Ozone treatment of textile effluents and dyes: effect of applied ozone dose,pH and dye concentration

The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye‐bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi‐batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD₅ (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm^?3 ozone consumption. Ozonation of acid dyes was a pseudo‐first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR‐183) dye solution with a concentration of 50 mg dm^?3 rose from 0.32 to 0.72 mg‐O₃ per mg dye decomposed as the dye concentration was increased to 500 mg dm^?3. © 2002 Society of Chemical Industry     

Photocatalytic properties of mesoporous TiO2 nanocomposites modified with carbon nanotubes and copper

The photocatalytic activity of mesoporous TiO₂ modified by the addition of carbon nanotubes (CNTs) and Cu is reported. Nanocomposites of carbon nanotubes (CNTs) containing varying amounts of Cu were formed by treatment with Cu²⁺ then reduced to Cu⁰ using NaBH₄ as the reducing agent. The mesoporous TiO₂, synthesized by a sol-gel method from titanium isopropoxide, was combined with the CNT/Cu nanocomposites to form the photocatalysts which were characterized by XRD, SEM, TEM, FTIR, XPS and BET surface area analysis. The photocatalytic properties of the mesoporous TiO₂ composites were studied by measuring the degradation of methyl orange (MO) which was optimal in the sample containing 20 wt% of the Cu-CNT nanocomposite. The degradation efficiency for MO was a synergistic effect of photo-degradation of TiO₂ and may be due to improvement of the electrical conductivity of the system by the presence of the CNT/Cu networks, since the photodegradation of MO and the photocatalytic activity of the photoactive systems increased with increasing copper content.     

Evaluation of Decolorization,Mineralization, and Toxicity Reduction of Tropaeolin O in Water by Ozonation with UV Irradiation

The combination of ozonation with UV irradiation can remove Tropaeolin O (AO6) and its by-products effectively and completely. The ozone dose affects the rate of decolorization, AO6 species removal, and dissolved organic carbon (DOC) reduction significantly. After 240 minutes of ozonation, the average DOC removal efficiency (η_DOC) for O₃ alone was about 0.79, while η_DOC for O₃/UV was 1.0. The average DOC removal rate was low at early stage of ozonation due to decolorization and low DOC. At later stage of ozonation, average DOC removal rate decreases because of the formation of persistent intermediates. The ozone consumption was consistent with η_DOC. The ratio of ozone consumption to ozone applied decreased from 14 to 12% when η_DOC < 40% because the decolorization in the early stage of the ozonation of AO6 may consume a relatively large amount of ozone. It was found that NO₂, NO, CO₂, and small amount of SO₂ was detected in the off-gas. The effective concentration (EC50) increased from 23.48% to 100%, suggesting that the toxic reduction was achieved, and O₃/UV system was superior to O₃ alone system     

O_3协同内电解处理分散艳蓝E-4R废水的研究

基于印染废水具有成分复杂、色度高、难降解物质多等特点,采用臭氧协同内电解(IE/O3)对分散艳蓝E-4R进行处理。实验结果表明,在染液浓度为1 g/L加入铁屑量为300 g,通臭氧进气量为150 L/h,pH=11,反应温度为40℃,铁屑粒径为0.9~2 mm,铁炭比为1∶1时处理效果最佳,脱色率、CODC r去除率和TOC去除率分别为99.66%,75.94%和56.84%。臭氧协同内电解在最佳条件下处理染液的脱色率和CODC r去除率均明显高于二者单独作用,CODC r去除率分别比单独作用高59.03%和37.63%。另外,比较降解染液中的有机卤化物的含量,发现在协同作用下对该染料的降解更为彻底,矿化程度更高,有机氯化物去除率达到50.60%。     

Enhanced electrical properties of polycarbonate/carbon nanotube nanocomposites prepared by a supercritical carbon dioxide aided melt blending method

Polycarbonate/carbon nanotube (CNT) nanocomposites were generated using a supercritical carbon dioxide (scCO₂) aided melt blending method, yielding nanocomposites with enhanced electrical properties and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Baytubes^® C 150 P CNTs were benignly deagglomerated with scCO₂ resulting in 5 fold (5X), 10X and 15X decreases in bulk density from the as-received CNTs. This was followed by melt compounding with polycarbonate to generate the CNT nanocomposites. Electrical percolation thresholds were realized at CNT loading levels as low as 0.83 wt% for composites prepared with 15X CNT using the scCO₂ aided melt blending method. By comparison, a concentration of 1.5 wt% was required without scCO₂ processing. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO₂ processing compared to direct melt blending, but was significantly worse than that of twin screw melt compounded nanocomposites reported in the literature. A rheologically percolated network was observed near the electrical percolation of the nanocomposites. The importance of maintaining longer carbon nanotubes during nanocomposite processing rather than focusing on dispersion alone is highlighted in the current efforts.     

Studies on the activation of hydrogen peroxide for color removal in the presence of a new Cu(II)-polyampholyte heterogeneous catalyst

In this work we describe the application of a new non-soluble and non-porous complex with copper ion based on ethylene glycol diglycidyl ether (EGDE), methacrylic acid (MAA) and 2-methylimidazole (2MI) in the decolorization of an azo dye Methyl Orange (MO) as a model pollutant at room temperature.The complex with copper ion was studied by ESR and SEM and was tested as a heterogeneous catalyst for H₂O₂ activation. A possible mechanism of interaction involves the production of hydroxyl radicals (confirmed by ESR), dioxygen and water.The Cu(II)-polyampholyte/H₂O₂ system acted efficiently in the color removal of MO. The adsorption and oxidative degradation of the azo-based dye followed pseudo-first-order kinetic profiles, and the rate constant for degradation had a second-order dependence on copper ion content in the mixture.A removal of MO higher than 90% was achieved in 20 min at pH 7.0, combining 0.8 mM of complexed copper ions in the mixture with 24 mM hydrogen peroxide.The dye adsorbed on the polyampholyte following a L4-type isotherm with 4.9 μmol g⁻¹ maximum loading capacity and 3.1 μM dissociation constant for the first monolayer.     

In situ preparation of polyimide/amino‐functionalized carbon nanotube composites and their properties

In order to improve the dispersion of carbon nanotubes (CNTs) in polyimide (PI) matrix and the interfacial interaction between CNTs and PI, 4,4′‐diaminodiphenyl ether (ODA)‐functionalized carbon nanotubes (CNTs‐ODA) were synthesized by oxidation and amidation reactions. The structures and morphologies of CNTs‐ODA were characterized using Fourier transform infrared spectrometer, transmission electron microscopy, and thermal gravimetric analysis. Then a series of polyimide/amino‐functionalized carbon nanotube (PI/CNT‐ODA) nanocomposites were prepared by in situ polymerization. CNTs‐ODA were homogeneously dispersed in PI matrix. The influence of CNT‐ODA content on mechanical properties of PI/CNT‐ODA nanocomposites was investigated. It was found that the mechanical properties of nanocomposites were enhanced with the increase in CNT‐ODA loading. When the content of CNTs‐ODA was 3 wt%, the tensile strength of PI/CNT‐ODA nanocomposites was up to 169.07 MPa (87.11% higher than that of neat PI). The modulus of PI/CNTs‐ODA was increased by 62.64%, while elongation at break was increased by 66.05%. The improvement of the mechanical properties of PI/CNT‐ODA nanocomposites were due to the strong chemical bond and interfacial interaction between CNTs‐ODA and PI matrix. POLYM. COMPOS., 35:1952–1959, 2014. © 2014 Society of Plastics Engineers     

Decolorization and Modeling of Synthetic Wastewater Using O3 and H2O2/O3 Processes

This research deals with the decolorization of synthetic wastewater, prepared with the acid 1:2 metal-complex textile dye C.I. Acid Blue 193, using the ozonation (O₃) and H₂O₂/O₃ processes. To minimize the number of experiments, they were performed using the 2^k factorial design. Five influential parameters were examined: initial dye concentration, ozone flow rate, initial pH value, decolorization time and H₂O₂ addition. The decolorization efficiency was 95% in 20 minutes (pH = 7; O₃ flow rate of 2 g/L.h) and a higher increase in the toxicity after the ozonation process (39%) indicates the formation of carcinogenic by-products. According to the variance test analysis, the initial dye concentration, the ozone flow rate, the initial pH value and the decolorization time and their first- and second-order interactions are significant, while the H₂O₂ addition was not important with respect to the discussed range. With the help of these significant factors a regression model was constructed and the adequacy of the model was checked. The obtained regression polynomial was used to model the relation between the absorbance and the influential parameters by fitting the response surface. This response surface may be used to predict the absorbance result from a set of influential parameters, or it can be rearranged in such a way as to predict the set of process decolorization parameters necessary to reduce the absorbance of wastewater with the given initial dye concentration, below the prescribed limit. It is also shown that the 2^k factorial design can be suitable for predicting the operating expenses of the ozonation.     

电絮凝处理甲基橙废水的实验及动力学模型

采用电絮凝法处理甲基橙模拟染料废水,研究了染料脱色的影响因素及其COD_Cr去除动力学。考察了静置时间、槽电压、极板间距、初始浓度、pH值以及电解质浓度对甲基橙染料脱色效率的影响。结果表明,槽电压为20 V,电流为0.4 A,极板间距为2.5 cm,废水体积为500 ml,甲基橙初始浓度为500 mg·L^-1,溶液pH值为3.0,电解质KCl的浓度为0.5 g·L^-1时,反应10 min后甲基橙脱色率可达97 %。根据电絮凝的絮凝沉淀理论和氧化反应机理,建立COD_Cr去除反应动力学模型,模型与实验数据拟合较好。通过模型参数的预测可以揭示甲基橙降解主要以絮凝沉淀为主,氧化降解为辅,同时溶液中二价铁Fe(II)的增加会影响COD_Cr去除率的下降。     

Controllable‐Nitrogen Doped Carbon Layer Surrounding Carbon Nanotubes as Novel Carbon Support for Oxygen Reduction Reaction

Novel nitrogen‐doped carbon layer surrounding carbon nanotubes composite (NC‐CNT) (N/C ratio 3.3–14.3 wt.%) as catalyst support has been prepared using aniline as a dispersant to carbon nanotubes (CNTs) and as a source for both carbon and nitrogen coated on the surface of the CNTs, where the amount of doped nitrogen is controllable. The NC‐CNT so obtained were characterized with scanning electron microscopy (SEM), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and nitrogen adsorption and desorption isotherms. A uniform dispersion of Pt nanoparticles (ca. 1.5–2.0 nm) was then anchored on the surface of NC‐CNT by using aromatic amine as a stabilizer. For these Pt/NC‐CNTs, cyclic voltammogram measurements show a high electrochemical activity surface area (up to 103.7 m² g^–1) compared to the commercial E‐TEK catalyst (55.3 m² g^–1). In single cell test, Pt/NC‐CNT catalyst has greatly enhanced catalytic activity toward the oxygen reduction reaction, resulting in an enhancement of ca. 37% in mass activity compared with that of E‐TEK.     

Application of ozone on the decolorization of reactive dyes — Orange-13 and Blue-19

This study investigated the feasibility of applying ozone (O₃) to reduce the color content of wastewater caused by two commercial reactive dyes (Blue-19 and Orange-13). In the bench-scale experiment, experimental parameters including pH, ozone dosage, and reaction time were evaluated in a 14-L reactor to obtain the optimal operating conditions. Results show that ozone dosage and pH dominated the effectiveness of the decolorization process. The color content could be reduced from 2000 to 200 ADMI (American Dye Manufacture Institute) values within a reaction time of 30 min with the ozone input rate of 2.66 g/h. The pH values of 3 and 10 favored decolorization of Blue-19 and Orange-13, respectively. This was due to the effects that reactive and oxidizing species of molecular ozone and hydroxyl radicals were predominant at low and high pH, respectively. Moreover, molecular ozone was more selective to certain dye structures during the oxidation process. Kinetic analyses show that decolorization of Orange-13 and Blue-19 followed first-order kinetics. The degree of decolorization was primarily proportional to the ozone dosage. Results from this study provide insights into the characteristics and mechanisms of decolorization by the O₃ technique. Results will also aid in designing a system for practical application.     

Mechanical properties and electrical conductivity in a carbon nanotube reinforced silicon nitride composite

The influence of carbon nanotubes (CNTs) addition on basic mechanical, thermal and electrical properties of the multiwall carbon nanotube (MWCNT) reinforced silicon nitride composites has been investigated. Silicon nitride based composites with different amounts (1 or 3 wt%) of carbon nanotubes have been prepared by hot isostatic pressing. The fracture toughness was measured by indentation fracture and indentation strength methods and the thermal shock resistance by indentation method. The hardness values decreased from 16.2 to 10.1 GPa and the fracture toughness slightly decreased by CNTs addition from 6.3 to 5.9 MPa m^1/2. The addition of 1 wt% CNTs enhanced the thermal shock resistance of the composite, however by the increased CNTs addition to 3 wt% the thermal shock resistance decreased. The electrical conductivity was significantly improved by CNTs addition (2 S/m in 3% Si₃N₄/CNT nanocomposite).     

OXIDATION OF C.I. ACID ORANGE 7 WITH OZONE AND HYDROGEN PEROXIDE IN A HOLLOW FIBER MEMBRANE REACTOR

The degradation of C.I. Acid Orange 7 by ozone combined with hydrogen peroxide was carried out in a hollow fiber membrane reactor, and batch recirculation mode of aqueous phase was employed. The effect of initial pH, hydroxyl radical scavenger, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration on the decolorization of C.I. Acid Orange 7 was investigated. The results showed that the decolorization of C.I. Acid Orange 7 fits the pseudo-half-order kinetic model. The rate constant increased with the increase of initial pH, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration. The presence of hydroxyl radical scavenger inhibited the decolorization rate by over 50%. The combination of ozone with hydrogen peroxide achieved a higher COD removal efficiency than ozone alone in the membrane reactor.     

Preparation and photoelectrocatalytic properties of titania/carbon nanotube composite films

Composite films of TiO₂ and carbon nanotubes (CNTs) were prepared on titanium sheets by liquid phase deposition and the photoelectrocatalytic (PEC) properties of the films were investigated through the degradation of methyl orange (MO) in 0.1 M solutions. It was demonstrated that CNTs in the TiO₂ film significantly decreased the charge transfer resistance and increased the anodic photocurrent response of the film under UV light irradiation when the bias was above −0.1 V. The PEC performance of the CNT-based composite film could be tuned by controlling the preparation parameters including the deposition time and calcination temperature. The deposition time and calcination temperature were optimized at 1 h and 450 °C, respectively. On the TiO₂/CNT film prepared under the optimized conditions, 95% of the added MO (10 mg L⁻¹) was degraded within 90 min, which was much higher than the 60% removal seen on the pure TiO₂ films.     

Effects of Dodecyl Trimethyl Ammonium Bromide Surfactant on Decolorization of Remazol Blue by a Living Aspergillus versicolor Strain

The effect of dodecyl trimethyl ammonium bromide (DTAB) cationic surfactant on Remazol Blue reactive dye bioremoval properties of a growing Aspergillus versicolor strain in a molasses medium was investigated in a batch system as a function of pH, dye and surfactant concentrations. To determine the optimal pH value in the presence of 0.5?mM DTAB pH 3 to 7 was examined and pH 6 was selected. The dye concentrations of 50, 100, 200, 400 and 800?mg/L were examined with 0.5?mM DTAB and maximum decolorization occurred in 100?mg/L dye (98.8?%). The surfactant concentration of 0.1, 0.5, 1 and 2?mM DTAB was performed in 100 and 800?mg/L dye. The effect of surfactant concentration (0.1 to 2?mM DTAB) in a fungal growth experiment has shown that DTAB inhibited fungal growth. The decolorization was increased from 53.6?% (dry weight: 1.31?g/L) to 100?% (dry weight:0.93?g/L) while the surfactant concentrations were increased from 0.1 to 1?mM. A. versicolor (dry weight: 0.93?g/L) showed its maximum dye removal activity, namely 100?% in 100?mg/L dye with 1?mM DTAB at pH 6 in 3?days. The use of surfactants in biological wastewater treatment process will save energy and lower energy costs (such as the required energy for treat techniques) by shortening the incubation period. The results showed that the A. versicolor strain, which produces laccase enzyme, can effectively decolorize reactive dyes by the enhancement of DTAB. Surfactant enhanced decolorization technology is one of the feasible approaches to remove textile dye from wastewater.     

Ozonation of Textile Effluents and Dye Solutions in the Presence of Activated Carbon under Continuous Operation

Abstract

Ozonation was found to be effective for the decolorization of solutions, but has only a slight effect on TOC removal. On the other hand, adsorption on activated carbon improves the TOC removal, but the progressive uptake of the organic contaminants during the adsorption process decreases its removal efficiency. Decolorization, mineralization, and ozone consumption of colored solutions were evaluated under continuous operation in a column by three different processes: ozonation, adsorption on a fixed activated carbon bed, and ozonation in the presence of the activated carbon bed. The introduction of an ozone flow in a fixed activated carbon bed enhances both the decolorization of the solutions and mainly the mineralization of the organic matter, even when the activated carbon was previously partially saturated. Activated carbon acts both as an adsorbent and as a catalyst in the ozonation of colored solutions. The column configuration plays an important role in the performance of this system. The configurations in series and with activated carbon in the upper part of the column showed the highest colour and TOC removal for dye solutions.

The results obtained clearly show that the combination of ozone and activated carbon is a promising technique for the final treatment of colored effluents. Practical applicability of this process was validated by treating two industrial textile effluents, collected after two different biological treatments.     

The control of diameter of carbon nanotube over Co-loaded Zeolite Y

This study examined carbon nanotubes (CNTs) with various outer diameters produced by the catalytic decomposition of acetylene over Co-loaded zeolite Y. The CNTs were grown at differed reaction temperatures, reaction times, and acetylene concentrations. In addition, the effect of the amount of Co dispersed over zeolite Y used as a support was determined. The shape and diameter of the synthesized CNT were identified by SEM and TEM analyzers. As a result, CNTs with various outer diameters were synthesized successfully. The average outer diameter of the synthesized CNTs increased with increasing amount of Co dispersed over zeolite Y regardless of the reaction temperature and reaction time. The outer diameter did not change with acetylene concentration, and the acetylene concentration was fixed to 10 cm³/min. Most of the CNT had large surface areas, >400 m²/g. The surface area increased with increasing outer diameter of the CNT until the outer diameter reached 60 nm but decreased with further increases in outer diameter.     

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.     

Chemical decolorization of the azo dye CI Reactive Orange 96 by various organic/inorganic compounds

Batch experiments were performed to investigate the possibility and kinetics of chemical decolorization of the reactive mono‐azo dye CI Reactive Orange 96 (RO 96) with various compounds such as cysteine, ascorbate, Ti(III)‐citrate, Fe(II)‐sulfate, and yeast extract. Cysteine and ascorbate (10 mmol dm^?3 respectively) decolorized RO 96 (0.19 mmol dm^?3) in the absence of oxygen. Increasing the concentration of either reductant (to 20 or 38 mmol dm^?3) enhanced the decolorization rate, showing first‐order kinetics with respect to both the concentration of the dye and of cysteine or ascorbate. The rate constants, k, for cysteine and ascorbate were 0.0003 and 0.0010 dm³mmol^?1 h^?1 respectively at pH 7.1 and 33 °C. Ti(III)‐citrate (10 mmol dm^?3) decolorized RO 96 (0.20 mmol dm^?3) within 5 min, independent of the presence of oxygen. Fe(II)‐sulfate was not effective in the decolorization of RO 96 at pH 8, whereas a rapid decolorization occurred at pH 12. This study suggests that a variety of abiotic processes may be involved in decolorization under anaerobic conditions. © 2002 Society of Chemical Industry     

Enhanced mechanical strength of chitosan hydrogel beads by impregnation with carbon nanotubes

Chitosan (CS) hydrogel beads were impregnated with carbon nanotubes (CNTs), and their mechanical strength, acid stability and adsorption capacity to the anionic dye, Congo red (CR), were investigated by comparing with a conventional reinforcing method of cross-linking with epichlorohydrin (ECH). CS/CNT hydrogel beads were manufactured by dispersing CNTs (0.01 wt.%) with cetyltrimethylammonium bromide (CTAB) (0.05 wt.%) into CS solution (1 wt.%). Maximum endurable force at complete breakdown of CS hydrogel beads increased from 1.87 to 7.62 N with incorporation of CNTs and its adsorption capacity increased from 178.32 to 423.34 mg g⁻¹ for adsorption of CR.