Explain The Different External Water Treatment Methods?

1.	Explain The Different External Water Treatment Methods?
Answer» External treatment is used to remove suspended solids, dissolved solids (particularly the Calcium and Magnesium ions which is a major cause of scale formation) and dissolved gases (oxygen and carbon dioxide). The techniques include Precipitation processes, in which chemicals are ADDED to precipitate calcium and magnesium as compounds of low solubility. The lime-soda process is typical of this class, but other precipitating agents such as caustic soda and sodium phosphate can be used when the composition of the raw water permits. Ion-exchange progresses, in which the hardness is removed as the water passes through bed of natural ZEOLITE or synthetic resin and without the formation of any precipitate. Ion exchange processes can be used for almost total demineralization if required, as is the case in large electric power PLANT boilers. De-aeration, in which gases are expelled by preheating the water before entering the boiler system. Water NORMALLY contains approximately 10 mg/1 of dissolved oxygen at ambient temperature Filtration, to remove suspended solids.

Answer»

External treatment is used to remove suspended solids, dissolved solids (particularly the Calcium and Magnesium ions which is a major cause of scale formation) and dissolved gases (oxygen and carbon dioxide). The techniques include Precipitation processes, in which chemicals are ADDED to precipitate calcium and magnesium as compounds of low solubility.
The lime-soda process is typical of this class, but other precipitating agents such as caustic soda and sodium phosphate can be used when the composition of the raw water permits.
Ion-exchange progresses, in which the hardness is removed as the water passes through bed of natural ZEOLITE or synthetic resin and without the formation of any precipitate. Ion exchange processes can be used for almost total demineralization if required, as is the case in large electric power PLANT boilers.
De-aeration, in which gases are expelled by preheating the water before entering the boiler system. Water NORMALLY contains approximately 10 mg/1 of dissolved oxygen at ambient temperature Filtration, to remove suspended solids.

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