engineering chemistry notes(water technology)

WATER TECHNOLOGY-I

1. Introduction
Water is nature’s most wonderful, abundant and useful compound.
Water is not only essential for the lives of animals and plants. But also occupies a unique position in industries.
Water is also used a coolant in power and chemical plants.
It is widely used in drinking, bathing, sanitary, washing, irrigation, fire-fights, air-conditioning and also production of industrial materials.

2. Effect of water on rocks and minerals:
Dissolution: some mineral constituents of rocks such as NaCl and CuSO4.2H2O readily dissolve in water.
Hydration: Some minerals are easily hydrated with the consequent increase in volume leading to disintegration of the rocks in which these minerals are present. Eg.

CaSO4 Hydration à CaSO4.2H2O (Gypsum)

Mg2SiO4 àMg2SiO4.XH2O (Serpentine)

Effect of dissolved oxygen: This leads to oxidation and Hydration

Fe3O4 àFe2O3 à3 Fe2O3.2H2O(Limonite)

2FeS2 + 7O2 + 2H2O à2FeSO4 + 2H2SO4

Effect of dissolved CO2: Water containing dissolved CO2 converts the insoluble carbonate of calcium, Magnesium and iron into their relatively soluble bicarbonates.

CaCO3 + H2O + CO2 --------------- Ca(HCO3)2

3. Types of Impurities present in water:

The natural water is usually contaminated by different types of impurities.
They are mainly 3 types..
Physical impurities
Chemical impurities
Biological impurities

1. PHYSICAL IMPURITIES:
a. Colour: Colour in water is caused by metallic substances like salts.
b. Turbidity: is due to the colloidal, extremely fine suspensions such as insoluble substances like clay, slit, and micro-organisms.
c. Taste: presence of dissolved minerals in water produces taste. Bitter taste can be due to the presence of Fe, Al, Mn, Sulphates, lime. Soap taste can be due to the presence of large amount of sodium bicarbonate.
d. Odour: In water is undesirable for domestic as well as industrial purpose.
2. CHEMICAL IMPURITIES:
a. In-organic-organic chemicals:
Inorganic chemicals:
1. Cations: Ca+2, Mg+2, Na+, K+, Fe+2, Al+3, Zn+2, Cu+2
2. Anions: Cl-, SO-2, NO3-, HCO3-, F-, NO2-
Organic chemicals: dyes, paints, petroleum products, pesticides, detergents, drugs textile materials, other organic related materials.
Acidity: surface and ground water attains acidity from industrial wastes like acid, mine, drainage, pickling liquors, usually acidity caused by the presence of free CO2, mineral acids, and weakly dissociated acids.
b. Gases: All natural waters contains dissolved atmosphere CO2, O2, NH3 gases, pollutant and sewage water contains nitrogen in the form of nitrogenous organic compounds and urea , which are partially converted into NH3.
c. Mineral matters: have organs from rocks and industrial effluents. These include mineral acids, Ca+2, Mg+2, Na+, K+, Fe+2, Al+3, Zn+2, Cu+2, Mn+2, Cl-, SO-2, NO3-, HCO3-, F-, NO3-, SiO2

3.BIOLOGICAL IMPURITES:
Biological impurities are Algae, pathogenic bacteria, fungi, viruses, pathogens, parasite-worms, etc. the source of these contamination is discharge of domestic and sewage wastes, excreta, etc.
A. Micro-organisms: algae, fungi, viruses, etc.
B. Water bodies in water include 1. Bacteria, organisms’ inhabitating the bottom sludge, and 2. Organisms and planktons developed at the water surfaces. These are inhibitated by different groups of worms like flat worms, hair worms, tiny roundworms, oligochetes, etc.


HARDNESS OF WATER

Hardness of water defined as which prevent the lathering of soap.This is due to presence of in water of certain salts of Ca+2, Mg+2 and other Heavy metals dissolved in it. Soaps are Sodium or Potassium salts of higher fatty acids like Oleic acid or Palmitic acid or stearic acids. C17H35COONaTemporary Hardness is mainly caused by Bicarbonates of Calcium, Magnesium and other heavy metals.

SOAP with HARDWATER REACTIONS

2C17H35COONa+CaCl2---- à(C17H35COO)2Ca+2NaCl
2C17H35COONa+MgSO4--à(C17H35COO)2Mg+Na2SO4

Hardness of water is mainly TWO types1.Temporary Hardness2. Permanent Hardness




1. Temporary Hardness mainly caused by the presence of dissolved Bicarbonates of Calcium, Magnesium and other Heavy metals and the carbonate of Iron.

Temporary hardness of water mainly responsible salts are…
1. Calcium bicarbonate Ca(HCO3)2
2. Magnesium bicarbonate Mg(HCO3)2

When bicarbonates are decomposed a, yielding insoluble carbonates or hydroxides, which are deposited as a crust at the bottom of vessel.
Temporary Hardness can be largely removed by mere Boiling of water.
Temporary Hardness is also known as….
Carbonate Hardness Alkaline Hardness
2. Permanent harness: It is due to the presence of dissolved Chlorides and sulphates of Calcium, Magnesium, Iron and other metals Permanent hardness responsible salts are….
CaCl2, MgCl2, CaSO4, MgSO4, FeSO4, Al2(SO4)3
Permanent Hardness cannot removed by boiling but it can be removed by the use of chemical agents.

Permanent Hardness also known as….
Non-Carbonate HardnessNon-Alkaline
Heat
• Ca(HCO3) 2 ---àCaCO3+H2O+CO2
Calcium bicarbonate
Heat
• Mg(HCO3)2 ----àMg(OH)2+2CO2
Magnesium bicarbonate

Explain the terms Temporary and permanent hardness of water.
Write a short note on hardness of water.
Hardness Distinguish between Temporary and Permanent Hardness of water.


DISADVANTAGES OF HARDWATER:
1. In Domestic use:
WASHING: hardwater, when used for washing purposes, does not producing lather freely with soap. As a result cleansing quality of soap is decreased and a lot of it is wasted. Hardwater reacts with soap it produces sticky precipitates of calcium and magnesium soaps. These are insoluble formations.
Bathing: hardwater does not lather freely with soap solution, but produces sticky scum on the bath-tub and body. Thus, the cleansing quality of soap is depressed and a lot o it is wasted.
Cooking: the boiling point of water is increased because of presence of salts. Hence more fuel and time are required for cooking.
Drinking: hardwater causes bad effects on our digestive system. Moreover, the possibility of forming calciumoxalate crystals in urinary tracks is increased.



2. INDUSTRIAL USE:
Textile Industry: Hardwater causes wastage of soap. Precipitates of calcium and magnesium soaps adhere to the fabrics and cause problem.
Sugar Industry: water containing sulphates, nitrates, alkali carbonates. Etc. if used in sugar refining, causes difficulties in the crystallization of sugar. Moreover, the sugar so produced may be de-liquescent.
Dyeing Industry: The dissolved salts in hardwater may reacts with costly dyes forming precipitates.
Paper Industry: Calcium, magnesium, Iron salts in water may affect the quality of paper.
Pharmaceutical Industry: Hardwater may cause some undesirable products while preparation of pharmaceutical products.
Concrete Making: Water containing chlorides and sulphates, if used for concrete making, affects the hydration of cement and the final strength of the hardened concrete.
Laundry: Hardwater, if used in laundry, causes much of the soap used in washing to go as waste Iron salts may even cause coloration of the clothes.


3. IN STEAM GENERATION IN BOILERS:
For steam generation, boilers are almost invariably employed. If the hardwater is fed directly to the boilers, there arise many troubles such as..
Scale and sludge formation: the hardness of water fed to the boiler may cause scale and sludge formation.
Corrosion: Hardwater may cause caustic embrittlement which is a type of boiler corrosion.
Priming and Foaming: Hardwater used in boiler causes priming and foaming which results in the formation of wet stream.
Caustic embrittlement




ESTIMATION OF HARDNESS BY EDTA METHOD:

The hardness of water is not a pollution parameter but indicate the eater quality in terms of Calcium and magnesium expressed in terms of CaCO3.
The analysis is done by complex metric titration using standard EDTA and EBT as an indicator.
EDTA is Ethylene diamaine tetra acetic acid whose structural formulae is




EDTA can form 4 to 6 dative bonds with cations like Calcium Magnesium.

PRINCIPLE: In this complex metric Titration, the water sample is titrated with standard solution of Di sodium salt of EDTA using EBT indicator.

PROCEDURE: To 50 mL of sample add 10-15 mL buffer solutions adjust the pH about 10 and then warm the solution. Add 2 drops o Eriochrome Block-T and it is titrated with 0.01 M EDTA solution changes its colour from red-wine to blue.

REACTIONS INVOLVED: EBT indicator when added to hard water at pH = 10, forms weak complexes with calcium and magnesium present in hard water. It results in the formation of Ca-EBT or Mg-EBT complexes which is wine-red, these are unstable.



During titration with EDTA, calcium first reacts to form relatively stable followed by magnesium to give Mg-EDTA+2 complex releasing the free indicator(blue) the colour changes from wine-red to blue at the endpoint.




Various steps involved in this method are…
Preparation of standard hard water: dissolve 1g of pure, dry CaCO3 in minimum quantity of dil.HCl and then evaporate the solution to dryness on a water bath. Dissolve the residue in distilled water to make 1 Litre solution. Each mL of this solution thus contains 1mg of CaCO3 equalent hardness.
1 mL hard water solution = 1mg of CaCO3 equalent hardness.
Preparation of EDTA solution: Dissolve 4 g of pure EDTA crystals + 0.lg MgCl2 in 1 Litre of distilled water.
Preparation of Indicator (EBT): Dissolve 0.5 g of Eriochrome Black-T in 100mL alcohol.
Preparation of Buffer solution: add 67.5g of NH4Cl to 570 mL of Con. Ammonia solution and then dilute with distilled water to 1 Litre.
Standardization of EDTA solution: Rinse and fill the burette with EDTA solution. Pipette out 50 mL of standard hard water in a conical flask. Add 10-15 mL of buffer solution and 4 to 5 drops indicator. Titrate with EDTA solution till wine-red colour changes to clear blue. Let volume used by V1 mL.
Titration of Unknown Hard water: Titrate 50 mL of water sample just in Step-5. let volume used be V2 mL.
Titration of Permanent hardness: take 250 mL of the water sample in a large beaker. Boil it. Till the volume is reduced to about 50 mL, filter it, wash the precipitate with distilled water, collecting filtrate and washing in a 250 mL measuring flask. Finally makeup the volume to 250 mL with distilled water. Then, titrate 50 mL of boiled water sample just as in Step (5). Let volume used by V3 mL.

CALCULATION:
V1 mL of EDTA is consumed by 50 mL standard hardwater.

50 mL of standard hard water = V1 mL of EDTA

50 * 1 mg of CaCO3 = V1 mL of EDTA

1 mL of EDTA =50/V1 mg of CaCO3 eq.

Now 50 mL of given/ unknown hard water =V2 mL of EDTA

V2*50/V1 mg of CaCO3 eq.

1 Lt or 1000 mL of given hard water = 1000*V2/V1 mg of CaCO3 eq.
Total hardness of water = 1000*V2/V1 mg/L
1 mg/L = 1ppm so,
= 1000*V2/V1 ppm


Now 50 mL of boiled water = V3 mL of EDTA
= V3*50/V1 mg of CaCO3 eq.
1000 mL of boiled water = 1000*V3/V1 mg of CaCO3 eq.
= 1000*V3/V1 ppm
So,
Permanent hardness = 1000*V3/V1 ppm
Temporary hardness = [Total hardness – Permanent hardness]

= 1000*V2/V1 – 1000*V3/V1

= 1000[(V2-V3) V1] ppm

Total hardness of water = 1000*V2/V1 ppm

Permanent hardness = 1000*V3/V1 ppm

Temporary hardness = 1000[(V2-V3) V1] ppm

Advantages of EDTA method:
This method is definitely prep arable to the other methods, because of the
1. Greater accuracy
2. Convenience and 3. More rapid procedure


Analysis of water

1. ALKALINITY: Alkalinity of water is due to the presence of carbonates and bicarbonates of calcium and magnesium. So the carbonate and bicarbonates in water can be determined by titrating the solution with standard acid like N/50 H2SO4 using first Phenolphthalein and later methyl orange as an indicator conversion of carbonates into bicarbonates occur.

In the II step to the solution using methyl orange as indicator (pH 4.2 to 5.4) bicarbonates present in the water and bicarbonates formed from carbonates gets neutralized.
The alkalinity of water is attributed to the presence of the

Caustic alkalinity (due to hydroxide & carbonate ions)

Temporary hardness (due to Bicarbonate ions)


PROCEDURE: Pipette out 100 mL of the water sample in a clean titration flask. Add to it 2 to 3 drops of a phenolphthalein indicator. Run in N/50 H2SO4 from burette. Till the pink colour is just dis-charged. Then to the same pink colour reappears.

CALCULATION:
let volume of acid used to phenolphthalein endpoint = V1 mL
And
Extra volume of acid used to Methyl orange endpoint = V2 mL

Phenolphthalein alkalinity P= V1 x 50 x 1000000 = 10 V1 ppm
50 x 100 x 1000

Methyl orange alkalinity M = (V1+V2) x 50 x 1000000 = 10(V1+V2) ppm
50 x 100 x 1000


CALCULATION OF ALKALINITY OF WATER:
ALKALINITY
OH- (ppm)
CARBONATE ion (ppm)
Bicarbonate ion (ppm)
P=0
P=1/2 M
P<1/2 M
P>1/2 M
P=M
0
0
0
(2P-M)
P=M
0
2P
2P
2(M-P)
0
M
O
(M-2P)
0
0








2.ESTIMATION OF CHLORIDES IN WATER
The chloride ions are present in water in the form of one or more of the compounds like CaCl2, MgCl2, NaCl etc. The estimation of chloride ions is generally made by titrating the water sample against a standard solution of silver nitrate using potassiumchromate as indicator. The added silvernitrate precipitate chloride ions as white ppt of silverchoride, as per the following chemical reactions..
NaCl + AgNO3 ------à AgCl + NaNO3
Cl- + Ag+ ------à AgCl
When all the chlorine ions are removed as AgCl ppt, the excess drop of silvernitrate reacts with potassiumchromate forming silverchromate, which is red in colour.
K2CrO4 + 2AgNO3 ----à Ag2CrO4 + 2KNO3
CrO4-2 + 2Ag+ ----à Ag2CrO4
The endpoint is therefore the change in colour from bright yellow due to brick red colour due to formation of Ag2CrO4 indicator. Then titrate it against N/50 AgNO3 solution till the colour changes from yellow to permanent brick-red.
Calculation:
Let volume of N/50 AgNO3 used = V mL
50 x Normality of free chlorine = V x [N/50]
Strength of free chlorine = V x 35.5 x 1000000
25 x 100 x 1000
= 14.2 x V ppm.

3. DISSOLVED OXYGEN:
The oxidation of KI by dissolved Oxygen determines the amount of dissolved Oxygen in water. Iodine is titrated with standard sodiumthiosulphate solution using starch as final indicator. The dissolved molecular Oxygen in water does not react with KI. So, an oxygen carrier is used to bring about the reaction between Oxygen and KI. Hence manganesehydroxide is produced as a result of the reaction of KOH and MnSO4.
2KOH + MnSO4 ---à Mn(OH)2 + K2SO4
2Mn(OH)2 + O2 ---à 2 MnO(OH)2
MnO(OH)2 + H2SO4 ---à MnSO4 + 2H2O + [O]
2KI + H2SO4 + [O] ---à K2SO4 + H2O + I2
2Na2S2O3 + I2 ------à 2NaI + Na2S4O6
The presence of sulphates, nitrates, etc. in rain water gives wrong results in determination of dissolved Oxygen in water because these ions also liberates Iodine from KI. In order to prevent the liberation of Iodine solution from nitrate, If present in water, sodium-azide (NaN3) is added to the alkaline Iodide solution. This reacts with nitrates and gives..
2NaN3 + H2SO4 --à 2HN3 + Na2SO4
HNO2 + HN3 -----à N20 + N2 + H2O
PROCEDURE: 250 mL of water is taken in bottle preventing it to contact with air. 2 mL of Manganoussulphate solution is added by means of pipette, and also 2 mL of alkalineiodine solution is also added. Shake the bottle thoroughly, and repeat the process thrice. The ppt is allowed to settle half-way and mix again. Then add to it Conc. H2SO4 insert the stopper and shake the bottle again allow the yellow solution to stand for 5 min. Withdraw 100 mL of solution and titrate it against N/100 solution (Na2S2O3 solution) using freshly prepared starch as indicator. The endpoint will be the disappearance of blue- colour. When the volume of Thiosulphate is V mL then dissolved oxygen content in water is 8 V ppm.
Methods of Treatment of Water for Domestic Purposes-

SEDIMENTATION: Sedimentation is the process of removing large suspended particles at the bottom of the reservoir. Which are collected due to gravity.
Sedimentation is the process of allowing to stand undisturbed in big tanks, about 5M deep, when most of the suspended particles settle down at the bottom, due to the force of gravity. The clear supernatant water is then drawn from tank with the help of pumps. The retention period in a sedimentation tank ranges from 2-6 hours.
In order to carry out the sedimentation process successfully, some of the chemicals are added to water before sedimentation. These chemicals are called Coagulants.
The coagulants when added to water, form an insoluble gelatinous, flocculent precipitates, which descends through the water and mixes-up into very fine suspended impurities forming bigger impurities forming bigger impurities or flocs, which easily settles down.
Some of the coagulants used for sedimentation process are alum, ferrous sulphate, sodium aluminate etc.
Chemical coagulants:
Alum: K2SO4. Al2(SO4)3. 24H2O
Alum is the most widely used in water treatment plants.
Al2(SO4)3 + Ca(HCO3)2 à 2Al(OH)3 + 3CaSO4 + 6CO2
NaAlO2 + 2H2O à Al(OH)3 + NaOH
FeSO4 + Mg(HCO3)2 à Fe(OH)2 + MgCO3 + CO2

2) FILTRATION: It is the process of removing colloidal matter and most of the bacteria, micro-organisms etc, by passing water through a bed of fine sand and other proper-sized granular materials. Filtration is carried out by using Sand-filter.
Sand filter is used for removing suspended particles, micro-organisms, bacteria etc., by passing through a finely graded sand bed. All the colloidal matter and sediments gets accumulated and water is purified.
OPERATION OF SAND FILTER: In sand filtration process, water is passed through different sized sand beds like fine, coarse and gravel beds. The suspended particles are unable to pass through the gaps in the sand bed, because of their size. Water is first passed through a fine sand-bed. The suspended particles are first collected and gets clogged in fine sand and then passed through sand-bed. Here colloidal matter gets collected and the water is free from sediments. After passing of water from coarse sand bed it enters through a bed of medium sized stones called gravel or gravel-bed. This is the last bed where water is filtered completely and the filtered wate is collected at the filter outlet. During the filtration process the fine pores of sand bed gets seized and clogged. In order to continue the filtration process, 2-3 cm of fine sand at the top is scrapped, replaced and leveled with makeup sand.

3) REMOVAL OF MICROORGANISMS:
Water after passing through Sedimentation, Coagulation and Filtration operations still contains a small quantity of Pathogenic bacteria.
Disinfection: The process of destroying/killing the disease producing Bacteria, microorganisms, etc. from the water and making it safe for use, is called disinfection.
Disinfectants: the chemicals or substances which are added to eater for killing the Bacteria.
The disinfection of water can be carried out by following methods:
A). BOILING: Water for 10-15 minutes, all the disease-producing bacteria are killed and water becomes safe for use.

B) BLEACHING POWER: It is used to purify the drinking water from micro organisms. The purification process is achieved by dissolving 1 kg of bleaching powder in 1000 kiloliters of water. This dissolved water solution is left undisturbed for many hours. When bleaching powder is mixed with water, the result of chemical reaction produces a powerful Germicide called Hypochlorous acid. The presence of chlorine in the bleaching powder produces disinfecting action, kills germs and purifies the drinking water effectively.
CaOCl2 + H2O -à Ca(OH)2 + Cl2
H2O + Cl2 à HCl + HOCl
HOCl + Germs à Germs are killed à water purified.

C) CHLORINE: Chlorination is the process of purifying the drinking water by producing a powerful Germicide like Hypochlorous acid. When this Chlorine is mixed with water it produces Hypochlorous acid which kills the germs present in water.
H2O + Cl2 à HOCl + HCl
Chlorine is basic (means pH value is more than 7) disinfectant and is much effective over the germs. Hence Chlorine is widely used all over the world as a powerful disinfectant. Chlorinator is an apparatus, which is used to purify the water by chlorination process.
BREAK-POINT CHLORINATION:
Break-point chlorination is a controlled process. In this process suitable amount of Chlorine is added to water. In order to kill all the bacteria present in water, to oxidize the entire organic matter and to react with free ammonia the chlorine required should be appropriate. Break-point determines whether chlorine is further added or not. By Chlorination, organic matter and disease producing Bacteria are completely eliminated which are responsible for bad taste and bad odour in water.
When certain amount of Chlorine is added to the water, it leads to the formation of Chloro-organic compounds and chloramines. Addition of some more chlorine leads to destruction of chloro-organic compounds and chloramines. The point at which free residual chlorine begins to appear is terms as “Break-point”.






OZONISATION: Ozone is powerful disinfectant and is readily dissolved in water. Ozone being unstable decomposes by giving Nascent Oxygen which is capable of destroying the Bacteria. This Nascent Oxygen removes the colour and taste of water and oxidizes the organic matter present in water. O3 à O2 + [O]