Bleaching powder is also referred to as T.C.L. powder. Beaching powder is nothing but a compound of Lime and Chlorine.
In fresh Bleaching powder, normally chlorine content is 33 % or more. Bleaching powder is unstable in nature and as the time passes the chlorine content reduces. To avoid loss of chlorine, it is necessary to store Bleaching powder in dry condition and away from direct sun light. If the Bleaching powder is in a bag, after use, the bag should be properly closed.
The percentage of chlorine, in the Bleaching power can be found out in a laboratory test. Such chlorine Tests are carried out in District Public Health Laboratories.
1. Formula for Circular Tanks:
Quantity of water in the tank (in liters) = 785 x (Tank Diameter in meter)2 x (Height of water column) – All measurement in Meters.
2. Formula for Square/Rectangular Tanks
Quantity of water in the tank (in lit) = length of tank (in m) x width of tank (in m) x height of water in the tank (in m) x 1000
Quantity of bleaching power required:
If the Bleaching powder contains 30% or more chlorine, then 5 gm Bleaching powder is required for proper disinfection of 1000 lits of water.
Let us understand this by an example.
If a square tank of size 4 m x 4 m (inner dimension) has 2.5 m depth of water in it then
– Volume of water in the tank = 4 x 4 x 2.5 x 1000 = 40,000 lit
Hence quantity of Bleaching Powder required for disinfection of this water = 40,000 x 5/1000 = 200 gms.
However, if the chlorine content of the bleaching powder is less than 30%, the quantity of bleaching powder for disinfection of the same quantity of water (40,000 lits) will have to be increased in the ratio of the theoretical content of chlorine and the actual content of chlorine.
Quantity of Bleaching Powder required for disinfection as per above formula should be taken in a plastic bucket and adding small quantity of water, a thick paste should be prepared. Then the bucket should be filled up to 50% to 75% by water and the paste should be thoroughly stirred with a wooden stick. This
solution should be allowed to stand for some time and then the supernatant should be poured in another bucket.
Then with the help of a rope, this bucket should be lowered in the GSR/ESR up to a depth of 0.3 to 0.5 m and let the chlorine solution get properly mixed in the water in the tank by stirring.
Do not mix/use the remnants of the first bucket in the tank water. It should be kept separately and disposed of properly.
Disinfected water has residual chlorine. Presence of residual chlorine is an indicator of proper disinfection. This residual chlorine also helps disinfection of likely pollution of water in the distribution network.
How much residual chlorine is there in the disinfected water can be determined by a very simple test. This test is called “Ortho Toluidine Test” or simply “O.T. Test”. O.T Test should indicate residual chlorine in following proportion:
How to carryout O.T. Test
The work of periodic testing of water sample and keeping record of the same should be vested with the person responsible for distribution of water.
The person concerned should carry out the testing as given below –
Use of Bleaching Powder in excess of the required quantity
There is a possibility of the source getting polluted at the start of monsoon and during heavy rains. This may result into epidemics. Hence it is very important to take utmost care in disinfection during such periods. In such situations use of Bleaching Powder, in excess of required quantity, is recommended. The extra dose of bleaching powder should be adjusted in such a way that the residual chlorine is more than 1 ppm. Adequate O.T. Test should ensure this.
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