5.4.1 Chemical Oxidative Processes
Chemical oxidative processes can be defined as treatment processes for water
purification, carried out at room temperature and normal pressure, based on the
in-situ generation of a powerful oxidizing agent, such as hydroxyl radicals (•OH), in
a concentration enough to decontaminate the water effectively (Glaze et al. 2008).
The chemical oxidative processes constitute a series of promising, efficient and
environmentally friendly methods to eliminate persistent organic pollutants from the
waters. The formation of oxidant radicals is produced by various chemical, photochemical, sonochemical or electrochemical reactions (Gogate and Pandit 2001;
Parsons 2004; Tarr 2003).
5.4.1.1 Fenton Type Oxidation
The oldest physicochemical oxidative process used is the Fenton method, in which a
mixture of a soluble iron (II) salt and H 2 O 2 , known as Fenton’s reagent, is applied to
degrade and destroy organic compounds (Andreozzi et al. 1999). Fenton’s chemistry
began at the end of the nineteenth century, when Fenton published, in pioneering
work, a detailed study on the use of a mixture of H 2 O 2 and Fe
2+ for the oxidation and
destruction of tartaric acid. The catalytic decomposition of H 2 O 2 by iron salts obeys
a radical complex and chain mechanism. More recent studies have shown that the
Fenton process was initiated by the formation of hydroxyl radicals, and could be
applied to the degradation of several organic pollutants (Gallard et al. 1998; Sudoh
et al. 1986), according to the following reaction (Oturan and Aaron 2014):
Fe
2þ
þ H 2 O 2 ! Fe
3þ
þ • OH þ OH
À
ð5:1Þ
If the reaction is carried out in an acid medium, the reaction can be rewritten as
follows:
Fe
2þ
þ H 2 O þ H
þ
! Fe
3þ
þ H 2 O þ • OH
ð5:2Þ
The Fenton process can be applied efficiently when the optimum pH value of the
contaminated aqueous medium is approximately 2.8–3.0.
In fact, under these conditions, the Fenton reaction can be propagated by the
catalytic behaviour of the Fe
3+ / Fe
2+ pair. It is worth noting that only a small catalytic
amount of Fe
2+ is required since this ion is regenerated from the so-called Fenton
type reaction between Fe
3+ and H 2 O 2 :
Fe
3þ
þ H 2 O 2 ! Fe
2þ
þ HO • 2 þ H
þ
ð5:3Þ
Fu and group have studied the role of Fe
2+ ion concentration in the degradation of
amaranth dye using the Fenton process and observed that after a particular
124
S. M. Sathianesan Vimala et al.
Chemical oxidative processes can be defined as treatment processes for water
purification, carried out at room temperature and normal pressure, based on the
in-situ generation of a powerful oxidizing agent, such as hydroxyl radicals (•OH), in
a concentration enough to decontaminate the water effectively (Glaze et al. 2008).
The chemical oxidative processes constitute a series of promising, efficient and
environmentally friendly methods to eliminate persistent organic pollutants from the
waters. The formation of oxidant radicals is produced by various chemical, photochemical, sonochemical or electrochemical reactions (Gogate and Pandit 2001;
Parsons 2004; Tarr 2003).
5.4.1.1 Fenton Type Oxidation
The oldest physicochemical oxidative process used is the Fenton method, in which a
mixture of a soluble iron (II) salt and H 2 O 2 , known as Fenton’s reagent, is applied to
degrade and destroy organic compounds (Andreozzi et al. 1999). Fenton’s chemistry
began at the end of the nineteenth century, when Fenton published, in pioneering
work, a detailed study on the use of a mixture of H 2 O 2 and Fe
2+ for the oxidation and
destruction of tartaric acid. The catalytic decomposition of H 2 O 2 by iron salts obeys
a radical complex and chain mechanism. More recent studies have shown that the
Fenton process was initiated by the formation of hydroxyl radicals, and could be
applied to the degradation of several organic pollutants (Gallard et al. 1998; Sudoh
et al. 1986), according to the following reaction (Oturan and Aaron 2014):
Fe
2þ
þ H 2 O 2 ! Fe
3þ
þ • OH þ OH
À
ð5:1Þ
If the reaction is carried out in an acid medium, the reaction can be rewritten as
follows:
Fe
2þ
þ H 2 O þ H
þ
! Fe
3þ
þ H 2 O þ • OH
ð5:2Þ
The Fenton process can be applied efficiently when the optimum pH value of the
contaminated aqueous medium is approximately 2.8–3.0.
In fact, under these conditions, the Fenton reaction can be propagated by the
catalytic behaviour of the Fe
3+ / Fe
2+ pair. It is worth noting that only a small catalytic
amount of Fe
2+ is required since this ion is regenerated from the so-called Fenton
type reaction between Fe
3+ and H 2 O 2 :
Fe
3þ
þ H 2 O 2 ! Fe
2þ
þ HO • 2 þ H
þ
ð5:3Þ
Fu and group have studied the role of Fe
2+ ion concentration in the degradation of
amaranth dye using the Fenton process and observed that after a particular
124
S. M. Sathianesan Vimala et al.