WATER TREATMENT-1(by Sarika Gupta)

WATER AND ITS TREATMENT:

WATER AND ITS TREATMENT PART-I AND PART-II

:

• Source of Water • A) Surface Waters – Rain Water – River Water – Lake Water – Sea Water • B) Underground Waters – Spring Water – Well Water

MAJOR IMPURITIES OF WATER:

MAJOR IMPURITIES OF WATER Turbidity, silt, mud, dirt Magnesium Carbonate, Calcium Bicarbonate , Sodium Hydroxide Potassium Sulfate, Ammonium Chloride, Iron Nitrate Manganese Phosphate Hydrogen sulfide and Carbon dioxide , Ammonia ,Methane , Oxygen , Chlorine other suspended matter Colloidal silica, Silica Oil Bacteria phage ,Microorganisms, plankton Organic Matter* ,Corrosion products (condensate )

Important Properties in water chemistry :

Important Properties in water chemistry • Natural Water may contain • 1) Conductivity 2) Turbidity • 3) Color 4) pH • 5) Alkalinity 6) Solids • 7) Hardness

ALKALINITY:

ALKALINITY • Alkalinity of water is refers to the total amount of those substance present in water which tend to increase the concentration of hydroxide ions on account of dissociation and hydrolysis in water. It is a measure of ability of water to neutralize acids. Total Alkalinity = Methyl Orange Alkalinity + Phenolphthalein Alkalinity

CAUSE OF ALKALINITY::

CAUSE OF ALKALINITY: Presence of HCO 3 - , HSiO 3 - ,SiO 3 - : Presence of salts of Weak acids: Presence of Buffer forming salts:

CLASSIFICATION OF ALKALINITY::

CLASSIFICATION OF ALKALINITY: IT IS OF THREE TYPES: 1) OH - (hydroxyl) ALKALINITY 2) CO 3 2- (carbonate) ALKALINITY 3) HCO 3 - (bicarbonate) ALKALINITY

COMBINATION POSSIBLE::

COMBINATION POSSIBLE: 1) OH - (hydroxyl) ALKALINITY 2) CO 3 2- (carbonate) ALKALINITY 3) HCO 3 - (bicarbonate) ALKALINITY 4) OH - + CO 3 2- ALKALINITY 5) HCO 3 - + CO 3 2- ALKALINITY

DETERMINATION OF ALKALINITY::

DETERMINATION OF ALKALINITY: PRINCIPLE: The type and extent of alkalinity of water sample is determined by TITRIMETRIC METHOD. OH - + H + H 2 O CO 3 2- + H + HCO 3 - P HCO 3 - + H + H 2 CO 3 M

STRUCTURE OF PHENOLPHTHALEIN :

STRUCTURE OF PHENOLPHTHALEIN

STRUCTURE OF METHYL ORANGE: :

STRUCTURE OF METHYL ORANGE:

Alkalinity relationships as determined by titrations. :

Alkalinity relationships as determined by titrations. Hydroxide Carbonate Bicarbonate P = O O O M P = M P O O P = 1/2M O 2P O P >1/2M 2P - M 2(M - P) O P <1/2 M O 2P M - 2P

PROCEDURE::

PROCEDURE: KNOWN VOLUME OF WATER SAMPLE + 1-2 DROPS OF Phenolphthalein. APPERANCE OF COLOR TITRATE WITH STD. ACID END POINT PINK TO COLORLESS TITRATE WITH SAME SAMPLE WITH SAME STD. ACID BY USING Methyl Orange INDICATOR. END POINT YELLOWOrange TODARK PINK THE VOL OF ACID CONSUMED IS NOTED. COLORLESS

CALCULATIONS:

CALCULATIONS FOR Phenolphthalein ALKALINITY: N 1 V 1 = N 2 V 2 (AWS) (STD. ACID) N 1 = N 2 V 2 / V 1 P ALK = N 1 X 50 X 1000 ppm FOR METHYLORANGE ALKALINITY: N 1 V 1 = N 2 V 2 (AWS) (STD. ACID) N 1 = N 2 V 2 / V 1 M ALK = N 1 X 50 X 1000 ppm

Alkalinity relationships as determined by titrations. :

Alkalinity relationships as determined by titrations. Hydroxide Carbonate Bicarbonate P = O O O M P = M P O O P = 1/2M O 2P O P >1/2M 2P - M 2(M - P) O P <1/2 M O 2P M - 2P RESULT: OH - (hydroxyl) ALKALINITY=--------ppm 2) CO 3 2- (carbonate) ALKALINITY=-----------ppm 3) HCO 3 - (bicarbonate) ALKALINITY=-----------ppm

HARDNESS OF WATER:

HARDNESS OF WATER It is defined as a characteristic property of water that prevents the lathering of soap. Hardness of water may also be defined as the soap-consuming capacity of water, or the capacity of precipitation of soap.

CAUSE OF HARDNESS:

CAUSE OF HARDNESS Hard water does not produce lather with soap solutions, but produces white precipitate (scum). For example, sodium stearate reacts with calcium: 2C 17 H 35 COONa + Ca 2+ → (C 17 H 35 COO) 2 Ca + 2Na + calcium stearate (insoluble in water)

Degree Of Hardness Of Drinking Water :

Degree Of Hardness Of Drinking Wa ter Soft 0-60 mg/L Medium 60-120 mg/L Hard 120-180 mg/L Very hard >180 mg/L

TYPES OF HARDNESS:

TYPES OF HARDNESS a)TEMPORARY HARDNESS /Carbonate/Alkaline This hardness refers to the amount of carbonate and bicarbonates of Ca & Mg in solution It can be removed or precipitated by boiling. This type of hardness is responsible for the deposition of scale in hot water pipes and kettles. b) Permanent/ Non-carbonate hardness/non-alkaline This hardness is caused by sulfate, chloride or nitrate of Ca & Mg . This type of hardness cannot be removed by boiling.

UNITS OF HARDNESS::

UNITS OF HARDNESS: There are several different scales used to describe the hardness of water in different contexts. 1)ppm 2)Mg/l 3)Clark’s Degree 4)Degree french

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Parts per million (ppm) Usually defined as one milligram of calcium carbonate (CaCO 3 ) per litre of water. Clark degrees (°Clark)/English degrees (°e or e) One degree Clark is defined as equivalent of CaCO 3 per 70,000 parts of water. French degrees (°F or f) One degree French is defined as 10 milligrams of calcium carbonate per litre of water, equivalent to 10 ppm. RELATIONSHIP: 1ppm= 1 mg/l = 0.07 °Clark =0.1 °F

EXPRESSION OF HARDNESS::

EXPRESSION OF HARDNESS: THE EQUIVALENT OF CaCO3 FOR A HARDNESS CAUSING SALT IS GIVEN BY: * EQUIVALENT OF CaCO3 = W X 50 E W=MASS OF HARDNESS PRODUCING SUBSTANCE E= EQUIVALENT MASS OF CaCO3

DETERMINATION OF HARDNESS::

DETERMINATION OF HARDNESS: EDTA METHOD

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CALCULATIONS FOR TOTAL HARDNESS: N 1 V 1 = N 2 V 2 (HWS) (STD. EDTA) N 1 = N 2 V 2 / V 1 TOT. HARDNESS = N 1 X 50 X 1000 ppm AFTER BOILING: N 1 V 1 = N 2 V 2 (HWS) (STD.EDTA) N 1 = N 2 V 2 / V 1 PERMANENT HARDNESS = N 1 X 50 X 1000 ppm TEMPORARY HARDNESS=TOT--- PERMANENT H

STRUCTURE OF EDTA::

STRUCTURE OF EDTA: Molecular weight : * EDTA 2Na:372

HEXADENTATE IONIC STRUCTURE OF EDTA::

HEXADENTATE IONIC STRUCTURE OF EDTA: It is also represented as H 2 Y 2- it is a strong chelating ligand,forms complex with bivalent cations like Ca & mg ions. The complex formed are stable in alkaline medium i.e. pH=8-10.

Metal- Edta complex::

Metal- Edta complex: Edta being a chelating ligand react with multivalent metal ions to form stable complex. In hard water, bivalent cations like Ca & Mg ions are present which form complex with edta. That`s why this method is used to determine hardness in water.

3-D STRUCTURE OF EDTA:

3-D STRUCTURE OF EDTA

STRUCTURE OF EBT::

STRUCTURE OF EBT:

SLUDGE FORMATION IN BOILERS: :

SLUDGE FORMATION IN BOILERS: In boilers, because of continuous evaporation of water, the concentration of salts increase progressively and after the saturation point is reached, precipitate form on the inner walls of boiler. SLUDGE: Sludge is a soft, loose and slimy precipitate formed within the boiler. It is formed at comparatively colder portions of the boiler and collects in the area where flow rate is slow. These are formed by substances which have greater solubilities in hot water than in cold-water. E.g.. MgCO3, MgCl2, CaCl2, MgSO4.

Disadvantages::

Disadvantages: a. As the sludge’s are poor conductor of heat they cause loss of heat. b. The working of the boiler is disturbed because of chocking of pipes by the sludge. PREVENTION: a. By using well softened water. b. By drawing off a portion of concentrated water frequently. SCALES: Scales are hard, adhering precipitates formed on the inner walls of the boilers. They stick very firmly on to the inner wall surface and are difficult to remove with chisel and hammer. causes of scale formation:Following are the causes a. decomposition of calcium bicarbonate: Ca(HCO3)2 CaCO3 + H2O + CO2 In low pressure boilers,CaCO3 causes scale formation. In High pressure boilers,CaCO3 becomes soluble. CaCO3 + H2O Ca(OH)2 + CO2 b. Decomposition of calcium sulphate: The solubility ofCaSO4 in water decreases with rise of Temperature. In super heated water CaSO4 is insoluble. This is the main cause in high-pressure boilers. c. Hydrolysis of Magnesium salts: Dissolved Magnesium salts undergo hydrolysis formingMg(OH)2 preci

SCALES::

SCALES: Scales are hard, adhering precipitates formed on the inner walls of the boilers. They stick very firmly on to the inner wall surface and are difficult to remove with chisel and hammer. causes of scale formation: Following are the causes a. decomposition of calcium bicarbonate: Ca(HCO3)2 CaCO3 +H2O + CO2 In low pressure boilers,CaCO3 causes scale formation. In High pressure boilers,CaCO3 becomes soluble.

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b. Decomposition of calcium sulphate: The solubility of CaSO4 in water decreases with rise of Temperature. In super heated water CaSO4 is insoluble. This is the main cause in high-pressure boilers. c . Hydrolysis of Magnesium salts: Dissolved Magnesium salts undergo hydrolysis forming Mg(OH)2 precipitate. MgCl2 + 2H2O Mg(OH)2 + 2 HCl Mg(OH)2 so found by hydrolysis of Magnesium salts is a soft type of scale.

Disadvantages::

Disadvantages: wastage of fuel: The scale formation causes decreases of heat transfer. As a result over heating is required this causes consumption of fuel. b. danger of Explosion: The hot scale cracks because of expansion and water suddenly comes incontact with overheated Iron plates. This causes in formation of large amount of steam suddenly. This results high pressure causing boiler to burst. Bagging: distortion of boiler material

PREVENTION: :

PREVENTION: a. External treatment: Efficient softening of water is to be carried out. b.Internal treatment: Suitable chemicals are added to the boiler water either to precipitate or to convert scale in to compounds.

INTERNAL TREATEMENT: :

INTERNAL TREATEMENT: Internal treatment of boiler water is carried out by adding proper chemicals to precipitate the scale forming impurities in the form of sludge and to convert the scale forming chemicals into compounds which will stay in dissolved form in water.

CONDITIONING::

CONDITIONING: COLLODIAL CONDITIONING : The addition of organic substances such as Kerosene, tannin, Gel etc., to the surface in low pressure boilers may prevent the scale formation. These substances gets coated over the scale forming precipitates and gives a loose and non-sticky precipitates which can be removed by using blow-down operation. PHOSPHATE CONDITIONING: The addition of sodium phosphate in hard water reacts with the hardness causing agents and gives calcium and magnesium phosphates which are soft and non-adhere and can be removed easily by blow-down operation. In this way, scale formation is removed in high-pressure boilers. 3CaCl2 + 2 Na3PO4 → Ca3(PO4)2 + 6NaCl

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CARBONATE CONDITIONING: In low-pressure boilers, scale-formation can be avoided by adding sodium carbonate to boiler water, when CaSO 4 is converted into calcium carbonate in equilibrium. CaSO 4 + Na 2 CO 3 → CaCO 3 + Na 2 SO 4 Consequently, deposition of CaSO 4 as scale doesn’t take place and calcium is precipitated as loose sludge of CaCO 3 which can be removed by blow-down operation.

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CALGON CONDITIONING: Involves in adding calgon to boiler water. It prevents the scale and sludge formation by forming soluble complex compound with CaSO 4 . Calgon = Sodium hexa Meta phosphate Na 2 [Na 4 (PO 3 ) 6 ] → 2Na+ + [Na 4 P 6 O 18 ] 2- 2CaSO 4 + [Na 4 P 6 O 18 ] 2- → [Ca 2 P 6 O 18 ] 2- + 2Na 2 SO 4

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SODIUM ALUMINATE: Sodium aluminate gets hydrolyzed yielding NaOH and a gelatinous precipitate of aluminum hydroxide. NaAlO2 + 2H2O → NaOH + Al (OH)3 The sodium hydroxide, so-formed, precipitates some of the magnesium as Mg (OH)2. MgCl2 + 2NaOH → Mg (OH)2 + 2NaCl The flocculent precipitate of Mg (OH)2 plus aluminum hydroxide, produced inside the boiler, entraps finely suspended and colloidal impurities, including oil drops and silica. The loose precipitate can be removed by pre-determined blow-down operation.

Diagrams of scale and sludge::

Diagrams of scale and sludge:

Boiler Corrosion::

Boiler Corrosion: The chemical or electro chemical eating away of metal by its environment in a boiler is known as boiler corrosion. The main reason for this problem is the presence of excess of oxygen in water. It can be prevented by mechanical deaerator, pre-heating and chemical treatment.

Caustic Embrittlement::

Caustic Embrittlement: The formation of brittle and incrystalline cracks in the boiler shell is called caustic embrittlement. It is a type of boiler corrosion and the main reason for this, is the presence of alkali-metal carbonates and bicarbonates in feed water and also the presence of sodium sulphate. In lime-soda process, it is likely that, some residual Na2 CO3 is still present in the softened water. ThisNa2CO3decomposes to give NaOH and CO2, due to which the boiler water becomes “Caustic”. Na2CO3+ H2O → NaOH+ CO2

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- This caustic water flows inside the boiler and causes some minutes hair-cracks, by capillary action. On evaporation of water, the dissolved caustic soda increases its concentration which attacks the surrounding area, thereby dissolving Iron of boiler as Sodium ferrate. This causes embrittlement of boiler parts such as bends, joints, reverts etc, due to which the boiler gets fail.

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- Therefore, caustic embrittlement can be prevented. a. By maintaining the pH value of water and neutralization of alkali. b. By using Sodium Phosphate as softening reagents, in the external treatment of boilers. c. Caustic embrittlement can also be prevented by adding Tannin or Lignin or Sodium sulphate which prevents the infiltration of caustic-soda solution blocking the hair-cracks