WATER TREATMENT
Disinfection
WATER TREATMENT
Required
Combined chlorine Free chlorine Chlorine dioxide Ozone UV Light
Ct or lt
10.000 C. Parvum
C. Parvum
1.000 Giardia
Mycobacterium
Legionella fortuitum
M. fortuitum
Poliovirus Legionella
E. coli C. Parvum
100
Legionella Adenovirus
Adenovirus Microsporidium Reovirus
MS-2
Rotavirus Calicivirus
Giardia Giardia Poliovirus
Poliovirus
10 E. coli Hepatitis A
M. fortuitum
Microsporidium
Calicivirus M. fortuitum C. Parvum C. Parvum
Calicivirus
Legionella Giardia Giardia
Legionella Poliovirus
1.0 E. coli Pneumophila E. coli
Microsporidium
Adenovirus
Poliovirus
0.10 Calicivirus
Adenovirus
Adenovirus
Calicivirus
0.01 E. Coli
,disinfectoin water treatment
Framework
This module will describe the aspects of water disinfection. For this, the purpose of disinfection will be
given, the kinetics, and the practical application.
The content of this module is abstracted from Alternative Disinfectants and Oxidants Guidance Manual
(EPA 1999) and Water treatment: Principles and design (MWH 2005).
Contents
This module has the following contents:
1. Introduction
2. Purpose of disinfection
2.1 Diseases and drinking water
2.2 Pathogens of primary concern
2.3 Recent waterborne outbreaks
2.4 Mechanism of pathogen inactivation
2.5 Other uses of disinfectants in water treatment
2.6 Current practice of disinfection (and oxidation)
2.7 Disinfection byproducts
3. Disinfection kinetics
3.1 Chick’s Law
3.2 Chick-Watson model
3.3 Other models
3.4 C t -values
4. Disinfection methods
4.1 Chlorine
4.2 Ozone
4.3 UV radiation
4.4 Chlorine dioxide
4.5 Other methods
Further reading
116
, water treatment disinfection
1 Introduction produced primarily as a result of chlorination
- organic oxidation byproducts such as alde-
The most important use of disinfectants in water hydes, ketones, assimilable organic carbon
treatment is to limit waterborne diseases and inac- (AOC), and biodegradable organic carbon
tivate pathogenic organisms in water supplies. (BDOC) that are associated primarily with
The first use of disinfection as a continuous pro- strong oxidants such as ozone, chlorine, and
cess in water treatment took place in a small town advanced oxidation
in Belgium in the early 1900s (White, 1992), where - inorganics such as chlorate and chlorite as-
chlorine was used as the disinfecting reagent. sociated with chlorine dioxide, and bromate
Since the introduction of filtration and disinfection that is associated with ozone, and has also
at water treatment plants, waterborne diseases, been found when chlorine dioxide is exposed
such as typhoid and cholera, have been virtually to sunlight.
eliminated. For example, in Niagara Falls, NY, The type and amount of DBPs produced dur-
USA, between 1911 and 1915, the number of ty- ing treatment depends largely on the type of
phoid cases dropped from 185 deaths per 100,000 disinfectant, water quality, treatment sequences,
people to nearly zero following the introduction of contact time, and environmental factors such as
filtration and chlorination (White, 1986). temperature and pH.
For nearly a century, chlorine gas or chlorine re- When considering the use of alternative disinfec-
agents (hypochlorite, etc.) were, by far, the most tants, systems should ensure that the inactivation
commonly used disinfectant chemicals for drinking of pathogenic organisms is not compromised.
water production Pathogens pose an immediate critical public health
In 1974, researchers in the Netherlands and the threat due to the risk of an acute disease outbreak.
United States demonstrated that trihalomethanes Although most identified public health risks associ-
(THMs) were being formed as a result of drink- ated with DBPs are chronic, long-term risks, many
ing water chlorination (Rook, 1974; Bellar et al., systems will be able to lower DBP levels without
1974). compromising microbial protection.
THMs form when chlorine or bromide reacts with
organic compounds in the water. THMs and other In this module the purpose of disinfection is pre-
disinfection byproducts (DBPs) have been shown sented first. Thereafter, the DBPs are discussed,
to be carcinogenic, mutagenic, etc. These health since they play an important role in the selection
risks may be small but�����������������������������
need to be taken seriously��, of the disinfection method.
when you consider the large population being After this, disinfection kinetics are presented.
exposed. Finally, an overview is given of the different dis-
infection methods, in which the pros and cons of
As a result of DBP concerns from chlorine, the wa- the major methods are provided.
ter treatment industry has placed more emphasis
on the use of disinfectants other than chlorine.
Some of these alternative disinfectants, however, 2 Purpose of disinfection
have also been found to produce DBPs as a re-
sult of either reactions between disinfectants and 2.1 Diseases and drinking water
compounds in the water or as a natural decaying Although the epidemiological relationship between
process of the disinfectant itself (McGuire et al., water and disease had been suggested as early
1990; Legube et al., 1989). as the 1850s, it was not until the development
These DBPs include: of the germ theory of disease by Pasteur in the
- halogenated organics, such as THMs, halo- mid-1880s that water as a carrier of disease-
acetic acids, haloketones, and others that are producing organisms was understood.
117
Disinfection
WATER TREATMENT
Required
Combined chlorine Free chlorine Chlorine dioxide Ozone UV Light
Ct or lt
10.000 C. Parvum
C. Parvum
1.000 Giardia
Mycobacterium
Legionella fortuitum
M. fortuitum
Poliovirus Legionella
E. coli C. Parvum
100
Legionella Adenovirus
Adenovirus Microsporidium Reovirus
MS-2
Rotavirus Calicivirus
Giardia Giardia Poliovirus
Poliovirus
10 E. coli Hepatitis A
M. fortuitum
Microsporidium
Calicivirus M. fortuitum C. Parvum C. Parvum
Calicivirus
Legionella Giardia Giardia
Legionella Poliovirus
1.0 E. coli Pneumophila E. coli
Microsporidium
Adenovirus
Poliovirus
0.10 Calicivirus
Adenovirus
Adenovirus
Calicivirus
0.01 E. Coli
,disinfectoin water treatment
Framework
This module will describe the aspects of water disinfection. For this, the purpose of disinfection will be
given, the kinetics, and the practical application.
The content of this module is abstracted from Alternative Disinfectants and Oxidants Guidance Manual
(EPA 1999) and Water treatment: Principles and design (MWH 2005).
Contents
This module has the following contents:
1. Introduction
2. Purpose of disinfection
2.1 Diseases and drinking water
2.2 Pathogens of primary concern
2.3 Recent waterborne outbreaks
2.4 Mechanism of pathogen inactivation
2.5 Other uses of disinfectants in water treatment
2.6 Current practice of disinfection (and oxidation)
2.7 Disinfection byproducts
3. Disinfection kinetics
3.1 Chick’s Law
3.2 Chick-Watson model
3.3 Other models
3.4 C t -values
4. Disinfection methods
4.1 Chlorine
4.2 Ozone
4.3 UV radiation
4.4 Chlorine dioxide
4.5 Other methods
Further reading
116
, water treatment disinfection
1 Introduction produced primarily as a result of chlorination
- organic oxidation byproducts such as alde-
The most important use of disinfectants in water hydes, ketones, assimilable organic carbon
treatment is to limit waterborne diseases and inac- (AOC), and biodegradable organic carbon
tivate pathogenic organisms in water supplies. (BDOC) that are associated primarily with
The first use of disinfection as a continuous pro- strong oxidants such as ozone, chlorine, and
cess in water treatment took place in a small town advanced oxidation
in Belgium in the early 1900s (White, 1992), where - inorganics such as chlorate and chlorite as-
chlorine was used as the disinfecting reagent. sociated with chlorine dioxide, and bromate
Since the introduction of filtration and disinfection that is associated with ozone, and has also
at water treatment plants, waterborne diseases, been found when chlorine dioxide is exposed
such as typhoid and cholera, have been virtually to sunlight.
eliminated. For example, in Niagara Falls, NY, The type and amount of DBPs produced dur-
USA, between 1911 and 1915, the number of ty- ing treatment depends largely on the type of
phoid cases dropped from 185 deaths per 100,000 disinfectant, water quality, treatment sequences,
people to nearly zero following the introduction of contact time, and environmental factors such as
filtration and chlorination (White, 1986). temperature and pH.
For nearly a century, chlorine gas or chlorine re- When considering the use of alternative disinfec-
agents (hypochlorite, etc.) were, by far, the most tants, systems should ensure that the inactivation
commonly used disinfectant chemicals for drinking of pathogenic organisms is not compromised.
water production Pathogens pose an immediate critical public health
In 1974, researchers in the Netherlands and the threat due to the risk of an acute disease outbreak.
United States demonstrated that trihalomethanes Although most identified public health risks associ-
(THMs) were being formed as a result of drink- ated with DBPs are chronic, long-term risks, many
ing water chlorination (Rook, 1974; Bellar et al., systems will be able to lower DBP levels without
1974). compromising microbial protection.
THMs form when chlorine or bromide reacts with
organic compounds in the water. THMs and other In this module the purpose of disinfection is pre-
disinfection byproducts (DBPs) have been shown sented first. Thereafter, the DBPs are discussed,
to be carcinogenic, mutagenic, etc. These health since they play an important role in the selection
risks may be small but�����������������������������
need to be taken seriously��, of the disinfection method.
when you consider the large population being After this, disinfection kinetics are presented.
exposed. Finally, an overview is given of the different dis-
infection methods, in which the pros and cons of
As a result of DBP concerns from chlorine, the wa- the major methods are provided.
ter treatment industry has placed more emphasis
on the use of disinfectants other than chlorine.
Some of these alternative disinfectants, however, 2 Purpose of disinfection
have also been found to produce DBPs as a re-
sult of either reactions between disinfectants and 2.1 Diseases and drinking water
compounds in the water or as a natural decaying Although the epidemiological relationship between
process of the disinfectant itself (McGuire et al., water and disease had been suggested as early
1990; Legube et al., 1989). as the 1850s, it was not until the development
These DBPs include: of the germ theory of disease by Pasteur in the
- halogenated organics, such as THMs, halo- mid-1880s that water as a carrier of disease-
acetic acids, haloketones, and others that are producing organisms was understood.
117
