Small Scale Purification

SMALL SCALE PURIFICATION

Boiling

  • Except for domestic purposes or for the sterilization of very limited amounts of water, boiling is impracticable in most circumstances, as for instance in the supply of water for a dairy form.
  • Boiling is however of great value when there is reason to believe that the filters of a public supply have become temporarily faulty or when owing to heavy flooding, surface water has gained entrance to wells or springs. When such an accident as the letter occurs, warning is usually given by the turbid appearance of the water.

Chlorination

  • Is the best method for the routine treatment of small supplies of water, the chlorine being readily obtainable in the form of chloride of lime (bleaching powder). The latter should be added to the water in such quantity that free chlorine will be available to the extent of at least one part per million of water. This may be done by first preparing a solution of chloride of lime consisting of 30 gms of chloride of lime to 250ml water, which will suffice to treat 2000 gallons of a water not containing an excessive amount of organic matter. After chlorination the water should be allowed to stand in an open tank for four hours before being used.
  • In the case of waters which contain much organic matter or are heavily contaminated by bacteria, super chlorination followed by dechlorination should be the method adopted . After standing for not less than 30 minutes, small quantities of this water may be dechlorinated by adding sodium thiosulphate , which removes the taste of chlorine

Potassium permanganate

  • Potassium permanganate very rapidly decomposes in the presence of organic matter, yielding nascent oxygen. It is feeble disinfectant in water, but has a specific action on the vibrio cholera owing to the lethal effect of oxygen on this particular organism. A better reaction is obtained by the addition to the water of some dilute acid .
  • This treatment is not used on a large scale but is sometimes adopted for the disinfection of wells and water tanks. The amount of permanganate added must obviously vary with the degree of pollution.
  • The treatment of wells is effected by adding to each gallon of water 3.9 gms of permanganate with 12 ml of strong hydrochloric acid, leaving for twenty four hours; pumping until the water is colourless , removing dead aquatic fauna.
Last modified: Wednesday, 9 March 2011, 9:27 AM