Removal Of Hardness

Health Hygiene & Sanitation

Lesson 24 : Special Treatment Of Water And Their Health Implications

Special Treatments

Removal Of Hardness

The hardness of water can be removed employing different methods:

  1. Removal of Temporary hardness
    1. Boiling
    2. Addition of lime
    3. Addition of sodium carbonate
    4. Permutit process
  2. Removal of Permanent hardness
    1. Addition of sodium carbonate
    2. Base exchange process
Removal Of Temporary Hardness
  1. Boiling : Boiling removes the temporary hardness by expelling carbon dioxide and precipitating the insoluble calcium carbonate. But for large scale it is a fuel consuming and expensive method.

  2. Addition of lime Addition of lime (Calcium hydroxide) reduces total hardness and magnesium. Lime absorbs the carbon dioxide and precipitates the insoluble calcium carbonate. In the Clarks method of softening water one ounce of quick lime is added to every 700 gallons of water for each degree (14.25 ppm) of hardness.

  3. Ca (OH)2 + Ca(HCO3)2 = 2CaCO3 + 2H2O

  4. Addition of sodium carbonate Sodium carbonate (soda ash) removes both temporary and permanent hardness

    • Na2 (CO)3 + Ca(HCO3)2 = 2NaHCO3 + CaCO3
    • CaSO4 + Na2 CO3 = CaCaO + Na2 SO4

  5. Permutit process or Base Exchange process : Permutit or Base Exchange process is used in the treatment of large water supplies. Sodium permutit is a complex compound of sodium, aluminium and silica (Na2 AI2 Si20 H20). It has the property of exchanging the sodium cation for the calcium and magnesium ions in the water. When hard water is passed through the permutit the calcium and magnesium ions are entirely removed by Base Exchange and the sodium permutit is finally converted into calcium and magnesium permutit. Water can be softened to zero hardness by this process. Since water of zero hardness is corrosive, a part of the raw water is mixed with the softened water to secure the desired hardness. After some uses permutit loses its effectiveness but it can be regenerated by treating with concentrated solution of sodium chloride or brine and washing away the soluble calcium and magnesium chloride formed. Permutit process removes both temporary and permanent hardness.

Water hardness and cardiovascular diseases:

An inverse statistical association has been reported between the hardness of drinking water and the death rate from cardiovascular diseases. Areas supplied with soft drinking water showed a significantly higher prevalence of arteriosclerotic heart disease or degenerative heart disease, hypertension, sudden deaths of cardiovascular origin, or a combination of these. The evidence is solely on circumstantial and statistical association. Further studies are, however, needed to establish a possible connection between certain water characteristics and the development of cardiovascular diseases.

Last modified: Wednesday, 25 April 2012, 7:11 AM