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| Sep 06, 2006 8:59 am |
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re: re: re: re: [Fufaji se poochcho] - All about water purifiers. |
FuFaji Lalit Vashishta
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Chemical impurities in water:
Dissolved gases ( eg. Chlorine)
Dissolved salts ( eg. carbonates, bicarbonates, chlorides, sulfates etc)
Trace pesticides, heavy metals, arsenic, cadmium etc.
( the chemical impurities are making way into regular use water because of the run-off from Industrial wastes, leachates from landfills, herbicides, pesticides
What are technologies which are used for this?
Dissolved gases ( eg. Chlorine) = This mainly removed by putting an Activated carbon bed in line. As the terms suggests that it is "Activated" so it is not something which will last lifelong. Dissolved Organic compounds are also adsorbed by the active carbon sites.
Dissolved salts :
You must have read about the term “Hard water” and “Soft water”
Hard water is water with high level of ionic content of Calcium and magnesium in the form of Carbonates and sulfates. Hard water is difficult to foam with soap – that is a easiest test to check if the water is hard or soft.
Hard water is safe enough to drink if the mineral content is not too high.
Hardness is reduced by using a SOFTENER - Softener is a device which replaces the Calcium and Magnesium ions by Sodium ions making the water soft. Zeolite resin bed is used and water is passed through this.
When we do a test of water – we calculate what is known as TDS = Total dissolved solids.
The heavy metallic ions are removed by acid and basic ions in an ION EXCHANGE BED also known as a de-mineraliser. Many household water systems have a cartridge with mixed resin filled in them. These resins have a fixed life and after that these have to be re-charged or in case of household systems these cartridges have to be replaced by new ones. The life of the cartridge can be calculated if we have chemical report of water in a particular locality. The life will vary from location to location, so you should not believe in companies making false claims, saying that their De-mideraliser will have so and so life in any part of India.
Second method to remove the TDS is Reverse Osmosis. This technique selectively removes the Ions from water – however for a good rejection the water recovery is very low. So we have to waste almost 50-60% water which is normally a water with concentrated salts which is rejected by the membrane.
For trace impurities like Arsenic and other pesticides, specific resins are used to remove them by absorption or iron oxidation and filtering the flocs ( normally in water supplies to cities, these problems are taken care at the municipal water treatment plants)
So to conclude the chemical impurities in water can be removed using softeners, demineralisers, activated carbon, reverse osmosis to remove the dissolved impurities.
The selection of the technology is specific to the quality of the feed water. Private Reply to FuFaji Lalit Vashishta (new win) |
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