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wastewater. The complex dye compounds are converted into simpler compounds
which can be further treated using biological treatment.
3.2 UV AOPs
Sunlight is a major source which is used as disinfectant to kill the growth of microorganisms [36]. In textiles, light fastness is an important parameter that is to be checked
in the dyed and printed fabrics, as light could deteriorate the colour to fade. Hence,
this can be used as a source of degradation of organic dye compounds present in
the textile wastewater. The sunlight is in the wave form and is classified as the
visible light, ultraviolet and infrared rays. Out of which, ultraviolet rays are the most
powerful one which is used to oxidize the compounds present in the polluted water.
Generally, ultraviolet irradiation is a photolysis process, and the principle of degradation of organic pollutant is by absorption of photons from the UV irradiation by
the compounds present in the wastewater, and the oxidation process continues due
to the energy released. The quantum yield and rate of the compound are responsible
for the photolysis rate of UV radiation [37]. UV irradiation can be used in advanced
oxidation processes, since the agents such as hydrogen peroxide, ozone and chlorine form free radicals when they are exposed to UV. In addition to that, the UV
treatment produces or simplifies the organic pollutants into simpler and less refractory organic compounds or converts it to water, carbon dioxide and mineral acids.
UV radiation-based free radical generation is very powerful in generating oxidation
species like hydroxyl radical when hydrogen peroxide exposed direct UV photolysis,
photo-Fenton reactions or heterogeneous photocatalysis.
In direct photolysis, the mechanism of degradation happens through the absorption of incident ray from the UV irradiation on the contaminant. For an effective
direct photolysis of the process, the contaminant in the wastewater should strongly
absorb the UV light, but not all the contaminant has good absorbency. To obtain
a very effective process, UV can be combined with hydrogen peroxide or ozone
or hydrogen peroxide/ozone. In combined process, UV irradiation with hydrogen
peroxide produces hydroxyl radical which can degrade the organic contaminants in
the wastewater. Generally, most of the textile dyestuffs consist of double bonds or
conjugated double bonds. The dyes with double bond consist of carbon, nitrogen or
oxygen atoms.
The degradation of organic and inorganic compounds in wastewater of environmental concern is extensively studied, and hydroxyl radical-driven photooxidation
process such as UV/hydrogen peroxide, UV/ozone, UV/ozone/H 2 O 2 and photocatalytic reactions shows significant results in degradation of the organic pollutants than
direct photolysis [38]. The photooxidation processes are discussed in detail.
R. Sukanya Devi et al.
wastewater. The complex dye compounds are converted into simpler compounds
which can be further treated using biological treatment.
3.2 UV AOPs
Sunlight is a major source which is used as disinfectant to kill the growth of microorganisms [36]. In textiles, light fastness is an important parameter that is to be checked
in the dyed and printed fabrics, as light could deteriorate the colour to fade. Hence,
this can be used as a source of degradation of organic dye compounds present in
the textile wastewater. The sunlight is in the wave form and is classified as the
visible light, ultraviolet and infrared rays. Out of which, ultraviolet rays are the most
powerful one which is used to oxidize the compounds present in the polluted water.
Generally, ultraviolet irradiation is a photolysis process, and the principle of degradation of organic pollutant is by absorption of photons from the UV irradiation by
the compounds present in the wastewater, and the oxidation process continues due
to the energy released. The quantum yield and rate of the compound are responsible
for the photolysis rate of UV radiation [37]. UV irradiation can be used in advanced
oxidation processes, since the agents such as hydrogen peroxide, ozone and chlorine form free radicals when they are exposed to UV. In addition to that, the UV
treatment produces or simplifies the organic pollutants into simpler and less refractory organic compounds or converts it to water, carbon dioxide and mineral acids.
UV radiation-based free radical generation is very powerful in generating oxidation
species like hydroxyl radical when hydrogen peroxide exposed direct UV photolysis,
photo-Fenton reactions or heterogeneous photocatalysis.
In direct photolysis, the mechanism of degradation happens through the absorption of incident ray from the UV irradiation on the contaminant. For an effective
direct photolysis of the process, the contaminant in the wastewater should strongly
absorb the UV light, but not all the contaminant has good absorbency. To obtain
a very effective process, UV can be combined with hydrogen peroxide or ozone
or hydrogen peroxide/ozone. In combined process, UV irradiation with hydrogen
peroxide produces hydroxyl radical which can degrade the organic contaminants in
the wastewater. Generally, most of the textile dyestuffs consist of double bonds or
conjugated double bonds. The dyes with double bond consist of carbon, nitrogen or
oxygen atoms.
The degradation of organic and inorganic compounds in wastewater of environmental concern is extensively studied, and hydroxyl radical-driven photooxidation
process such as UV/hydrogen peroxide, UV/ozone, UV/ozone/H 2 O 2 and photocatalytic reactions shows significant results in degradation of the organic pollutants than
direct photolysis [38]. The photooxidation processes are discussed in detail.