Advanced Oxidation Processes (AOP)—Effective Innovative …
175
from the effluents before their discharge on to the soil and water bodies, in addition
to water recovery.
In general, the unutilized dyes from the processing industry are harmful for the
ecology, since these effluents discharged are coloured and contain high concentrations of pollutants like organic dyes, salts. They also contribute higher biological
oxygen demand/chemical oxygen demand (BOD/COD) values [3, 4]. The use of
dyes will not be abandoned as humans are aesthetically interested in dyed textile.
Many types of dyes are used to treat different fibres in the manufacture of textiles.
The textile chemical processing sector consumes large quantities of water and chemicals for pre-treatment and dyeing processes of textile materials, which in turn leads
to large amount of wastewater contribution [5, 6]. It is already known and acceptable
that those group of pollutants posing numerous problems (affectation of photosynthesis in water plants, carcinogenicity, etc.) and therefore decolourization of textile
effluents become a major environmental concern [7]. The effluents from textiles
contain large amount of recalcitrant unfixed dyes (as acid dyes, basic dyes, reactive
dyes, sulphur dyes, disperse dyes, chrome dyes, optical brightener) which include
the dyes which are not fixed or unreacted to the fibre of different textiles during the
process (fibres as wool and nylon, cotton and viscose, polyester and acrylic) and
are considered emerging contaminants. Synthetic dyes, in the dyeing effluent, are
carcinogenic and mutagenic in nature, and they must be removed from the dyeing
effluent before the effluent is discharged.
There are wide number of chemical structures of synthetic dyes. The effluent
consists of wide range of chemical reagents which are used in the dyeing and finishing
processes, contains different chemical structures and different concentration and
compositions of both organic and inorganic compounds, which causes a serious
problem when they are discharged to the environment [8, 9]. The chemical classes
of dyes employed more frequently on industrial scale are the azo which contributes
about 60–70% of the total dyes used and also other classes like, anthraquinone,
indigoid, sulphur, phthalocyanine derivatives and triphenylmethyl (trityl).
Removal of various toxic dyes requires a complex series of hybrid physicochemical (coagulation sorption, reverse osmosis and ion exchange) and biological
processes (aerobic and anaerobic biodegradation). The dyes in the effluent exhibit
complex structures and are dependent on the types of dyes used, and this makes their
removal difficult even after combining various hybrid processes. Several methods
available or reported in the literature to address the above issues are provided in
Table 1.
Lately, the inclusion of advanced oxidation processes (AOP) in the treatment train
has been suggested for the treatment of textile industry effluent. AOPs involve the
generation of hydroxyl radicals, exploiting the high reactivity and unselectively of the
intermediate hydroxyl radicals (OH
• ) to attack the organic molecules at accelerated
rate constants vs. standard oxidation processes (KOH, organic substance, usually in
order of 10
6 –10
11 M
−1 S
−1 ) [24, 25]. In wastewater treatment, AOP refers mainly
to processes that yield OH
• through ozone (O 3 ), hydrogen peroxide (H 2 O 2 ) and UV
light simultaneously, or their combination as O 3 , O 3 /UV, O 3 /H 2 O 2 , UV/H 2 O 2 . Other
interesting technologies include ozonation alone is often considered as an AOP in
175
from the effluents before their discharge on to the soil and water bodies, in addition
to water recovery.
In general, the unutilized dyes from the processing industry are harmful for the
ecology, since these effluents discharged are coloured and contain high concentrations of pollutants like organic dyes, salts. They also contribute higher biological
oxygen demand/chemical oxygen demand (BOD/COD) values [3, 4]. The use of
dyes will not be abandoned as humans are aesthetically interested in dyed textile.
Many types of dyes are used to treat different fibres in the manufacture of textiles.
The textile chemical processing sector consumes large quantities of water and chemicals for pre-treatment and dyeing processes of textile materials, which in turn leads
to large amount of wastewater contribution [5, 6]. It is already known and acceptable
that those group of pollutants posing numerous problems (affectation of photosynthesis in water plants, carcinogenicity, etc.) and therefore decolourization of textile
effluents become a major environmental concern [7]. The effluents from textiles
contain large amount of recalcitrant unfixed dyes (as acid dyes, basic dyes, reactive
dyes, sulphur dyes, disperse dyes, chrome dyes, optical brightener) which include
the dyes which are not fixed or unreacted to the fibre of different textiles during the
process (fibres as wool and nylon, cotton and viscose, polyester and acrylic) and
are considered emerging contaminants. Synthetic dyes, in the dyeing effluent, are
carcinogenic and mutagenic in nature, and they must be removed from the dyeing
effluent before the effluent is discharged.
There are wide number of chemical structures of synthetic dyes. The effluent
consists of wide range of chemical reagents which are used in the dyeing and finishing
processes, contains different chemical structures and different concentration and
compositions of both organic and inorganic compounds, which causes a serious
problem when they are discharged to the environment [8, 9]. The chemical classes
of dyes employed more frequently on industrial scale are the azo which contributes
about 60–70% of the total dyes used and also other classes like, anthraquinone,
indigoid, sulphur, phthalocyanine derivatives and triphenylmethyl (trityl).
Removal of various toxic dyes requires a complex series of hybrid physicochemical (coagulation sorption, reverse osmosis and ion exchange) and biological
processes (aerobic and anaerobic biodegradation). The dyes in the effluent exhibit
complex structures and are dependent on the types of dyes used, and this makes their
removal difficult even after combining various hybrid processes. Several methods
available or reported in the literature to address the above issues are provided in
Table 1.
Lately, the inclusion of advanced oxidation processes (AOP) in the treatment train
has been suggested for the treatment of textile industry effluent. AOPs involve the
generation of hydroxyl radicals, exploiting the high reactivity and unselectively of the
intermediate hydroxyl radicals (OH
• ) to attack the organic molecules at accelerated
rate constants vs. standard oxidation processes (KOH, organic substance, usually in
order of 10
6 –10
11 M
−1 S
−1 ) [24, 25]. In wastewater treatment, AOP refers mainly
to processes that yield OH
• through ozone (O 3 ), hydrogen peroxide (H 2 O 2 ) and UV
light simultaneously, or their combination as O 3 , O 3 /UV, O 3 /H 2 O 2 , UV/H 2 O 2 . Other
interesting technologies include ozonation alone is often considered as an AOP in