Decolorization of azo dye acid black 1 by the UV/H2O2 process and optimization of operating parameters

An advanced oxidation process, UV/H2O2, was applied for decolorization of a di-azo dye (acid black 1). The effects of operating parameters such as hydrogen peroxide dosage, UV dosage and initial dye concentration, on decolorization have been evaluated. The acid black 1 solution was completely decolorized under optimal hydrogen peroxide dosage of 21.24 mmol/l and UV dosage of 1400 W/l in less than 1.2 min. The decolorization rate followed pseudo-first order kinetics with respect to the dye concentration. The rate increased linearly with volumetric UV dosage and nonlinearly with increasing initial hydrogen peroxide concentration. It has been found that the degradation rate increased until an optimum of hydrogen peroxide dosage, beyond which the reagent exerted an inhibitory effect. For real case application, an operation parameter plot of rate constant was developed. To evaluate the electric power and hydrogen peroxide consumption by UV/H2O2 reactor, 90% color removal was set as criteria to find the balance between both factors.     

Effects of gap size and UV dosage on decolorization of C.I. Acid Blue 113 wastewater in the UV/H2O2 process

The wastewater from textile dyeing industry is difficult to be treated successfully according to both high variability of composition and color intensity. To investigate the effects of reactor gap size and UV dosage on the decolorization of dye wastewater, a commercially available azo dye C.I. Acid Blue 113 was chosen as a model compound. UV/H2O2 processes with various gap sizes and setups of plug flow reactor and recirculated batch reactor were proposed to deal with the dye wastewater in this study. The experimental parameters including the design of reactor configurations of annular gap size, and in batch system or plug flow reactors and hydrogen peroxide dosage, UV dosage were investigated. The gap size of reactor was adjusted by different diameter of reactor shells in order to optimize the reactor configuration. The color removal percentage was used to evaluate the treatment efficiency. An optimal hydrogen peroxide concentration of 46.53 mM was observed in this study for highest decolorization rate. Besides, the pseudo-first-order rate constant of 3.14 min(-1) was obtained by plug flow reactor with 0.5 cm gap size, 120.70 W/l of UV dosage and 23.27 mM of H2O2 dosage. The first-order rate constant, which was about 20 times less than that of plug flow reactor, was obtained 0.1422 min(-1) by recirculated batch reactor with 2.0 cm gap size, 7.0 W/l of UV and 23.27 mM of H2O2 dosages. Ultimately, we developed an effective pre-treatment or treatment technology for dye wastewater to provide the dyeing industries and dye manufacturers an alternative to meet the effluent standards.     

Kinetics of decolorization of an azo dye in UV alone and UV/H(2)O(2) processes

The decolorization of C.I. Acid Red 27 (AR27), a monoazo anionic dye, was studied in the ultraviolet radiation (UV) alone and UV plus hydrogen peroxide (UV/H(2)O(2)) processes. The experimental results indicated that the kinetics of both oxidation processes fit well by pseudo-first order kinetics. The reaction rate was sensitive to the operational parameters and increased with increasing H(2)O(2) concentration and light intensity. The reaction orders of H(2)O(2) concentration and light intensity in both processes were obtained with linear regression method. A regression model was developed for pseudo-first order rate constant (k(ap,UV/H(2)O(2))) as a function of the Cconcentration and UV light intensity. (k(ap,UV/H(2)O(2)))=(2 x 10(-4)I(0.75)(0) + k(3)I(1.38)(0)[H(2)O(2)](n)(0))phi(AR27). As a result of two opposing effects of H(2)O(2) concentration at low and high concentrations, n has a value of 0.49 and -0.39 and k(3) has a value of 3 x 10(-4) and 0.1 for the regions of 0 mg l(-1) < [H(2)O(2)](0) < 650 mg l(-1) and 650 mg l(-1) < [H(2)O(2)](0) < 1500 mg l(-1)1, respectively. PhiAR27 is the initial dye concentration correlation index for developing of model for different initial concentrations of AR27. This rate expression can be used for predicting k(ap,UV/H(2)O(2) at different conditions in UV alone and UV/H2O2 processes. The results show that UV alone cannot be an efficient method for decolorization of AR27 in comparison with UV/H(2)O(2) process, therefore the first term of the model can be neglected.     

Photolytic decolorization of Rose Bengal by UV/H(2)O(2) and data optimization using response surface method

Rose Bengal (C.I. name is Acid Red 94) was irradiated with UV light in the presence of hydrogen peroxide. The photoinduced decolorization of the dye was monitored spectrophotometrically. The apparent rate of decolorization was calculated from the observed absorption data and was found to be pseudo first order. A systematic study of the effect of dye concentration and H(2)O(2) concentration on the kinetics of dye decolorization was also carried out. Dye decolorization increased with increasing H(2)O(2) concentration and decreasing dye concentration. The maximum dye decolorization was determined as 90% with 0.005 mM dye at optimum 0.042 M H(2)O(2) and pH 6.6. Additionally, the effect on decolorization of this dye in the presence of some additives (ions) was also investigated. It was seen that sulphite caused a maximum effect on % decolorization of the dye solution. A plausible explanation involving the probable radical initiated mechanism was given to explain the dye decolorization. The experimental data was also optimized using the response surface methodology (RSM). According to ANOVA results, the proposed model can be used to navigate the design space. It was found that the response of Rose Bengal degradation is very sensitive to the independent factors of dye concentration, H(2)O(2) concentration, pH and reaction time. The proposed model for D-optimal design fitted very well with the experimental data with R(2) and R(adj)(2) correlation coefficients of 0.85 and 0.80, respectively.     

Degradation of dyehouse effluent containing C.I. Direct Blue 199 by processes of ozonation, UV/H2O2 and in sequence of ozonation with UV/H2O2

The decolorization and mineralization of cotton dyeing effluent containing C.I. Direct Blue 199 (DB 199) by advanced oxidation processes (AOPs) such as ozonation, UV/H(2)O(2), and in sequence of ozonation with UV/H(2)O(2) processes were evaluated in this study. By ozonation alone, the color removal was almost 100% for DB 199 and greater than 80% for dye bath effluent rapidly within 5 and 15 min, respectively. Meanwhile, the reduction of total organic carbon (TOC) was about 60% for DB 199 and almost no change for dye bath effluent, respectively due to incomplete mineralization. On the other hand, by UV/H(2)O(2) alone, the color removing not only took longer time but obtained lower removal efficiencies for DB 199 and dye bath effluent about 80% and 95% in 30 and 120 min, respectively. Nevertheless, it was more effective than ozonation for TOC removal while about 75% and 80% in 30 and 120 min, respectively. As a result, this study conducted the combination with the above two processes in order to shorten time demand as well as the higher removal efficiencies of both color and TOC simultaneously. Thus, the sequence process was designed to begin with ozonation to rapidly remove color proficiently, following by UV/H(2)O(2) in order to promptly remove remaining TOC efficiently. The successful process design by sequence of ozonation with UV/H(2)O(2) has proved the significant improvement for the removal of both color and TOC in dye bath effluent shortly. Besides, the lab prepared dye solution was substantially much easier to be decolorized than field dye bath effluent so that the lab results were utilized to design the further applications of pilot or full scale.     

Application of Box-Wilson experimental design method for the photodegradation of bakery's yeast industry with UV/H2O2 and UV/H2O2/Fe(II) process

Decolorization and mineralization of bakery's yeast industry effluent by photochemical advanced oxidation processes (AOPs) utilizing UV with hydrogen peroxide and Photo-Fenton, were investigated in a laboratory scale photo-reactor equipped with a 16 W low-pressure mercury vapor lamp. The Box-Wilson experimental design method was employed to evaluate the effects of major process variables (e.g. pH, oxidant dose, and irradiation time) on the decolorization efficiency. Response function coefficients were determined by regression analysis of the experimental data and prediction results agreed with the experimental results. The optimum hydrogen peroxide concentration and irradiation time were found to be 5 mM and 50 min at pH 3, respectively, for UV/H2O2 process. In the Photo-Fenton process application, maximum decolorization efficiency (96.4%) was obtained at the optimum reaction conditions that were 100 mM H2O2 and 1 mM Fe(II) doses at pH 3, and 10 min of irradiation time.     

Effect of operational parameters on the decolorization of C.I. Reactive Blue 19 in aqueous solution by ozone-enhanced electrocoagulation

The aim of this paper was to investigate the efficiency of the ozone-enhanced electrocoagulation (EC) process in the decolorization of C.I. Reactive Blue 19 in water using iron electrodes. We determined the effects of various operating parameters such as initial pH, initial dye concentration, current density, salt concentration, temperature, ozone flow rate, and distance between electrodes on decolorization efficiency in a laboratory-scale reactor. Increasing the initial dye concentration decreased the decolorization efficiency, whereas increasing the distance between electrodes increased it. The other operating factors had both positive and negative effects. With an initial pH of 10.0, an initial dye concentration of 100mg/L, current density of 10mA/cm2, salt concentration of 3000mg/L, temperature of 30 degrees C, ozone flow rate of 20mL/min, and distance between electrodes of 3cm, over 96% of the color was removed after 10min. As a consequence, removal of total organic carbon (TOC) was over 80%.     

Degradation of C.I. Reactive Red 2 through photocatalysis coupled with water jet cavitation

The decolorization of an azo dye, C.I. Reactive Red 2 was investigated using TiO(2) photocatalysis coupled with water jet cavitation. Experiments were performed in a 4.0 L solution under ultraviolet power of 9 W. The effects of TiO(2) loading, initial dye concentration, solution pH, geometry of cavitation tube, and the addition of anions on the degradation of the dye were evaluated. Degradation of the dye followed a pseudo-first order reaction. The photocatalysis coupled with water jet cavitation elevated degradation of the dye by about 136%, showing a synergistic effect compared to the individual photocatalysis and water jet cavitation. The enhancement of photocatalysis by water jet cavitation could be due to the deagglomeration of catalyst particles as well as the better contact between the catalyst surfaces and the reactants. Venturi tube with smaller diameter and shorter length of throat tube favored the dye decolorization. The degradation efficiency was found to increase with decreasing initial concentration and pH. The presence of NO(3)(-) and SO(4)(2-) enhanced the degradation of RR2, while Cl(-), and especially HCO(3)(-) significantly reduced dye decolorization. The results of this study indicated that the coupled photocatalysis and water jet cavitation is effective in degrading dye in wastewater and provides a promising alternative for treatment of dye wastewater at a large scale.     

Photo-catalytic degradation of toxic dye amaranth on TiO2/UV in aqueous suspensions

The photo-catalytic degradation of an azo dye − Amaranth (AM) - has been investigated in TiO₂/UV aqueous suspensions. The results obtained from the experiments during H₂O₂/TiO₂ addition show that the highest decolorization rate is provided by the combination of (UV + TiO₂ + H₂O₂). The decolorization efficiencies were 17%, 26%, 38% and 64% in the runs UV, UV + H₂O₂, UV + TiO₂ and (UV + TiO₂ + H₂O₂) after approximately 100 min illumination periods, respectively. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. Different experimental conditions, such as temperature, pH and presence of electron acceptor were investigated. The temperature effect was investigated at the range of 293-313 K and it was observed that decolorization rate increased by the increase in temperature. Chemical oxygen demand and dye absorbance of the photodegraded dye solution substantially decreased. Effect of pH was also investigated and it was observed that the lower the pH the higher the degradation. In addition, an enhancement in the photodegradation rate was observed by the addition of hydrogen peroxide as an electron acceptor. The adsorption trends of Amaranth at various initial concentrations followed the Langmuir isotherm trend. This work adds to the global discussion on the role of the advanced oxidation processes in water treatment.     

Photocatalytic degradation of C.I. Direct Red 23 in aqueous solutions under UV irradiation using SrTiO3/CeO2 composite as the catalyst

The photocatalytic degradation of C.I. Direct Red 23 (4BS) in aqueous solutions under UV irradiation was investigated with SrTiO3/CeO2 composite as the catalyst. The SrTiO3/CeO2 powders had more photocatalytic activity for decolorization of 4BS than that of pure SrTiO3 powder under UV irradiation. The effects of catalytic dose, pH value, initial concentration of dye, irradiation intensity as well as scavenger KI were ascertained, and the optimum conditions for maximum degradation were determined. Under the irradiation of a 250 W mercury lamp, the best catalytic dose was 1.5 g/L and the best pH was 12.0. Light intensity exhibited a significant positive effect on the efficiency of decolorization, whereas the initial dye concentration showed a significant negative effect. Under the conditions of a catalytic dose of 1.5 g/L, pH of 12.0, initial dye concentration of 100mg/L, light intensity of 250 W, and air flow rate of 0.15 m3/h, complete decolorization, as determined by UV-visible analysis, was achieved in 60 min, corresponding to a reduction in chemical oxygen demand (COD) of 69% after a 240 min reaction. A tentative degradation pathway based on the sensitization mechanism of photocatalysis is proposed.     

Optimization of decolorization of methylene blue by lignin peroxidase enzyme produced from sewage sludge with Phanerocheate chrysosporium

Optimization of decolorization of methylene blue (MB) dye by lignin peroxidase (LiP) enzyme produced by white-rot fungus Phanerochaete chrysosporium using sewage treatment plant (STP) sludge as a major substrate was carried out in the laboratory. Optimization by the one-factor-at-a-time (OFAT) and statistical approach was carried out to determine the process conditions on optimum decolorization of MB dye using LiP enzyme in static mode. The OFAT method indicated that the optimum conditions for decolorization of MB dye (removal: 14-40%) was at temperature 55 degrees C, pH 5.0 with hydrogen peroxide (H(2)O(2)) concentration 4.0mM, MB dye concentration 20mg/L and LiP activity 0.487U/ml. The addition of veratryl alcohol to the reaction mixtures did not contribute any further increases in decolorization. The initial concentration of MB and the activity of LiP enzyme were further optimized using response surface methodology (RSM). The contour and surface plots suggested that the optimum initial concentration of MB and LiP activity predicted were 15mg/L and 0.687U/ml, respectively for the removal of 65%. The validation of the model showed that the decolorization process gave the higher removal of 90% in agitation mode compared to the static mode with 65% for 60min of incubation time by LiP enzyme.     

A kinetic model for the decolorization of C.I. Acid Yellow 23 by Fenton process

The decolorization of azo dye C.I. Acid Yellow 23 (AY23) by Fenton process was investigated. The decolorization rate is strongly dependent on the initial concentrations of the Fe(2+) and H(2)O(2). The optimum operational conditions were obtained at pH 3. A kinetic model has been developed to predict the decolorization of AY23 at different operational conditions by Fenton process. The model allows to simulate the system behavior involving the influence of hydrogen peroxide, Fe(II) and dye concentrations.     

Effects of gap size and UV dosage on decolorization of C.I. Acid Orange 7 by UV/H2O2 process

Wastewater from textile processing plants can be highly colored and difficult to decolorize. During the past few years attention has been drawn to chemical techniques that could be used to textile wastewater decolorization. A crucial feature in designing such systems is the optimization of operating conditions. In the present study, advanced oxidation treatment, the UV/H(2)O(2) process has been applied to decolorization of the azo dye C.I. Acid Orange 7 (AO7) in aqueous solution in a batch photo reactor. The effects of the reactor gap size and UV dosage on decolorization of dye have been investigated. The method of study involved monitoring the rate of dye solution decolorization during irradiation by a low-pressure mercury lamp and varying gap size and volume of the reactor. The rate of color removal was studied by measuring of the absorbance at characteristic wavelength. The gap size of the reactor was adjusted by different depths of the reactor. The results of this study showed that the removal efficiency of AO7 is optimal with 0.3 cm gap size and 83.33 Wl(-1) of UV dosage.     

Design equation with mathematical kinetic modeling for photooxidative degradation of C.I. Acid Orange 7 in an annular continuous-flow photoreactor

The decolorization of C.I. Acid Orange 7 (AO7), an anionic monoazo dye of acid class was investigated using UV/H(2)O(2) process in an annular continuous-flow photoreactor (ACFP) as a function of oxidant, dye concentrations, reactor length and volumetric flow rate. The removal efficiency of AO7 was a function of operational parameters and increased with increasing initial concentration of H(2)O(2) but it was low at high flow rate and initial concentration of AO7. Results indicated that the decolorization rate was pseudo-first order kinetic with respect to the dye concentration. A rate equation for decolorization of AO7 was obtained by kinetic modeling. Design equation for ACFP reactor was obtained with combination of kinetic model and rearranged tubular reactor design equation. Design equation was used for predicting concentration of AO7 and also electrical energy per order (E(EO)) at different conditions. The calculated results obtained from design equation and kinetic model were in good agreement with experimental data.     

Degradation of malachite green in aqueous solution by Fenton process

In this study, advanced oxidation process utilizing Fenton's reagent was investigated for degradation of malachite green (MG). The effects of different reaction parameters such as the initial MG concentration, initial pH, the initial hydrogen peroxide concentration, the initial ferrous concentration and the reaction temperature on the oxidative degradation of MG have been investigated. The optimal reacting conditions were experimentally found to be pH 3.40, initial hydrogen peroxide concentration=0.50mM and initial ferrous concentration=0.10mM for initial MG concentration of 20mg/L at 30 degrees C. Under optimal conditions, 99.25% degradation efficiency of dye in aqueous solution was achieved after 60 min of reaction.     

Photodegradation of direct yellow-12 using UV/H2O2/Fe2+

A detailed investigation of photodegradation of direct yellow-12 (DY12) using UV/H(2)O(2)/Fe(2+) has been carried out in a photochemical reactor. Experiments studied degradation as a function of concentration, decolorization and reduction in chemical oxygen demand (COD). The effect of operating parameters, such as UV, pH, amount of Fenton's reagent (H(2)O(2) and FeSO(4)), and amount of DY12 dye has also been determined. It has been observed that simultaneous utilization of UV irradiation with Fenton's reagent increases the degradation rate of DY12 dye. The dye quickly losses its color and there is an appreciable decrease in COD value, indicating that the dissolved organic have been oxidized. The kinetics of degradation of the dye in dilute aqueous solutions follows pseudo-first order kinetics. Final products detected at the end of the reaction include NO(3)(-), NO(2)(-), N(2)O, NO(2), SO(2), CO(2) and CO. Results indicate that dye degradation is dependent upon pH, UV-intensity, concentration of Fenton's reagent and dye. Acidic pH has been found to be more suitable in comparison to neutral and alkaline. The optimum concentration of Fenton's reagent (H(2)O(2)/Fe(2+)) was found as 1500/500 mg l(-1) for 50 mg l(-1) DY12 dye in water at pH 4. The results indicate that the treatment of DY12 dye wastewater with UV/Fe(2+)/H(2)O(2) system is efficient.     

Pilot scale annular plug flow photoreactor by UV/H2O2 for the decolorization of azo dye wastewater

A pilot scale annular plug flow photoreactor with thin gap size, which combines with UV irradiation and hydrogen peroxide, was employed to deal with colored dyeing wastewater treatment. In the experiment, a mono-azo dye acid orange 10 was the target compound. The experimental parameters such as flow rate, hydrogen peroxide dosage, UV input power, pH and dye initial concentrations in a pilot scale photoreactor with flow rate of 9.32 m3day(-1) were investigated. Ultimately, the degradation rates were calculated and compared with a 100-l batch reactor. In our plug flow photoreactor design, the degradation rate of acid orange 10 was 233 times higher than that of 100-l annular batch reactor with same UV light source. The residence time needed for 99% decolorizing of 100 l of 20 mgl(-1) acid orange 10 wastewater was 26.9 min for the thin gap plug flow reactor and was far shorter than that of batch reactor needed.     

Bioaugmentation on decolorization of C.I. Direct Blue 71 by using genetically engineered strain Escherichia coli JM109 (pGEX-AZR)

The study showed that Escherichia coli JM109 (pGEX-AZR), the genetically engineered microorganism (GEM) with higher ability to decolorize azo dyes, bioaugmented successfully the dye wastewater bio-treatment systems to enhance C.I. Direct Blue 71 (DB 71) decolorization. The control and bioaugmented reactors failed at a around pH 5.0. However, the bioaugmented one succeeded at around pH 9.0, the influent DB 71 concentration was 150 mg/L, DB 71 concentration was decreased to 27.4 mg/L in 12h. The 1-3% NaCl concentration of bioaugmented reactors had no definite influence on decolorization, DB 71 concentration was decreased to 12.6 mg/L in 12h. GEM was added into anaerobic sequencing batch reactors (AnSBRs) to enhance DB 71 decolorization. Continuous operations of the control and bioaugmented AnSBRs showed that E. coli JM109 (pGEX-AZR) could bioaugment decolorization. The concentrations of activated sludge and GEM were still more than 2.80 g/L and 1.5 x 10(6)cells/mL, respectively, in the bioaugmented AnSBR. All the microbial communities changed indistinctively with time. The microbial community structures of the control AnSBR were similar to those of the bioaugmented one.     

Removal of C.I. Acid Orange 7 from aqueous solution by UV irradiation in the presence of ZnO nanopowder

The removal of C.I. Acid Orange 7 (AO7) from aqueous solution under UV irradiation in the presence of ZnO nanopowder has been studied. The average crystallite size of ZnO powder was determined from XRD pattern using the Scherrer equation in the range of 33 nm. The experiments showed that ZnO nanopowder and UV light had a negligible effect when they were used on their own. The effects of some operational parameters such as pH, the amount of ZnO nanopowder and initial dye concentration were also examined. The photodegradation of AO7 was enhanced by the addition of proper amount of hydrogen peroxide, but it was inhibited by ethanol. From the inhibitive effect of ethanol, it was deducted that hydroxyl radicals played a significant role in the photodegradation of the dye. The kinetic of the removal of AO7 can be explained in terms of the Langmuir-Hinshelwood model. The values of the adsorption equilibrium constant, K(AO7), and the kinetic rate constant of surface reaction, k(c), were 0.354(mg l(-1))(-1) and 1.99 mg l(-1)min(-1), respectively. The electrical energy consumption per order of magnitude for photocatalytic degradation of AO7 was lower in the UV/ZnO/H(2)O(2) process than that in the UV/ZnO process. Accordingly, it could be stated that the complete removal of color, after selecting desired operational parameters could be achieved in a relatively short time, about 60 min.     

Sonochemical degradation of Basic Blue 41 dye assisted by nanoTiO2 and H2O2

The sonolysis of Basic Blue 41 dye in aqueous solution was performed at 35 kHz using ultrasonic power of 160 W and aqueous temperature of 25+1 degrees C within 180 min. The TiO2 nanoparticles were used as a catalyst to assist the sonication process. The effect of experimental parameters such as pH, H2O2 concentration and initial dye concentration on the reaction were investigated. It was recognized that in lower pH values the dye removal rate decreased. However, dye removal increased via increase in H2O2 concentration and lowering the initial dye concentration. All intermediate compounds were detected by integrated gas chromatography-mass spectrometry (GC/MS) and also ion chromatograph (IC). During the decolorization, all nitrogen atoms and aromatic groups of Basic Blue 41 were converted to urea, nitrate, formic acid, acetic acid and oxalic acid, etc. Kinetic studies revealed that the degradation process followed pseudo-first order mechanism with the correlation coefficient (R2) of 0.9918 under experimental conditions. The results showed that power ultrasound can be regarded as an appropriate tool for degradation of azo dyes to non-toxic end products.