Complete Decolourization Research Articles

Enhanced electrokinetic remediation of polluted kaolinite with an azo dye

In this work, the feasibility of the combination of electrokinetic remediation and electrochemical oxidation for the remediation of polluted soil with organic compounds had been development and evaluated in kaolinite spiked with Reactive Black 5 (RB5) an azo dye. The process consists in the use of two combined phenomena to achieve a full remediation of RB5 spiked kaolinite and the degradation of the organic pollutant. Those phenomena were soil electrokinetic treatment combined to liquid electrochemical oxidation. Reactive Black 5 (0.39 g dye kg −1) could be effectively removed from the kaolinite matrix by electrokinetics, however the removal results largely depended on the operating conditions. Complete removal of RB5 was achieved using K 2SO 4 as processing fluid (which enhanced the desorption of RB5 from the kaolinite matrix) and operating with pH control at 7 on the anode. This favoured the alkalinization of the system and, at high pH values, RB5 was ionized and migrated towards the anode chamber where it was collected and could be oxidized electrochemically. Also, it must be pointed out that in these optimized conditions the electric power consumption (56 kW/mg of removed dye) was ten times lower compared to the unenhanced electrokinetic process (with no pH-control in the electrode solutions). Separate electrochemical decolourization tests of RB5 showed the effectiveness of K 2SO 4 in the efficiency of the process. A linear relationship between K 2SO 4 concentration and the decolourization rate was found. Thus, nearly complete decolourization was achieved after 2 and 3 h of electrochemical treatment when the electrolyte concentration was 0.1 and 0.01 M of K 2SO 4, respectively.

Kinetics of the TiO<SUB align=right>2-catalysed photodegradation of reactofix navy blue 2GFN dye

UV-irradiated TiO2-catalysed as well as uncatalysed photodegradation of the dye, reactofix navy blue 2GFN, has been studied under various reaction conditions. The kinetics have been followed at 603 nm, the λmax of the dye, in the visible region. The rate of the reaction depends on [dye] and [O2], and on [TiO2] when its concentration is below 0.2 g L-1. On increasing [TiO2] beyond 0.2 g L-1, the rate attains a limiting value. On increasing pH, the rate decreases slightly. At 7.0 pH and 0.2 g L-1 TiO2, the photodegradation kinetics is in conformity with the following experimental rate law. Robs=k2[dye]+k3[dye][O2] + k8K1K2[dye][O2] —————————————(1+K2[dye])(1+K1[O2]) here k2 and k3 are related to uncatalysed and k8 to TiO2 catalysed pathways. The complete decolourisation of the dye is achieved in about 20 minutes.

Photocatalytic degradation of Direct Yellow 12 dye using UV/TiO 2 in a shallow pond slurry reactor

The adsorption and photocatalytic degradation of diazo Direct Yellow 12 (Chrysophenine G), commonly used as a cotton, paper and leather dye has been investigated in aqueous suspension of semiconductor oxide TiO 2 as photocatalyst in a non-concentrating shallow pond slurry type reactor under UV light. The adsorption of dye on the semiconductor shows a strong dependence on the pH and follows a Langmuir adsorption model. The studies include dark adsorption experiments at different pH conditions and their effect on initial rate of photodegradation. The effect of initial concentration of dye, catalyst loading, pH, addition of oxidant on the reaction rate was ascertained and optimum conditions for maximum degradation was determined. The disappearance of the organic molecule follows approximately a pseudo-first kinetic order according to the Langmuir–Hinshelwood model. COD analysis of the dye under optimum conditions showed 94% reduction in COD after 2.5 h and complete decolourisation as determined by UV–vis analysis was achieved in 1.5 h.

Efficiency of the coagulation/flocculation method for the treatment of dyebath effluents

Textile dyeing processes are among the most environmentally unfriendly industrial processes, because they produce coloured wastewaters that are heavily polluted with dyes, textile auxiliaries and chemicals. The coagulation/flocculation method was studied as a wastewater treatment technique for the decolourization of residual dyebath effluents after dyeing cotton/polyamide blends using reactive and acid dyes. It was discovered that a combination of aluminium sulphate and a cationic organic flocculant yields an effective treatment for residual dyebath wastewaters since almost complete decolourization was achieved, TOC, COD, AOX, BOD and the anionic surfactants were reduced and the biodegradability was increased.

Photooxidation of a reactive azo-dye from the textile industry using UV/H2O2 technology: process optimization and kinetics

The homogeneous advanced oxidation process of UV/H2O2 was utilized to decolourize CI Reactive Red 195A (RR195A) as one of the most used dyes in the textile industry in Queensland. The UV radiation source was a low-pressure mercury arc lamp (60W emitting at 253.7nm). In this study, the effects of initial hydrogen peroxide (H2O2) dosage, dye concentration, pH and temperature were examined to find out the optimum operating conditions of the treatment process. Complete decolourization was achieved in the relatively short time of 20-30 minutes irradiation. Faster decolourization was achieved at low pH and high temperature. The removal rate increased with increasing initial concentration of H2O2 up to an optimum value. The decolourization reaction was found to follow at least initially first order kinetics with respect to the dye concentration. However, even after near complete removal of the active dye from the solution, approximately 60% of the COD was still remaining, indicating only partial breakdown of the dye molecule. In general, the result indicates that the UV/H2O2 technology proved to have good potential for removing dyestuff from wastewater but further treatment might be necessary to achieve complete mineralization of the organic intermediates.

Electrochemical studies on textile dye naphthol yellow S with particular reference to colour removal

Aromatic nitro dyes are resistant to chemical and biological oxidation and to hydrolysis because of electron withdrawing nitro groups. Consequently they are environmentally persistent and remediation of waste streams and contaminated water is difficult. In the present work, the electrochemical study has been carried out on the nitro acid dye naphthol yellow S predominantly used in textile dyeing. On the basis of results of the electrochemical study experimental conditions are optimized for the controlled potential electrolysis or the model dye. Complete decolourisation resulted after 1 to 3 h of controlled potential electrolysis. Kinetics of decolourisation was monitored and half-life period determined. Chromatographic study revealed formation of single decomposition product and COI) decreased substantially in the decolourised solution.

Optimisation of electrochemical decolourisation process of an azo dye, Methyl Orange

AbstractThe decolourisation of an azo dye, Methyl Orange, by an electrochemical technology was studied in a reaction cell with a working volume of 1 dm3, using graphite for both electrodes (anode and cathode). No decolourisation was detected in the treatment of pure solutions of Methyl Orange, but significant decolourisation was observed in the presence of NaCl, the influence of which was established. The extent of decolourisation, treatment time, and electrical consumption largely depended on the applied potential difference; the optimum value being around 5V. To achieve effective decolourisation, the NaCl concentration should be increased as the concentration of azo dye increases. Thus, almost complete decolourisation was achieved in 60 min for an effluent containing 40 kg m−3 NaCl and 90 g m−3 of dye. Increasing temperature (from 20 to 40°C) did not improve the efficiency of electrochemical oxidation. Copyright © 2004 Society of Chemical Industry

Chestnut shell and barley bran as potential substrates for laccase production by Coriolopsis rigida under solid-state conditions

The potential of two lignocellulosic wastes chestnut shell and barley bran for laccase production by the white-rot fungus Coriolopsis rigida under solid-state conditions was assessed. These materials were selected due to their availability and low cost, since they are by-products of the food processing industries abundant in most countries. Barley bran gave the highest laccase activities, showing a maximum value of 3 · 10 5 nkat/L, which was around 25-fold higher than the value attained in the chestnut shell cultures. In addition, the ability to degrade three structurally different dyes (Indigo Carmine, Methyl Orange and Methyl Green) by the extracellular liquid from the barley bran copper-supplemented cultures (1 mM) was analysed. Nearly complete decolourization was obtained for the dyes Indigo Carmine and Methyl Green, whereas Methyl Orange showed more resistance to decolourization.

Electrochemical decolourisation of structurally different dyes

The electrochemical decolourisation of structurally different dyes (bromophenol blue, indigo, poly R-478, phenol red, methyl orange, fuchsin, methyl green and crystal violet) by means of the application of DC electric current was assessed. It was found that the electrochemical process allowed a colour removal of all dyes studied, although the decolourisation rate largely depended on the chemical structure of the different dyes. Nearly complete decolourisation was achieved for bromophenol blue followed by methyl orange and methyl green, whereas phenol red was hardly decolourised (30% in 60 min). In mixtures of two dyes, the decolourisation rate became similar for both dyes. However, the addition of a redox mediator, (Co 2+/3+) clearly enhanced the degradation rate of all tested dyes, but the simplest dye molecules were attacked firstly, followed by dyes with more complex chemical structures. The results revealed the suitability of the process to effectively decolourise wastewaters from dyeing process.

Optical in situ analysis of starch granules under high pressure with a high pressure cell

With a High Pressure Cell developed by Hartmann, Pfeifer, Dornheim, and Sommer [Chemie Ingenieur Technik 75 (11) (2003) 1763] withstanding a pressure of 300 MPa in combination with an inverse microscope the pressure treatment of wheat starch, tapioca starch and potato starch suspensions for 1 h at 300 MPa was investigated in situ. Images with both high optical resolution and high quality up to pressures of 300 MPa were obtained. The loading of the cell was easy and uncomplicated. Wheat starch granules showed a thorough swelling of most granules during pressurisation. Tapioca starch and potato starch, showing no detectable swelling, were therefore more resistant to pressure than wheat starch. A pressure treatment of iodine stained wheat starch and tapioca starch suspensions resulted in a complete decolouration of the starch granules while pressurised potato starch granules discoloured only slightly.

Decolourization and Detoxification of Methyl Red by Aerobic Bacteria from A Wastewater Treatment Plant

Bacterial cultures from a wastewater treatment plant degraded a toxic azo dye (methyl red) by decolourization. Complete decolourization using a mixed-culture was achieved at pH 6, 30 °C within 6 h at 5 mg/l methyl red concentration, and 16 h at 20—30 mg/l. Four bacterial species were isolated that were capable of growth on methyl red as the sole carbon source, and two were identified, namely Vibrio logei and Pseudomonas nitroreducens. The Vibrio species showed the highest methyl red degradation activity at the optimum conditions of pH 6--7, and 30—35 °C. Analysis by NMR showed that previously reported degradation products 2-aminobenzoic acid and N,N-dimethyl-1,4-phenylenediamine were not observed. The decolourized dye was not toxic to a monkey kidney cell line (COS-7) at a concentration of 250 μM.

Electrochemical treatment of distillery effluent using catalytic anodes

Electrochemical treatment processes can provide valuable contributions to the protection of the environment through the minimization of waste and toxic materials in effluents. Complete decolourisation of the distillery effluent is a difficult task. The industry treated effluent still has a brown colour. This paper reports complete colour removal of industry treated distillery effluent through an electrochemical technique. Electrolysis of distillery effluent was carried out in a static electrochemical reactor. Two different types of anodes, planar graphite (Gr) and titanium substrate insoluble anodes (TSIA) were chosen for the treatment of distillery effluent. Lead dioxide coated on titanium (PbO2–Ti) and ruthenium oxide coated on titanium (RuO2–Ti) electrodes were used as TSIA. Current density (C.D.) was varied from 1.5 to 5.5 A dm−2. Complete decolourisation was obtained in both cases. A maximum of 92% of chemical oxygen demand (COD) reduction, 98.1% of biological oxygen demand (BOD) reduction and 99.5% of absorbance reduction were obtained in the set up in which RuO2–Ti as anode and stainless steel as cathode were used. A probable mechanism has been proposed for the oxidation of organics present in the effluent.

Use of laccase together with redox mediators to decolourize Remazol Brilliant Blue R

A pure fungal laccase, obtained from a commercial formulation used in the textile industry, did not decolourize Remazol Brilliant Blue R (RBBR). Decolourization was only observed when a small molecular weight redox mediator was added together with the laccase. Under the conditions specified, violuric acid (5.7 mM) was the most effective mediator studied and almost complete decolourization was observed within 20 min. In contrast, 1-hydroxybenzotriazole (HOBT, 11 mM) decolourized RBBR at about a two-fold slower rate and to a lesser extent. Also, higher concentrations of HOBT were inhibitory which could be due to inactivation of laccase by the toxic HOBT radical. The commercial laccase formulation that contained phenothiazine-10-propionic acid as the mediator was least effective, giving 30% decolourization under equivalent conditions. We suggest that similar laccase plus mediator systems could be used for the detoxification of related anthraquinone textile dyes.

A packed-bed fungal bioreactor for the continuous decolourisation of azo-dyes (Orange II)

The degradation of an azo dye, Orange II, by immobilised Phanerochaete chrysosporium in a continuous packed bed bioreactor for periods longer than 30 days has been carried out. Nearly complete decolourisation (>95%) was achieved when working at a high dye load rate of 0.2 g l −1 d −1, a temperature of 37 °C, a hydraulic retention time (HRT) of 24 h and applying oxygen gas in a pulsed flow. These conditions allowed Manganese peroxidase (MnP) production and the subsequently Orange II decolourisation. A correlation between residual MnP activity in the effluent and decolourisation was established. Apparently, for decolourisation to be effective, a minimum MnP activity was required, no substantial increase in efficiency at MnP activities higher than 10 U 1 −1 was observed. The treatment caused, the breakdown of the chromophoric group as well as the cleavage of the aromatic ring.

Advanced chemical oxidation of reactive dyes in simulated dyehouse effluents by ferrioxalate-Fenton/UV-A and TiO2/UV-A processes

Effective degradation of various mono- and bifunctional aminochlorotriazine reactive dyes in simulated dyehouse wastewater was achieved by the application of ferrioxalate-photo-Fenton [Fe(C2O4)33−/H2O2/UV-A; 300 nm>λ>400 nm] and titanium dioxide-mediated heterogeneous photocatalytic (TiO2/UV-A) treatment processes. These so-called advanced oxidation processes were studied in a novel batch photoreactor that was irradiated by a solar simulating installation. Decolorization by the ferrioxalate-photo-Fenton oxidation process was found to proceed three times faster than the photocatalytic process, while the latter was more efficient in reducing the optical density at 280 nm wavelength (UV280nm). Complete decolourization and partial mineralization with 17–23% total organic carbon (TOC) and 73–86% UV280nm removals were achieved by the ferrioxalate-Fenton/UV-A and TiO2/UV-A processes, respectively, within a 1-h treatment time. Emphasis was placed on the effect of dyehouse effluent strength on decolourization kinetics, along with possible advantages of the ferrioxalate-Fenton/UV-A process over the conventional photo-Fenton (Fe2+/H2O2/UV-C) process. The results of these experiments showed that the more dilute the dyehouse effluent the faster the decolourization rate. On the basis of spectrophotometric measurements, dye decomposition could be successfully fitted to the empirical Langmuir–Hinshelwood kinetic model.

Understanding anaerobic decolourisation of textile dye wastewater: mechanism and kinetics

Worldwide, some 280,000 tons of textile dyes are discharged per annum. Degradation of the predominant highly soluble reactive dyes is poor within activated sludge plants, and instead requires anaerobic pretreatment for reductive cleavage of the chromogenic azo bond to precede aerobic degradation. The mechanism for the anaerobic reductive cleavage, which results in decolourisation, is not well understood. Further, thermophilic anaerobic pre-treatment has not been reported, although the wastewater is produced at high temperature (50–80°C). This project therefore aimed to compare decolourisation kinetics under mesophilic (35°C) and thermophilic (55°C) conditions and elucidate biotic and abiotic factors in the decolourisation of the dye, Reactive Red 235. Preliminary experiments indicated that acclimation of the up-flow anaerobic sludge blanket (UASB) biomass was unnecessary and there was no dye toxicity at expected wastewater concentrations (0.05–0.1g/L). Decolourisation of Reactive Red 235 was studied under batch conditions with intact and autoclaved biomass, and also using the pre-reduced supernatant from a spent culture (0.2 μm filtered). Based on HPLC identification of the dye and reaction products, first-order kinetics was observed and rate constants of –0.0096/min (thermophilic) and –0.0034/min (mesophilic) were estimated for intact, viable biomass. Abiotic decolourisation was 60–80% lower for the autoclaved samples, and under 12–35% lower for the filtered supernatant. Hence it may be concluded that active anaerobic cells give the most efficient and complete decolourisation, especially under thermophilic conditions. Nonetheless, abiotic reduction does occur and has implications for the design of a novel uncoupled reactor system.

A Study of the Microbial Degradation of Metal Phthalocyanine Textile Dyes by High-performance Liquid Chromatography and Atomic Absorption

The investigation of the degradation of two commercially available dyes (Remazol Turquoise Blue and Everzol Turquoise Blue) by the lignin-degrading fungus Phanerochaete chrysosporium and comparison with that of a phthalocyanine whose structure is known (Heligon Blue) are presented. Atomic absorption showed a large release of copper from the biomass at day 7. Polarography served to speciate the copper present in the supernatant. Day 5 sees the complete disappearance of the main dye peak with the release of free copper into the supernatant. Day 7 sees a large increase in the free copper signal with two other electroactive species also present in the supernatant, all of which are seen to decrease at day 8. Visible spectroscopy shows that the main decolourization takes place between day 4 and day 6, with complete decolourization occurring at day 7. HPLC analysis again confirms the above results, with possible degradation products detected at 254 nm occurring at 3.621 and 4.170 min at day 7 which may well correlate with those found in polarographic analysis at –1050 and –1150 mV. Day 7 also sees a large increase in a peak at 2.744 min.

Degradation of textile dye by solar light using TiO2 and ZnO photocatalysts

The photocatalytic degradation of a textile dye, reactive red 2 in presence of sunlight using TiO2 and ZnO as photocatalysts is reported. The experimental studies have indicated complete decolourisation of the dye in a short period and degradation within 8 hr of irradiation. ZnO was found to be more effective in the removal of colour than TiO2, but the degradation efficiency was found to be more with TiO2. ZnO decomposes on prolonged irradiation while TiO2 is not photocorrosive. The percent degradation of the dye is high for both the catalysts at an optimum concentration of the catalysts. The first order rate constant is found to increase with decreasing dye concentration.

Advanced Oxidation of Synthetic Dyehouse Effluent by O3, H2O2/O3 and H2O2/UV Processes

Ozonation, hydrogen peroxide combination with ozone, and UV light processes were investigated for the treatment of synthetic dyehouse effluent containing six reactive dyestuffs and their assisting chemicals. The decrease in DOC, UV - absorbance at 254 nm, decolourization kinetics, and acute toxicity towards the bioluminescent marine bacteria Vibrio fischeri were used to examine the treatment performance of these oxidation processes. Data indicated that in all examined processes rapid and complete decolourization could be achieved, but optimum oxidation conditions such as H2O2 dose and reaction pH had to be established for effective treatment. Toxicity of the samples decreased abruptly to non - detectable levels during the first minutes of all advanced oxidation processes. However, none of the oxidation combinations was able to bring about effective mineralization of the wastewater within 60 min reaction period. For comparative purposes, the electrical energy requirements per order of pollutant removal were calculated for all treatment systems.

Application of photocatalytic oxidation treatment to pretreated and raw effluents from the Kraft bleaching process and textile industry

Treatability of mixed raw, coagulated and biologically pretreated textile and pulp wastewater and effluents from different process stages by enhanced heterogenous photocatalytic oxidation process was investigated. Treatment performances have been evaluated in terms of COD, TOC, BOD 5, and colour removal. Results clearly indicate that photocatalytic oxidation process enhanced with 15 mM H 2O 2 was more efficient in removal of pollutants for pretreated wastewater samples. By the application of photocatalytic treatment, 52 and 87% COD removals were obtained for biotreated Kraft bleaching and textile effluents, respectively. Addition of only 1 mM ferric ion speeded up the oxidation time of the textile effluent significantly, but it had no impact on total COD reduction. While complete colour removal of the textile wastewater was achieved within the first hour of photocatalytic treatment, complete decolourisation could not be obtained for pulp effluents, except for the coagulated wastewater throughout the reaction period. Biologically pretreated textile wastewater was found to have potential for reuse after photocatalytic treatment.