Water treatment systems don’t remove 100% bacteria from the waste water effluent. Bacteria and virus free water is obtained after disinfection. Chlorination is one of the most effective disinfection processes. Chlorine has a higher degree of persistence in water distribution systems. In Chlorination process, hypochlorous acid acts as disinfecting agent (Solsona and Mendez, 2003). Hypochlorous acids are formed when chlorine hydrolizes in water. When hypochlorous acids splits into H+ and OCl ions, bacteria and viruses are inactivated and enzymatic activities are inhibited [hydroinstrument, n.d.).

Gaseous chlorine, chlorinated lime, sodium hypochlorite and calcium hypochlorite are chlorine-related compounds for water disinfection. Chlorine gas (Cl2) is highly toxic and liquefied under pressure. Chlorinated lime (CaO.2CaCl2.O.3H2O) is corrosive dry white powder (Solsona and Mendez, 2003). Sodium hypochlorite (NaClO) is corrosive and yellowish liquid solution, commonly called “liquid bleach” (hydroinstrument, 2013), and calcium hypochlorite (Ca (ClO)2.4H2O) is corrosive inflammable powder or granules and tablets (Solsona and Mendez, 2003). Sodium hypochlorite (NaClO) produces hypochlorous acid (HClO) and hypochlorite (ClO) ions, in water which affects bacteria and viruses by inactivating and inhibiting enzymatic activities. Sodium hypochlorite affects biological functions of proteins and produces deleterious effects on DNA (Martinez-Hernandez et al., 2013).

Chlorination can be applied in drinking water operations such as treatment of ground water, industrial process water, chilling water, cooling tower systems, drip irrigation systems, swimming pools, sanitary sewage, package treatment plants, and process waste water and plating wastewater (Martinez-Hernandez et al.,2013). In the chlorination process, chlorine has two forms in water: free chlorine and combined chlorine. Sodium hypochlorite or chlorine gas produces free chlorine when added to water. When free chlorine and ammonia reacts, combine chlorine is formed which includes monochloramine and dichloramine (Rosemount analytics, 2013)


Hydroinstruments (n.d.) Basic Chemistry of Chlorination. [Online [Available at [Accessed on 19 October 2013].

Martinez-Hernandez, S., Vazquez-Rodriguez, G.A., Beltran-Hernandez, R.I., Prieto-Garcia, F., Miranda-Lopez, J.M., Franco-Abuin, C.M., Alvarez-Hernandez, A., Iturbe, U., and Coronel-Olivares, C. (2013) Resistance and Inactivation Kinetics of Bacterial Strains Isolated from the Non-Chlorinated and Chlorinated Effluents of  a WWTP.  International Journal of Environmental Research Public Health. Vol 10, pp. 3363-3383.

Rosemount Analytical (2013) Measurement of Total Chlorine in Municipal Wastewater Effluent. [Online] Available at www. [Accessed on 19 October 2013]

Solsona, F. and Mendez, J.P. (2003) Water Disinfection. [Online] Available at [Accessed on 20 October 2013].


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