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To abate the arsenic and fluoride effect to human health, international organizations have lowered the maximum allowable limits of these pollutants in drinking
water. The World Health Organization suggests a maximum permissible limit of
arsenic and fluoride in water of 10 μg/L and 1.5 mg/L, respectively. Reaching a low
arsenic and fluoride concentration requires the application of low-cost and efficient
technologies to allow safe drinking water supply for human consumption. In the
following section, we review the most relevant technologies for the elimination of
these pollutants from drinking water, making emphasis in its fundamentals.
3.2 General Strategies for Arsenic and Fluoride Removal
from Water
Currently, there are full-scale technologies for the elimination of arsenic and fluorine
from drinking water. The efficiency of any treatment strategy depends on the raw
water composition, the volume of water to be treated, and the final target concentration of the pollutants. In addition, the selection of the most suitable treatment depends
strongly on cost-effectiveness during implementation and use. For drinking water
supply, physicochemical treatments are the methods of choice, being the most relevant coagulation/precipitation, membrane processes, ion exchange, membrane filtration, and adsorption. In the following section, we briefly review the fundamentals of
these technologies, including the specifics for fluorine and arsenic removal from water.
3.2.1 Coagulation and Flocculation
Coagulation and flocculation process includes the addition of chemicals to remove
stable colloidal particles from water, including natural organic matter. This process
typically takes place in two stages: coagulation followed by flocculation. Figure 3.3a
represents the typical configuration of a water clarification system. During coagulation, chemicals are added to neutralize the charges of the colloidal particles, creating
neutral particles that can be attached. Each particle carries a similar charge, and almost
all the colloidal impurities in the water are negatively charged. Generally, the size of
the colloidal particles is around 0.01–1µm; therefore, the attractive forces between the
particles are less than the repelling forces of the electric charges (Teh et al. 2016).
The colloids present in the aqueous solution attract ions from the opposite
charges, named counterions. The counterions, attracted by electrostatic forces and
van der Waals forces, will form a compact layer around the charge of the colloid
(Fig. 3.3B). Therefore, the counterions tend to remain discrete and dispersed in the
suspension. The stability of the colloidal particles can be explained quantitatively
by the estimates of the attractive energy such as van der Waals forces and the repulsion energy. Another estimate attractive energy is the superposition of electric double layers, in terms of the distance between particles (Fig. 3.3C). Once the colloidal
3 Metal Oxyhydroxide Composites for Halogens and Metalloid Removal
To abate the arsenic and fluoride effect to human health, international organizations have lowered the maximum allowable limits of these pollutants in drinking
water. The World Health Organization suggests a maximum permissible limit of
arsenic and fluoride in water of 10 μg/L and 1.5 mg/L, respectively. Reaching a low
arsenic and fluoride concentration requires the application of low-cost and efficient
technologies to allow safe drinking water supply for human consumption. In the
following section, we review the most relevant technologies for the elimination of
these pollutants from drinking water, making emphasis in its fundamentals.
3.2 General Strategies for Arsenic and Fluoride Removal
from Water
Currently, there are full-scale technologies for the elimination of arsenic and fluorine
from drinking water. The efficiency of any treatment strategy depends on the raw
water composition, the volume of water to be treated, and the final target concentration of the pollutants. In addition, the selection of the most suitable treatment depends
strongly on cost-effectiveness during implementation and use. For drinking water
supply, physicochemical treatments are the methods of choice, being the most relevant coagulation/precipitation, membrane processes, ion exchange, membrane filtration, and adsorption. In the following section, we briefly review the fundamentals of
these technologies, including the specifics for fluorine and arsenic removal from water.
3.2.1 Coagulation and Flocculation
Coagulation and flocculation process includes the addition of chemicals to remove
stable colloidal particles from water, including natural organic matter. This process
typically takes place in two stages: coagulation followed by flocculation. Figure 3.3a
represents the typical configuration of a water clarification system. During coagulation, chemicals are added to neutralize the charges of the colloidal particles, creating
neutral particles that can be attached. Each particle carries a similar charge, and almost
all the colloidal impurities in the water are negatively charged. Generally, the size of
the colloidal particles is around 0.01–1µm; therefore, the attractive forces between the
particles are less than the repelling forces of the electric charges (Teh et al. 2016).
The colloids present in the aqueous solution attract ions from the opposite
charges, named counterions. The counterions, attracted by electrostatic forces and
van der Waals forces, will form a compact layer around the charge of the colloid
(Fig. 3.3B). Therefore, the counterions tend to remain discrete and dispersed in the
suspension. The stability of the colloidal particles can be explained quantitatively
by the estimates of the attractive energy such as van der Waals forces and the repulsion energy. Another estimate attractive energy is the superposition of electric double layers, in terms of the distance between particles (Fig. 3.3C). Once the colloidal
3 Metal Oxyhydroxide Composites for Halogens and Metalloid Removal