Azo Dye Concentration Research Articles

Decolorization and mineralization of Allura Red AC azo dye by solar photoelectro-Fenton: Identification of intermediates

The degradation of 2.5L of Allura Red AC solutions in sulfate medium containing 0.50mM Fe2+ has been studied by solar photoelectro-Fenton (SPEF) using a flow plant equipped with a Pt/air-diffusion cell and a solar photoreactor. Comparative electro-Fenton treatment yielded rapid total decolorization but poor mineralization, since most products were slowly destroyed by OH formed from Fenton’s reaction between Fe2+ and H2O2 generated at the air-diffusion cathode. In contrast, the potent action of UV radiation from sunlight in SPEF allowed the rapid photolysis of recalcitrant intermediates, thus giving rise to a quick mineralization. Sulfate and nitrate ions, along with a large proportion of volatile N-derivatives, were always released. The increase in current density and decrease in azo dye concentration accelerated the decolorization and mineralization in SPEF, although lower current efficiency and greater specific energy consumption were obtained. The most cost-effective SPEF treatment was found for 460mgL−1 azo dye in 0.05M Na2SO4 at 50mAcm−2, which yielded 95% mineralization with 81% current efficiency and 8.50kWhm−3. No significant effect of sulfate concentration was found. Up to 16 aromatic intermediates and 11 short-chain carboxylic acids, including oxalic and oxamic as the most persistent ones, were detected by GC–MS and HPLC. The large oxidation ability of SPEF can be explained by the quick photolysis of Fe(III)-oxalate complexes and other undetected intermediates.

Photocatalytic degradation of textile dye CI Basic Yellow 28 wastewater by Degussa P25 based TiO<sub>2</sub>

Wastewaters of textile industry cause high volume colour and harmful substance pollutions. Photocatalytic degradation is a method which gives opportunity of reduction of organic pollutants such as dye containing wastewaters. In this study, photocatalytic degradation of C.I. Basic Yellow 28 (BY28) as a model dye contaminant was carried out using Degussa P25 in a photocatalytic reactor. The experiments were followed out at three different azo dye concentrations in a reactor equipped UV-A lamp (365 nm) as a light source. Azo dye removal efficiencies were examined with total organic carbon and UV-vis measurements. As a result of experiments, maximum degradation efficiency was obtained as 100% at BY28 concentration of 50 mgL-1 for the reaction time of 2.5 h. The photodegradation of BY28 was described by a pseudo-first-order kinetic model modified with the langmuir-Hinshelwood mechanism. The adsorption equilibrium constant and the rate constant of the surface reaction were calculated as Kdye = 6.689u10-2 L mg-1 and kc = 0.599 mg L-1min-1, respectively.

The photocatalytic removal of azo dye by nickel-doped titanium dioxide nanoparticles coated on Iranian natural zeolite clinoptilolite fixed substrate

Aims: The purpose of this study was to remove azonium compound using the photocatalytic property of nickel (Ni)-doped titanium dioxide (TiO 2 ) nanoparticles coated on Iranian natural zeolite. Materials and Methods: Nickel-doped TiO 2 nanoparticles with the molar ratios of 0, 0.17, 2, 9% Ni/TiO 2 were prepared via the sol-gel process and coated on Iranian natural zeolite clinoptilolite (CLI). Afterward, X-ray diffraction, scanning electron microscopy and inductively coupled plasma studies were conducted to describe Ni and titanium. Photocatalytic removal of azo dye in concentrations of 25 and 50 mg/L was performed by fixing the composite under ultraviolet irradiation. Results: TiO 2 nanoparticles in both the anatase and rutile phases were obtained via the sol-gel method with the ratios of 86.33%, (34.44 nm particle size) and 13.67% (18 nm particle size) and were then coated on Iranian natural CLI zeolite. The results indicated that the photocatalytic removal efficiency of the 9% Ni/TiO 2 -CLI samples, in which the azo dye concentrations were 25 and 50 mg/L, was 93% and 79% at 160 min. In addition, the composition of the 9% Ni/TiO 2 -CLI possessed the greatest removal rate difference of azo dye at the concentrations of 25 and 50 mg/L. Conclusion: Application of Iranian CLI as a substrate is the most cost-effective way to increase the photocatalytic activity. Furthermore, adding Ni to TiO 2 can increase the photocatalyst removal efficiency of azonium compound.

Influence of azo dye concentration on activated sludge bacterial community in the presence of functionalized polyurethane foam.

Immobilized quinones exhibit good catalytic performance in the biodecolorization of azo dyes. However, in practical activated sludge systems, little is known about the effect of azo dye concentration on microbial communities in the presence of immobilized quinones. 454 Pyrosequencing was used to investigate structural changes and to determine the key microorganisms involved in Reactive Red X-3B decolorization in the presence of anthraquinone-2-sulfonate immobilized on polyurethane foam (AQS-PUF). Our results show that the AQS-PUF-supplemented system exhibited better stability and decolorization performance during a 30-day run than polyurethane-foam-only (PUF-supplemented) and control systems. Analysis of pyrosequencing data showed that the AQS-PUF-supplemented system had the highest bacterial diversity, followed by the control and PUF-supplemented systems during decolorization. Reactive Red X-3B and AQS-PUF significantly influenced bacterial communities at the class level: Erysipelotrichia and the most dominant Deltaproteobacteria showed significant positive correlations with Reactive Red X-3B, while unclassified Firmicutes were found to be significantly correlated with AQS-PUF. At the genus level, Desulfomicrobium, which represents 8-44 % of the total population, displayed a significant positive correlation with Reactive Red X-3B. Some bacteria, including Desulfovibrio, Shewanella, and Clostridium with relative abundances of less than 6 %, were positively correlated with AQS-PUF. These findings provide a novel insight into the changes that occur in the bacterial community during immobilized AQS-mediated decolorization. Less abundant quinone-reducing bacteria play important roles in accelerating the effect of AQS-PUF on biodecolorization.

Upflow fixed bed bioelectrochemical reactor for wastewater treatment applications

A cylindrical Upflow Fixed Bed Reactor (UFB-BER) with granular activated carbon, steel mesh electrodes and anaerobic microorganisms, was constructed for analyzing how hydrodynamic parameters affect the reactions involved during wastewater treatment processes for azo dye degradation. Dye removal percentage was not compromised by decreasing HRTm (99–90% upon changing HRTm from 4 to 1h in single pass mode). Using the residence time distribution method for hydrodynamic characterization, it was found that a higher dispersion in the reactor occurs for HRTm=1h, than for HRTm=4h. A kinetic analysis suggests that this dispersion effect could be associated to a higher specific reaction rate dependent on the azo dye concentration.

Investigation of water decolorization by Fenton oxidation process in batch and continuous systems

Nowadays, advanced oxidation methods such as Fenton and modified Fenton processes draw considerable attention to dye removal in textile wastewater. In Fenton process, low concentrations of Fe+2 and H2O2 solutions are used and these Fenton reagents generate OH⋅ radicals including high oxidation potential. The Fenton process, in which non-toxic and harmless reagents are applied at low concentrations, is very useful for decolorization of wastewater since it is very effective and less polluting. In this study, decolorization of the water samples containing azo dyes like Acid Red 88 (AR 88) was performed by Fenton oxidation process on a laboratory-scale setup. The aqueous solutions prepared by AR 88 dye were used for effective decolorization by Fenton oxidation method in batch process under various reaction conditions. By this method, the effects of solution temperature, pH, stirring speed, and concentration on the decolorization of the samples were investigated. The decolorization reaction kinetics of AR 88 dye was also determined in the batch system. Then, the Fenton oxidation experiments were carried out in the continuous system under the optimum conditions of stirring rate = 250 rpm; pH 2; [H2O2] = 1.0 mM; [Fe2+] = 0.1 mM; azo dye concentration [AR 88] = 0.12 mM; and T = 30°C. These optimum conditions were determined in the batch system studies. The efficiency of decolorization for both systems was about 99% and the decolorization kinetics of the water samples containing AR 88 dye was found as the second-order. The experimental results also showed that the Fenton’s reagent was effective for the degradation of AR 88 dye using H2O2 and Fe2+ solutions at low concentrations.

The kinetic of dyes degradation resulted from food industry in wastewater using high frequency of ultrasound

The ultrasound techniques have employed to study the effect of high frequency on the degradation of methyl orange dye, MOD, from a model of industrial wastewater. Three different initial concentrations of methyl orange (10, 30 and 50ppm), with three different power supply’s to ultrasound device voltages (15, 20 and 25V), and two different liquid volumes (15 and 20ml) were investigated here on the effect of MOD degradation. Results show that as the concentration of azo dyes increases, the degradation increases. It was also found that as the liquid volume increases, the ability to degraded azo dyes decreases. The best condition achieved for degradation of azo dyes obtained at 50ppm, 15ml, and 25V. The degradation data results are best fitted with a first order kinetic degradation model. The degradation rate constant was calculated by best fitting and found to be equal to an average value for 25 and 20V to 0.0114min−1.

Effective Electro-Fenton Degradation of Reactive Black 5 Dye using Modified Electrode with Cu-Zeolites

The electrocatalytic production of hydroxyl radical (HO•) on the surface of zeolite modified electrode (ME) employing Cu-Zeolites (ZSM5 and β) with different theoretical ionic exchange (15 and 100%) was investigated (ME/Cu-Zeolites). The i-E characteristic of ME/Cu-ZSM-5 presented the faradic process associated to redox couple Cu2+/Cu+. On the other hand, voltammetric studies showed that in presence of H2O2, the cathodic peak current of ME/Cu-Zeolites increases followed by a decrease in the corresponding anodic current. This suggested that hydroxyl radical was produced by a cooperative effect of the acidic properties of zeolite and copper that acts as a redox mediator on the electrode surface via an electrocatalytic mechanism. Experiments of degradation using azo dye Reactive Black 5 as probe molecule exhibited that the concentration of azo dye decreased in the time, this confirms the formation of hydroxyl radical on the surface of modified electrode; kinetics parameters demonstrated that the ME/Cu- β with 15% of ionic exchange presented the highest catalytic activity.

CYTOGENOTOXICITY EVALUATION OF WATER CONTAMINATED WITH SOME TEXTILE AZO DYES USING RAPD MARKERS AND CHROMOSOMAL ABERRATIONS OF ONION (Allium cepa) ROOT CELLS

The Allium cepa assay is an efficient test for chemical screening and in situ monitoring for genotoxicity of environmental contaminants. This test has been used widely to study genotoxicity of many chemicals pollutions revealing that these compounds can induce chromosomal aberrations in root meristems of Allium cepa. In this study, we aimed to determine genotoxic effects of some textile azo dyes by using the Allium cepa chromosome aberrations test and random amplification of polymorphic DNA (RAPD) analyses. The onion (Allium cepa L.) roots were exposed to different concentrations of three textile azo dyes. The mitotic index of samples exposed to EC50 (500 μg/ml) of selected azo dyes for RLB, RN and SGL was 10.8, 10.3 and 8.8, respectively. The results indicated that the root length of Allium cepa reduced with an increasing azo dye concentration. A random amplification of polymorphic DNA (RAPD) analysis from the extracted DNA was carried out using ten 10-base pair random primers. Ten primers produced 54 bands between 100-1600 base pairs in gel electrophoresis. The number of disappearing bands in profiles was differenced from one to five bands of azo dyes treatment compared to total bands in control and new bands were appeared in treatments. Obtained results from this study revealed that the total chromosomal aberrations and RAPD profiles were performed as useful tool for detection and biomarker assays for the evaluation of genotoxic effects on textile azo dyes polluted plants.

Chemical and spectrophotometric studies of naphthol dye as an inhibitor for aluminium alloy corrosion in binary alkaline medium

The inhibition of a substituted naphthol compound, 4-(4-nitrophenylazo)-1-naphthol (44NIN), on the corrosion of aluminium (Al) in a basic medium was studied by classical chemical (gravimetric) and spectrophotometric (UV–Vis and FTIR) methods at 303–333 K. 44NIN demonstrated an excellent inhibiting property to Al corrosion in the aerated binary alkaline solution as shown from the results. The inhibition efficiency was found to increase with the azo dye concentration but not with temperature. Thermodynamic and adsorption evaluation for this inhibition process were accessed and thoroughly discussed. The UV–visible absorption spectra of the solution containing this dye after the immersion of Al specimen indicate the possible formation of a 44NIN–Fe type complex. The FTIR was carried out of the dye and protective film formed on the surface of the metal in the electrolyte containing the dye after a 72 h immersion period. These results show a correlation between the inhibitive effect and molecular structural information of 44NIN in this typical heterogeneous alkaline system.

Enhanced azo dye removal through anode biofilm acclimation to toxicity in single-chamber biocatalyzed electrolysis system

Azo dye is widely used in printing and dyeing process as one of refractory wastewaters for its high chroma, stable chemical property and toxicity for aquatic organism. Biocatalyzed electrolysis system (BES) is a new developed technology to degrade organic waste in bioanode and recover recalcitrant contaminants in cathode with effective decoloration. The ion exchange membrane (IEM) separate anode and cathode for biofilm formation protection. Azo removal efficiency was up to 60.8%, but decreased to 20.5% when IEM was removed. However, expensive ion exchange membrane (IEM) not suitable for further practical application, bioelectrochemical activity of bioanode is sensitive to the toxicity of azo dye. A gradient increase of azo dye concentration was used to acclimate anode biofilm to pollutant toxicity. The azo removal efficiency can be enhanced to 73.3% in 10h reaction period after acclimation. The highest removal efficiency reached 83.7% and removal rates were increased to 8.37 from 3.04 g/h/L of dual-chamber. That indicated the feasibility for azo dye removal by single-chamber BES. The IEM cancellation not only decreased the internal resistance, but increased the current density and azo dye removal.

Successful treatment of high azo dye concentration wastewater using combined anaerobic/aerobic granular activated carbon-sequencing batch biofilm reactor (GAC-SBBR): simultaneous adsorption and biodegradation processes

The application of a granular activated carbon-sequencing batch biofilm reactor (GAC-SBBR) for treatment of wastewater containing 1,000 mg/L Acid Red 18 (AR18) was investigated in this research. The treatment system consisted of a sequencing batch reactor equipped with moving GAC as biofilm support. Each treatment cycle consisted of two successive anaerobic (14 h) and aerobic (8 h) reaction phases. Removal of more than 91% chemical oxygen demand (COD) and 97% AR18 was achieved in this study. Investigation of dye decolorization kinetics showed that the dye removal was stimulated by the adsorption capacity of the GAC at the beginning of the anaerobic phase and then progressed following a first-order reaction. Based on COD analysis results, at least 77.8% of the dye total metabolites were mineralized during the applied treatment system. High-performance liquid chromatography analysis revealed that more than 97% of 1-naphthyalamine-4-sulfonate as one of the main sulfonated aromatic constituents of AR18 was removed during the aerobic reaction phase. According to the scanning electron microscopic analysis, the microbial biofilms grew in most cavities and pores of the GAC, but not on the external surfaces of the GAC.

The Comparison of Photocatalytic Degradation and Decolorization Processes of Dyeing Effluents

Treatment of dye effluents resulting from the industrial scale dyeing of cotton, polyacrylic fibres, leather, and flax fabrics by photocatalytic methods was investigated. Photocatalytic processes were initiated by UV-a light (λmax366 nm) and were conducted in the presence of TiO2, TiO2/FeCl3, or FeCl3as photocatalysts. It was found that the photocatalytic process carried out with TiO2and TiO2/FeCl3was the most effective method for decolorization of textile dyeing effluents and degradation of dyes, except for effluents containing very high concentrations of stable azo dyes. During the photocatalytic degradation of anionic dyes, a mixture of TiO2/FeCl3was more effective, while in the case of cationic dyes, more suitable seems to be TiO2alone.

Efficient azoic dye degradation by Trametes trogii and a novel strategy to evaluate products released

Culture filtrates from the white rot fungus Trametes trogii were used for the degradation of two azo dyes: Xylidine and Methyl Orange. These culture filtrates showed a great potential for decolorizing even high concentrations of both azo dyes, without the addition of redox mediators, possibly due to the synergistic action of their high contents of laccase (104 U ml−1), accompanied by Mn-peroxidase (0.54 U ml−1), cellobiose dehydrogenase (0.45 U ml−1) and glioxal oxidase (0.38 U ml−1) activities. 75% of Methyl Orange (980 ppm) and 96% of Xylidine (480 ppm) were degraded after 24 h, degradation occurred after 6 days with a 94% of Xylidine removed (1440 ppm). Biodegradation products from Xylidine were determined by capillary electrophoresis followed by MALDI-TOF mass spectra. Neither aromatic amines nor colored quinones were detected, major metabolites being naphtalene sulphonate and xylene.

Photocatalytic mineralization of azo dye Acid Orange 7 under solar light irradiation

Abstract The objective of this study was to investigate mineralization of hazardous water soluble azo dye Acid Orange 7 (AO7) under photocatalytic process. In this experiment, sunlight was used as the source for UV irradiation and titanium dioxide, TiO2 as catalyst. The effects of some process variables on decolorization such as amount of TiO2, azo dye concentration and dosage of hydrogen peroxide (H2O2) were examined. TiO2-based photocatalytic degradation is an effective, economic and faster mode of removing azo dye AO7 from aqueous solution. The presence of sunlight enhanced the decolorization rate of AO7 and mineralized the intermediate products completely. The mineralization of AO7 was supported by the UV–Vis and ion chromatography analysis. The addition of proper amount of H2O2 could optimize the decolorization rate of AO7. The photocatalytic degradation of AO7 followed first-order kinetic model.

Electrochemical oxidation of methyl orange azo dye at pilot flow plant using BDD technology

Solutions of methyl orange azo dye were degraded by electrochemical oxidation using a 3L flow plant with a boron-doped diamond (BDD)/stainless steel cell operating at constant current density, ambient temperature and liquid flow rate of 12Lmin−1. A 23 factorial design considering the applied current density, azo dye concentration and electrolysis time as variable independents was used to analyze the process by response surface methodology. LC–MS analysis revealed the formation of seven oxidation products from the cleavage of the NN group of the dye, followed by deamination, formation of a nitro group and/or desulfonation of the resulting aromatics.

Phytoremediatgion of wastewater containing azo dye by sunflowers and their photosynthetic response

Azo dyes, as the largest group of synthetic dyes released from textile and dyestuff industries, have caused serious environmental problems. We investigated the removal ability and physiological response of sunflowers to simulated wastewater containing azo dyes with concentration similar to real wastewater or above. The percent decolorization of the three azo dyes within 4days varied greatly. For the same dyes, the percent decolorization was descending with the primary dye concentration increasing. The percent decolorization of Bismark browny, Evans blue and Orange G at same concentration was also descending. The average percent decolorization of the three azo dyes at 100mg/L within 4days was 62.64%. The physiological effects of the tested azo dyes on sunflowers were also very different. The stress effects of Bismark browny, Evans blue and Orange G at same concentration were also descending. All tested azo dyes reduced significantly normalized relative transpiration (NRT), net photosynthesis rate (Pn), transpiration intensity (Tr) and stomatal conductance (Gs) of sunflowers. The percent of decline of all the indicators such as NRT, Pn, Tr and Gs was less than 50% when concentration of azo dyes was 100mg/L. The result showed that sunflowers can survive in water containing 100mg/L all tested azo dyes. We conclude that sunflowers can be used for phytoremediation of wastewater containing azo dyes.

Activated carbon xerogels for the removal of the anionic azo dyes Orange II and Chromotrope 2R by adsorption and catalytic wet peroxide oxidation

Activated carbon xerogels (ACXs) were tested for the removal of azo dyes in aqueous solutions, either by adsorption or by catalytic wet peroxide oxidation (CWPO). Two azo dyes, Orange II (OII) and Chromotrope 2R (C2R), were chosen as model pollutants. The ACXs were produced by activation of an organic resorcinol–formaldehyde xerogel (RFX). Three different activation procedures were carried out producing five distinct ACXs: steam at 1073K (ACX-S), chemical impregnation with H3PO4 at 773K (ACX-P) and alkali activation with dry KOH at 973K (ACX-K), using three different mass ratios of KOH/RFX, namely 1:1 (ACX-K1), 2:1 (ACX-K2) and 4:1 (ACX-K4).The results obtained in the adsorption experiments carried out at pH=3, T=303K, adsorbent load of 0.1gL−1 and azo dye concentration of 100mgL−1 show that the interaction between the carbon materials and the anionic dyes is enhanced with the basicity of the carbon surfaces. ACX-K materials, the carbon materials with higher basicity amongst those prepared, exhibit high adsorption performances for the removal of both dyes, namely from over 215mgg−1 (for adsorption of C2R on ACX-K2 after 150min) up to 499mgg−1 (for adsorption of OII on ACX-K4 at the same period of time). Furthermore, with ACX-K materials in CWPO (i.e., using H2O2) increments in the removal of C2R as high as 33%, 24% and 20%, in comparison to the removals obtained by adsorption, where obtained when ACX-K1, ACX-K2 and ACX-K4 were respectively tested at 303K. Increasing the operating temperature (T=323K), the removal increments achieved by CWPO, compared to the removals obtained by adsorption at the same temperature, increase 67%, 59% and 49%, when ACX-K1, ACX-K2 and ACX-K4 were respectively tested. Recycling studies with ACX-K1 puts in evidence the high stability of this catalyst in CWPO, since it was observed, after a first reaction run, that the catalytic activity of this material is not affected by its successive reuse.Increasing the operating temperature (T=323K) and the adsorbent load (0.5gL−1), ACX-K4 is able to completely remove the C2R content by adsorption. In the case of ACX-K1 and ACX-K2, adsorption removals over 97% of the C2R content are attainable.

Decolourisation of textile wastewater in a submerged anaerobic membrane bioreactor

Azo dye decolourisation can be easily achieved by biological reduction under anaerobic conditions. The aim of this study was to evaluate the applicability of submerged anaerobic membrane bioreactors (SAMBRs) for the decolourisation of dyeing wastewater containing azo dyes. The reactive orange 16 was used as model of an azo dye. The results demonstrated that very high decolourisation (higher than 99%) can be achieved by SAMBRs. Although decolourisation was not significantly influenced by the azo dye concentrations up to 3.2gL−1, methane production was greatly inhibited (up to 80–85%). Since volatile fatty acids accumulated in the treatment system with the azo dye concentration increase, methanogenes seem to be the most sensitive microbial populations of the anaerobic ecological community. The results demonstrated that anaerobic process combined with membrane filtration can deal with highly concentrated wastewaters that result from stream separation of industrial discharges.

Effect of heterojunction on photocatalytic properties of multilayered ZnO-based thin films

In the present study, the effects of the heterojunctions on the optical and structural characteristics and the resulting photocatalytic properties of multilayered ZnO-based thin films were investigated. The junctions were composed of semiconducting ZnO nano-porous films coated on the In2O3 and SnO2 counterpart layers. The multilayered ZnO films based on the triple-layered Ag-doped indium oxide (AIO)/tin oxide (TO)/zinc oxide (ZnO), indium oxide (IO)/Ag-doped tin oxide (ATO)/zinc oxide (ZnO), indium oxide (IO)/tin oxide (TO)/zinc oxide (ZnO) and tin oxide (TO)/indium oxide (IO)/zinc oxide (ZnO) have been fabricated by subsequent sol–gel dip coating. Their structural and optical properties combined with photocatalytic characteristics were examined toward degradation of Solantine Brown BRL (C.I. Direct Brown), an azo dye using in Iran textile industries as organic model under UV light irradiation. Effects of operational parameters such as initial concentration of azo dye, irradiation time, solution pH, absence and presence of Ag doping and consequent of sublayers on the photodegradation efficiencies of ZnO nultilayered thin films were also investigated and optimum conditions were established. It was found that the photocatalytic degradation of azo dye on the composite films followed pseudo-first order kinetics. Photocatalytic activity of AIO/TO/ZnO interface composite film was higher compared with other films and the following order was observed for films activities: AIO/TO/ZnO>IO/TO/ZnO>ATO/IO/ZnO>TO/IO/ZnO. Differences in the film efficiencies can be attributed to differences in crystallinity, interfacial lattice mismatch, and surface morphology. Besides, the presence of Ag doping between layers that may act as trap for electrons generated in the ZnO over layer thus preventing electron–hole recombination.