CHEM DECODE 1_2

Unit I: Water Technology

1.1: Impurities in Water

  • Common impurities present in natural water can be classified into the following types:

    • A) Suspended impurities

      • Examples: Clay, mud, organic matter, industrial waste.

      • Effects: Cause turbidity and odour in water.

      • Removal Methods: Filtration.

    • B) Colloidal impurities

      • Composition: Colloidal particles such as clay, mud, and organic matter.

      • Effects: Make the water appear turbid.

      • Removal Methods: Coagulation, sedimentation followed by filtration.

    • C) Dissolved impurities

      • Subdivided into:

        1. Dissolved gases (e.g., CO2, Cl2, H2S, SOx, NOx)

        2. Dissolved salts (e.g., bicarbonates, sulphates, and chlorides of Ca, Mg, Fe, Al, Na, K).

      • Removal Methods: Special softening procedures.

1.2: Hardness of Water

  • Definition of Hardness: Hardness is defined as the total amount of hardness-causing impurities present in a finite volume of water.

    • Mainly caused by soluble bicarbonates, chlorides, sulphates, nitrates of Ca, Mg, along with heavy metals (Fe, Al, and Mn).

  • Types of Hardness:

  1. Alkaline Hardness (Temporary Hardness):

    • Caused by bicarbonates which can be removed by boiling and filtration (forms insoluble carbonates/hydroxides).

  2. Non-Alkaline Hardness (Permanent Hardness):

    • Caused by chlorides, sulphates, and nitrates that cannot be easily removed by boiling. Requires special softening methods.

  • Comparison:

    • Temporary hardness can be removed by boiling, while non-alkaline hardness requires special treatment.

1.3: Calculation of Hardness

  • Expression of Hardness:

    • The hardness of water is expressed in terms of Calcium Carbonate (CaCO3) equivalence due to calculations based on its stabilizing properties.

1.4: Ion Exchange Methods

  • Zeolite/Permutit Methods:

    • Zeolites are hydrous sodium aluminosilicates used to soften water by exchanging sodium ions with hardness-causing cations (Ca2+, Mg2+).

    • Regeneration involves washing zeolite with a concentrated sodium chloride solution to restore its softening capacity.

1.5: Boiler Corrosion and Scale Formation

  • Causes of Boiler Corrosion:

    1. Saturated dissolved gases (e.g., oxygen and carbon dioxide).

    2. Dissolved salts leading to acid formation upon hydrolysis.

  • Preventive Measures:

    • Use of reducing agents and deaeration processes to remove dissolved gases.

  • Differences:

    • Scales are hard deposits formed from dissolved salts that precipitate out at high temperatures, while sludges are soft, slimy buildup formed at cooler sections of the boiler.

1.6: Water Treatment Techniques

  • Demineralization and Electrodialysis are key methods used in water purification, focusing on the removal of ionic impurities.

2.1: Conductometric Measurements

  • Specific conductance, cell constant, and equivalent conductance are crucial parameters used in the titration processes and water quality assessments.