Azo Dye Concentration Research Articles

Investigation of isolation and immobilization of a microbial consortium for decoloring of azo dye 4BS

Eight high-effective decolorization strains were isolated by enrichment using Direct Fast Scarlet 4BS as sole source of carbon and energy. The optimal microbial consortium consisting of fungus 8-4* and bacterium 1-10 was selected by optimizing combination decolorization experiments with these eight freely suspended strains, whose decolorization activity was higher than individual strains due to synergistic reaction with each other. The optimal microbial consortium was also immobilized using polyvinyl alcohol (PVA) as the carrier. This paper optimized the immobilization and operational conditions, investigated the effect of the environmental factors (temperature, pH and dissolved oxygen (DO)) and initial dye concentration on the rate of decolorization by immobilized microbial consortium. The results showed that the optimal decolorization activity was observed in pH range (5–8), temperature range (25–40°C) under shaking culture of high DO level. Decolorization with the optimal microbial consortium gave a relatively high maximum decolorization activity (ca. 81.25mgl−1h−1), which occurred at a dye concentration of 1000mgl−1, suggesting the applicability of the strains in remediation of wastewater containing high azo dye concentrations. The immobilized beads could be reused for more than 30 cycles, without losing any degradation capacity. The changes of UV-visible spectra and the change curve of COD of 4BS solution before and after decolorization cultivation and the proliferation and distribution of microbial consortium in gel beads were also microscopically observed, which could be used for conferring the decolorization mechanisms of dye 4BS.

Diacetylene-Containing Polymers XIV: Poly(octa-3,5-diynylene-1,8-dicarboxyalates) containing some polar azo dyes

A series of novel polymers having polar azo dyes were synthesized and characterized. Although their chromophore contents are very high, their second order nonlinear (2-NLO) response was very poor. The poor 2-NLO responses are thought to be due to poor orientation because of their improper main chain conformations, as well as their low glass transition temperatures. They undergo slow cross-linking on standing at room temperature, and rapidly on heating at temperalures above 150°C, through the diacetylene units of the main chains. Nevertheless, these polymers are interesting materials as azo-polymers because of their very high concentration of azo dyes, which are distributed homogeneously in the polymers. Synthesis and characterization are described, and the most important factor for the 2-NLO polymers is discussed.

Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes

The sonochemical decolorization and decomposition of azo dyes, such as C. I. Reactive Red 22 and methyl orange, were performed from the viewpoints of wastewater treatment and to determine the reaction kinetics. A low concentration of the azo dye solution was irradiated with a 200 kHz and 1.25 W/cm 2 ultrasound in a homogeneous aqueous solution. The azo dye solutions were readily decolorized by the irradiation. The sonochemical decolorization was also depressed by the addition of the t-butyl alcohol radical scavenger. These results indicated that azo dye molecules were mainly decomposed by OH radicals formed from the water sonolysis. In this paper, we propose a new kinetics model taking into account the heterogeneous reaction kinetics similar to a Langmuir–Hinshelwood mechanism or an Eley–Rideal mechanism. The proposed kinetics model is based on the local reaction site at the interface region of the cavitation bubbles, where azo dye molecules are quickly decomposed because an extremely high concentration of OH radicals exists in this region. To confirm the proposed kinetics model, the effects of the initial concentration of azo dyes, irradiated atmosphere and pH on the decomposition rates were investigated. The obtained results were in good agreement with the proposed kinetics model.

Decolorization and inhibition kinetic of Direct Black 38 azo dye with granulated anaerobic sludge

Decolorization and inhibition kinetics of C.I. Direct Black 38 (DB 38) at concentrations varying between 200 and 3200mgl−1 were investigated with partially granulated anaerobic mixed culture using glucose (3000mgl−1COD) as carbon source and electron donor during batch incubation. Various models reported in literature (Monod, 0, 1 and 2 order) were tested in order to determine the most suitable substrate removal kinetic. The interpretation of kinetic data showed the first order kinetic was found to be the most appropriate kinetic among the kinetic models tested. Increases in dye concentrations from 0 to 3200mgl−1 reduce the degradation rate constant (k1) values from 0.0062 to 0.0017h−1 in batch studies performed with DB 38. Decolorization was achieved effectively under test conditions but ultimate mineralization of azo dyes was not observed. The course of the decolorization process approximates to second order kinetic at 200, 400, and 800mgl−1 of BD 38, and to first order kinetic at 1600 and 3200mgl−1 of BD 38 concentration. Aromatic amine accumulation was observed proportionally at a higher DB38 concentration. A competitive kinetic model that describes the anaerobic co-metabolism of increasing DB 38 dye concentrations with glucose as co-substrate has been developed based on the experimental data. The competitive inhibition constants were 1520 and 400mgl−1 for 200 and 1600mgl−1 of DB 38 dye, respectively. The average competitive inhibition constant was 914±574mgl−1.The slope of inhibited reaction is KS/Rmax (1+I/KID). However, the Rmax values did not significantly vary. The half saturation constants were found to be greater in high azo dye concentrations compared to the dye-free samples. The slope of inhibited reactor increased by a factor of (1+ID/KID).

A batch kinetic study on decolorization and inhibition of Reactive Black 5 and Direct Brown 2 in an anaerobic mixed culture

Decolorization and inhibition kinetic characteristics of two azo dyes namely Reactive Black 5 (RB 5) and Direct Brown 2 (DB 2) were investigated with partially granulated anaerobic mixed culture using glucose (3000 mg l −1 COD) as carbon source and electron donor during batch incubation. Monod, zero-, first-, and second-order reaction kinetic models were tested in order to determine the most suitable rate model of substrate and color removal kinetic. The course of the decolorization and substrate removal process approximates to first-order kinetic model under batch conditions. Decolorization, and substrate removal were achieved effectively under test conditions but ultimate removal of azo dyes and substrate were not observed at high dye concentrations. Aromatic amine and volatile fatty acid accumulation were observed proportionally at a higher azo dye concentration. A competitive kinetic model that describes the anaerobic co-metabolism of increasing RB 5 and DB 2 dye concentrations with glucose as co-substrate has been developed based on the experimental data.

Manipulation of anchoring strength in an azo-dye side chain polymer by photoisomerization.

The generation of surface anisotropy by photochemical means has been proposed as an attractive method to align liquid crystals. In this paper, we present an experimental study of the alignment induced on a liquid crystal by a polymer film containing azo-dye groups in the side chain. Optical measurements were performed in nematic liquid crystal cells to determine the azimuthal and zenithal anchoring strengths as a function of the irradiation energy and chromophores concentration. It was observed that the director tends to align perpendicular to the polarization direction of the incident light and the orientation process consists essentially of a rotation of the director in the plane parallel to the boundary surfaces. However, the concentration of azo-dye groups in the polymer film must exceed a minimum value to get a macroscopical effect on the liquid crystal alignment. It is shown that the azimuthal anchoring strength can be varied two orders of magnitude by controlling the irradiation energy and azo-dye concentration.

Near-Infrared Raman Spectra of Azo Dye Produced by a Nitrogen-Dioxide-Gas-Selective Coloration Reaction in a Porous Glass Chip

We directly observed azo dye in a porous glass chip by near-infrared (NIR) Raman spectroscopy. We produced the dye by a modified Saltzman reaction by using sulfanilamide (SFA) and N, N-dimethyl-1-naphthylamine (DMNA) as reagents and used it for the selective sensing of atmospheric nitrogen dioxide gas (NO2). The use of NIR laser excitation is particularly advantageous for the direct measurement of azo dye because it avoids the problem of interference from fluorescence. We obtained the 1597 cm−1 band assigned to the phenyl group stretching mode and the 1415 cm−1 band assigned to the azo group stretching mode. The Raman intensity and visible absorption intensity of the peaks of the azo dye in a porous glass chip increased as we increased the exposure time to NO2. This allowed us to monitor the NO2-sensing reaction in a porous glass chip using NIR Raman spectroscopy. Furthermore, we determined the depth profiles of the azo dye concentration in the porous glass chip by confocal NIR Raman spectroscopy and found that they were different in the early and later NO2-exposure stages. This result indicates that the consumption of the NO2-sensing reagents that accompany azo dye production occurs preferentially at the surface to the deeper regions of the porous glass chip.

Birefringence and dichroism of oriented epoxy thermoset films

AbstractA series of oriented liquid–crystalline epoxy thin films were prepared by the in situ polymerization of a liquid–crystalline diepoxide, 1,4‐phenylene bis[4‐(2,3‐epoxypropoxy)benzoate], with an aromatic diamine, 4,4′‐diaminobiphenyl, in a 7.0‐T magnetic field. The birefringent measurements of the oriented films were made from 543.5 to 830 nm. In this range, the values of birefringence (Δn) range from 0.155 to 0.130. When they are extrapolated to the microwave region, Δn = 0.105. The dichroism of a guest azo dye, 4‐(4‐nitrophenylazo)‐3‐hexyloxyaniline, in the oriented thin films was examined in the visible region. From the results, the order parameter of the polymer was calculated to 0.65 by extrapolating the concentration of the guest azo dye to zero. The guest azo dye compound does not affect the birefringence. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 915–919, 2001

Kinetics of bacterial decolorization of azo dye with Escherichia coli NO3

Kinetic characteristics of azo dye decolorization by Escherichia coli NO3 were determined quantitatively using C.I. Reactive Red 22 as the model azo dye substrate. The effects of substrate (dye) concentration and the environmental factors (temperature, pH, dissolved oxygen (DO) level) on the rate of bacterial decolorization were investigated. The stability and efficiency of the E. coli NO3 strain in long-term repetitive operations were also examined. The results showed that the dependence of the specific decolorization rate on azo dye concentration could be described by a conventional substrate-inhibition model. Decolorization with E coli NO3 gave a relatively high maximum decolorization activity (ca. 100 mg dye g cell −1 h −1), which occurred at a dye concentration of 2000 mg l −1, suggesting the applicability of the strain in remediation of wastewater containing high azo dye concentrations. Dependence of the decolorization rate on temperature followed the Arrehnius equation over a normal temperature range (20–45°C), while the optimal pH for decolorization was around 7–9. DO level significantly inhibited the bacterial decolorization, which could not occur if the DO level exceeded 0.5 mg l −1. During four repeated runs, the E. coli NO3 always maintained a higher decolorization rate than that obtained from the original run.

Anaerobic–aerobic biotreatment of simulated textile effluent containing varied ratios of starch and azo dye

Combined anaerobic–aerobic treatment was used to treat a simulated textile industry wastewater (overall HRT 1.8 days). The azo dye (PROCION Red H-E7B) and starch concentrations were varied in a series of 1-week experiments to determine the effect of starch:dye ratio on COD, BOD and colour removal. The treatment efficiency of the system at 1.9 g l −1 starch and 0.15 g l −1 dye remained constant over 130 days despite seven intervening 1-week periods of operation at other starch:dye ratios. Most colour removal occurred in the UASB reactor (1 d HRT), and the BOD:COD of the UASB reactor effluent increased by up to 47%. The maximum overall COD removal was 88% and the BOD removal was up to 99%. A maximum of 77% colour removal overall was achieved with starch and dye concentrations of 3.8 and 0.15 g l −1, giving a final true colour of 0.21 TCU. At both 0.15 and 0.75 g l −1 dye a starch concentration of 3.8 g l −1 rather than 1.9 g l −1 gave a significant improvement in colour removal. However, at 3.8 g l −1 starch volatile fatty acid levels in the UASB reactor rose, while at 2.9 g l −1 starch they did not. It is recommended that if colour removal efficiency decreases, carbohydrate should be added to the anaerobic reactor at a maximum sludge loading rate between 0.11 and 0.15 kg COD kg −1 TVS d −1.

Synthesis and polarized light-induced birefringence of new polymethacrylates containing carbazolyl and azobenzene pendant groups

Low Tg copolymers of [11(N-carbazolyl)undecylmethacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo]-phenoxyalkylmethacrylate] have been synthesized and the polarized light-induced birefringence of thick films (70 μm) has been investigated at a constant deducted temperature relative to Tg (T − Tg = 10 °C). The optical properties of these copolymers have been studied in relation to the azo-dye content and the length of the alkyl spacer between the azo-dye and the methacrylic backbone. They have been compared with the dispersion of (4-methoxy-2,5-dimethylphenyl)-(4-nitrophenyl)diazene (DMNPAA) within a poly[11(N-carbazolyl)undecyl-methacrylate] and a poly[N-vinylcarbazole] (PVK) matrix. The experimental curves have been fitted by biexponentials, so emphasizing the effects of the copolymer structure on the kinetics of the writing process. The photoinduced orientation is more than three orders of magnitude higher in a grafted material compared to the dispersion version. The azo-dye concentration also has an important role in both the amplitude and the dynamics of the photo-orientation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 205–213, 2000

Microbial decolorization of azo dyes by Proteus mirabilis.

A bacterium identified as Proteus mirabilis was isolated from acclimated sludge from a dyeing wastewater treatment plant. This strain rapidly decolorized a deep red azo dye solution (RED RBN). Features of the decolorizing process related to biodegradation and biosorption were also studied. Although P. mirabilis displayed good growth in shake culture, color removal was best in anoxic static cultures. For color removal, the optimal pH and temperature were 6.5-7.5 and 30-35 degrees C, respectively. The organism exhibited a remarkable color removal capability, even at a high concentration of azo dye. More than 95% of azo dye was reduced within 20 h at a dye concentration of 1.0 g L-1. Decolorization appears to proceed primarily by enzymatic reduction associated with a minor portion, 13-17%, of biosorption to inactivated microbial cells.

Aggregation of Azo Dyes with Cationic Amphiphiles at Low Concentrations in Aqueous Solution

The aggregation of a series of n-alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (CmpyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in the spectra of the dyes. Precipitates formed in aqueous solutions from the cationic surfactants and MO and pMR are CnTA−MO, CnTA−pMR, and Cmpy−MO salts and consist of an equimolar ratio of surfactant and dye. In similar experiments with EO, MR, MY, or ABS as the solvatochromic dye molecules, no precipitation occurred, although surfactant−EO salts precipitated at high EO concentration. Dye−surfactant salts formed from CnTAB and MO were found to form myelins in phase penetration experiments. Temperatures at which myelins start to form increase upon increasing alkyl chain length of the surfactant as revealed by optical microscopy. The formation of vesicles from C10TA−MO and from C12TA−MO crystals was indicated by electron microscopy. The presence and position of the ionic group in the dye molecule is important in determining the association. The importance of hydrophobic interactions is revealed by the chain length dependence on the aggregation process and the observation that interactions are absent in ethanol. Electrostatic interactions also play an important role, as shown by the effect of NaCl on the binding process.

Photoassisted Fenton Degradation of Nonbiodegradable Azo Dye (Orange II) in Fe-Free Solutions Mediated by Cation Transfer Membranes

Photoassisted degradation of nonbiodegradable Orange II is shown to be catalyzed by Nafion cation-transfer membranes exchanged with Fe ions in the presence of H2O2. The Nafion membranes in the oxidative media used degraded Orange II with similar kinetics as found in the homogeneous Fe3+/H2O2 photoassisted catalysis, avoiding the drawbacks of the homogeneous treatment. The treatment of this model textile dye is shown to proceed via a Fenton-like process without sludge production because of the selective H2O2 decomposition on the Fe ions exchanged on the membrane. The effect of the concentration of H2O2, solution pH, azo dye concentration, and light intensity (visible light) on the degradation of Orange is reported in detail. The activity of the membranes during the Orange II decomposition was tested for 1500 h and was observed to remain fairly stable within this period. The Fe/Nafion membranes consisted mainly of Fe2O3 (78%) before reaction and Fe2O3 (14%) after light irradiation during Orange II oxidation...

Salient features of heat transfer during vigorous surface evaporation and vaporization of sedimentation products in a rotor film-type evaporator

UDC 535.52:66.045 Processing of solutions and suspensions that yields a dry end product is a promising application of rotor film-type evaporators (RFEs), which make it possible to replace periodic multistage processes with continuous combined processes. In view of this, it is a very urgent matter to study the heat exchange during deep concentration of solutions and suspensions. As shown by many studies, heat exchange in RFEs is complex and is determined by both the hydrodynamic conditions in the evaporator and the properties of the product being processed, the design features and rotation frequency of the rotor, and the heat flux density, Despite the complexity of the process, numerous attempts have been made to obtain an equation to describe it. In studies [1, 2] on heat exchange in an articulated-rotor RFE during evaporation of toluene, water, ethyl alcohol, and sugar syrup Dieter concluded that the heat-transfer coefficient does not depend on the spraying density and the heat flux density and increases with the rotation frequency of the rotor. The data reported by different authors for articulated-rotor evaporators are very contradictory. In [3] Marchenko obtained a criterial dependence by generalizing experimental data on vaporization of water, but it takes no account of the influence of the rotation frequency of the rotor on the heat-transfer coefficient. In [4] Kibrik established a relation between the heat-transfer coefficient and the design features of the rotor. In a study of convective heating and evaporation of distilled water, glycerin solutions, and solutions of S-150 additive in benzine in an articulated-rotor RFE [5] Golova obtained criterial equations, which in our opinion take insufficient account of the influence of the design features of the rotor, since the only the influence of the number of rotors was considered. Shevchuk [6] investigated how the heat transfer is affected by a large number of factors: the flow rate of the liquid, the physicochemieal properties of the products studied (distilled water, aqueous solutions of glycerin and esters of unsaturated higher fatty acids), the rotation frequency of the rotor, the direction of the specific heat flux (during convective heat exchange), the instantaneous length of the evaporator, and the design features of the rotor. The studies were carried out in glass and metal evaporators. After analyzing the hydrodynamic and heat-exchange laws by using a semi-empirical theory of turbulent transfer, Nikitin and Fedorov [7] obtained computational relations for determining the heat-transfer coefficient in the RFE heating zone during processing of pseudoplastic solutions. In our opinion, they did not take sufficient account of the influence that the rotor design features and the variation of the non-Newtonian liquids have in the process of solvent removal. The first attempt to study heat exchange during concentration of NaCI and NaNO 3 solutions to obtain a dry product in a RFE with rigidly fastened blades was made by Lysenko [8]. The average heat-transfer coefficient was found to increase with the heat flux. It is difficult to agree with that conclusion, when the physics of the process and the relation obtained are considered. The heat exchange in a RFE during concentration of azo dyes (they were obtained in dry form) was studied by Nagieva [9]. Arbitrarily dividing the RFE with a combined rotor (with hinged blades at the top and rigid blades at the bottom) into three zones (a zone of heating and onset of evaporation of the initial product, a zone of intensive evaporation, and a drying zone), she obtained criterial relations for each zone and for each product studied. It should be noted that the rotor design features and the non-Newtonian properties of the suspension in the second zone are not taken into account in those relations.

Degradation of commercial azo dyes in water using ozonation and UV enhanced ozonation process

The chemical oxidation of eight non-biodegradable azo dyes by ozonation and photooxidation process was studied in a pilot scale photochemical (UV/ozone) reactor. In experiments with ozone bubbling, the degradation of eight azo dyes was found to occur in the absence of UV light. The degradation rate of azo dyes was observed to be first order with respected to both azo dye and ozone concentrations. The pH of the solution decreased while the azo dyes degraded. UV light did not significantly enhance the degradation ability of the ozonation reaction under various conditions. No degradation was observed when the azo dye solution was irradiated by UV light alone. Effects of ozone dosage, and initial concentrations of azo dyes are discussed. Time for removal of 50 % of azo dye and rate constants can be used to determine the decomposition rate of each azo dye by different oxidation processes as a function of various conditions.

Decolorization of mono-azo dyes in wastewater by advanced oxidation process: A case study of acid red 1 and acid yellow 23

Advanced Oxidation Processes (AOPs) have been used as emerging wastewater treatment technologies which can effectively handle various hazardous organics in wastewater and groundwater. The photooxidation of two non-biodegradable azo dyes, acid red 1 and acid yellow 23, were studied in an UV/hydrogen peroxide photochemical reactor with a 5 kW low pressure mercury lamp. It was observed that the decomposition of both azo dyes were pseudo-first order reactions with respect to the azo dye concentrations. Simultaneously, the effects of hydrogen peroxide dosage, pH, initial concentration of the azo dyes and intensity of UV light were also studied. Moreover, the time required for the 50% removal of azo dyes and observed pseudo-first order rate constants were used as parameters to show the efficiency of azo dye treatment.

Characterization of an extracellular azo dye-oxidizing peroxidase from Flavobacterium sp. ATCC 39723

A peroxidase from Flavobacterium sp. ATCC 39723 was selected from nine peroxidase-producing bacterial strains for its highest azo dye-oxidizing capacity among the peroxidases examined. Comparison of azo dye No. 1 (3,5-dimethyl-4-hydroxyazobenzene-4′-sulfonic acid) oxidation with native and heat-inactivated enzyme preparations, and with and without H 2O 2, confirmed the involvement of this peroxidatic enzyme in azo dye decolorization. The peroxidase activity in this gram-negative Flavobacterium sp. was predominantly extracellular. The enzyme was actively expressed in a minimal medium with sodium glutamate as sole carbon source. The addition of either pentachlorophenol or azo dye No. I into culture media did not enhance enzyme production. The Flavobacterium peroxidase was concentrated by ultrafiltration and partially purified by Q-Sepharose column chromatography. The optimal conditions for azo dye oxidation by the Flavobacterium peroxidase were pH 7–8, and 5 mM H 2O 2 concentration, when the azo dye concentration was held constant at 50 μM. Cobalt chloride, mercury chloride, and manganese sulfate had significant inhibitory effects on dye oxidation by the peroxidase. Although guaiacol was a strong inhibitor of dye oxidation by this enzyme, veratryl alcohol was not, even at I mM concentration. A heme protein inhibitor, potassium cyanide, showed considerable inhibition. The substrate specificity of the peroxidase toward 22 azo dyes was also examined. Specificity was compared to that of another peroxidase from the Streptomyces sp. YCED 105. The presence of syringyl or guaiacyl groups in the dye structures resulted in enhanced oxidation by both peroxidases. These data showed that azo dyes can be made more readily oxidizable by bacterial peroxidases by appropriately modifying the substitution pattern of their aromatic rings.

Spectrophotometric determination of traces of nitrite by concentration of azo dye on an anion-exchange resin: Application to sea waters

A sensitive and accurate method for the determination of 0.001–0.100 μg-at. NO 2 --N per liter in sea water is described. The sample (500–1000 ml) is treated with sulfanilic acid and N-(1-naphthyl)ethylenediamine, and drawn through a column of Dowex 1-X8 resin. The azo dye collected on the column is then eluted with 10–25 ml of 60% acetic acid and the absorbance is determined at 550 nm. The effects of the amounts of reagents, pH, flow rate and eluting solvents are discussed. Data are presented on the nitrite content in deep waters of Suruga Bay which have been measured by the proposed method.