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Methods of water purification






General methods:

- clarification (eliminating the sediment),

– discoloration (eliminating the coloured colloids),

- disinfection (eliminating the infectious agents like bacteria, viruses, etc.).

Special мethods: ( deironing, defluoridation, desalination, softening,

fluoridation, mineralization)

Methods of water disinfection

1. Chemical disinfection (Chemical processes for the removal of undesirable elements):

1.1. Сhlorination

1.2. Оzonization

1.3. Oligodynamic effect of silver

2. Physical non-reagent methods (Physical processes for the removal of undesirable elements):

2.1. Вoiling

2.2. Ultraviolet irradiation

2.3. Gamma irradiation (γ -irradiation)

2.4. Water disinfection with ultrasound


Appendix

 

Laboratory control over water chlorination

2.1. Determining active chlorine content in chlorinated lime (1%).

2.2. Chlorination of river water with normal chlorine doses

2.3. Determination of residual chlorine in tap water.

Water chlorination is one of the main ways of water disinfection nowadays. Gaseous chlorine, chlorinated lime, chloramin, calcium and sodium hypochloride can be used for water chlorination. Chlorine is considered the best choice due to its ability to oxidize bacteria, organic and mineral substances dissolved and suspended in water.

The amount of chlorine which is necessary for oxidizing 1 litre of water containing organic, inorganic and bacterial substances impairing its physical properties within 30 minutes, is called chlorine absorption of water. Chlorine absorptivity of water can be easily established experimentally.

The combination of chlorine with chemical substances gives rise to residual active chlorine in water. It demonstrates that the process of water purification is over and chlorinated water does not contain any bacteria. Tap water should contain small amounts of residual active chlorine (0.3 – 0.5 mg/l) so that water chlorination could be considered an efficient means of water disinfection. Excessive chlorine residue above 0.5 mg/L makes the water unfit for drinking as it entails a deterioration of organoleptic properties of water giving rise to unpleasant taste and odor.

Residual chlorine content is used to control the efficiency of water disinfection. Small doses of chlorine in the amount equal to chlorine demand of water should be added to water. Chlorine demand for water is calculated as the sum of values of chlorine absorptivity and residual chlorine (0.3 – 0.5 mg/l).


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