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Degradation of azo-reactive dyes by ultraviolet radiation in the presence of hydrogen peroxide

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Degradation of azo-reactive dyes by ultraviolet radiation in the presence of hydrogen peroxide

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This paper summarizes the results of a degradation test of several azo-reactive dyes and cotton textile wastewater under UV irradiation in the presence of H2O2. Five of the most commonly used azo-reactive dyes from both the Levafix and Remazol types were tested. 4-l Dye solutions of 100 mg/l were prepared immediately before irradiation. A batch mode water-jacketed immersion photoreactor was utilized. The radiation source was a 120 W UV lamp emitting at 253.7 nm and protected by a quartz tube. Complete destruction of the color of the dye solutions was succeeded in the first 20–30 min of irradiation. Almost all the aromatic rings and 80% of TOC were destroyed after 2 h of irradiation. The textile wastewater color was completely removed in less than 1 h while 90% of the aromatic rings and 70% of the wastewater COD were removed after 2 h of irradiation. UV/H2O2 proved capable of the complete degradation and mineralization of the above azo reactive dyes.
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Degradation of azo-reactive dyes by ultraviolet
radiation in the presence of hydrogen peroxide
D. Georgiou*, P. Melidis, A. Aivasidis, K. Gimouhopoulos
Department of Environmental Engineering, Demokritos University of Thrace, 67100 Xanthi, Greece
Received 24 July 2000; received in revised form 8 August 2001; accepted 21 October 2001
Abstract
This paper summarizes the results of a degradation test of several azo-reactive dyes and cotton textile wastewater
under UV irradiation in the presence of H
2
O
2.
Five of the most commonly used azo-reactive dyes from both the
Levafix and Remazol types were tested. 4-l Dye solutions of 100 mg/l were prepared immediately before irradiation. A
batch mode water-jacketed immersion photoreactor was utilized. The radiation source was a 120 W UV lamp emitting
at 253.7 nm and protected by a quartz tube. Complete destruction of the color of the dye solutions was succeeded in the
first 20–30 min of irradiation. Almost all the aromatic rings and 80% of TOC were destroyed after 2 h of irradiation.
The textile wastewater color was completely removed in less than 1 h while 90% of the aromatic rings and 70% of the
wastewater COD were removed after 2 h of irradiation. UV/H
2
O
2
proved capable of the complete degradation and
mineralization of the above azo reactive dyes. #2002 Elsevier Science Ltd. All rights reserved.
Keywords: Azo-reactive dyes; Hydrogen peroxide; Hydroxyl radicals; Textile wastewater; Ultraviolet radiation
1. Introduction
Textile industries produce large amounts of
wastewater due to high consumption of water pri-
marily in the dyeing and finishing operations. A
well-known characteristic of textile wastewater is a
high content of polluting compounds. The sources
of the polluting compounds when cotton is utilized
are the natural impurities extracted from the
fiber, the processing chemicals and dyes. The main
problem occurring is that the color that remains
due to the dyestuff used may cause disturbance to
the ecological system of the receiving water [1–3].
Wastewater from cotton textile operations is
very hard to treat by conventional activated sludge
systems. The color remains due to the non-bio-
degradable nature of the dyes. Physical-chemical
methods such as, coagulation/flocculation, acti-
vated carbon adsorption and reverse osmosis tech-
niques have been developed in order to remove the
color [4–6]. However, the latter methods can only
transfer the contaminants (dyes) from one phase
to the other leaving the problem essentially
unsolved. Therefore, attention has to be focused
on techniques that lead to the complete destruc-
tion of the dye molecules.
0143-7208/02/$ - see front matter #2002 Elsevier Science Ltd. All rights reserved.
PII: S0143-7208(01)00078-X
Dyes and Pigments 52 (2002) 69–78
www.elsevier.com/locate/dyepig
* Corresponding author. Tel.: +30-541-28865; fax: +30-
541-62955.
E-mail address: dgeorgio@env.duth.gr (D. Georgiou).
Chemical oxidation using ultraviolet radiation
(UV) in the presence of hydrogen peroxide (H
2
O
2
)
is a very promising technique. UV wavelengths of
200–280 nm lead to disassociation of H
2
O
2
,with
mercury lamps emitting at 254 nm being the most
commonly used. UV/H
2
O
2
systems generate
hydroxyl radicals (OH) which are highly powerful
oxidizing species. Hydroxyl radicals can oxidize
organic compounds (RH) producing organic rad-
icals (R), which are highly reactive and can be
further oxidized. The main reactions that occur
during UV/H
2
O
2
oxidation are as follows [7]:
H2O2!
UV 2OHo ð1Þ
H2O2 ! HO
2þHþð2Þ
RH þOHo ! H2OþRo ! further-oxidation
ð3Þ
UV/H
2
O
2
systems have led to complete degra-
dation (mineralization) and conversion to CO
2
,
H
2
O and inorganic salts several compounds such
as, aliphatic acids, alcohols, chlorinated aliphatic
compounds, benzene, phenols, chlorinated phe-
nols, pesticides and numerous others [7–12].
Several dyes utilized by textile industries (includ-
ing azo-reactive ones) have also been successfully
degraded by the above technique [13–15]. Azo
reactive dyes are among the most commonly used
to dye cotton nowadays. Therefor, the objective of
this paper is to study the degradation of five dif-
ferent and most representative azo-reactive dyes
utilized by a nearby cotton textile industry, using a
UV/H
2
O
2
technique. Moreover, the same tech-
nique is to be applied to wastewater obtained from
the latter textile industry.
2. Experimental
2.1. Reagents
Azo-reactive dyes were obtained from DyStar
(Germany). A total of five of the most representa-
tive and commonly used dyes from both the Levafix
and Remazol types were tested. The characteristics
of these dyes were provided by DyStar and are
summarized in Table 1. The structural formulae of
the reactive groups (Table 1) and also that of the
Remazol Black B dye are given in Fig. 1. All dyes
have a similar to the Remazol Black B dye struc-
ture, the only difference is the kind and number of
reactive groups.
Textile wastewater was obtained from a nearby
industry (Komotini, Greece), the characteristics of
which are presented in Table 2. The sample was
withdrawn from a point immediately after the equal-
ization basin of the wastewater processing plant and
it was centrifugated prior to irradiation tests in order
to remove suspended particles. Analytical grade
H
2
O
2
(30% w/w, Fischer Scientific) was used.
2.2. Apparatus and methods
All experiments were carried out in a batch
mode water-jacketed immersion photoreactor.
The radiation source was an UV lamp (120 Watt,
emission at 253.7 nm, manufactured by Heraeus,
Germany) which was protected by a quartz tube.
Temperature was maintained at 25 5C (tem-
perature rose from 20 to 30 C during the 2 h
experiments). The dye solution (4 l) was projected
at the bottom of the reactor and collected in a 5-l
reservoir from which it was continuously pumped
Table 2
Cotton textile wastewater characteristics
BOD
5
(mg/l)
COD
(mg/l)
Ph Absorbance (m
1
)
436 nm 525 nm 620 nm
80 150 8.2 13.4 16.9 5.4
Table 1
Dyes and their properties (DyStar)
Name Azo type Reactive group
Levafix yellow
E-3GA
Monoazo Difluorchlorpyrimidine (FCP)
Levafix red ERN Monoazo Monohalogentriazine (MHT)
Levafix blue EBNA Diazo Difluorchlorpyrimidine (FCP)
Vinylsulphonyl (VS)
Remazol red RR Monoazo Vinylsulphonyl (VS)
Monohalogentriazine (MHT)
Remazol black B Diazo Vinylsulphonyl2
70 D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78
(250 ml/min), as shown in Fig. 2. Samples were
withdrawn from the reservoir at certain time inter-
vals and analyzed for color, absorbance at 254 nm,
pH and total organic carbon (TOC) or chemical
oxygen demand (COD). A UV/VIS Lambda 2S
Perkin Elmer spectrophotometer and a TOC-4000
Shimadzu analyzer were utilized.
The dye solutions (100 mg/l) were prepared
immediately before irradiation using deionized
water.
3. Results and Discussion
The results from the irradiation tests of the
Remazol black B solutions (100 mg/l) using dif-
ferent concentrations of H
2
O
2
are summarized in
Fig. 3. Even a small amount of H
2
O
2
(0.1 g/l) was
enough for the complete destruction of color in
less than 1 h. Complete destruction of color was
also achieved in less than a half-hour utilizing
higher amounts of hydrogen peroxide (0.5–2 g/l).
No color destruction was observed though under
UV radiation in the absence of H
2
O
2
.
The UV–VIS spectrums of Remazol black B
solution at different time intervals from a 2-h
irradiation test (H
2
O
2
=1 g/l) are shown in Fig. 4.
The visible region spectra was flattened in less
than 20 min while absorbance in the UV area
vanished after 120 min of irradiation.
More than 50% of color removal was observed
in the first 10 min for all dye solutions. Complete
removal of the color was achieved after 20–30 min
of irradiation, in all cases (Figs. 5–9).
Absorbance measurements of the samples at 254
nm were taken as an indication of the aromatic
Fig. 1. The structural formulas of the reactive groups (Table 1) and the Remazol black B dye.
D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78 71
compounds’ content. The destruction of the aro-
matic rings becomes evident in Fig. 5–9. More
than 90% of the initial absorbance vanished after
2 h of irradiation.
TOC was also highly reduced in all cases. A frac-
tion of less than 20% of the initial one remained in
the end of the experiments (more than 80% removal)
as shown in Fig. 5–9. It becomes evident that the
reaction trend is as follows: azo reactive dyes are
degraded initially resulting to intermediate products
(containing aromatic rings) which in turn are further
degraded to simpler products till complete degrada-
tion to CO
2
, water and inorganic salts.
Fig. 10 illustrates the variation of pH with time.
All dye solutions became slightly acidic as the pH
dropped to a constant value of 3–3.5 after 30 min
of irradiation. It is important to note that pH
remained constant at its initial value (pH
in
=6–7)
when one of the following, e.g. UV radiation or
H
2
O
2
or a dye was not present during the exper-
iment. It is evident that under UV radiation the
existence of the perhydroxyl anion (HO
2
)
becomes important [reaction (2)]. Moreover, no
color destruction was observed in the absence of
UV radiation after 48 h of experiment.
The results from the irradiation test of the cot-
ton textile wastewater—using 1 g/l H
2
O
2
—are
summarized in Fig. 11. It is interesting to note here
that, even though the total dye concentration in the
wastewater was at least 5 times less than the one in
the previously tested dye solutions, almost the same
or more time was needed for the complete destruc-
tion of the wastewater color. That was due to the
non-selective nature of the hydroxyl radical (OH)
reactivity (e.g. hydroxyl radicals also reacted with
and were consumed by other organic compounds
present in the wastewater such as the natural
impurities extracted from the cotton fiber, sizes,
detergents and finishing chemicals).
The rise of COD in the first 20 min of irradiation
was attributed to the destruction of the dye mol-
ecules to simpler compounds that are less resistant
to chemical oxidation. Finally, almost 70% of the
COD and more than 90% of the aromatic content
of the textile wastewater were removed after 2 h of
irradiation (Fig. 11).
Fig. 2. Flowsheet of the UV irradiation device.
72 D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78
Fig. 3. UV/VIS spectrums of Remazol black B vs. time (min).
D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78 73
Fig. 4. UV irradiation tests of Remazol black B with various H
2
O
2
concentrations.
Fig. 5. UV irradiation of Levafix yellow E-3GA (H
2
O
2
=1 g/l).
74 D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78
Fig. 6. UV irradiation of Levafix red ERN (H
2
O
2
=1 g/l).
Fig. 7. UV irradiation of Levafix blue EBNA (H
2
O
2
=1 g/l).
D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78 75
Fig. 8. UV irradiation of Remazol red RR (H
2
O
2
=1 g/l).
Fig. 9. UV irradiation of Remazol black B (H
2
O
2
=1 g/l).
76 D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78
Fig. 10. The variation of pH with time.
Fig. 11. UV irradiation test of the cotton textile wastewater.
D. Georgiou et al. / Dyes and Pigments 52 (2002) 69–78 77
4. Conclusion
The degradability of five of the most commonly
used azo-reactive dyes under UV/H
2
O
2
conditions
was examined. Dye solutions of 100 mg/l were
prepared immediately before irradiation. A batch
mode water-jacketed immersion photoreactor was
utilized. The radiation source was a 120 W UV
lamp emitting at 253.7 nm and protected by a
quartz tube. Complete destruction of the color was
succeeded in the first 20–30 min of irradiation.
Almost all the aromatic rings and 80% of TOC
were destroyed after 2 h of irradiation. UV/H
2
O
2
is
capable of the complete mineralization of the above
azo reactive dyes. The same technique was also
applied to cotton textile wastewater. Complete
color removal was achieved in less than 1 h while
90% of the aromatic rings and 70% of the waste-
water COD were removed after 2 h of irradiation.
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... The presence of hydrogen peroxide accelerates reactive dye degradation UV light. Georgiou et al., found that with 1 g/L H2O2, complete decolorization of a active dyes in solution was achieved in 20-30 min under UV radiation [90]. Duri treatment, the dye solutions became acidic (pH 3-3.5) which may harm the cotton ture and damage operating equipment. ...
... The presence of hydrogen peroxide accelerates reactive dye degradation under UV light. Georgiou et al., found that with 1 g/L H 2 O 2 , complete decolorization of azo reactive dyes in solution was achieved in 20-30 min under UV radiation [90]. During the treatment, the dye solutions became acidic (pH 3-3.5) which may harm the cotton structure and damage operating equipment. ...
... The proposed mechanism is that dyes are excited by visible light and electrons of excited dye molecules transfer to oxygen, forming superoxide that leads to decolorization [96]. Table 3. Possible ways to remove reactive dyes from cotton [67,89,90]. ...
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Effective water and waste management strategies enable us to decrease water consumption and pollution load of wastewaters. Typical examples of low-waste technologies are lanolin recovery in wool scouring, hydroxide recovery in cotton mercerizing, recovery of synthetic sizes and reuse of dye baths. Wastewaters are treated by a sequence of physical–chemical and biological processes. Traditionally, coagulation/flocculation(c/F) has been favored as the first treatment step followed by biological treatment as the second step. More recently a reverse sequence of treatment has been utilized in several cases with success. Novel technologies have been developed such as catalytic oxidation, decoloration by ozone, adsorption/desorption. Their practical use is, however, still rare. Joint treatment with municipal wastewaters has been favored wherever possible.
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This article presents a comprehensive review of the chemistry underlying the hydrolysis of ferric and aluminum salts, the probable composition of the various hydrolysis products, and suggests the possibility that these highly hydrated materials may very likely have a polymeric structure. It is emphasized throughout the paper that the effect of the multivalent ferric and aluminum ions upon coagulation is not brought about by the ions themselves but by their hydrolysis products. A discussion by A.P. Black follows the article.
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Effective water and waste management strategies enable us to decrease water consumption and pollution load of wastewaters. Typical examples of low-waste technologies are lanolin recovery in wool scouring, hydroxide recovery in cotton mercerizing, recovery of synthetic sizes and reuse of dye baths. Wastewaters are treated by a sequence of physical-chemical and biological processes. Traditionally, coagulation/flocculation (C/F) has been favored as the first treatment step followed by biological treatment as the second step. More recently a reverse sequence of treatment has been utilized in several cases with success. Novel technologies have been developed such as catalytic oxidation, decoloration by ozone, adsorption/desorption. Their practical use is, however, still rare. Joint treatment with municipal wastewaters has been favored wherever possible.
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The development, utilization and improper management of synthetic organic chemicals in recent years has led to the contamination of surface and groundwater supplies at an increasing rate. Many of these chemicals have been determined to have significant toxic effects and are not adequately treated by conventional water and wastewater treatment processes; thus, they may pose significant environmental and public health problems. Tests were conducted to determine the feasibility of treating textile dyeing and finishing wastewater, and water contaminated by two organic pollutants (dimethyl phthalate and isophorone) with a UV light catalyzed oxidation process using hydrogen peroxide as an oxidant (the 'UV/hydrogen peroxide' process).
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Hazardous compounds are often present in water at low concentration levels, which can make their removal difficult and costly by conventional treatment processes. This project investigated the destruction of hazardous compounds in water by ultraviolet catalyzed oxidation using hydrogen peroxide as the oxidizing agent. The effectiveness of this process was determined for typical halogenated aliphatics, including trichloroethylene, tetrachloroethylene, tratrachloroethane, dichlormethane, chloroform, carbon tetrachloride and ethylene dibromide. The reactions were conducted in a batch reactor equipped with a low pressure ultraviolet lamp. The rates of decomposition increased with increasing hydrogen peroxide concentration and temperature, and were highly dependent on chemical structure. With trichloroethylene, for example, the concentration was reduced from 50 ppm to less than 1 ppm in 50 min at 20°C and in 10 min, at 40°C. All of the reacted chlorine was converted to chloride ion, indicating that the chlorinated structures were destroyed by UV catalyzed oxidation.
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Chemical oxidation technologies are useful in the oxidative degradation or transformation of a wide range of pollutants for the treatment of drinking water, groundwater, wastewater, and contaminated soils. The application status and potential of three chemical oxidation treatment methods which generate powerful oxidants (hydroxyl radicals): ultraviolet light (uv)/hydrogen peroxide (H[sub 2]O[sub 2]) process, Fenton's reagent treatment, and titanium dioxide (TiO[sub 2])-assisted photocatalytic degradation, are described and discussed. These oxidation methods are known to effectively degrade and, in several cases, mineralize contaminants ranging from inorganic compounds (such as cyanides) to chlorinated aliphatic compounds and complex aromatic compounds in reaction times on the order of a few minutes to a few hours. Of the three oxidation systems discussed, the technology for the uv/H[sub 2]O[sub 2] process is the most advanced, with numerous successful full-scale treatment units already in existence. Applications of both the Fenton's reagent and TiO[sub 2]-assisted photodegradation processes are currently being developed, with the concepts proven in numerous laboratory-scale studies for a wide range of contaminants. However, both of these processes have only been studied at the pilot/field scale to a limited extent. The application of Fenton's reagent as a pretreatment step prior to biological treatment for industrial wastes and contaminated soils appears promising. Improved system configuration and quantum efficiency of photoreactors are likely to improve the economics of TiO[sub 2]-assisted photodegradation for groundwater treatment, especially with the use of solar illumination. 203 refs., 6 figs., 4 tabs.
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The decolorization and mineralization of some azo and anthraquinone dyes by photoactivated hydrogen peroxide has been studied. The degradation process seems to occur according to a similar mechanism for all the selected dyes. Decolorization is complete in a relatively short time and follows apparent first order kinetics, whereas mineralization requires longer irradiation times. Initially fluorescent intermediates are generated in all cases by hydroxylation of the studied compounds. A simple kinetic model, describing adequately the process, has been proposed; pH does not influence significantly the process in the range going from 3 to 9.
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Photodegradation of carbetamide ((R)-1-(ethylcarbamoyl)ethyl carbanilate) and metoxuron (3-(3-chloro-4-methoxyphenyl)-1,1-dimethylurea) in the presence of hydrogen peroxide, titanium dioxide and ozone was investigated with ultraviolet radiations (λ > 290 nm). Several photoproducts were isolated and identified by spectrometric methods. The results suggest that the degradation pathways of these compounds in the presence of UV-H2O2 and UV-TiO2 are hydroxylations of the aromatic ring. UV-ozonation rapidly photooxydized all pesticides. The opening of the aromatic rings was observed, producing lower molecular weight carboxylic acids. Further photooxidation converts the acids to CO2, H2O, HCl and NH3.
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We describe an environmentally friendly process of oxidative decoloration of chlorotriazinyl reactive azo dyes with hydrogen peroxide, activated with UV irradiation. A comparison of this process with other oxidative decolorations is given. The influence of the synthetic route, the dyebath components, and the reaction conditions of the decoloration process is described. Decoloration efficiency is evaluated with respect to the time-dependent reduction of the color intensity, as well as with ecological parameters such as COD, BOD5 and TC. The method proved to be suitable for the decoloration of reactive azo dyes of triazinyl type.