Decolorization of azo dyes by photo electro adsorption process using polyaniline coated electrode

This study is a report on the photo electro adsorption (PEA) decolorization of a mixture of three azo dyes, i.e., Acid Red 88 (AR88), Acid Blue 92 (AB92), and Acid Orange 2 (AO2) with polyaniline-modified electrode as a conductive polymer. Aniline was electropolymerized on steel electrode by being immersed in a solution containing HClO₄ as the supporting electrolyte and NaClO₄ as the dopant. This modified electrode was then used in a non-continuous reactor using UV irradiation for the decolorization of azo dyes. To obtain the best conditions for high decolorization efficiency, experiments were carried out at different operational conditions, including initial dye concentration, pH, and bias potential. The morphology of polyaniline film was analyzed by scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectrum was obtained to characterize polyaniline and dyes. Energy consumption was calculated to be 3.6 kWh/m³ after 36 min of treatment process. Maximum removal of 96% was achieved for the mixture of AR88, AB92, and AO2 in aqueous solution at pH 5, initial dye concentration of 30 mg L⁻¹, and bias potential of 1.3 V after 40 min of PEA process. The results indicate that the PEA process could be effectively applied to the removal of industrial effluents.     

Kinetics of the Decolorization by Fenton's Reagent

Fenton's reagent was employed in the decolorization of aqueous solutions of one of three dyestuffs (Acid Red 27, Reactive Blue 81, Acid Blue 62). The decolorization with Fenton's reagent was found to be simple and fast. In order to determine the reaction kinetics of the decolorization the stopped-flow technique under pseudo-first order conditions was used. Experiments were carried out at pH=2, at the excess of ferrous salts (FeCl₂·4H₂O or FeSO₄·7H₂O). The rate constants of the decolorization determined by us are in the same order of magnitude: 90 to 100 dm³/(mol-s) for FeSO₄·7H₂O/H₂O₂, and 40 to 50 dm³/(mol-s) for FeCl₂·4H₂O/H₂O₂ systems. The difference between the rate constants for both ferrous salts indicates that the Fenton's reaction may proceed via different mechanisms.     

Degradation of C.I. Acid Orange 7 by heterogeneous Fenton oxidation in combination with ultrasonic irradiation

BACKGROUND: A mesoporous alumina supported nanosized Fe₂O₃ was prepared through an original synthesis procedure and used as a heterogeneous catalyst for the Fenton process degradation of the model azo dye C.I. Acid Orange 7 enhanced by ultrasound irradiation (US/Fe₂O₃‐Al₂O₃‐meso/H₂O₂ system). The effect of various operating conditions was investigated, namely hydrogen peroxide concentration, initial pH, ultrasonic power and catalyst loading. RESULTS: The results indicated that the degradation of C.I. Acid Orange 7 followed a pseudo‐first‐order kinetic model. There exists an optimal hydrogen peroxide concentration, initial pH, ultrasonic power and catalyst loading for decolorization. The aggregate size of the spent catalyst was reduced after dispersion in water by ultrasonic irradiation. A very low level of iron leaching was observed ranging from < 0.1 to 0.23 mg L^?1. The intermediate products of C.I. Acid Orange 7 degradation were identified using gas chromatography–mass spectrometry (GC‐MS). CONCLUSION: The optimal conditions for efficient C.I. Acid Orange 7 degradation were pH close to 3, hydrogen peroxide concentration 4 mmol L^?1, catalyst loading 0.3 g L^?1, and ultrasonic power 80 W. Copyright © 2011 Society of Chemical Industry     

Rapid decolorisation of dyeing wastewater by FeIII(2,2′:6′,2″-terpyridine)activated peroxymonosulphate

The discharge of coloured textile printing and dyeing wastewater causes environmental pollution. Disposing of wastewater efficiently, simply and with low consumption, is a problem that must be addressed. Herein, a catalytic method for rapid decolorisation of organic dyes was devised employing a terpyridine iron complex to activate oxidised permonosulphate. CI Acid Red 1 was used as the simulated pollutant, the influences of operating parameters on the fading effects of wastewater were explored. According to the results, the produced catalytic system exhibits a universal catalytic effect. Even when the dye concentration reaches 76.4 mg/L, the dyeing wastewater may be effectively decolorised. In addition, when anions (HCO₃⁻, SO₄²⁻, Cl⁻) were present in the solution, the degradation effect of CI Acid Red 1 was still effective. Interestingly, active species such as sulphate radicals and singlet oxygen were detected in the catalytic degradation system by radical capture experiments. The removal rate of total organic carbon can achieve a percentage of 26.22% in 2 hours. This research provides a unique, enzyme-like catalytic system for the rapid breakdown of dye contaminants.     

Removal of diazo and triphenylmethane dyes from aqueous solutions through an adsorption process

Direct Red 31, Acid Black 1 and Acid Green 16 belonging to diazo and triphenylmethane classification of dye chemicals are widely used during the manufacture of leather. The spent dyestuffs in wastewater escape biological treatment owing to their poor biodegradability. An adsorption procedure was used in this study for the removal of dyes from aqueous solution using Rice Bran‐based Activated Carbon (RBAC). The molecular weight of the dye chemicals, the mass of RBAC and the diameter of RBAC particle had positive effects on the rate of adsorption. Initial concentration of dye chemicals, pH of the dye solution and temperature of adsorption showed a negative impact on adsorption. The enthalpies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were −32.1,−23.4 and −21.7 KJ mol⁻¹ respectively, indicating the adsorption was an exothermic physical process. The entropies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were −96.94,−59.92 and −26.96 J K⁻¹ mol ⁻¹ respectively, suggesting that RBAC favours the adsorption process. © 1999 Society of Chemical Industry     

Colour in textile effluents – sources,measurement, discharge consents and simulation: a review

This paper aims to review the problem of colour in textile effluents, the different classes of dyes available and their contribution to the problem. Through new regulations, pressure is being placed on water companies all over the world to reduce the amount of colour in sewage effluent. Dyes exhibit low toxicity to mammals and aquatic organisms and therefore colour consents are normally applied for aesthetic and industrial reasons rather than for prevention of toxicity. The absorbance, ADMI values and concentrations of dyes in effluent are examined here with particular reference to reactive azo dyes used in cotton processing. Colour consents, the problem of colour in textile wastewaters and the importance for research in this area are also discussed. Dye concentrations of 0.01 g dm⁻³ up to 0.25 g dm⁻³ have been cited as being present in dyehouse effluent, depending on the dyes and processes used. ADMI values ranged from 50 to 3890 units for the dyeing of cotton. It was concluded that 1500 ADMI units was a reasonable value to aim for when simulating coloured effluents. Simulated textile effluents may be used for research purposes. These should resemble real wastes as closely as possible, but it is often difficult to replicate the ADMI values, absorbance and spectra of real effluents. The concentrations of dye used in simulated effluents examined in literature varied from 0.01 g dm⁻³ to 7 g dm⁻³. As absorbance and ADMI values change with the types of dye used, it is difficult to relate these values to dye concentrations. A concentration of 0.18 g dm⁻³ of a Red or Yellow dye or 0.43 g dm⁻³ of a blue dye would provide an ADMI of approximately 1500 units and fits within the range of dye concentrations presented in literature. A dye mixture simulating colour in a real textile effluent is suggested and some limitations of simulating actual wastewaters discussed. © 1999 Society of Chemical Industry     

Laccase immobilization on radiation synthesized epoxy functionalized polyethersulfone beads and their application for degradation of acid dye

The enzymatic degradation of textile dyes offers an alternative approach over the conventional waste water treatment processes. Covalent immobilization of the enzymes onto insoluble supports not only permits their reusability and easy separation of enzymes from the product but also, if properly performed, may improve their activities, stability and hence reduces the cost of process. In the present work, epoxy functionalized polyethersulfone (PES) was synthesized via radiation induced polymerization of poly(2,3-epoxypropyl methacrylate) [poly(EPMA)] in PES-NMP (N-methyl-2-pyrrolidone) solution using ⁶⁰Co-gamma radiation source. Poly(EPMA)-functionalized-PES [poly(EPMA)-f-PES] beads were fabricated via phase inversion route using water as the anti solvent. Laccase was covalently immobilized on to the beads via one step-room temperature coupling reaction of amine group of enzyme with the epoxy group of poly(EPMA). Enzyme activity was assayed using 2,2′-azino-bis(3-ethylthiazoline-6-sulfonate) (ABTS) as the substrate. Effect of temperature and pH on the free and immobilized enzyme activity was studied. The immobilized laccase was successfully employed to degrade Acid Red 1 (AR1) dye in aqueous solution. Room temperature incubation of the laccase immobilized poly(EPMA)-f-PES beads with AR1 dye (∼10 ppm) resulted in ∼88% degradation of the dye over a period of 15 days.     

Oxidation of Acid Red-151 Aqueous Solutions by the Peroxone Process and its Kinetic Evaluation

Oxidation of an azo dye solution, namely, Acid Red 151 by the peroxone process was investigated experimentally at different pH values, initial dye and ozone concentrations, and the initial molar ratios (r) of hydrogen peroxide to ozone. At pH 2.5 in this process, the obtained color and chemical oxygen demand (COD) removals were higher than those at pH of 7 and 10. The best value of r yielding the highest treatment efficiency at each pH was determined as 0.5. The application of the “initial rates method” to the kinetic data for peroxone oxidation of aqueous Acid Red 151 solutions showed that the individual orders with respect to O₃ and dye were one, the total order of the reaction being two. The rate constants based on the initial rates of dye degradation were determined as 98.9, 77.3 and 65.7 mM^?1min^?1 at the pH values of 2.5, 7 and 10, respectively.     

An oxidative desulfurization method using ultrasound/Fenton's reagent for obtaining low and/or ultra-low sulfur diesel fuel

The total development trend in the world is towards continuously lower of sulfur content as a quality standard of diesel fuels. Integrating of an oxidative desulfurization unit with a conventional hydrotreating unit can bring benefits to producing low and/or ultra-low sulfur diesel fuels. Using the hydrotreated Middle East diesel fuel as a feedstock, four processes of the oxidative desulfurization have been studied: a hydrogen peroxide–acetic acid system and a Fenton's reagent system both without/with ultrasound. Results showed that the oxidative desulfurization reaction mechanics fitted apparent first-order kinetics. The addition of Fenton's reagent could enhance the oxidative desulfurization efficiency for diesel fuels and sono-oxidation treatment in combination with Fenton's reagent shows a good synergistic effect. Under our best operating condition for the oxidative desulfurization: temperature 313 K, ultrasonic power 200 W, ultrasonic frequency 28 kHz, Fe²⁺/H₂O₂ 0.05 mol/mol, pH 2.10 in aqueous phase and reaction time 15 min, the sulfur content in the diesel fuels was decreased from 568.75 μg/g to 9.50 μg/g.     

Crystal structure and surface species of CuFe2O4 spinel catalysts in steam reforming of dimethyl ether

The application of catalytic ozonation processes for the decolourisation and mineralisation of coloured aqueous solutions was studied. One acid azo dye, CI Acid Blue 113, and two reactive dyes, CI Reactive Yellow 3 and CI Reactive Blue 5, with azo and anthraquinone chromophores, respectively, were used as representative textile dyes. The catalytic activities of activated carbon, cerium oxide and a ceria-activated carbon composite were evaluated in the removal of the selected dyes. In all cases, with an initial dye concentration of 50 mg/L, a complete decolourisation was achieved by single ozonation in short reaction times (less than 10 min). The ceria-activated carbon composite allowed the highest removal of total organic carbon. For dye concentrations of 50 mg/L, mineralisation degrees of 100%, 98% and 97% were achieved with the composite after 2 h of reaction, respectively for CI Reactive Blue 5, CI Acid Blue 113 and CI Reactive Yellow 3. The activity of the catalyst containing cerium was affected by the presence of carbonate and bicarbonate ions due to their scavenging effect towards hydroxyl radicals; for example the mineralisation degree of CI Reactive Blue 5 (C₀ = 300 mg/L) after 120 min of reaction was only 63%, contrasting with the value of 85% obtained in the absence of carbonates. All the catalytic systems were evaluated in the treatment of textile effluents, collected before or after conventional biological treatment. Catalytic ozonation was proven to be effective when used as tertiary treatment for bio-treated effluents.     

Removal of water‐soluble azo dye by the magnetic material MnFe2O4

Magnetic ferrite material, MnFe₂O₄, as a novel adsorbent was prepared and characterized. Adsorption tests indicated that it is an excellent adsorbent for the removal of the azo dye Acid Red B (ARB) from water. After adsorbing ARB and recovery by the magnetic separation method, it can be regenerated by Fenton's reagent. The pseudo‐first‐order and second‐order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The adsorption capacity was highly affected by the pH of the solution, and pH 3.8 was optimal. After regeneration, the adsorption capacity of MnFe₂O₄ increased significantly, which was the result of a decrease in average pore diameter, an increase in surface area of the adsorbent and the adsorption of ferric hydroxide produced in the regeneration reaction. The adsorption can be described with the Langmuir model and the maximum adsorption capacity for ARB was 53.8 mg g^?1 adsorbent. FTIR study for ARB on MnFe₂O₄ indicated that the adsorption of ARB occurred via the azo group and the sulfonic group of the dye through the formation of a complex with the adsorbent surface. Copyright © 2004 Society of Chemical Industry     

Degradation of C.I. Basic Red 29 solution by combined ultrasound and Co-H2O2 system

Ultrasonic degradation of Basic Red 29 (BR29) textile dye in the presence of Co²⁺-H₂O₂ system was investigated in this study. The effects of presence of ultrasonic power, concentrations of cobalt (II) acetate (Co(II)Act) and H₂O₂, temperature and initial pH on the BR29 degradation were examined. Initial dye concentration of 20 mg/L BR29 was used in the study as a model solution. In sonication experiments, an ultrasonic bath at a frequency of 40 kHz was employed. Best experimental conditions were also obtained in the studies as follows: 1000 mg/L Co(II)Act, 1000 mg/L H₂O₂, 40 °C and original pH of 6.70.According to the results, after 30 min of sonication in the presence of Co²⁺-H₂O₂ dye removal efficiency of practically 100% was achieved. It was also found that US enhanced the degradation rate of BR29.     

A new flow reactor for the treatment of polluted water with microwave and ultrasound

Microwave (MW) and high‐intensity ultrasound (US) provide innovative techniques for the degradation of persistent organic pollutants (POPs). When Fenton's reagent is used to treat industrial wastes, organic pollutants are degraded by highly reactive hydroxyl radicals (HO·) that can oxidize almost any organic compound to carbon dioxide and water. These reactions, when carried out under US or MW, are faster and much more efficient. The present work assesses the combined effect of US and MW using a new flow reactor developed in our laboratory. In this 5 L pilot reactor the liquid was pumped in parallel through a modified domestic MW oven and through a cell where it was irradiated with two US generators working at 20 and 300 kHz, while MW irradiation took place in a modified domestic oven. We studied the degradation of 2,4‐dibromophenol (0.1 g L^?1 in water) by Fenton's reagent, assessing the contribution of each energy source to the overall effect, and found that MW and US‐300 kHz played the main role. A modest amount of oxidant (6 mL 30% H₂O₂ per 1 L of polluted water) sufficed to achieve complete degradation within 6 h, at which time organic compounds were no longer detectable. Even if no Fenton's reagent was added, about one half of the pollutant was degraded after 3 h irradiation. Copyright © 2007 Society of Chemical Industry     

The effect of pH and temperature on the dye sorption of wool powders

The sorption behavior of wool powders for three acid dyes (C. I. Acid Red 88, C. I. Acid Red 13 and C. I. Acid Red 18) and a basic dye (methylene blue) was investigated as a function of pH and temperature. The sorption capacity of wool powders depends on the pH of dye solution. The maximum uptake of acid dyes and methylene blue by wool powders occurred at pH 2.5 and pH 7.5, respectively. The effect of pH on the sorption of the hydrophilic dyes (C. I. Acid Red 13 and C. I. Acid Red 18) was more significant than that of the uptake of the hydrophobic dye (C. I. Acid Red 88). Increasing temperature enhanced the dye sorption ability of coarse wool powders, but did not impact that of fine wool powders. The dye‐absorption models of wool powders agree with the Langmuir isotherm. Comparison to activated charcoal and other sorbents indicates that fine wool powders have excellent dye sorption capacity even at room temperature, and may be used as a potential sorbent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Degradation of disperse azo dyes from waters by solar photoelectro-Fenton

Solutions of the azo dyes Disperse Red 1 (DR1) and Disperse Yellow 3 (DY3), commonly used in the Chilean textile industry, in 0.1 mol dm⁻³ Na₂SO₄ and 0.5 mmol dm⁻³ Fe²⁺ of pH 3.0 were comparatively degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 dm³ recirculation flow plant containing a BDD/air-diffusion cell coupled with a solar photoreactor. Organics were oxidized in EF with hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between electrogenerated H₂O₂ and added Fe²⁺. The oxidizing power of SPEF was enhanced by the additional production of hydroxyl radicals from the photolysis of Fe(III) hydrated species and the photodecomposition of Fe(III) complexes with intermediates by UV light of solar irradiation. Total decolorization, complete dye removal and almost overall mineralization for both dye solutions were only achieved using the most potent SPEF process, yielding higher current efficiencies and lower energy consumptions than EF. Final carboxylic acids like pyruvic, acetic, oxalic and oxamic were detected during the SPEF treatments. NO₃⁻ ion was released as inorganic ion. The use of a solution pH of 2.0–3.0 at 50 mA cm⁻² was found preferable for SPEF. Synthetic textile dyeing solutions containing the dyes were treated under these conditions yielding lower decolorization rate, slower dye removal and smaller mineralization degree than only using 0.1 mol dm⁻³ Na₂SO₄ due to the parallel oxidation of organic dyeing components. However, lower energy consumptions were obtained by the destruction of more amounts of total organic carbon, indicating that SPEF is a useful and viable method for the remediation of textile industrial wastewaters with high contents of disperse azo dyes.     

Dye aggregation and interaction of dyes with a water‐soluble polymer in ink‐jet ink for textiles

Detailed understanding of the interaction between dyes and additives and the aggregation behaviour of the dye molecules in aqueous solutions is required to develop ink‐jet ink for textiles. In the present study, the aggregation behaviour of three acid dyes (CI Acid Red 88, CI Acid Red 13 and CI Acid Red 27) containing different number of sulphonate groups in aqueous solutions was investigated by means of visible absorption spectroscopy. As a result, the higher the solubility of the dyes in water (the larger the number of sulphonate groups in the dyes), the lower are the aggregation constants of the dyes. For all the dyes, the aggregation constants decreased with increasing temperature, indicating the exothermic process of the dye aggregation. The thermodynamic process for CI Acid Red 88 with one sulphonate group is less enthalpic and more entropic than that for CI Acid Red 13, which contains two sulphonate groups. CI Acid Red 27, which includes three sulphonate groups, hardly forms any aggregates. To elucidate the effects of the polymer additive, the binding constants of the dyes with the water‐soluble polymer, poly(vinylpyrrolidone) and the aggregation constants of the dyes in aqueous polymer solutions were also estimated. In addition, the binding constants were influenced by the number of sulphonate groups in the acid dyes: the larger number of sulphonate groups diminished the binding constants. The aggregation constants in the presence of poly(vinylpyrrolidone) were smaller than those in its absence at every temperature for all dyes. This suggests that poly(vinylpyrrolidone) has disaggregation effects. Furthermore, poly(vinylpyrrolidone) makes the aggregation process less enthalpic with a greater entropic change. Thus, the aggregation process of the dyes in the polymer solutions is thermodynamically different from that in water, reflecting the interactions between the dyes and the polymer.     

Effectiveness of ozonation and catalytic ozonation (iron oxide) in the degradation of sunset yellow dye

Azo dyes present in industrial effluents represent a hurdle that regular treatments cannot overcome. In this study, the application of ozone and a catalytic (iron oxide) ozone treatment were proposed as a means of degrading aqueous sunset yellow dye. In order to understand the factors involved, a rotatable central composite design was applied using the variables time, initial dye concentration (C₀), pH, ozone inlet concentration (O₃), and mass of catalyst, which varied in each case. All variables were significant in colour removal. Extremes in pH, lower C₀, and higher ozone concentrations are conditions that favour dye degradation. A complete colour loss occurred for certain combinations of these parameters. The application of iron oxide as a catalyst did not present a satisfactory improvement in the reaction rate. Chemical oxygen demand and total organic carbon showed minimum values of 80% and 78%, respectively, for the worst experimental conditions (pH 7.0, C₀ of 45 mg · L⁻¹, and 5 g O₃ · m⁻³), while their values were 88% and 83% for the best conditions applied. There was no immobilization of Artemia salina nauplii, even for the experimental run where the maximum concentration of dye of the set was used (45 mg dye · L⁻¹). Ozonation is a promising alternative in the degradation of aqueous sunset yellow dye, being favoured in acidic or basic media, which is especially important since food effluents usually present low pH and show low toxicity. The mathematical model proposed can be useful in the design of wastewater treatment processes.     

Sorption kinetics for the removal of dyes from effluents onto chitosan

The ability of chitosan, a biosorbent obtained by the processing of waste seafood shells, to remove five acid dyes from effluents has been studied. Chitosan is a deacetylated bio‐polymer of chitin. The effect of varying initial dye concentration on the rate of adsorption has been investigated. The rate data have been analyzed using three kinetic models, namely, a pseudosecond order, the Ritchie modified second order, and the Elovich models. The sorption kinetics of Acid Green 25, Acid Orange 10, Acid Orange 12, Acid Red 18, and Acid Red 73 onto chitosan can be best correlated by the Elovich equation. The kinetic model was determined in accordance with the agreement between the rate equations and the differentiation of kinetic equations. The values of rate constants for the three models are in the range of 0.003–2.230, 0.004–0.237, and 0.0173–405 for the pseudosecond order, the Ritchie modified second order and the Elovich models, respectively. The sensitivity analysis, by plotting the reciprocal of the rate, Z_L = (d_q/d_t)^?1 against time, is used to identify the true kinetic model. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Property Characterization and Photocatalytic Activity Evaluation of BiGdO3 Nanoparticles under Visible Light Irradiation

BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min⁻¹ with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment.     

Decolourisation of aqueous dyes by sequential oxidation treatment with ozone and Fenton's reagent

Combined oxidation with ozone and Fenton's reagent (‘Fentozone’ process) for decolourisation of aqueous dyes was studied and compared with traditional Fenton's reagent. Although the ‘Fentozone’ process was found to be effective at a wide range of pH values, the maximum colour removal was achieved at pH 4. The effect of pre‐ozonation on colour removal efficiency of aqueous dyestuffs in the subsequent treatment with Fenton's reagent was investigated. The reaction kinetics using water‐soluble acid and reactive dyes were also studied. Our experimental results show that pre‐ozonation can considerably accelerate decomposition of dyestuffs in the subsequent treatment with Fenton's reagent. Different concentrations of ferrous sulfate were used to investigate their influences on the removal of colour. The rate of reaction increased with increasing doses of ferrous sulfate. © 2002 Society of Chemical Industry