Impact of Ozonation on Decolorization and Mineralization of Azo Dyes: Biodegradability Enhancement,By-Products Formation,Required Energy and Cost

In the present study ozonation process was implemented to analyze the effect of ozonation time on the rate of chemical oxygen demand (COD) removal, mineralization and rate of decolorization of azo dyes. Three types of azo dyes i.e. Acid Red 14, Direct Red 28 and Reactive Black 5 were selected. Decolorization and mineralization of samples were conducted in batch scale. The COD and color removal efficiency were found to be increasing at a certain time of ozonation. The results with Acid Red 14, Congo Red and Reactive Black 5 dyes solutions lead to maximum COD reduction of 75%, 67% & 50% respectively. 93%, 92% and 94% color removal were achieved after 25 min of ozonation time of the same dyes which highlighted that ozonation process was found to be more efficient for reactive dye decolorization. Ozonation by-products analyzed by ion chromatography resulted that it partially mineralized with the formation of chloride, fluoride, sulphate, nitrate and oxalate ions. During ozonation process a rapid decrease in pH value indicated the acidic nature of by-products. The effect of buffered dye solutions on the ozonoation process highlighted that the decolorization efficiency decreases in comparison to unbuffered dye solutions. Ozonation led to enhancement of biodegradability ratio (BOD₅/COD) and increased electrical conductivity of the dye solutions. Optimum ozonation time required for degradation of dye solutions reflected the evaluation of energy consumption and cost of the treatment after ozonation.     

Degradation of azo dye C.I. Acid Red 18 in aqueous solution by ozone-electrolysis process

In this paper, the degradation of azo dye C.I. Acid Red 18 (AR18) with initial concentration of 100 mg L⁻¹ in aqueous solution by ozone-electrolysis process (OEP) as hybrid method of advance oxidation process was investigated. All experiments were performed in a 450 mL mixed semi-batch reactor to obtain the optimal conditions. The effects of NaCl concentration as supporting electrolyte, current density and initial pH on the removal efficiency of AR18 solution were investigated. The efficiency of color and TOC removal were compared as functional of degradation and decolorization of AR18. The results of UV/vis spectra showed that the AR18 structures were destroyed under ozone-electrolysis reaction. This investigation revealed ozone-electrolysis presents good efficiency for both solution decolorization and total organic carbon (TOC) removal. Results of experiments indicated that ozone-electrolysis process has a synergistic effect on decolorization rate of AR18.     

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.     

Mineralization of the Pharmaceutical β-Blocker Atenolol by Means of Indirect Electrochemical Advanced Oxidation Process: Parametric and Kinetic Study

Atenolol is a β-blocker that can be found in urban wastewaters and which is not removed efficiently by conventional wastewater treatments. In the present study, electro-Fenton (EF) process was used to assess the degradation and mineralization of pharmaceutical atenolol in aqueous solutions. Electrolyses of 250 mL of atenolol solution (0.17 mM), at initial pH 3, were carried out in an undivided electrolytic cell in galvanostatic mode. Influence of material cathode (graphite, stainless steel, and platinized titanium), applied current (100–500 mA), sulfate dosage (0.01–0.5 M), and catalyst ferrous ions concentration (1–10 mM), on the oxidation efficiency was studied. Atenolol mineralization was monitored by COD dosage. Kinetic analysis indicated that atenolol mineralization followed a pseudo-first order model and the rate constant increased with rising current, ferrous ions concentration (up to 5 mM) and electrolyte concentration. Results showed that graphite cathode, 0.5 M Na₂SO₄ electrolyte, 0.3 A and 5 mM FeSO₄ catalyst were the best conditions for atenolol mineralization. In these optimal conditions, after 240 min more than 87% of the initial COD was removed. The corresponding current efficiency (CE) and specific energy consumption (SEC) were 22.33% and 0.194 kWh/kg COD, respectively. This latter corresponds to 0.078 kWh/m³ of treated wastewater.     

Degradation of C.I. Acid Red 88 aqueous solution by combination of Fenton's reagent and ultrasound irradiation

BACKGROUND: Pollution caused by industrial wastewater has become a common problem for many countries. In particular, dye pollutions from industrial effluents disturb human health and ecological equilibrium. The discharge of highly colored synthetic dye effluents is aesthetically displeasing and can damage the receiving water body by impeding penetration of light. Azo dyes can be reduced to more hazardous intermediates on anaerobic conditions. Therefore, an effective and economic treatment of effluents containing a diversity of textile dyes has become a necessity for clean production technology for textile industries. Herein we wish to report the degradation of Acid Red 88 by the combination of Fenton's reagent and ultrasound irradiation. RESULTS: The results show that the combination of ultrasonic irradiation and Fenton's reagent is effective for the degradation of Acid Red 88 aqueous solution. Furthermore, it can achieve better results than either Fenton's reagent or ultrasound alone. The optimum conditions for the degradation of Acid Red 88 aqueous solution were 1.96 mmol L^?1 H₂O₂, 0.108 mmol L^?1 Fe²⁺, pH 3.0, and ultrasonic irradiation frequency of 40 kHz. A degradation efficiency of 98.6% was achieved within 135 min. CONCLUSION: We have provided an efficient and convenient procedure for the degradation of Acid Red 88 aqueous solution. In the present procedure, the azo linkage of Acid Red 88 is broken and some carbonyl compounds are formed, but the complete mineralization of dye cannot be achieved. Copyright © 2008 Society of Chemical Industry     

Electro-Fenton treatment of synthetic organic dyes: Influence of operational parameters and kinetic study

This work investigates oxidative decolorization of two different dyes, Methylene blue and Titan yellow in aqueous solution using an environmentally friendly advanced electro-chemical oxidation (electro-Fenton) process. The effect of operating conditions like H₂O₂ concentration, current density, initial dye concentration was studied in a batch stirred cell. Individual decolorization decay kinetics for both dyes was investigated. The second-order absolute rate constants (L mol^?1 s^?1) between hydroxyl radical and dye have been calculated from experimental data by fitting it to the decolorization model. The apparent kinetic constants, k _app (s^?1) for Methylene blue and Titan yellow dye decolorization were also determined. The experimental data showed a good fit to the theoretical model, which can predict data in a wide range of % dye decolorization. This process also reduces COD of the dye solution, and the unit energy demand (UED) in kWh/kg COD removed for different electrical current has been reported.     

Electrochemical degradation of azo dye C.I. Reactive Red 195 by anodic oxidation on Ti/SnO2-Sb/PbO2 electrodes

This study investigated the electrochemical degradation of C.I. Reactive Red 195 (RR195) in aqueous solution on a Ti/SnO₂-Sb/PbO₂ electrode. The influence of operating variables on the mineralization efficiency was studied as a function of the current density, the initial pH, the initial concentration of the dye and the addition of NaCl. The efficiency of RR195 mineralization decreased with increased initial concentration, from 100 mg L⁻¹ to 400 mg L⁻¹. The current density had both a positive and a negative effect on degradation rates, and no significant effect of initial pH on RR195 mineralization was observed. Measurement of absorbance was used to discriminate the effect of NaCl in the electro-oxidation process. We found that the decolouring efficiency increased whereas the mineralization efficiency decreased with the increasing concentration of NaCl. The intermediates formed during the degradation were detected by gas chromatography-mass spectrometry, and the major aromatic intermediates identified were 1-(3,6,8-trihydroxy-1-naphthyl)urea, nitrobenzene, benzo-1,4-quinone, (3,6,8-trihydroxy-1-naphthyl)carbamic acid and phthalic acid. Quantitative measurement of organic and inorganic ions was done by ion chromatography. On the basis of the reaction products identified, a possible degradation pathway for the anodic oxidation of RR195 in aqueous solution is proposed.     

Anaerobic and aerobic treatment of a simulated textile effluent

A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this effluent contained one reactive azo dye, PROCION Red H‐E7B (1.5 g dm⁻³); sizing agent, Tissalys 150 (1.9 g dm⁻³); sodium chloride (1.5 g dm⁻³) and acetic acid (0.53 g dm⁻³) together with nutrients and trace elements, giving a mean COD of 3480 mg dm⁻³. An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic effluent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77–247 68% of the true colour of PROCION Red H‐E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (B _v) 1.24 g COD dm⁻³day⁻¹) and the UASB at a 2 day HRT (B _v 1.74 g COD dm⁻³day⁻¹) gave comparable COD removals but the UASB gave better true colour removal. Effluent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm⁻³, and further treatment would be required to meet consent standards. © 1999 Society of Chemical Industry     

Decolorisation of aqueous reactive dye Remazol Red 3B by electrocoagulation

The present study demonstrated the applicability of the electrocoagulation method for the removal of reactive dye, Remazol Red 3B, in a batch study. Iron electrode material was used as a sacrificial electrode in monopolar parallel mode in this study. The effects of the initial pH, current density, conductivity, initial concentration of dye and electrolysis time on the removal of Remazol Red 3B were investigated to determine optimum operating conditions. High decolorisation efficiency (>99%) for Remazol Red 3B dye solution was obtained with optimal value of process parameters, such as 15 mA cm^?2 of current density, 10 min of electrolysis time, pH 6 and 500 mg l^?1 dye concentration. The energy consumption, electrode consumption and operating costs under optimum operating conditions were calculated as 3.3 kW h kg dye^?1, 1.2 kg Fe kg dye^?1 and 0.6 € m^?3, respectively.     

Anodic oxidation of azo dye C.I. Acid Red 73 by the yttrium-doped Ti/SnO2-Sb electrodes

This work was conducted to study the ability of anodic oxidation of azo dye C.I. Acid Red 73 (AR73) using the yttrium-doped Ti/SnO₂-Sb electrodes. The effects of Sb doping level, yttrium doping level, thermal decomposition temperature and cycle times of dip-coating thermal decomposition on the properties of the electrodes were investigated. The results showed that the excellent electrochemical activity of Ti/SnO₂-Sb-Y electrode can be achieved at a 7∶1 molar ratio of Sn∶Sb and thermal decomposition temperature of 550°C. Moreover when the cycle times of dip-coating and thermal decomposition were up to 10 times, the performance of the electrode tends to be stable. The Ti/SnO₂-Sb electrodes doped with yttrium (0.5 mol-%) showed the most excellent electrochemical activity. In addition, the influences of operating variables, including current density, initial pH, dye concentration and support electrolyte, on the colour removal, chemical oxygen demand (COD) removal and current efficiency were also investigated. Our results confirmed that the current efficiency increased with the concentrations of dye and sodium chloride. Moreover, increasing the current density and the initial pH would reduce the current efficiency.     

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     

Treatment of textile dye wastewater by using an electrochemical bipolar disc stack reactor

Textile dye house wastewater from a reactive dye processing unit was treated by using an electrochemical oxidation technique. The experiments were carried out in an electrochemical bipolar disc reactor using RuO₂ coated on titanium as anode and titanium as cathode. The sodium chloride present in the effluent was used as supporting electrolyte. Operating parameters such as current density, reservoir hold‐up and electrolysis time were studied for maximum Chemical Oxygen Demand (COD) reduction and other relevant parameters such as current efficiency and power consumption per kg of COD removal were calculated. The higher flow rate and lower reservoir hold‐up resulted in improved COD removal. The applied current density was also found to significantly influence the reduction of COD. A suitable mathematical model is also proposed to illustrate the relationship between the basic parameters. Pseudo mass transfer coefficients were also evaluated for different experimental conditions. Copyright © 2004 Society of Chemical Industry     

Use of a PbO2 electrode of a lead-acid battery for the electrochemical degradation of methylene blue

In this work, the electrochemical degradation efficiency of synthetic azo dye, methylene blue, at positive electrode PbO₂ of lead-acid battery was investigated. The structure and morphology of the electrode was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectrometry. The influence of several operating parameters on electro-oxidation of 100 mL of methylene blue solution 100 mg/L was studied. Results indicated that lead-acid battery electrode is effective for removing color and chemical oxygen demand (COD). It is found that current density, the stirring speed, and the supporting electrolyte concentration have a positive effect on decolorization and mineralization, and no significant effect of the distance between the electrodes on methylene blue degradation and COD removal was observed. By contrast, the percentage of color and COD removal decreases with increasing of pH. Kinetic analysis of the results revealed that the COD removal follows a pseudo-first-order kinetics.     

Integration of photocatalysis and membrane distillation for removal of mono- and poly-azo dyes from water

The paper reports investigations on the application of anatase-phase TiO₂ for the removal of azo dyes in a hybrid system coupling photocatalysis with direct contact membrane distillation (DCMD, MD). The process was conducted in a laboratory-scale installation equipped with a PP capillary module. The influence of reaction temperature and initial concentration of azo dyes on the effectiveness of their photodegradation was especially investigated. Two mono-azo dyes: Acid Red 18 (AR18) and Acid Yellow 36 (AY36) and one poly-azo dye, Direct Green 99 (DG99) were applied as model compounds. The increase of the reaction temperature from 313 to 333 K resulted in an improvement of the efficiency of photodecomposition of the dyes, as was found on the basis of changes of their masses in the feed solution. The comparison of the results obtained during photocatalysis alone and hybrid photocatalysis-MD process revealed that the reduction of feed volume in MD did not affect the photodegradation rate of the azo dyes. An improvement of the effectiveness of the degradation of dyes was obtained by an application of solutions with lower initial concentration (10 instead of 30 mg/dm³). Regardless of the process parameters applied, the product (distillate) was almost pure water with conductivity lower than 0.3 mS/m and pH above 5.2.     

Electrochemical treatment of methyl parathion based on the implementation of a factorial design

Commercial methyl parathion was treated by an electrochemical method using Ti/Pt as anode, Stainless Steel 304 as cathode and sodium chloride as electrolyte. Based on a number of preliminary experiments, a factorial experimental procedure was designed in order to optimize the electrolysis efficiency, in terms of removed COD and energy consumed kW h per kg of removed COD. The parameters examined were the temperature, the stirring rate of the brine solution, the input rate of the organic material, the current density, the electrolyte concentration and the concentration of Fe ²⁺ ions added. In the experimental range studied, the lower energy consumption measured was 6.61 kW h ( kg COD _r) ^–1 and the higher COD reduction measured was 86.3. From a mathematical model, the optimum conditions for the electrochemical treatment of MeP for 2.03 kW h ( kg COD _r) ^–1 were found to be Input rate of MeP 4300 mg COD min^–1, NaCl concentration 4.5, 4 g l^–1 of added FeSO₄, current density 0.47 A cm^–2, temperature 45 °C and stirring rate 400 rpm. An experiment was conducted under these optimum conditions which resulted in a satisfactory removal of the organic load (in terms of COD, BOD ₅). Furthermore, a significant improvement in the COD/BOD₅ ratio was achieved, rendering the effluent amenable to further biological treatment.     

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     

Electrochemical oxidation of Basic Blue 3 dye using a diamond anode: evaluation of colour,COD and toxicity removal

BACKGROUND: Textile industries generate considerable amounts of waste‐water, which may contain strong colour, suspended particles, salts, high pH and high chemical oxygen demand (COD) concentration. The disposal of these coloured wastewaters poses a major problem for the industry as well as a threat to the environment. In this study, electrochemical oxidation of Basic Blue 3 (BB3) dye was studied in a bipolar trickle tower (BTT) reactor using Raschig ring shaped boron‐doped diamond (BDD) electrodes in recirculated batch mode. The effects of current density, temperature, flow rate, sodium sulfate concentration (Na₂SO₄) as supporting electrolyte, and initial dye concentration were investigated. RESULTS: The best experimental conditions obtained were as follows: current density 0.875 mA cm^?2, temperature 30 °C, flow rate 109.5 mL min^?1, Na₂SO₄ concentration 0.01 mol L^?1. Under these conditions, 99% colour and 86.7% COD removal were achieved. Toxicity tests were also performed on BB3 solutions under the best experimental conditions. CONCLUSION: Based on these results, the BDD anode was found to be very successful for the simultaneous degradation of BB3 and removal of COD. Additional toxicity test results also showed that electrochemical treatment using a BDD Raschig ring anode in a BTT reactor is an effective way of reducing toxicity as well as removing colour and COD. Copyright © 2010 Society of Chemical Industry     

臭氧强化电絮凝处理直接耐晒大红4BS模拟染料废水

采用臭氧强化电絮凝法处理直接耐晒大红4BS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。考察了电流密度、溶液初始pH 值、染料初始浓度、支持电解质浓度、反应温度和臭氧流量对臭氧强化电絮凝法处理4BS染料脱色效率的影响。结果表明,电流密度15 mA·cm^-2,pH值10.0,4BS染料初始浓度100 mg·L^-1,支持电解质浓度3000 mg·L^-1,臭氧流量06 L·h^-1,20 ℃下反应50 min后4BS脱色率达94％以上。COD_Cr去除符合拟二级动力学。     

Degradation of Alizarin Red by electro-Fenton process using a graphite-felt cathode

The removal of the anthraquinone dye Alizarin Red S (AR) has been investigated by electro-Fenton process using a commercial graphite-felt to electrogenerate in situ hydrogen peroxide and regenerate ferrous ions as catalyst. The effect of operating conditions such as applied current, catalyst concentration, and initial dye content on AR degradation has been studied. AR decay kinetic, the evolution of its oxidation intermediates and the mineralization of the aqueous solutions were monitored during the electrolysis by UV–Vis analysis and TOC measurements. The experimental results showed that AR was completely removed by the reaction with OH radicals generated from electrochemically assisted Fenton's reaction, and the decay kinetic always follows a pseudo-first-order reaction. Applying a current of 300 mA and with catalyst concentration of 0.2 mM Fe²⁺, 95% of the initial TOC was removed in 210 min of electrolysis, meaning the almost complete mineralization of the organic content of the treated solution.