymes is essential for the metabolic process of the micro-organisms, so death of the micro-organisms results due to inactivation of enzymes. liquid chlorine is most effective apparatus used for this purpose is known as chlorinator , which is high tower, having a number of baffle plates. Water and proper quantity of concentrated chlorine solution are introduced at its top. The treated water is taken out from the bottom.
chlorine (i) Time of contact: - The death rate is maximum to start and it goes on decreasing with time. (ii) Temperature of water: - As the temperature is increases the death rate of micro-organisms is to kill. (iii)p. H value: - The low p. H value required
Advantage of chlorine 1. It is effective & economical. 2. It required little space for storage. 3. It is used at low & high temp. 4. It introduce no salt impurities in treated water. 5. It is most ideal disinfectant.
disadvantages (i) Excess chlorine produce unpleasant taste and Adour. (ii) Excess chlorine causes irritation on muscus membra. (iii) It is more effective below 6. 5 p. H and less eff. at high p. H
Break point chlorination or free residual chlorine It chlorine is added to sample of water after few minutes, the residual chlorine is available in the water to estimate when the graph is plotteci between residual chlorine and applied chlorine the point at which the concentration of residual chlorine decreases in known as “break point” and the addition of chlorine at break point is known as “break point chlorination” The concentration of residual chlorine decreases at break point due to the presence of organic matter, reducing substances & free amino ammonia, all tastes adours disappears.
Advantages of break point chlorination 1. It oxidises organic comp. ammonia and other disease producing bacterias. 2. It remouves odour colour and taste from water
Dechlorination Over chlorination after “break point” produces unpleased task and odour. To remove it water passes through a bed of molecular carbon or addition of small quantity of sulphur doixide, sodium thio sulphate. SO 2 + Cl 2 + 2 H 2 O H 2 SO 4 + 2 HC Na 2 SO 3 + Cl 2 + H 2 O Na 2 SO 4 + 2 HCl
By using chloramines When chlorine and ammonia are mixed in the radio 2: 1 volume a compound chloramines is formed. Cl 2 + NH 3 Cl. NH 2 + HCl Chloramine is much more Latina than chlorine alone and consequently it is a better bactericidial than chlorine alone. Cl. NH 2 + H 2 O HOCl + NH 3
Disinfection by ozone Ozone is an excellent disinfectant which is producing by passing silent electric discharge through cold and dry orygen 3 O 2 2 O 3 Ozone is highly unstable and breaks down liberation nascent oxygen O 3 O 2 + [o] The nascent oxygen is very powerful oxidizing agent and kills all the bacteria as well as oxidizes the organic matter present in water
Chemical analysis of water The estimation of free chlorine in water is based on the oxidation of potassium iodide by free chlorine. when water is treated with on excess of potassium iodide solution the free chlorine present in the water oxidizes potassium iodide and liberates an equivalent amount of iodine, forming dupviolet colour. Cl 2 + 2 Ki 2 KCl + I 2 The amount of liberated “iodine” can be estimated by litratina the resulting solution aqainst standant sodium thiosulphate solution using starch as tinal indicatot I 2 + 2 Na 2 S 2 O 3 2 Na. I + Na 2 S 4 O 6 I 2 + starch Deap blue comlex
Procedure Take out 10 ml of 10 y. KI solution in a stoppered 150 ml conical flask. Add to it 50 ml of water sample, holdina the point of the pipette just about the iodide solution.