1 Introduction
On the earth’s surface, approximately two-thirds of the portion is full of water in the
form of oceans and freshwater. The contribution from the oceans is around 97.2% of
its availability, whereas the freshwater source contributes about 2.7%, of which
0.35% is contaminated due to various anthropogenic activities (Akshay et al. 2020).
In general, water contamination occurs due to the presence of undesirable chemicals,
microbes, and suspended solids. The presence of these contaminants in water could
lead to waterborne diseases such as dysentery and cholera. Water scarcity and
contamination are major problems in most of the places across the world. According
to the World Health Organization report (WHO), 844 million people do not have
safe water all over the world (WHO/UNICEF 2017).
The main reasons for water contamination are climate change, population, and
industrialization (Okello et al. 2015). It is necessary to provide cost-effective water
treatment technologies for low-income countries. To have safe and drinkable water,
the WHO set guidelines for centralized and decentralized water treatment systems.
Figure 6.1 shows the water treatment process involved in a centralized system to
provide safe water. In most of the countries, water treatment plant undergoes various
physicochemical processes such as sedimentation, coagulation/flocculation, etc.
(Matsumoto et al. 1995). This chapter discusses the strategies and limitations
involved in both chemical and physical disinfectants.
2 Chemical Disinfectants
2.1 Chlorination
The pathogenic microorganisms (viruses, bacteria, and protozoa) are of utmost
concern in water treatment. Over the years, chemical control of microorganisms is
the most important and widely accepted method for a water treatment plant. Chlorine
compounds such as chlorine gas, chlorine dioxide, chloramines, and hypochlorite
are widely used to treat water (Zhang et al. 2012). Particularly, the addition of
chlorine in water reacts with organic matter, reducing agents and ammonia. Chlorination is preferred not only for killing microbes and also for odor removal in water.
One of the main drawbacks of chlorination is toxic to humans if the concentration
exceeds above the permissible limit. During chlorination, chlorine reacts with
natural organic matter (NOM), iodide (I
À ), and bromide (Br
À ) to generate various
harmful disinfection by-products (DBPs), including trihalomethanes (THM),
haloacetic acids, etc. (Richardson et al. 2007). The predominant organic matters in
water are humic and fulvic acids. The formation of DBPs is influenced by chlorine
dosage, contact time, organic matter, pH, temperature, etc. Based on the animal and
epidemiological studies, these by-products may produce adverse effects on humans
(carcinogenicity or cytotoxic). The required concentration of chlorine for bacteria,
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N. R. Srinivasan et al.
On the earth’s surface, approximately two-thirds of the portion is full of water in the
form of oceans and freshwater. The contribution from the oceans is around 97.2% of
its availability, whereas the freshwater source contributes about 2.7%, of which
0.35% is contaminated due to various anthropogenic activities (Akshay et al. 2020).
In general, water contamination occurs due to the presence of undesirable chemicals,
microbes, and suspended solids. The presence of these contaminants in water could
lead to waterborne diseases such as dysentery and cholera. Water scarcity and
contamination are major problems in most of the places across the world. According
to the World Health Organization report (WHO), 844 million people do not have
safe water all over the world (WHO/UNICEF 2017).
The main reasons for water contamination are climate change, population, and
industrialization (Okello et al. 2015). It is necessary to provide cost-effective water
treatment technologies for low-income countries. To have safe and drinkable water,
the WHO set guidelines for centralized and decentralized water treatment systems.
Figure 6.1 shows the water treatment process involved in a centralized system to
provide safe water. In most of the countries, water treatment plant undergoes various
physicochemical processes such as sedimentation, coagulation/flocculation, etc.
(Matsumoto et al. 1995). This chapter discusses the strategies and limitations
involved in both chemical and physical disinfectants.
2 Chemical Disinfectants
2.1 Chlorination
The pathogenic microorganisms (viruses, bacteria, and protozoa) are of utmost
concern in water treatment. Over the years, chemical control of microorganisms is
the most important and widely accepted method for a water treatment plant. Chlorine
compounds such as chlorine gas, chlorine dioxide, chloramines, and hypochlorite
are widely used to treat water (Zhang et al. 2012). Particularly, the addition of
chlorine in water reacts with organic matter, reducing agents and ammonia. Chlorination is preferred not only for killing microbes and also for odor removal in water.
One of the main drawbacks of chlorination is toxic to humans if the concentration
exceeds above the permissible limit. During chlorination, chlorine reacts with
natural organic matter (NOM), iodide (I
À ), and bromide (Br
À ) to generate various
harmful disinfection by-products (DBPs), including trihalomethanes (THM),
haloacetic acids, etc. (Richardson et al. 2007). The predominant organic matters in
water are humic and fulvic acids. The formation of DBPs is influenced by chlorine
dosage, contact time, organic matter, pH, temperature, etc. Based on the animal and
epidemiological studies, these by-products may produce adverse effects on humans
(carcinogenicity or cytotoxic). The required concentration of chlorine for bacteria,
118
N. R. Srinivasan et al.