Decolorization Rate Constants Research Articles

Decolorization Kinetics of Azo Dye (Methyl Orange) in Fenton Process with High Entropy Alloys as Catalyst

This study explored the decolorization kinetics of azo dye (methyl orange) with the presence of high entropy alloys (HEAs) as a catalyst in the Fenton process. The kinetic reaction of the azo dye was determined using the first and second-order kinetics model. The slope from the first pseudo kinetics model was determined to compute the decolorization rate constant (K) This present work showed that the model was significantly well fitted with the experimental data. The highest K value of HEA catalyst was occurred at 30 minutes within 60 minutes of the Fenton reaction. The obtained result also showed the efficiency of the high entropy alloys (HEAs) rapidly degraded the azo dyes.

TiO2-functionalized biochar from pistachio nutshells: adsorptive removal and photocatalytic decolorization of methyl orange

Pistachio nutshells-derived biochar (PNS-BC) was utilized as a cost-effective adsorbent for competently removing a model dye, methyl orange (MO) from wastewater. Three concentrations of TiO2; 1%, 2%, and 3% were used to decorate the biochar. Analysis of morphology, stability, and structure of the three adsorbents (PNS, PNS-BC, and the TiO2 functionalized biochar; TiO2@PNS-BC) was extensively explored using various characterization techniques. The synergistic photocatalytic-adsorptive efficiency of the three adsorbents was compared. In this regard, a Box-Behnken (BB) design-based multivariate scheme was inaugurated with the target of maximizing MO removal (%R) while using the minimum possible of chemicals and resources. The impact of five variables; %TiO2, dose of TiO2-PNS, reaction time, dye concentration, and pH on the magnitude of %R was investigated. Results show that 97.69% removal of MO could be recognized over 120 min using adsorption compared to 99.47% removal over 30 min using 3% TiO2@PNS-BC as a photocatalyst. A 3% TiO2@PNS-BC was the best catalyst (compared to 1% and 2%) with a decolorization rate constant of 0.12741 min−1, ~ 1.5 × faster compared to the decolorization of MO using adsorption alone. Adsorption of MO conformed well to Langmuir isotherm. A maximum adsorption capacity (qmax) of 142.38 mg/g was achieved. Adsorption kinetics fitted well with the pseudo-second order (PSO) model. Results obtained indicated that biochar of PNS is a promising, cost-effective, and economical adsorbent.

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h−1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Enhanced photocatalytic activity of g-C[formula omitted]N[formula omitted]–n-p type flower-like ZnO/BiOBr heterojunction for hexavalent chromium and dye wastewater degradation

Construction of a composite g-C3N4, a 2D material with a layered structure, and flower-like ZnO/BiOBr heterojunction photocatalyst is an optimal strategy for the enhancement of photocatalytic performance to reduce the charge carrier recombination at the interface and increase the UV light absorption range to improve simultaneous oxidation of methyl orange (MO) and reduction of Cr(VI) using synthesized photocatalysts. Since the electron requirements for Cr(VI) reduction are theoretically higher than that of MO degradation, the amount of ZnO/BiOBr heterojunction catalyst and the different molar ratios of Bi/Zn for Cr(VI) degradation have been studied. The involved hydroxyl radicals (•OH) and superoxide anion radicals (•O2−) were also investigated. With the initial concentration of C0=20 mg/L of MO and C0=10 mg/L of Cr(VI) at pH 2, the optimized amount of 0.05 g g-C3N4-0.2 g ZnO/BiOBr-0.5 (molar ratio of Bi/Zn=0.5) and 0.05 g g-C3N4-0.4 g ZnO/BiOBr-2 (molar ratio of Bi/Zn=2) were observed to achieve 99.3 % in 130 min of dye decolorization (rate constant=0.036 min −1) and 96 % of Cr(VI) removal in 180 min (rate constant=0.0105 min −1), respectively, indicating more electron requirements observed for Cr(VI) reduction are higher than that of MO degradation theoretically and experimentally. The rate constants were 20 % higher than those of the compared experiments, demonstrating excellent photocatalytic activity that is superior to that of pristine composite either g-C3N4-ZnO-BiOBr or ZnO-BiOBr alone. After four reuse cycles, the photoactivity of the photocatalyst was not significantly reduced, demonstrating the stability of the synthesized g-C3N4-ZnO/BiOBr. Therefore, the synthesized g-C3N4-n-p type flower-like ZnO/BiOBr heterojunction catalyst has outstanding potential for the Cr(VI) removal, and MO dye decolorization. The results showed that the flower-like structure can promote the desorption of high levels of active surface oxygen and enhance reducibility.

Electrostimulation for promoted microbial community and enhanced biodegradation of refractory azo dyes

Excess azo dyes are detrimental to natural water systems and human health. To effectively treat dye wastewater, two-dimensional cylindrical electrodes were introduced into traditional biofilm reactor (BR), and thus a novel two-dimensional biofilm electrode reactor (2D-BER) was developed. In the 2D-BER, at low current density from 0.53 ± 0.05 mA m-2 to 12.61 ± 1.24 mA m-2, the electrostimulation increased microbial growth; while at higher current density above 12.61 ± 1.24 mA m-2, the electrostimulation exhibited an inhibition effect to microorganisms. Microbial decolorization in the 2D-BER demanded the participation of co-substrate as carbon source, and the order of decolorization with different co-substrates was glucose > sucrose > starch. An appropriate concentration of glucose improved dye decolorization, but high level of glucose (1 g/L) resulted in a slight decline of decolorization. UV-Vis, FT-IR and GC-MS analysis showed that azo dye was firstly decomposed into various aromatic anilines and then degraded into small molecules. By analyzing the differences in the microbial communities in the 2D-BER and BR, it was found that the electrostimulation prompted the growth and proliferation of electroactive decolorization bacteria, such as Bellilinea, Desulfobulbus, Geobacter and Desulfovibrio, thus leading to high decolorization rate constant of 0.0313 h-1 in the 2D-BER. Considering the excellent decolorization due to the synergism of bioelectrochemistry and microbial catalysis, the electrostimulation technology shows good application prospects in azo dye wastewater treatment.

Degradation of Methyl Orange by ozone microbubble process with packing in the bubble column reactor

ABSTRACT The performance of the ozone microbubble(MB) process for the degradation of Methyl Orange (MO) in a bubble column reactor with added packing was investigated. The highest decolorization efficiency of 96.04% was achieved by the ozone MB process with packing, which was 10.17% and 62.02% higher than that of the ozone MB process without packing and the ozone millimeter bubble(MLB) process, respectively while keeping other operating parameters the same. In addition, the saturation gas holdup, ozone mass transfer coefficient, and decolorization rate constant of the ozone MB process with packing were 15.32%, 0.260 min−1, and 0.027 min−1, respectively, which were much better than those of the ozone MB process without packing and the ozone MLB process. The study also suggested that within a certain porosity range, the types of packings did not affect the performance of the ozone MB process in the degradation of MO. Moreover, the optimum operating conditions were initial concentration of MO of 30 mg/L, initial pH of 3, circulating liquid flow of 75 L/h, and ozone dosage of 0.56 mg/L. The decolorization efficiency was 99.28% within 120 min.

A novel multi array dielectric barrier discharge plasma gas diffuser for wastewater treatment: The role of reactive species

Employment of efficient and economical methods for recovery of water has come into sharp focus regarding the growing demand for fresh water which has led to water crisis in a recent past. In this respect, cold atmospheric plasma technology has recently attracted scholars’ attention due to its various chemical and physical effects which can contribute to the removal of contaminations in wastewater. Although the energy efficiency and the rate of pollution elimination from water have been studied extensively, only few studies have been conducted on reactive species that play a major role in eliminating pollution. We studied the chemical reactive species involved in the decomposition of crystal violet (CV), a model organic compound, by a novel multi array dielectric barrier discharge (MADBD) plasma gas diffuser. The plasma generated gas mixture immediately contacts with the water in the form of gas bubbles to insure a good mass transfer between short and long live reactive species and water. Effects of operating parameters including electrode length, input power, flow rate, and solution volume over CV decolorization and energy efficiency were investigated. Experimental results showed that for the best operating conditions decolororization, energy efficiency, and CV decolorization rate constant were 95%, 7.8 g/kWh, and 2.83 min−1, respectively. An investigation of positive control experiments and the effect of scavengers of relevant reactive species reveal that the most key reactive species leading to the CV decolorization in MADBD plasma was ozone (O3) while short live species and reactive nitrogen species had small effect on CV degradation.

Optimization of Fenton Technology for Recalcitrant Compounds and Bacteria Inactivation

In this work, the Fenton technology was applied to decolorize methylene blue (MB) and to inactivate Escherichia coli K12, used as recalcitrant compound and bacteria models respectively, in order to provide an approach into single and combinative effects of the main process variables influencing the Fenton technology. First, Box–Behnken design (BBD) was applied to evaluate and optimize the individual and interactive effects of three process parameters, namely Fe2+ concentration (6.0 × 10−4, 8.0 × 10−4 and 1.0 × 10−3 mol/L), molar ratio between H2O2 and Fe2+ (1:1, 2:1 and 3:1) and pH (3.0, 4.0 and 5.0) for Fenton technology. The responses studied in these models were the degree of MB decolorization (D%MB), rate constant of MB decolorization (kappMB) and E. coli K12 inactivation in uLog units (IuLogEC). According to the results of analysis of variances all of the proposed models were adequate with a high regression coefficient (R2 from 0.9911 to 0.9994). BBD results suggest that [H2O2]/[Fe2+] values had a significant effect only on D%MB response, [Fe2+] had a significant effect on all the responses, whereas pH had a significant effect on D%MB and IuLogEC. The optimum conditions obtained from response surface methodology for D%MB ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 1.0 × 10−3 mol/L and pH = 3.2), kappMB ([H2O2]/[Fe2+] = 1.7, [Fe2+] = 1.0 × 10−3 mol/L and PH = 3.7) and IuLogEC ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 7.6 × 10−4 mol/L and pH= 3.2) were in good agreement with the values predicted by the model.

Bismuth Oxide Prepared by Sol-Gel Method: Variation of Physicochemical Characteristics and Photocatalytic Activity Due to Difference in Calcination Temperature

Research on synthesis of bismuth oxide (Bi2O3) using sol-gel method with varying calcination temperatures at 500, 600, and 700 °C has been done. This study aims to determine the effect of calcination temperature on the characteristics of the obtained products which encompasses crystal structure, surface morphology, band-gap energy, and photocatalytic activity for the decolorization of methyl orange dyes through its kinetic study. Bismuth oxide prepared by sol-gel method was undertaken by dissolving Bi(NO3)3·5H2O and citric acid in HNO3. The mixture was stirred then heated at 100 °C. The gel formed was dried in the oven and then calcined at 500, 600, and 700 °C for 5 h. The obtained products were a pale yellow powder, indicating the formation of bismuth oxide. This is confirmed by the existence of Bi–O and Bi–O–Bi functional groups through FTIR analysis. All three products possess the same mixed crystal structures of α-Bi2O3 (monoclinic) and γ-Bi2O3 (body center cubic), but their morphologies and band gap values are different. The higher the calcination temperature, the larger the particle size and the smaller the band gap value. The accumulative differences in characteristics appoint SG700 to have the highest photocatalytic activity compared to SG600 and SG500 as indicated by its percent degradation value and decolorization rate constant.

Electrocatalysis enhancement of α, β-PbO2 nanocrystals induced via rare earth Er(III) doping strategy: Principle, degradation application and electrocatalytic mechanism

Novel Ti/Sb2O3–SnO2/Er–PbO2 anodes were fabricated based on doping Er ions into the PbO2 crystal and enhanced electrocatalytic degradation efficiency for organic pollutants was achieved successfully. The doping principle, possible degradation pathway of methylene blue and electrocatalytic mechanism have been discussed in depth. Based on the comprehensive analysis of crystal parameters by X-ray diffraction (XRD) results and typical formulas, the doping principle was confirmed to be the partial substitution of Pb ions by Er ions in PbO2 nanocrystal and might form point defects. Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) investigation indicated that the Ti/Sb2O3–SnO2/Er–PbO2 anodes possessed higher oxygen overpotential and better conductivity than undoped electrodes. The optimum conditions for the degradation of methylene blue were obtained via studying the effects of different parameters, such as electrolyte concentration (0.01–0.4 M Na2SO4), current density (20–60 mA cm−2), initial methylene blue concentration (10–70 mg L−1) and initial pH (3–11). At the optimum conditions, the total organic carbon (TOC), the decolorization rate constant (kdec) and the energy consumption (EC) reached up to 65.34%, 0.036 min−1 and 0.08 (kWh(gTOC))−1, respectively. Moreover, the electrocatalytic degradation mechanism of the Ti/Sb2O3–SnO2/Er–PbO2 anodes to methylene blue was proposed to be that, the presence of point defects induced an increase of electron transport tunnels, and promoted the production of more hydroxyl radicals (OH) and SO4-. The possible electrocatalytic mineralization pathway of methylene blue at Ti/Sb2O3–SnO2/Er–PbO2 anodes was also speculated by UV–visible absorption spectroscopy, gas chromatography combined with mass spectrometry (GC-MS) and liquid chromatography combined with mass spectrometer (LC-MS). This work will provide significant references for exploring the mechanism between doped electrodes materials and electrocatalytic degradation performance.

The application of thermally activated persulfate for degradation of Acid Blue 92 in aqueous solution

Thermally activated persulfate (TAP) was applied for the degradation of Acid Blue 92 (AB92) dye in its aqueous solution. The effects of pH (3–11), temperature (298–333 K), contact time (15–75 min), sodium persulfate (SPS) concentration (0.05–0.5 mM) and initial AB92 concentration (50–400 mg/L) on the degradation of AB92 using TAP were examined. The initial and residual AB92 concentrations were determined spectrophotometrically at the wavelength of 260 nm and the dye mineralization was examined via the total organic carbon analysis. In addition, the chemical oxygen demand was also measured. The activation energy (Ea) of AB92 degradation was calculated as 17.38 kJ mol−1 based on the Arrhenius equation. Maximum degradation efficiency of 86.47% was reached after 75 min of treatment at a pH of 5, AB92 concentration of 200 mg/L, SPS concentration of 0.5 mM and temperature of 333 K. The degradation efficiency declined with the addition of different sodium chloride concentrations and organic radical scavengers. AB92 degradation was reduced from 86.5 to 74%, 65, and 59.1% using ethylenediaminetetraacetic acid, tert-butanol, and ethanol, respectively. A kinetic model was also developed to estimate the pseudo-first-order constants as a function of the main operational parameters (initial dye concentration and TAP concentration). Decolorization rate constants (k) of 0.0009, 0.001, 0.0012, 0.0014, and 0.0018 min−1 were obtained at 303, 308, 313, 328, and 333 K, respectively, using the Langmuir–Hinshelwood kinetic model. The results obtained indicate that the TAP degradation process has great potential for the reduction of azo dyes in aqueous environments.

Bioelectrochemical decolorization of a reactive diazo dye: Kinetics, optimization with a response surface methodology, and proposed degradation pathway

Bioelectrochemical systems (BESs) have shown great potential for azo dye removal. However, comprehensive evaluation of the bioelectrochemical decolorization performance for reactive diazo dyes remains limited, particularly the kinetics and operation parameter optimization. This study evaluated the decolorization of the diazo dye Reactive Black 5 (RB5) in BESs, particularly with regard to kinetics, parameter optimization using response surface methodology (RSM), and the degradation pathway. The results indicated that the pseudo–first–order kinetic rate constant of RB5 decolorization increased from 0.023 ± 0.001 to 0.146 ± 0.008 h−1 with a decrease in cathode potential from −400 mV to −500 mV. RSM optimization suggested that the linear effects of RB5 concentration, cathode potential and hydraulic retention time (HRT), interaction of RB5 concentration with cathodic HRT, and the quadratic effect of cathodic HRT were most influential on the bioelectrochemical decolorization of RB5. Further, the decolorized RB5 products in the BESs were characterized by ultraviolet–visible spectrophotometry, Fourier-transform infrared spectroscopy, and liquid chromatograph–mass spectrometry. From this, a potential decolorization mechanism is proposed based on cleavage of azo bonds.

Adsorption-Induced Dye Stability of Cationic Dyes on Clay Nanosheets.

Rhodamine 6G (R6G) was adsorbed on smectite clays, a natural montmorillonite, a synthetic saponite, and synthetic hectorites, and the decolorization of the dyes upon visible light irradiation was examined for aqueous suspensions and cast films. Excellent dye stability was achieved when a natural montmorillonite was used. Apart from R6G, better photostability was also achieved when the tris(2,2'-bipyridine)ruthenium(II) complex was adsorbed on a natural montmorillonite. The excited state of the dye was quenched efficiently by the impurities in the natural montmorillonite. From the relationship between the excited-state quenching (as derived from photoluminescence quantum efficiency and photoluminescence intensity) and the decolorization rate constant, the quenching of the excited state of the dye adsorbed on the natural montmorillonite was proposed as the important mechanism for the stabilization of dyes upon photoirradiation.

A comparative study of the decolorization capacity of the solar-assisted Fenton process using ferrioxalate and Al, Fe-bentonite catalysts in a parabolic trough reactor

Abstract In this work, the decolorization efficiency of Reactive Red 120 (RR120) synthetic solution using ferrioxalate (CuOFeB) and Al, Fe-bentonite (AlFeB) catalysts in the solar-assisted Fenton process was evaluated, as well as impact of H2O2 photolysis on the process efficiency.The photo-Fenton oxidation of dye has been investigated using a concentrating solar parabolic reactor with constant solar radiation of 550 W/m2 and 950 W/m2 for spring and summer periods, respectively. Experimental data has proved that photolysis of hydrogen peroxide has an important role in the process of decolorization, achieving a decolorization efficiency over 80.78% at pH 7. Under the optimal reaction conditions, both catalysts showed a good stability in the processes with dye removal over 90%. The mineralization efficiency depends on the intensity of the solar radiation, wherein ∼50% was achieved under the higher solar intensity. Comparing reaction rate it is important to note that the larger specific surface area of AlFeB (155.83 m2/g) makes him a superior catalyst and thus solar-assisted Fenton process with this catalyst fast and efficient. Based on the decolorization rate constants, the examined processes can be placed in the following order: AlFeB (950 W/m2) > AlFeB (550 W/m2) > CuOFeB (950 W/m2) > CuOFeB (550 W/m2). These findings are confirmed on real effluent, whereby a greater degree of decolorization (91.89%) and mineralization (43%) has been achieved with AlFeB catalyst compared to CuOFeB (30.09% and 15%) during the process.

Enhanced photocatalytic degradation of textile wastewater using Ag/ZnO thin films

In this work, photodegradation of a synthetic textile wastewater composed of a mixture of three reactive azo dyes (RO 122, RR 195 and RY 145) was performed using silver doped zinc oxide (Ag/ZnO) thin films. The photocatalyst preparation was conducted through sol-gel method and was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and ultraviolet-visible (UV–vis) spectroscopy. The photocatalytic activity of Ag/ZnO thin film was assessed by measuring the decolorization rate constant of the dyes mixture spectrophotometrically. The chemical structure of each dye influences the photodegradation rate either in mixture or in individual dyes solutions. Several parameters which influence photocatalytic degradation such as catalyst dose, dyes concentrations as well as addition of hydrogen peroxide as an electron acceptor have been studied. The results revealed that these parameters should be optimized to obtain the maximum photocatalytic degradation.

Synergistic effect of microbubbles and activated carbon on the ozonation treatment of synthetic dyeing wastewater

Abstract The performance of catalytic microbubble (MB) ozonation using a commercial granular activated carbon (AC) as catalyst in synthetic acid red 3R wastewater treatment was more efficient than that of coarse bubble (CB) and MB ozonation alone. The ozone mass transfer coefficient, ozone decomposition coefficient, decolorization rate constant, TOC removal rate constant, and ozone reaction efficiency achieved in catalytic MB ozonation were 0.253 min−1, 0.093 min−1, 0.342 min−1, 0.0242 min−1 and 0.128 mg(TOC removed)/mg(ozone consumed), respectively. The average ozone utilization efficiency in catalytic MB ozonation was as high as 98.3%. The synergistic effect of collapsing ozone MBs and catalytic activity of AC enhanced hydroxyl radicals ( OH) oxidation in catalytic MB ozonation which provided about 75% of oxidative capacity for TOC removal, even at a low pH. The enhanced OH oxidation was crucial for the mineralization of acid red 3R in catalytic MB ozonation where some OH scavengers could make TOC removal less efficient, especially Na2CO3. In addition, the catalytic activity of this commercial AC seemed stable after five recycling cycles. UV–Vis spectra and GC–MS analyses indicated that acid red 3R was oxidized-degraded by a pathway of azo bond cleavage, formation of naphthalene- and benzene-type compounds, further generation and final mineralization of small organic acids, which initially reduced the pH and increased the value again during catalytic MB ozonation. Therefore, the catalytic MB ozonation with commercial granular AC was a promising solution for wastewater treatment by ozonation process.

KINETIC BEHAVIOR OF SOME AZO DYES DECOLORIZATION BY VARIATION OF ZINC OXIDE AND TITANIUM DIOXIDE CONCENTRATIONS

The decolorization of three monoazo dyes (acid orange 7, direct orange 34, and methyl orange), one diazo dye (direct yellow 86) and one tetraazo dye (direct red 80) were mediated by n-type semiconductors as ZnO and TiO2 under pseudo-first order conditions at 30 oC. The decolorization rate constants of these azo dyes were determined, varying the semiconductor concentration for the majority of them from 1.0 to 10.0 g L-1. In general, the highest rate constants were displayed for ZnO. This work elucidates that the decolorization capacity depends on the charge, structure, and adsorption of the azo dye on the semiconductor surface as well as the agglomeration of the photocatalyst particles.

Electro-enhanced goethite activation of peroxydisulfate for the decolorization of Orange II at neutral pH: Efficiency, stability and mechanism

The decolorization of Orange II by an electro-enhanced goethite (α-FeOOH) activating peroxydisulfate (PDS) process (EC/α-FeOOH/PDS process) is reported in this study. Sulfate radicals was produced by activating PDS with Fe(II), which was generated continuously from the cathodic reduction of Fe(III) on α-FeOOH surface. The decolorization of Orange II showed little dependence on the initial pH. The comparison of Orange II decolorization under different systems was investigated. The surface properties of α-FeOOH before and after reaction were investigated by X-ray Photoelectron Spectroscopy (XPS). The radical species generated in EC/α-FeOOH/PDS process were determined by Electron Paramagnetic Resonance (EPR). On the basis of the results, the mechanism of Orange II decolorization in EC/α-FeOOH /PDS process was proposed. The catalyst α-FeOOH maintained its high activity during repeated batch experiments. Response surface methodology (RSM) based on Box–Behnken statistical experiment design (BBD) was applied to analyze the experimental variables. The response surface methodology models were derived from the experimental results and the response surface plots of the pseudo-first-order decolorization rate constant were developed accordingly.

Photoassisted Electrochemical Treatment of Azo and Phtalocyanine Reactive Dyes in the Presence of Surfactants.

An electrochemical treatment (EC) was applied at different intensities to degrade the chromophoric groups of dyes C.I. Reactive Black 5 (RB5) and C.I. Reactive Blue 7 (Rb7) until uncolored species were obtained. Decolorization rate constants of the azo dye RB5 were higher than the phtalocyanine Rb7 ones. In addition, the EC treatment was more efficient at higher intensities, but these conditions significantly increased the generation of undesirable by-products such as chloroform. The combination of EC with UV irradiation (UVEC) drastically minimized the generation of chloroform. The photo-assisted electrochemical treatment was also able to achieve decolorization values of 99%. Finally, mixtures of dyes and surfactants were treated by EC and UVEC. In the presence of surfactants, the decolorization kinetic of dyes was slowed due to the competitive reactions of surfactants degradation. Both methods achieved total decolorization and in both cases, the generation of haloforms was negligible.

Decoloration Kinetics of Waste Cooking Oil by 60Co γ-ray/H2O2

In order to decolorize, waste cooking oil, a dark red close to black solution from homes and restaurants, was subjected to 60Co γ-ray/H2O2 treatment. By virtue of UV/Vis spectrophotometric method, the influence of Gamma irradiation to decoloration kinetics and rate constants of the waste cooking oil in the presence of H2O2 was researched. In addition, the influence of different factors such as H2O2 concentration and irradiation dose on the decoloration rate of waste cooking oil was investigated. Results indicated that the decoloration kinetics of waste cooking oil conformed to the first-order reaction. The decoloration rate increased with the increase of irradiation dose and H2O2 concentration. Saponification analysis and sensory evaluation showed that the sample by 60Co γ-ray/H2O2 treatment presented better saponification performance and sensory score. Furthermore, according to cost estimate, the cost of the 60Co γ-ray/H2O2 was lower and more feasible than the H2O2 alone for decoloration of waste cooking oil.