Reuse of spent dyebath following decolorisation with ozone

Spent reactive dyebaths were decolorised by treatment with ozone and reused in the bleaching, whitening and dyeing of two textile substrates. The study shows that the reuse of a spent dyebath is possible with little modification to the standard processes for dyeing cotton with reactive dyes, provided that the pH of the treated dyebath is adjusted. Moreover, the cycle of decolorisation and reuse was successfully repeated. Renovated reactive dyebaths were also reused for bleaching cotton fabric with hydrogen peroxide, whitening with optical brightener and dyeing polyester fabric with disperse dyes. The whiteness index of bleached and whitened cotton was comparable to that of the same fabric given a control treatment with fresh baths. Likewise, there was a negligible colour difference between polyester dyed using liquor from a spent reactive dyebath and the same fabric dyed in a new bath.     

Comparison of different ultrasound support methods during colour and chemical oxygen demand removal of disperse and reactive dyebath solutions by ozonation

In this study, the effects of ozonation, ozonation with ultrasonic bath and ozonation with ultrasonic homogeniser processes on colour and chemical oxygen demand removal properties of disperse (CI Disperse Red 60, CI Disperse Blue 337) and reactive (CI Reactive Blue 171 and CI Reactive Blue 19) dyebath solutions with and without dyeing auxiliaries were investigated. Chemical oxygen demand (in mg/l) and colour (in Hazen) measurements of the studied dyebath solutions were determined. The ozonation process caused simultaneous chemical oxygen demand removal during decolorisation. However, the improvement in chemical oxygen demand reduction was less than of that on decolorisation. The application of the combination of ozonation with ultrasonic homogeniser is the most efficient process and creates a great time advantage over the other process types studied (ozonation alone and ozonation with ultrasonic bath) to reach the same colour and levels of chemical oxygen demand removal.     

One‐bath union dyeing of a modified wool/acrylic blend with acid and reactive dyes

Pretreated wool/acrylic fibre was obtained by a facile amidoximation process. Fibre characterisation (nitrogen content, tensile strength, shrinkage, infrared spectra and X‐ray diffraction) proved the success of the pretreatment. Union dyeing of wool/acrylic fabrics with acid and reactive dyes, namely CI Acid Red 40, CI Acid Blue 25, CI Reactive Red 194 and CI Reactive Blue 25, was obtained using a one‐bath dyeing process. Different factors that may affect the dyeability of the blend fibre, such as dyebath pH, liquor ratio, temperature, time and dye concentration, were evaluated with respect to the dye exhaustion, fixation, colour strength, levelling and fastness properties. Excellent to good fastness was obtained for all samples, irrespective of the dye used. The result of the investigation offers a new viable method for union dyeing of wool/acrylic fibres in a one‐dyebath process.     

Nanofiltration for the possible reuse of water and recovery of sodium chloride salt from textile effluent

During the reactive dyeing of cotton, salts such as sodium chloride (NaCl) are placed in a dyebath to aid the exhaustion of various dyes onto the fabric while bases are added to raise the pH from around neutral to pH 11 to achieve fixation. Afterwards, the used dyebath solution, called dyebath spent liquor, is discharged with almost all the salts and bases added as well as unfixed dyes. Consequently, many raw materials are lost in the waste stream ending up in the environment as pollutants. In this study possibilities of reusing the water and salts of dyebaths were investigated using a nanofiltration membrane. When the NaCl concentration in the spent liquor was increased from 10 to 80 g/L, the NaCl rejection by the membrane was found to decrease initially; however, the NaCl rejection increased over time, which was not expected. The aggregation of dye was also studied and found to decrease in the concentrate when the salt concentration was increased. This information is useful for the textile industry in evaluating the treated water quality for the purpose of reuse.     

Adsorption and fixation behaviour of CI Reactive Red 195 on cotton woven fabric in a nonionic surfactant Triton X‐100 reverse micelle

To achieve the goals of saving water and being salt‐free in the coloration of cotton fabric with reactive dye, nonionic reverse micelles were prepared and optimised with a surfactant, Triton X‐100, n‐octanol and isooctane by injecting a small amount of CI Reactive Red 195 aqueous solution. The adsorption, diffusion and fixation of this dye on cotton fabric in Triton X‐100 reverse micelle and bulk water were then investigated. The equilibrium and kinetic data of the dye adsorption process were evaluated. The colour strength and fixation rate of cotton fabrics dyed in the micelle and in bulk water were also examined and compared. The results indicated that the amount of dye adsorbed increased with the increasing temperature and the initial dye concentration. The dye adsorption process could be described using the Langmuir isotherm and pseudo‐second‐order kinetic equations. It was found that CI Reactive Red 195 showed a stronger adsorption property on cotton fabric in Triton X‐100 reverse micelle than in bulk water without the addition of sodium chloride. Using Triton X‐100 reverse micelle as the dyeing medium offered the reactive dye better diffusion performance within the cotton fibre as compared with bulk water. Moreover, higher fixation of the dyes absorbed on the cotton fibre was achieved when the optimum concentration of sodium carbonate was used as the alkali agent in Triton X‐100 reverse micelle.     

Novel heterogeneous photocatalysts prepared with waste wool and Fe3+ or Cu2+ ions for degradation of CI Reactive Red 195: a comparative study

In order to reuse waste wool, two transition metal ions, Fe³⁺ and Cu²⁺, were coordinated to with it to prepare a series of metal–wool complexes as new heterogeneous Fenton photocatalysts for the degradation of a typical azo dye, CI Reactive Red 195, in aqueous solution. The effect of the initial metal ion concentration and temperature on the reaction was investigated. Furthermore, the catalytic performance of the resulting metal–wool complexes was evaluated with respect to the dye decoloration efficiency at different pH levels under visible irradiation. The results demonstrated that increasing the initial metal ion concentration and temperature enhanced ion coordination to produce complexes of increased metal content. The obtained Fe–wool showed a higher metal content than the Cu–wool. The light adsorption performance in the UV and visible regions of Cu–Fe–wool is stronger than that of Fe–wool or Cu–wool. Furthermore, Cu–Fe–Wool was found to have a higher catalytic activity than the other two complexes under visible irradiation, especially in the alkaline pH range.     

Sonochemical destruction of textile dyestuff in wasted dyebaths

Ultrasonic degradation at 300 kHz of basic azo and reactive anthraquinone dyes was investigated in dyebath wastewater at acidic and near-acidic pH. For all conditions, it was found that colour decay was exponential, levelling off at a non-zero plateau and slowing down with increased acidity. It was also found that the bleaching rate of a dyebath was more sensitive to the dye structure than to the dyebath matrix. The rate of azo dye bleaching was slower than that of anthraquinone dyes at both test pH levels regardless of the unfavourable conditions in the latter dyebath against oxidation by hydroxyl radicals. The addition of hydrogen peroxide to the dyebaths rendered a slight enhancement in the degree of colour decay and a significant increase in the overall degradation of the dyestuff.     

Effect of Fenton's reagent on the degradability of CI Reactive Yellow 15

As an advanced oxidation method, Fenton's reagent has an advantage that it combines both oxidation and coagulation techniques. The aim of this study was to efficiently operate Fenton's reagent oxidation to degrade a reactive dye, CI Reactive Yellow 15, which is non-biodegradable and has high chemical oxygen demand. In addition, performance of the Fenton oxidation process for dye solution was determined by measuring the chemical oxygen demand and colour removal. The influence of the main operating parameters, iron sulphate and hydrogen peroxide concentration, pH, temperature and dye concentration have been studied, in a batch-type operation. The results obtained show that the best pH value for decolorisation was pH 3, with an average decolorisation of 98.7% and average removal of chemical oxygen demand ca. 93.3% at 15 °C for a 0.065 molar ratio of Fenton's reagent. An increase in temperature resulted in higher removal rates.     

pH control for dyeing polyamide in a reused acid dyebath

The pH control that can be achieved in a reused dyebath was investigated. The study involved a phosphate buffer system and four pH sliding systems, including ammonium sulphate and three hydrolysable organic esters. Instead of discharging the dyebath after each dyeing cycle, the residual dyebath was analysed using a UV-Vis spectrophotometer and reconstituted to the required concentration of dyes, auxiliaries and acid donors. The dyebath was reused for 10 cycles and colour reproducibility, levelness and fastness of the dyed samples were measured after each recycling. In comparison with ammonium sulphate and sodium dihydrogen phosphate, hydrolysable organic esters gave a stable and effective pH shifting in the dyebath reuse system. In addition, hydrolysable organic esters resulted in a very low amount of salt in residual dyebath. No deterioration in colour fastness of the dyed fabrics over 10 cycles of dyebath reuse was evident.     

Experimental study and modelling of an azo colourant dynamic adsorption onto functional cross-linked chitosan/ceramic particles in a fixed bed column

The use of azo dyes in industrial activities generates a large volume of contaminated wastewater; these pollutants in water bodies affect aquatic biota and human health. A functional biocomposite sorbent material was synthesized using cross-linked chitosan with oxalic acid that forms a coating on alumina ceramic particles (AOCh). The removal of Reactive Red 195, a reactive azo dye, using a fixed-bed adsorption column filled with this material was tested. AOCh was physico-chemically characterized by Fourier transform infrared spectroscopy–total attenuated reflection (FTIR-ATR), scanning electron microscopy–energy dispersion spectrometry X-ray (SEM-EDS), X-ray diffraction (XDR), thermo-gravimetric analysis (TGA), and Z-potential. The dynamic adsorption performance was analyzed from experimental breakthrough curves obtained in fixed-bed columns by modifying different operating conditions (bed depth, volumetric flow rate, and dye inlet concentration). Equilibrium adsorption isotherms were determined under dynamic conditions and compared with batch results. The maximum adsorption capacity of the dynamic equilibrium isotherm obtained from the continuous assays was 331 mg/g; this value was the highest in comparison to other tested materials reported in the literature. Different dynamic adsorption models were applied to fit experimental data, including Thomas, Bohart–Admas, Yoon–Nelson, logistic general model, bed depth surface time (BDST), and modified dose response (Yan) models. A critical analysis of these equations was presented, showing the equivalences and the relationship among the coefficients. The Yan model achieved the highest level of agreement between the experimental and predicted values of the breakthrough curves. The use of this model enables scaling-up the industrial process for dye removal. The present work proposed a novel biosorbent material and contributes to the analysis of industrial dye removal under dynamic conditions.     

Decolorisation and mineralisation of homo- and hetero-bireactive dyes under Fenton and photo-Fenton conditions

The degradation of two commercial reactive dyes, CI Reactive Red 141 (homo-bireactive) and CI Reactive Red 238 (hetero-bireactive), using Fenton's reagent in the dark and under either artificial or solar irradiation, has been investigated. The main parameters that govern the complex reactive system, i.e. type of irradiation, temperature and initial concentrations of iron(II) and hydrogen peroxide, have been studied at pH 3. Temperature and the use of light have beneficial effects on the removal of colour, aromatic compounds, total organic carbon, acute toxicity, given as changes in EC₅₀ values (against the marine photobacteria Vibrio fischeri ) and changes in the biodegradability. The advanced oxidation processes used in this study have proven to be highly effective for the treatment of such types of reactive dyes and several advantages concerning the technique application arise from the study. The possibility of a combined advanced oxidation process-biological treatment is proposed.     

Study of the cytotoxicity of reactive dyeing effluent treated by Fenton oxidation

Fenton oxidative wastewater treatment of CI Reactive Black 5 and CI Reactive Blue 19 effluent was performed after a simulated laboratory‐scale dyeing process, and the cytotoxicity of the treated effluent was evaluated using human skin cell lines. Among the components for Fenton oxidation, the human skin cell results showed that iron(II)sulfate at 150 mm did not show any significant cytotoxic effect, while other components, such as Glauber's salt solution (20 g l^?1; 14%), CI Reactive Black 5 (30 mg l^?1; 24%), caustic soda (5 g l^?1; 30%), CI Reactive Blue 19 (30 mg l^?1; 32%), hydrogen peroxide (0.01 m ) and soda ash (5 g l^?1) showed cytotoxic potential; the reagent sodium sulfite (30 mm ; 48%) exhibited the strongest cytotoxicity level. Fast decolorisation (>95%) was achieved within 10 min for CI Reactive Black 5, while for CI Reactive Blue 19 it took longer (1.5 h) to achieve the same decolorisation. Studies showed that decolorisation for both dyes followed second‐order kinetics. In spite of the remarkable efficacy of the Fenton oxidation process in removing colour within a short period of time, the resulting treated wastewater (within a reaction time of 1.5 h) also showed cytotoxicity towards the human HaCaT skin keratinocyte cell line. This observation can be explained by the strong oxidant and intermediate species produced during the advanced oxidation process, and a treatment step using sodium sulfite and a prolonged residence time can help to reduce the cytotoxicity.     

Colour recipe prediction using ant colony algorithm: principle of resolution and analysis of performances

This paper presents a new method for colour recipe prediction using ant colony optimisation. Three reactive dyes, namely CI Reactive Yellow 145, CI Reactive Red 238 and CI Reactive Blue 235, were used for colour formulation. Samples of 100% cotton fabrics were used for dyeing. The objective was to assure, control and optimise the colour formulation step by determining the dyes to be applied and their respective concentrations to reproduce the desired shades. The criterion of optimisation is to minimise the colour differences [Colour Measurement Committee (2:1)] between the target colour and the colour obtained by the proposed recipe. Errors between the proposed recipe and actual concentrations are also evaluated. The developed algorithm showed good performances with small colour differences between the target and reproduced colours (all lower than 0.7).     

季铵型阳离子聚丙烯酰胺的无盐染色行为

以季铵型阳离子聚丙烯酰胺作为一种新的阳离子助剂对棉纤维进行处理,应用于活性染料无盐染色,对染色过程中染料与处理后棉纤维之间的吸附类型、吸附热力学及吸附动力学进行了研究。结果表明,无盐染色过程符合Langmuir吸附模型;吸附过程是放热自发进行的,低温有利于染料的吸附;吸附动力学符合二级动力学模型,属于化学吸附过程。与传统有盐染色结果相比,染色后的阳离子化棉纤维色深增加,染料利用率提高。     

A study on the spectral changes of reactive textile dyes and their implications for online control of dyeing processes

Evidence is presented that confirms the colour changes of a widely used trichromatic mixture of bifunctional reactive dyes (Levafix CA) under alkaline conditions, showing that they occur slowly and throughout the dyeing time, and not instantly after alkali addition to the dyebath. Thus, it is impossible to determine the specific absorptivity of the dyes at each moment of the dyeing process. An investigation into the relationship of the type of reactive group to the dye and the visible spectral changes over time was undertaken. Model reactive dyes were studied. The samples collected from the simulated dyebaths were monitored online using an automated system and their absorption on the whole of the visible spectrum was measured. The studies of dyes that included halo‐s‐triazinyl groups revealed the existence of hypochromic shifts in the spectra of the dyes in the presence of an electrolyte (sodium chloride or sodium sulphate) and bathochromic and hyperchromic shifts, when evaluated in the presence of alkaline agents. However, the vinylsulphonyl derivatives present a more stable spectral profile. The use of buffer solution at pH 5 was an efficient method to stabilise the absorption profile of Levafix CA trichromatic samples.     

Cathodic decolourisation of textile waste water containing reactive dyes using a multi‐cathode electrolyser

The reductive decolourisation of textile dyestuffs containing an azo group was investigated by direct cathodic electron transfer CI Acid Red 27 and CI Acid Yellow 9 were used as model compounds for azo dyes. Reactive dyes, eg CI Reactive Red 4, CI Reactive Orange 4, and CI Reactive Black 5, which are in technical use for cellulose dyeing were investigated as representatives of practical importance. A basic characterisation of the reduction–decolourisation behaviour of the dyes was achieved by redox titration with Fe(II)–triethanolamine as reducing agent and parallel spectrophotometric observation of changes in the chromogenic system. From the redox titration experiments basic data describing the experimental conditions for successful cathodic electron transfer can be derived. The electrochemical dyestuff reduction experiments were performed in batch trials using a multi‐cathode electrolyser with high cathode area. According to the typical composition of such dyebaths 0.12 mol dm^?3 NaOH was used as ground electrolyte. The absorbance of the investigated dyestuff solutions could be decreased to below 20% of the initial value. For a 50% decrease in absorbance, electrical energy of about 6 kWh m^?3 is consumed. The process is of particular interest for the treatment of concentrated dyestuff solutions as they are used in continuous dyeing processes. © 2001 Society of Chemical Industry     

Removal of reactive dyes from wastewater using Fe(III) coagulant

The coagulation-flocculation process was employed for the treatment of reactive dye wastewaters, with ferric chloride hexahydrate employed as the coagulant. The process was found to be very effective with a more than 99.5% colour removal. Typical representatives of monochlorotriazine reactive dyes, with azo and anthraquinone chromophores, were CI Reactive Red 45 and CI Reactive Green 8, which were chosen as the model dyes. In order to determine the optimum pH range and coagulant concentration, a series of jar tests was done. Further experiments were conducted using a square flocculation tank with turbine impeller applying rapid and slow mix operations. The optimisation of initial rapid mixing, which has an important role in the overall coagulation process efficiency, was carried out. The optimum combination of velocity gradient and time of rapid mix was suggested for reactive dye wastewater treatment. Sedimentation curves for both model dyes were also obtained.     

Photoassisted degradation of CI Reactive Red 195 using an Fe(III)‐grafted polytetrafluoroethylene fibre complex as a novel heterogeneous Fenton catalyst over a wide pH range

Polytetrafluoroethylene fibre was grafted with acrylic acid to form an effective ligand, which coordinated with Fe(III) ions to prepare an Fe(III)‐grafted polytetrafluoroethylene fibre complex. The photoassisted degradation of a typical azo dye, CI Reactive Red 195, using the Fe(III)‐grafted polytetrafluoroethylene fibre complex as a novel heterogeneous Fenton catalyst in a wide pH range of 3–9 was investigated. In order to achieve better degradation in a higher pH range, the effect of Fe content, incorporation of Cu(II) ions and UV light irradiation on dye degradation was also examined. The results indicated that dye degradation was effective in the presence of the Fe(III)‐grafted polytetrafluoroethylene fibre complex. Fast degradation of the dye can take place in an acidic environment. Increasing the Fe content or incorporating Cu(II) ions can significantly accelerate dye degradation, and UV light irradiation is much more effective than visible light irradiation in a higher pH range, especially in the alkaline pH range.     

Non-formaldehyde durable press finishing of dyed fabrics: evaluation of cotton-bound polycarboxylic acids

The polycarboxylic acids 1,2,3,4-butanetetracarboxylic acid and citric acid are used as nonformaldehyde durable press finishing agents instead of formaldehyde-releasing N -methylol compounds. In this study, isocratic HPLC is applied in an attempt to quantify the polycarboxylic acids that react with cellulosic material dyed with CI Reactive Red 195, CI Reactive Yellow 145 and CI Reactive Blue 221. Subsequently, the fabrics are cured with formulations containing butanetetracarboxylic acid and citric acid or a combination of both. The chromatographic determination reveals that an increase in the depth of shade results in a decrease of the amount of butanetetracarboxylic acid, except in the case when the cotton is dyed with CI Reactive Blue 221, a copper formazan complex-based dyestuff. Colour measurements indicate that the Δ E * values decrease in the order CI Reactive Yellow 145, CI Reactive Red 195 and CI Reactive Blue 221.     

Prediction of recipes for cotton cationisation and reactive dyeing to shade match conventionally dyed cotton

Cationisation allows cotton to be dyed with anionic dyestuffs (including anionic pigment dispersions) without the need for salt, and with decreased usage of dye, water, and energy. Appropriate cationisation levels play a part in dyeing properties such as fabric levelness, in fastness properties such as lightfastness, and in the overall cost of the cationisation treatment. The objective of this work is to assess whether it is possible simultaneously to predict a dye recipe and cationisation treatment level for cotton to yield a colourless or nearly colourless dyebath at the completion of the dyeing to match the shade of conventional fibre reactive dyeing of cotton. It has been shown that it is possible to model a cold pad batch cationisation process, relate the colour yield data and cationisation level for individual dyes, and finally predict a dyeing recipe and the required corresponding cationisation treatment to match the shade of conventional fibre reactive dyeing of cotton. The predicted dye recipe and cationisation amount yield colourless or nearly colourless dyebaths at the conclusion of the dyeing process.