CHLORINATION A Refresher: The effectiveness of chlorine disinfection is based on five factors: 1. pH 2. temperature 3. contact time 4. concentration 5. other substances in water The essential reaction of chlorine in water is as follows: 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � Chlorine + water -> Hypochlorous acid + Hydrochloric acid � � CL2 + H2O -> HOCl + HCl � � Hypochlorous acid -> Hydrogen + Hypochlorite ion � � HOCl -> H+ + OCl- � � Hydrochloric acid -> Hydrogen + Chloride ion � � HCl -> H+ + Cl- � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 HOCl is the preferred form for disinfection. pH strongly influences the ratio of HOCl to OCl-. Generally, lower pH's promote the formation of HOCl while higher pH's promote the formation of OCl-. Time required for good disinfection is greater for OCl-. The difference in contact time needed for good disinfection is negligible between pH 7.0 to pH 8.5 but is markedly longer above pH 8.5. Some of the common substances that react with chlorine are ammonia, iron, manganese, hydrogen sulfide, and dissolved organic materials. Chlorine reacts with ammonia to form "chloramines"(compounds containing both nitrogen and chloride ions). 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � ammonia + hypochlorous acid -> Monochloramine + water � � NH3 + HOCl -> NH2Cl + H2O � � � � Monochloramine + hypochlorous acid -> Dichloramine + water � � NH2Cl + HOCl -> NHCl2 + H2O � � � � Dichloramine + Hypochlorous acid -> Trichloramine + water � � � NHCl2 + HOCl -> NCl3 + H2O � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Monochloramine and Dichloramine are effective disinfectants but are not considered as efficient as Free Chlorine. It may take up to 25 times more available combined chlorine to accomplish the same bacteriacidal action as free chlorine and up to 100 times the contact time. Estimated Effectiveness 旼컴컴컴컴쩡컴컴컴컴컴� � HOCl � 1 � � OCl- � 1/100 � � NCL3 � >NHCl2 � � NHCL2 � 1/80 � � NH2Cl � 1/150 � 읕컴컴컴컴좔컴컴컴컴컴� Free available chlorine measurements refer to the HOCl and OCl- forms in water. Combined available cholrine measurements essentially refer to chloramines + Free Chlorine (technically all combined forms of chlorine + free chlorine).