Chlorination and Ozone Treatment of Water

Hardness due to calcium or magnesium ions, present as carbonates, is produced when shghdy acidic water trickles through limestone (CaCOj) or dolomite (CaCO -MgCOj). 

Such hard water can be softened by removing these ions. One of the methods for softening water is the lime—soda process. The lime—soda process takes advantage of the facts that calcium carbonate (CaCOj) is much less soluble than calcium bicarbonate [Ca(HCOj)2] and that magnesium hydroxide is much less soluble than magnesium bicarbonate. The raw materials added to the water in this process are hydrated lime (Ca(OH)2) and soda (Na2COj). 

The overall result of the lime—soda process is to precipitate almost all the calcium and magnesium ions in the form of calcium carbonate and magnesium hydroxide and to leave sodium ions as replacements. 

Iron present as Fe and manganese present as Mn can be removed from water by oxidation with air (aeration) to higher oxidation states. If the pH of the water is 7 or above (either naturally or through the addition of lime), the insoluble compounds Fe(OH)j and Mn02(H20) are produced and precipitate from solution. 

The desire for and achievement of soft water for domestic use has sparked a rather heated health debate. Soft water is usually acidic and contains Na ions in the place of di- and trivalent metal ions. An increased intake of Na is known to be related to heart disease. The acidic soft water is also more likely to attack metallic pipes, joints, and fixtures, resulting in the dissolution of toxic ions such as One way to avoid sodium ions in drinking 

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