- Water softening
A water softener reduces the dissolved
calcium, magnesium, and to some degree manganeseand ferrous ironion concentration in hard water.
These "hardness ions" cause three major kinds of undesired effects. Most visibly, metal ions react with
soaps and calcium-sensitive detergents, hindering their ability to lather and forming a precipitate—the familiar "bathtub ring". Presence of "hardness ions" also inhibits the cleaning effect of detergent formulations. Second, calcium and magnesium carbonates tend to adhere to the surfaces of pipes and heat exchanger surfaces. The resulting build-up of scale can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this can lead to failure of the boiler. [cite web |url=http://www.chem1.com/CQ/hardwater.html |title=Hard water and water softening |accessdate=2007-10-08 |author=Stephen Lower |month=July | year=2007 |year= |month= |format= |work= |publisher=] Third, the presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion, in which one metal will preferentially corrodewhen in contact with another type of metal, when both are in contact with an electrolyte.
Conventional water-softening devices intended for household use depend on an
ion-exchange resinin which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionicfunctional groups of the polymeric resin. A class of minerals called zeolitesalso exhibits ion-exchange properties; these minerals were widely used in earlier water softeners. Water softeners may be desirable when the source of water is a well, whether municipal or private.
Chelators are used in
chemical analysis, as water softeners, and are ingredients in many commercial products such as shampoosand food preservatives. Citric acidis used to soften water in soaps and laundry detergents. A commonly used synthetic chelator is EDTA.
Ion-exchange resin devices
How it works
The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind metal ions, which are positively charged. The resins initially contain
univalent hydrogen, sodiumor potassiumions, which exchange with divalentcalcium and magnesium ions in the water. This exchange eliminates precipitation and soap scum formation. As the water passes through both kinds of resin, the hardness ions replace the hydrogen, sodium or potassium ions which are released into the water. The "harder" the water, the more hydrogen, sodium or potassium ions are released from the resin and into the water.
As these resins become loaded with hardness ions they gradually lose their effectiveness and must be regenerated by passing a concentrated brine, usually of
sodium chlorideor potassium chloride, or hydrochloric acid solution through them. Most of the salts used for regeneration gets flushed out of the system and may be released into the soil or sewer. These processes can be damaging to the environment, especially in arid regions.Fact|date=June 2007 Some jurisdictions prohibit such release and require users to dispose of the spent brine at an approved site or to use a commercial service company. Most water softener manufacturers provide metered control valves to minimize the frequency of regeneration. It is also possible on most units to adjust the amount of salt used for each regeneration. Both of these steps are recommended to minimize the impact of water softeners on the environment and conserve on salt use.Fact|date=June 2007 Using acid to regenerate lowers the pH of the regeneration waste.
In industrial scale water softening plants, the effluent flow from re-generation process can be very significant. Under certain conditions, such as when the effluent is discharged in admixture with domestic sewage, the calcium and magnesium salts may precipitate out as hardness scale on the inside of the discharge pipe. This can build up to such an extent so as to block the pipe as happened to a major chlor-alkali plant on the south Wales coast in the 1980s.Fact|date=June 2007
Effects of sodium
For people on a low-sodium diet, the increase in sodium levels (for systems releasing sodium) in the water can be significant, especially when treating very hard water. A paper by
Kansas State Universitygives an example: "A person who drinks two liters (2L) of softened, extremely hard water (assume 30 gpg) will consume about 480 mg more sodium (2L x 30 gpg x 8 mg/L/gpg = 480 mg), than if unsoftened water is consumed." This is a significant amount, as they state: "The American Heart Association (AHA) suggests that the 3 percent of the population who must follow a severe, salt-restricted diet should not consume more than 400 mg of sodium a day. AHA suggests that no more than 10 percent of this sodium intake should come from water. The EPA’s draft guideline of 20 mg/L for water protects people who are most susceptible." [cite web |url=http://www.oznet.ksu.edu/library/H20QL2/MF1094.PDF |title=Sodium in Drinking Water |accessdate=2007-04-03 |author=Michael H. Bradshaw, G. Morgan Powell|month=October | year=2002 |year= |month= |format= |work= |publisher= Kansas State University] Most people who are concerned with the added sodium in the water generally have one faucet in the house that bypasses the softener, or have a reverse osmosisunit installed for the drinking water and cooking water, which was designed for desalinisationof sea water.
* [http://www.water-research.net/hardness.htm Wilkes University hard water site]
* [http://www.riversideca.gov/municipal_code/Title_14/12/245.html Riverside County CA water softener restrictions]
* [http://www.pwgazette.com/howsoftenerswork.htm Water softener diagram]
* [http://www.uwsp.edu/cnr/gndwater/privatewells/Water%20Softener%20Use%20Raises%20Questions%20for%20System%20Owners.htm#SofteningProcess Water softener regeneration]
* [http://www.chem1.com/CQ/gallery.html Gallery of water-related pseudoscience] - Chemist's site providing explanations of how alternatives to water softening, such as catalytic water conditioning, are not scientifically grounded
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