Advanced Oxidation Processes (AOP)—Effective Innovative …
183
3.2.1 UV/H 2 O 2
In photooxidation process, the free radical hydroxyl is generated from hydrogen
peroxide in the presence of UV irradiation. This process is the combination of H 2 O 2
and UV light in a synergistic effect to degrade organic dyes and chemicals present
in the textile wastewater and other pathogenic microorganisms in aqueous solutions
[39]. The successful degradation of the dyes and chemicals is obtained due to the
generation of hydroxyl radicals from the UV/H 2 O 2 process.
H 2 O 2 −→ hv2
• OH
(3.1)
The decomposition of the hydrogen peroxide is induced by the photoreaction
and is the initiation of the reaction starts as per Eq. (3.1). Equations (3.2) and (3.3)
indicate the propagation of the reactions
H 2 O 2 +
• OH → H 2 O + HO
•
2
(3.2)
HO
•
2 + H 2 O 2 → H 2 O + O 2 +
• OH
(3.3)
The net reaction of the propagation as observed in reactions (3.2) and (3.3) is
the decomposition of hydrogen peroxide into molecular oxygen and water. Since
the wash water (water used for pre-treatment and washing) may contain hydrogen
peroxide after bleaching of the textile materials, the residual peroxide may be used for
this photooxidation process only if the solution contains active peroxide compounds.
The termination of this chemical reaction may be of different reactions like radicalradical recombination.
The decomposition of H 2 O 2 involves more complex mechanisms, and the explanation of this decomposition is found in the literature and includes species like
HO 2
− ; HO
•−
2 and O
•−
2 in the chain decomposition mechanism. The efficiency of the
UV/H 2 O 2 photooxidation is highly dependent on the generation of hydroxyl radical
which in turn is dependent on the UV absorption capacity of the hydrogen peroxide
and the chemical constituents and characteristics of the textile wastewater subjected
to degradation [40]. The optical property of the effluent and the specific constituents
present in it plays a significant role in generation of hydroxyl radical. The chemicals
in the effluent are responsible for the transmittance resulting in reduction of hydroxyl
radical generation. In addition to this, the presence of natural organic matter, inorganic
ions and organic acid can reduce the degradation efficiency of specific contaminants.
The effluent absorption capacity can be measured by measuring the UV radiation
transmittance of the effluent at 254 and 172 nm. Strong absorbance values of UV
light by effluent are due to the presence of natural organic matter and aromatic
compounds. In such cases, the treatment of organic contaminants with higher UV
radiation absorbance results in lower transmittance at these UV light wavelengths,
will be more difficult to degrade and is costly.
183
3.2.1 UV/H 2 O 2
In photooxidation process, the free radical hydroxyl is generated from hydrogen
peroxide in the presence of UV irradiation. This process is the combination of H 2 O 2
and UV light in a synergistic effect to degrade organic dyes and chemicals present
in the textile wastewater and other pathogenic microorganisms in aqueous solutions
[39]. The successful degradation of the dyes and chemicals is obtained due to the
generation of hydroxyl radicals from the UV/H 2 O 2 process.
H 2 O 2 −→ hv2
• OH
(3.1)
The decomposition of the hydrogen peroxide is induced by the photoreaction
and is the initiation of the reaction starts as per Eq. (3.1). Equations (3.2) and (3.3)
indicate the propagation of the reactions
H 2 O 2 +
• OH → H 2 O + HO
•
2
(3.2)
HO
•
2 + H 2 O 2 → H 2 O + O 2 +
• OH
(3.3)
The net reaction of the propagation as observed in reactions (3.2) and (3.3) is
the decomposition of hydrogen peroxide into molecular oxygen and water. Since
the wash water (water used for pre-treatment and washing) may contain hydrogen
peroxide after bleaching of the textile materials, the residual peroxide may be used for
this photooxidation process only if the solution contains active peroxide compounds.
The termination of this chemical reaction may be of different reactions like radicalradical recombination.
The decomposition of H 2 O 2 involves more complex mechanisms, and the explanation of this decomposition is found in the literature and includes species like
HO 2
− ; HO
•−
2 and O
•−
2 in the chain decomposition mechanism. The efficiency of the
UV/H 2 O 2 photooxidation is highly dependent on the generation of hydroxyl radical
which in turn is dependent on the UV absorption capacity of the hydrogen peroxide
and the chemical constituents and characteristics of the textile wastewater subjected
to degradation [40]. The optical property of the effluent and the specific constituents
present in it plays a significant role in generation of hydroxyl radical. The chemicals
in the effluent are responsible for the transmittance resulting in reduction of hydroxyl
radical generation. In addition to this, the presence of natural organic matter, inorganic
ions and organic acid can reduce the degradation efficiency of specific contaminants.
The effluent absorption capacity can be measured by measuring the UV radiation
transmittance of the effluent at 254 and 172 nm. Strong absorbance values of UV
light by effluent are due to the presence of natural organic matter and aromatic
compounds. In such cases, the treatment of organic contaminants with higher UV
radiation absorbance results in lower transmittance at these UV light wavelengths,
will be more difficult to degrade and is costly.