Water Analysis, Treatments, and Uses

Water Analysis, Treatments, and Industrial Applications

• Water is crucial for all living beings and human activities.
• Less than 1% of the world's water resources are readily available,necessitating careful and economical use of water.

Specifications of Water

• Different uses of water require different water specifications.
• The textile industry needs soft water, free from organic matter, as hard water reduces dye solubility and organic matter causes foul smells.
• Laundries need soft water without color, manganese (Mn), and iron (Fe), as hardness increases soap consumption, and Mn and Fe salts can discolor fabric.
• Boilers need water with zero hardness to prevent scale formation, which reduces heat transfer and can lead to corrosion.
• The paper industry needs water free from SiO2, as it produces breaks in paper, turbidity and alkalinity affect color and brightness, and hardness increases ash content.
• Sugar industries require water free from hardness, as it makes it difficult to crystallize sugar.
• Dairies and the pharmaceutical industry need ultrapure, colorless, tasteless, odorless water that is free of pathogenic organisms.
• Water treatment removes undesirable impurities to make water suitable for domestic or industrial use.

Impurities in Water:

• Impurities can be physical, bacteriological, or chemical.
• Physical impurities include suspended and colloidal matter.
• Bacteriological impurities include bacteria, fungi, and algae.
• Chemical impurities include dissolved gases, dissolved organic salts, and dissolved inorganic salts.

Water Sources:

• Water sources include surface water (flowing and still), rainwater, underground water, and seawater.

• River water contains dissolved minerals but has a variable composition.

• Lake water has a constant composition with a high quantity of organic matter.

• Rainwater is the purest form of natural water but dissolves atmospheric gases and particles.

• Underground water is free from organic impurities and is clearer with dissolved salts.

• Seawater is very impure due to evaporation and the addition of impurities from rivers.

Hardness of Water:

• Hardness is a water sample's capacity to consume soap.
• It is caused by the presence of calcium (Ca), magnesium (Mg), and other heavy metal ions.
• Hard water does not lather easily with soap but forms a white scum due to insoluble calcium and magnesium salts.

Hard vs Soft Water

• Hard water does not lather, contains dissolved Ca and Mg salts, reduces cleansing quality, elevates boiling point, and wastes time/fuel for cooking; hardness exceeds 100 mg/L.
• Soft water lathers easily, does not contain Ca and Mg salts, has good cleansing quality, and requires less cooking time/fuel; hardness is below 100 mg/L.

Types of Hardness:

• Temporary hardness is caused by dissolved bicarbonates of Ca, Mg, and iron carbonates, and be removed by boiling water.
  • Boiling decomposes bicarbonates into insoluble carbonates or hydroxides.
  • Temporary hardness is also known as carbonate hardness or alkaline hardness.
  • It is determined by titration with HCl using methyl orange as an indicator.
• Permanent hardness is caused by dissolved chlorides and sulfates of calcium, magnesium, iron, and other heavy metals, and can't be removed by boiling.
  • Permanent hardness is also known as non-carbonate or non-alkaline hardness.
• Total Hardness = Carbonate Hardness (Temporary) + Non-carbonate Hardness (Permanent).

Degree of Hardness:

• Hardness is expressed in terms of equivalent amounts of CaCO3 in mg/L.
  • CaCO3 is chosen as the standard mainly because it is having great convenience to calculate as the molecular weight in 100 and its equivalent weight is 50.
  • CaCO3 is useful as a standard because it can be easily precipitated in the lime-soda processes.
• Hardness-causing impurities are converted to their respective weights equivalent to CaCO3 and expressed in parts per million (ppm).

Multiplication factors for different salts:

• Ca(HCO3)2: 100/162
• Mg(HCO3)2: 100/146
• CaSO4: 100/136
• MgSO4: 100/120
• CaCl2: 100/111
• MgCl2: 100/95
• CaCO3: 100/100
• MgCO3: 100/84
• CO2: 100/44
• Mg(NO3)2: 100/148
• HCO3: 100/122
• OH: 100/34
• CO32-: 100/60
• NaAlO2: 100/164
• Al2(SO4)3: 100/114
• FeSO4·7H2O: 100/278
• H+: 100/2

Units of Hardness:

• Parts per million (ppm) represents the parts of calcium carbonate equivalent hardness per 10^6 parts of water.
• Milligrams per liter (mg/L) are equivalent to the mg of CaCO3 equivalent hardness per liter of water; 1 mg/L = 1 ppm.
• Clarke's degree (°Cl) is the number of grains of CaCO3 equivalent hardness per gallon of water.
• Degree French (°Fr) = Parts of CaCO3 equivalent hardness per 10^5 parts of water.
  • 1 ppm = 0.1 °Fr = 0.07 °Cl
  • 1 °Fr = 10 ppm = 10 mg/L = 0.7 °Cl
  • 1 °Cl = 14.3 ppm = 14.3 mg/L = 1.43 °Fr

Determination of Hardness by EDTA Method:

• EDTA is Ethylenediamine tetraacetic acid.
• EDTA's disodium salt is used to dissolve in water easily. EDTA binds to metal ions like Ca2+ and Mg2+.
• Ca2+ or Mg2+ gives highly stable chelate complex via oxygen or nitrogen from EDTA molecule, used in complexometric titration.

Principle of EDTA Method:

• The di-sodium salt of EDTA forms complexes with Ca2+ and Mg2+, as well as with other metal cations, in aqueous solution.

• Total hardness is determined by titrating Ca2+ and Mg2+ with disodium EDTA, using an ammoniacal buffer solution containing NH4Cl-NH4OH at pH 10 with Eriochrome Black-T (EBT) as the indicator.

• At pH 10, EBT indicator forms a wine red colored complex with Ca2+ and Mg2+ ions in hard water.

• EDTA breaks the complex during titration, giving metal-EDTA complex and releasing EBT, changing the solution to blue.

• The equivalence point can be noted to determine water hardness.

Advantages of EDTA Method:

• Greater accuracy.
• Quick.
• Convenient.

Alkalinity and Its Determination:

• Alkalinity is the concentration of salts increasing OH- concentration upon hydrolysis, raising pH.
• Natural water is usually alkaline due to HCO3, SiO32-, and sometimes CO32- ions; boiler water alkalinity includes OH- & PO42- ions.
• Alkalinity is determined by the presence of (i) OH only (ii) CO32- only (iii) HCO3- only (iv) OH & CO32- together (v) HCO3- & CO32- together.
• Hydroxide and bicarbonates do not exist together.

Alkalinity of Natural Water

• Alkalinity in natural waters arises from hydroxides, carbonates, and bicarbonates of calcium and magnesium; it measures the water's ability to neutralize acids.

Determining Alkalinity:

• Titrate the sample with a standard strong acid solution and phenolphthalein indicator if above pH 8.3.
• When the indicator changes from pink to colorless, the pH has been lowered to 4.5, neutralizing hydroxide and converting the carbonate.
• The measured alkalinity is called phenolphthalein alkalinity [P].
• Continue titrating using methyl orange indicator until the solution is yellow to red, which shows complete neutralization of all bicarbonate ions.

Alkalinity Numerical Calculation:

• When standard acid solution is added to alkaline water :

  • OH + H ---> H2O
  • CO32- + H ---> HCO3
  • HCO3 + H ---> H2O + CO2

• The total acid used in both stages neutralizes hydroxide, carbonate, and bicarbonate.

• Calculation table:

  • P = 0, OH- = 0, CO3-- = 0, HCO3- = M
  • P = 1/2M, OH- = 0, CO3-- = 2P, HCO3- = 0
  • P < 1/2M, OH- = 0, CO3-- = 2P, HCO3- = (M-2P)
  • P > 1/2M, OH- = (2P-M), CO3-- = 2(M-P), HCO3- = 0
  • P = M, OH- = P=M, CO3-- = 0, HCO3- = 0

Significance of Alkalinity:

• Used to calculate lime and soda for water softening.
• High alkalinity may cause Caustic Embrittlement and precipitate deposits in boiler feed water.
• Bicarbonates of calcium and magnesium leads to temporary hardness and, if not treated, can cause scale in boilers.

Hardness & Strength:

• Hardness = Strength (in mg/l) × Chemical equivalent wt. of CaCO3 / Chemical equivalent wt. of hardness producing salt
• Strength = Hardness (in mg/l) × Chemical equivalent wt. of hardness producing salt / Chemical equivalent wt. of CaCO3