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5.2.1.5 Disinfection
Deactivation, removal or killing of pathogenic microorganisms is called disinfection. Following disinfectants are dominantly used for disinfection of water.
Chlorine
0.5 mg/l of residual residual-free chlorine at a pH of less than 8 and contact period
of 30-minutes will eliminate pathogenic bacteria, but there is a risk of generating generation of trihalomethanes, which is a class of known carcinogens.
Chlorine Dioxide
Even though an effective level of protection is achieved at 0.2 mg/l for 15 minutes,
the CℓO 2 oxidising action on organic matter releases the CℓO 2
−
ion, which is toxic
and generates an unpleasant taste to water.
Ozone
0.4 mg/l and a contact period of 4 minutes are recommended to eliminate pathogenic bacteria. Presence of free of soluble manganese will result in pink tint which
will then develop into a brown coloured MnO 2 precipitates.
Chloramines
Chloramines are weak disinfectants but have strong persistent residual effect. In
nations where a high level of residual disinfectant is needed, the use of chloramines
is made after disinfection with chlorine or ozone.
UV Radiation
UV disinfection is widely used in portable treatment units just before consumption
as it will not remain in water like chemicals. It is the only disinfectant that does not
create by-products. Since UV does not have residual effect, another disinfectant
with residual effect must be used before releasing water into distribution network.
5.2.1.6 Ion Exchange
Ion exchange is a process of exchange of ions among two electrolytes or an electrolyte solution that is complex. Typical anthropogenic ion exchangers are functionalized porous or gel polymers. Ion exchanges are used to remove hardness from water.
Ion exchangers are of three types:
• Cation exchangers that exchange cations
• Anion exchangers that exchange anions
• Amphoteric exchangers that exchange both cations and anions simultaneously
Mixed beds of cations and anions can also be used for simultaneous exchange of
anions and cations.
Deionization process involves using hydrogen-cation and hydroxide-anion resins, thereby replacing all anions in water with OH
−
ions and all cations with H
+
ions.
5.2 Engineering Control
5.2.1.5 Disinfection
Deactivation, removal or killing of pathogenic microorganisms is called disinfection. Following disinfectants are dominantly used for disinfection of water.
Chlorine
0.5 mg/l of residual residual-free chlorine at a pH of less than 8 and contact period
of 30-minutes will eliminate pathogenic bacteria, but there is a risk of generating generation of trihalomethanes, which is a class of known carcinogens.
Chlorine Dioxide
Even though an effective level of protection is achieved at 0.2 mg/l for 15 minutes,
the CℓO 2 oxidising action on organic matter releases the CℓO 2
−
ion, which is toxic
and generates an unpleasant taste to water.
Ozone
0.4 mg/l and a contact period of 4 minutes are recommended to eliminate pathogenic bacteria. Presence of free of soluble manganese will result in pink tint which
will then develop into a brown coloured MnO 2 precipitates.
Chloramines
Chloramines are weak disinfectants but have strong persistent residual effect. In
nations where a high level of residual disinfectant is needed, the use of chloramines
is made after disinfection with chlorine or ozone.
UV Radiation
UV disinfection is widely used in portable treatment units just before consumption
as it will not remain in water like chemicals. It is the only disinfectant that does not
create by-products. Since UV does not have residual effect, another disinfectant
with residual effect must be used before releasing water into distribution network.
5.2.1.6 Ion Exchange
Ion exchange is a process of exchange of ions among two electrolytes or an electrolyte solution that is complex. Typical anthropogenic ion exchangers are functionalized porous or gel polymers. Ion exchanges are used to remove hardness from water.
Ion exchangers are of three types:
• Cation exchangers that exchange cations
• Anion exchangers that exchange anions
• Amphoteric exchangers that exchange both cations and anions simultaneously
Mixed beds of cations and anions can also be used for simultaneous exchange of
anions and cations.
Deionization process involves using hydrogen-cation and hydroxide-anion resins, thereby replacing all anions in water with OH
−
ions and all cations with H
+
ions.
5.2 Engineering Control