Municipalities need to supply water free from any contaminants. The water to be supplied should be free from any hardness as it is used for drinking, bathing and washing purposes. If the water has enough hardness, it forms less lather which isn’t good for washing and bathing purposes. Municipalities supply mainly constitutes of domestic, commercial and fire demand etc. The water with too much hardness isn’t good for consumption as well.
HARD WATER AND ITS EFFECTS
Hard water can cause problems because the calcium and magnesium ions react with the higher fatty acids of soap to form an insoluble gelatinous curd, thereby causing a waste of the soap (this reaction has been objected and countered. It does not take place with modern detergents).
In boilers, which are mainly prerequisite in any industry as well as domestic water heating, the calcium and magnesium in hard waters form a hard adherent scale on the plate which in turn results in the poor heat conductivity of the scale, fuel consumption is increased, and the boiler deteriorates rapidly through the external overheating of the plates (Corrosion). Sodium carbonate (permanent hardness), if present, hydrolyzes to produce free alkali that causes caustic embrittlement and failure of the boiler plates.
WATER SOFTENING AND VARIOUS METHODS
Water softening can be achieved either by adding chemicals that form insoluble precipitates or by ion exchange. On a small scale, chemicals used for softening include ammonia, borax, calcium hydroxide (slaked lime), or tri-sodium phosphate, usually in conjunction with sodium carbonate (soda ash).
Another method, also known as lime-soda method of water softening must be followed by sedimentation and filtration in order to remove the precipitates. Raw water can be chemically softened on a large scale by the addition of just enough lime to precipitate the calcium as carbonate and the magnesium as hydroxide, whereupon sodium carbonate is added to remove the remaining calcium salts.
Ion exchange is a common industrial method of water softening which has been opted out by most number of industries. The process is accomplished by passing the water through columns of a natural or synthetic resin that trades sodium ions for calcium and magnesium ions. After the process, the column has been in use for some time, calcium and magnesium begin to appear in the water leaving the column. At that point, regeneration occurs by passing a concentrated solution of common salt slowly through the column; the excess sodium ions displace the ions that produce the hardness so that, after flushing with water, the bed of exchanger is ready to be used again.
The exchangers used for this purpose are natural aluminosilicates, but later, synthetic resins were developed which are used now instead. A home water softener usually works similarly and constitutes of zeolite or another ion-exchange resin in a tank connected directly into the water system.
HOW TO INDIAN MUNICIPALITIES WATER SOFTENING WORK?
Most common method for removing hardness at household level is boiling. As per Bureau of Indian standards, the total hardness is prescribed as 300 and 600mg/L. Iron presence concentration in drinking water supplies more than 0.3mg/L is of major concern since it promotes the growth of iron bacteria in water conveyance and distribution system. Iron bacteria do not cause health problems in people, but they may have the following possible effects: corrosion of metal pipes and equipment, clogging, formation of offensive odour and imparts taste due to the death of the bacteria, etc.
However, there are various others methods for iron, calcium and magnesium hardness, removal from groundwater such as reverse osmosis, ion exchange, chemical treatment with lime-soda ash method, chemical precipitation, adsorption filtration, absorption, aeration, etc.
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