Water and its Treatment

 Water and its Treatment

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. It is widely used in drinking, bathing, sanitary, washing, irrigation, fire-fights, air-conditioning and also production of industrial materials. The distribution of water on the Earth’s surface is extremely uneven. Only 3% Of freshwater (69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers and swamps.) of water on the surface is fresh; the remaining 97% resides in the ocean. Looked at another way, only one percent of the water on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.

Types of Impurities present in water:

The natural water is usually contaminated by different types of impurities.

They are mainly three types.

➢ Physical impurities

➢ Chemical impurities

➢ Biological impurities

1.       Physical impurities:

➢ Colour: in water is caused by metallic substances like salts.

➢ Turbidity: is due to the colloidal, extremely fine suspensions such as insoluble substances like clay, slit, and micro-organisms.

➢ Taste: presence of dissolved minerals in water produces taste. Bitter taste can be due to the presence of Fe, Al, Mn, Sulphates and lime. Soap taste can be due to the presence of large amount of sodium bicarbonate.

➢ Odour: In water is undesirable for domestic as well as industrial purpose.

2.       Chemical impurities:

➢ Inorganic chemicals: Cations(Al+3 , Ca+2, Mg+2, Fe+2, Zn+2, Cu+2 Na+ , K + ), Anions(Cl− , SO4 −2 , NO3 − , HCO3 − , F− , NO2 − )

➢ Organic chemicals: dyes, paints, petroleum products, pesticides, detergents, drugs textile materials, other organic related materials. 3. Biological Impurities:

➢ Biological impurities are Algae, pathogenic bacteria, fungi, viruses, pathogens, parasite-worms.

Hardness of water

 Hardness of water defined as which prevent the lathering of soap. This is due to presence of certain salts like Ca⁺², Mg⁺² and other heavy metals dissolved in water. Soaps (Sodium or Potassium salts of higher fatty acids) like Stearic acids (C₁₇H₃₅COONa).

Soft Water: The water which gives more lather with soap is called soft water.

C₁₇H₃₅COONa + H₂O → C₁₇H₃₅COOH + NaOH

Hard Water: The water which does not give lather with soap is called hard water. This is due to presence of certain salts like Ca⁺², Mg⁺² and other heavy metals dissolved in water.

2C₁₇H₃₅COONa + CaCl₂/MgCl₂ → (C₁₇H₃₅COO) ₂ Ca/Mg + 2NaCl