Chemical Disinfection

Chemical Disinfection

	Chemical Disinfection Bleaching powder Bleaching powder or chlorinated lime is a white amorphous powder with a pungent smell of chlorine. When freshly made, it contains about 33 % of 'available chlorine'. It is however an unstable compound. On exposure to air, light and moisture, it rapidly loses its chlorine content. But when mixed with excess of lime, it retains its strength; this is called stabilised bleach'. Bleaching powder should be stored in a dark, cool, dry place in a closed container that is resistant to corrosion.
Chlorine solution Chlorine solution may be prepared form bleaching powder. If 4 kg of bleaching powder with 25% available chlorine is mixed with 20 litres of water, it will give a 5% solution of chlorine. The solution should be kept in a dark, cool place in a closed container. High test hypochlorite HTH or perchloron is a calcium compound which contains 60-70% available chlorine. It is more stable than bleaching powder and deteriorates much less on storage. Solutions prepared from HTH are also used for water disinfection. Chlorine tablets Under various trade names (viz. halazone tablets) are available in the market. They are quite good for disinfecting small quantities of water, but they are costly.
Iodine Iodine may be used for emergency disinfection of water. Two drops of 2% ethanol solution of iodine will suffice for one litre of clear water. A contact time of 20-30 minutes is needed for effective disinfection. Iodine does not react with ammonia or organic compounds to any appreciable extent hence it remains in its active molecular form, over a wide range of pH values and water conditions and persist longer than either chlorine or bromine. But its use invokes high costs.
Potassium permanganate Once widely used, it is no longer recommended for water disinfection. Although a powerful oxidising agent, it is not a satisfactory agent for disinfecting water. It may kill cholera vibrios but is of little use against other disease organisms. It also alters the colour, smell and taste of water.

Home | Site map | Submit Article | Directory | Search