Article by shubham

We call water “hard” if it contains a lot of calcium or magnesium dissolved in it. A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion 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 precipitate out as hard deposits to the surfaces of pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate ions but also happens to some extent even in the absence of such ions. 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.

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 corrode when in contact with another type of metal, when both are in contact with an electrolyte. However the sodium (or potassium) ions released during conventional water softening are much more electrolytically active than the calcium or magnesium ions that they replace and galvanic corrosion would be expected to be substantially increased by water softening and not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more plumbo-solvent than hard water

Ion-exchange resin devices Conventional water-softening devices intended for household use depend on an ion-exchange resin in which “hardness” ions trade places with sodium ions that are electrostatically bound to the anionic functional groups of the polymeric resin. A class of minerals called zeolites also 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.

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, sodium or potassium ions, which exchange with divalent calcium and magnesium ions in the water. As the water passes through the resin column, 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.

waste water treatment plant that cannot be discharged to sanitary sewers for treatment at a centralized waste water treatment plant must be treated on the site where it originated. Systems for on-site treatment of wastewater are referred to as “septic systems”, “on-site disposal systems”, subsurface disposal systems” or “individual sewerage systems”(SSDS) among others.

Sewage flows from the original area into the septic tank where the heavier solids settle to the bottom forming a sludge deposit. Lighter solids, such as grease, float to the top and form a scum layer. The liquid flows from the septic tank into an absorption system where it soaks into the soil. This process provides treatment of the sewage by gravity settling and skimming, biological decomposition and soil filtration. Proper functioning of an individual sewerage system depends on adequate design, proper construction, careful use and maintenance.

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Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.

Regeneration

As these resins become loaded with undesirable cations and anions they gradually lose their effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium ions) then regeneration is usually effected by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them.

For anionic resins a solution of sodium or potassium hydroxide (lye) is used. If potassium chloride is used the same exchange process takes place except that potassium is exchanged for the calcium, magnesium and iron instead of sodium. This is a more expensive option and may be unsuited for people on potassium-restricted diets.

waste water treatment plant covers the mechanisms and processes used to treat waters that have been contaminated in some way by anthropogenic industrial or commercial activities prior to its release into the environment or its re-use.

Most industries produce some wet waste although recent trends in the developed world have been to minimise such production or recycle such waste within the production process. However, many industries remain dependent on processes that produce wastewaters.

Water treatment for the production of drinking water is dealt with elsewhere. (See water purification.) Many industries have a need to treat water to obtain very high quality water for demanding purposes. Water treatment produces organic and mineral sludges from filtration and sedimentation. Ion exchange using natural or synthetic resins removes calcium, magnesium and carbonate ions from water, replacing them with hydrogen and hydroxyl ions. Regeneration of ion exchange columns with strong acids and alkalis produces a wastewater rich in hardness ions which are readily precipitated out, especially when in admixture with other wastewaters.