Decolorization Of Indigo Carmine Research Articles

Indigo carmine biodegradation by endophytic Microbacterium zeae K5: Enzymatic insights, degradation mechanism, and ecotoxicity analysis

The enormous amount of colored effluent release from dying industries into fresh and marine reservoirs, causing ecotoxicity and serious health problems. Pertaining to this, the current research emphasis on the decolorization and degradation treatment of Indigo carmine (IC). The decolorization of IC with endophytic Microbacteium zeae K5, isolated from the root of the Salix purpurea plant was studied. In a minimal salt medium with shaking, full dye decolorization (400 mg/L) was achieved within a 24 h incubation period. During dye degradation, the activities of enzymes such as laccase (12.02 U/g), manganese peroxidase (4.23 U/g), and quinone dehydrogenase (0.09 U/g) were also observed. The biodegradation of IC into isatin sulfonic acid and isatin was confirmed by UV–VIS spectrophotometry and GC-MS analysis of dye samples extracted with ethyl acetate. Finally, phytotoxicity studies revealed that the IC degraded metabolites toxicity was lower than that of the parent dye compound. The current study demonstrated isolate M. zeae K5 has ability to efficiently break down IC, indicating its potential for future bioremediation uses.

Synthesis and Characterization of Cross-Linked Aggregates of Peroxidase from Megathyrsus maximus (Guinea Grass) and Their Application for Indigo Carmine Decolorization.

We present the synthesis of a cross-linking enzyme aggregate (CLEAS) of a peroxidase from Megathyrsus maximus (Guinea Grass) (GGP). The biocatalyst was produced using 50%v/v ethanol and 0.88%w/v glutaraldehyde for 1 h under stirring. The immobilization yield was 93.74% and the specific activity was 36.75 U mg-1. The biocatalyst surpassed by 61% the free enzyme activity at the optimal pH value (pH 6 for both preparations), becoming this increase in activity almost 10-fold at pH 9. GGP-CLEAS exhibited a higher thermal stability (2-4 folds) and was more stable towards hydrogen peroxide than the free enzyme (2-3 folds). GGP-CLEAS removes over 80% of 0.05 mM indigo carmine at pH 5, in the presence of 0.55 mM H2O2 after 60 min of reaction, a much higher value than when using the free enzyme. The operational stability showed a decrease of enzyme activity (over 60% in 4 cycles), very likely related to suicide inhibition.

Carbon Dots Modification Surface of Titanium Dioxide and Their Photocatalytic Activity

This work, we develop the efficient visible-light-responsive titanium dioxide photocatalyst using carbon dots as a sensitizer (C-dots/TiO2). C-dots was synthesized via a simple one-pot reaction by microwave-assisted pyrolysis method using orange juice as carbon precursors. C-dots/TiO2 samples were prepared by a facile route. Moreover, the micro-structure and optical properties of as-prepared C-dots/TiO2 have been evaluated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible diffuse reflection spectroscopy (DRS). The modification surface of TiO2 with carbon dots enhanced the light absorption in visible region. The photocatalytic properties of as-prepared pure TiO2 and C-dots/TiO2 were also explored indigo carmine decolorization under visible light. The photocatalytic results revealed that the C-dots/TiO2 exhibited higher catalytic performance than the pure TiO2 under visible light.

Evaluation of spatial distribution of the oxidation of glass beads simulating soil using high-voltage pulsed discharge

The spatial distribution of soil oxidation using a high-voltage pulse generator was evaluated using indigo carmine. The results showed that the amount of indigo carmine decolorization increased with increasing charging voltage and energy input. It was also found that the decolorization of indigo carmine occurred on the surface of the needle electrode, in the discharge path, and near the ground electrode. The probability of discharge penetrating soil increased with decreasing the gap length between the electrode tip and soil surface, which promoted the decolorization reactions. The amount of indigo carmine decolorization per volume decreased with increasing soil depth. When the soil depth was large, discharges reaching the ground electrode could not be confirmed. This suggests that the oxidation reaction of indigo carmine depends on a discharge that penetrates the soil.

Pyrolyzed synthesis of boron nitride for photocatalytic degradation of indigo carmine studies

A non-metal type photocatalytic layered boron nitride (BN) material was synthesized by precursor conversion hydrothermal process followed by adequate temperature pyrolysis. The characterization of BN was performed through various analytical instrumental techniques. The results show that a hexagonal crystal structure BN with a strong BN bond was formed. The photocatalytic decolorization of indigo carmine (IC) dye was examined using synthesized BN with influencing factors like time, pH, catalyst, and dye concentration under ultra-violet light (UV) illumination. The decolorization efficiency was found to be 88%. The optimization of operating parameters was investigated and also found a model equation of decolorization efficiency through response surface methodology (RSM) based box - behnken design (BBD). The photocatalytic decolorization mechanism was suggested based on the experiments performed.

Eco-friendly TEMPO/laccase/O2 biocatalytic system for degradation of Indigo Carmine: operative conditions and laccase inactivation.

The biocatalytic system laccase/TEMPO/O2 has attracted the attention of researchers over the past two decades. A variety of applications for the system include organic synthesis, modification of cellulose, and oxidative degradation of environmental contaminants. A rigorous and predictable quantitative assessment of the change in enzymatic activity under the influence of a mediator is important for such a system. In this study, the operative conditions for carrying out a model reaction for the degradation of the synthetic dye Indigo Carmine in the presence of Trametes versicolor laccase/TEMPO were determined and the enzyme inactivation under the action of a mediator and substrate was studied. The long-term stability of Trametes versicolor laccase was assessed and the regression model of the response surface of laccase activity under the influence of TEMPO was created. It has been shown that laccase is inactivated in the presence of TEMPO, but the addition of the dye, CuSO4 or CuCl2 reduces this effect. The system under study can be used repeatedly for the Indigo Carmine decolorization, however, a gradual falling rate during the process is observed from cycle to cycle. This is due to two reasons - firstly, a decrease in the enzyme activity with each batch and secondly, the consumption of the mediator (22% within 5 days). Relatively high enzyme activity (>40%) is maintained after 73 cycles (1 portion of IC contained 25 μM) using 500 μM TEMPO and 0.12 U mL-1 laccase. The laccase/TEMPO system has shown its effectiveness in the treatment of artificial wastewater containing high concentrations of Indigo carmine (0.5 g L-1). In this case, the dye solution becomes 100% colorless within 5 hours in the presence of dye bath components and within 7.5 hours in a buffer solution.

Co-immobilized spore laccase/TiO2 nanoparticles in the alginate beads enhance dye removal by two-step decolorization.

Combinatorial application of different dye removal methods with specific features can lead to a novel and robust decolorizing system. In this study the bacterial spore laccase and TiO2 nanoparticles were co-entrapped to enhance dye degradation. The optimum entrapment conditions were achieved in the presence of alginate 2% (w/v) and Ca2+ (0.2M), Cu2+ (0.05M) and Zn2+ (0.25M) as matric polymer and counterions, respectively. Immobilized laccase showed a wide range of pH and temperature stability in comparison to the free spores. The entrapped degradation systems include single laccase, single TiO2, laccase + TiO2 (one-step remediation), TiO2/laccase (two-step remediation), and laccase/TiO2 (two-step remediation) that result to the 22%, 26% 45.6%, 47.6%, and 69.3% indigo carmine decolorization in 60 min. In the kinetic studies, the half-life of indigo carmine (25 mg/l) in the remediation processes containing laccase, TiO2, laccase + TiO2, TiO2/laccase, and laccase/TiO2 was calculated as 173, 138, 161, 115, and 57 min, respectively. The degradation products by co-entrapped system were not toxic against Sorghum vulgare. The results showed two-step decolorization by co-entrapped spore laccase and TiO2 nanoparticles, including the pretreatment of dye by laccase, and then, treatment by TiO2 has potential for degradation of indigo carmine.

A novel composite silver nanoparticles loaded calcium oxide stemming from egg shell recycling: A potent photocatalytic and antibacterial activities

Industrial wastewater resulted from textile dyeing process is considered as a big environmental problem. Therefore, recycling of wastewater offers environmental and economic values specially if the materials used are resulted from recycling of other kinds of waste. From this point of view and for the first time this work deals with the study the wastewater recycling by calcium oxide resulted from eggshell recycling. Calcium oxide (CaO) nanocrystals were created by the thermal annealing of chicken egg shell at 1100 °C for 2 h s. Heat treatment at 200 °C in air for 2 h s of the resulted CaO with silver oxalate gave the novel composite, silver nanoparticles loaded calcium oxide (Ag-NPs @ CaO). By applying electronic spectra (UV–Vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy with the energy dispersion spectrum analysis (SEM-EDX) and transmittance electronic microscope (TEM), the materials were characterized. The energy band gap was calculated from the equation of Tauc for CaO and Ag-NPs@CaO and measured to be 2.1 and 2 eV, respectively. Indigo carmine (IC) as a model of photocatalytic decolorization was performed using both CaO and Ag@CaO nanoparticles under sunlight exposure. The impacts of various variables such as solution pH, dose quantity, temperature and irradiation time were studied. Both catalysts displayed an effective photocatalytic activity in IC decolorization but Ag@CaO composite displayed a stronger activity than CaO. The percentages of dye degradation were ≈99.21% and 99.45% in case of CaO and Ag@CaO, respectively. The antibacterial efficiency was measured against some Gram-negative and Gram-positive bacteria. Ag@CaO provided powerful weapons against the drug-resistant bacteria. These findings give a promising and economic strategy for all those who are interested in industries which involve dyeing process.

Magnetic Eu-doped MgFe2O4 nanomaterials: An investigation of their structural, optical and enhanced visible-light-driven photocatalytic performance

We report a facile route of Eu doped MgFe2O4 magnetic nanomaterial ferrite synthesis using Oxalyl Dihydrazide as photocatalyst via simple approach of combustion process. The doping concentration of Eu was varied from 0.1 to 5 mol% with the MgFe2O4 system. Eu doped MgFe2O4 photocatalysts were characterized and analyzed by varied analytical methods to determine its physicochemical properties. The visible light driven photocatalytic activity of Eu doped samples were studied for the photo decolorization of Indigo carmine (IC) dye in waste water treatment. Photoluminescence studies demonstrated the efficient charge carrier separation suggesting the potential use of present samples in fabricating white component of white light emitting diodes.The present results demonstrate the effect of doping europium on particle size, agglomeration, light absorption, band gap value and photocatalytic charge carrier dynamics, thereby providing a mechanistic insight in to the process. The Powder X-ray diffraction analysis revealed nano crystallanity with a crystallite size ranging 14–28 nm. The microscopic analysis confirmed the porous and voids morphology due to auto-ignition during the combustion reaction. The reusability test confirms a good photo-stability and recyclability. Hence, Eu doped MgFe2O4 is proposed as a potential candidate for waste water treatment.

Efficiency of glucose oxidase immobilized on tannin modified NiFe2O4 nanoparticles on decolorization of dye in the Fenton and photo-biocatalytic processes

Immobilized enzymes are significantly studied both environmental and textile industries. In this work, glucose oxidase was immobilized on the tannin coated NiFe2O4 magnetic nanoparticles for decolorization of indigo carmin. The as-synthesized all magnetic nanoparticles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–vis spectroscopy, Thermogravimetric analysis, Vibrating sample magnetometer and Scanning electron microscopy. The activity of the free and immobilized glucose oxidase in various temperature and pH values was investigated. Finally, the produced immobilized glucose oxidase was applied for decolorization of indigo carmine due to production of H2O2. The decolorization yields of indigo carmine are 98.6% and 37.6% of the glucose oxidase immobilized on tannin modified NiFe2O4 in presence of the both of UV-light and iron(II)chloride for 90 min, respectively. The results exude that the obtained photocatalysts exhibit excellent both photocatalytic efficiency and easy separation from dye solution by an external magnet.

Comparison of N‐Hydroxy Compounds as Mediators in Laccase‐Catalysed Decolorization of Indigo Carmine

AbstractA comparative study of N‐hydroxy compounds – violuric acid, 1‐hydroxybenzotriazole and N‐hydroxyphthalimide as the redox mediators during laccase‐catalyzed Indigo Carmine decolorization has been carried out. It is shown that the enzymatic oxidation of N‐hydroxy‐mediators to radicals >N‐O•, which act as a real oxidizing agent for indigo carmine, is a rate‐limiting stage. The effectiveness of N‐hydroxy compounds as the mediators in the Indigo Carmine decolorization in the presence of laccase Trametes versicolor increases in the following order: N‐hydroxyphthalimide < 1‐hydroxybenzotriazole < violuric acid. The main reason for the low activity of N‐hydroxyphthalimide is the low rate of generation of phthalimide‐N‐oxyl radicals in the process of oxidation by laccase of N‐hydroxyphthalimide, which is confirmed by inhibition of the studied process by ascorbic acid. The initiation rate corresponds to the total process rate and is equal to 4.20×10−8, 2.82×10−8, 2.90×10−9 M s−1 with the participation of violuric acid, 1‐hydroxybenzotriazole and N‐hydroxyphthalimide, respectively.

Comparison of indigo carmine decolorization by Pseudomonas aeruginosa and crude laccase enzyme from Funalia trogii.

The effects of incubation time, temperature, initial pH, and dye concentration on the indigo carmine decolorization activity of Pseudomonas aeruginosa ATCC 10145 and some factors on the decolorization potential of crude laccase enzyme obtained from Funalia trogii ATCC 200800 were comparatively investigated. This bacterium showed effective decolorization activity at all agitation and temperature values. Indigo carmine was greatly decolorized by P. aeruginosa at all pH values except pH 10. A decrease in decolorization activity occurred with increasing dye concentration, but this bacterium effectively decolorized the dye within 24 h. The decolorization process was through microbial metabolism, not biosorption. No decolorization or laccase activity could be obtained by the cell-free intracellular extract or culture filtrate of this bacterium. On the other hand, crude laccase effectively decolorized indigo carmine under highly acidic conditions, especially at pH 3.0 as 57% in 300 seconds. This activity decreased progressively due to the increase in pH values. In a short incubation period and at high temperature values, the crude laccase enzyme removed the color of the dye at 50 °C (56%), 60 °C (45%), and 70 °C (38%). These data are important for improving methods for decolorization of textile dyes used at high temperatures in various industrial applications.

Catalytic reactivity of new Ni(II), Cu(II) and Sn(II) complexes for decolorization of indigo carmine in aqueous solution, high efficiency of copper complex

A new Ni(II), Cu(II) and Sn(II) Schiff base complexes were synthesized in this work. The characterization of the new complexes is carried out by elemental analysis, FT‐IR, UV–Visible, 1H NMR and 13C NMR spectroscopy, conductance analysis, magnetic measurements and thermal gravimetric analysis. It was found that the ligand behaves as a dibasic bidentate which coordinated to the metal center through two deprotonated hydroxyl groups to form tetrahedral complex with Ni(II) and octahedral complex with Cu(II). The ligand acts as neutral bidentate through azomethine nitrogen and thiazol sulfur to form octahedral complex with Sn(II). The synthesized complexes are evaluated as catalysts for oxidative degradation of indigo carmine dye using H2O2 as oxidant and the efficiency of the catalysts is determined. The copper complex shows the best catalytic action with efficiency 92.17% after 25 min.

Improving the Indigo Carmine Decolorization Ability of a Bacillus amyloliquefaciens Laccase by Site-Directed Mutagenesis

Indigo carmine is a typical recalcitrant dye which is widely used in textile dyeing processes. Laccases are versatile oxidases showing strong ability to eliminate hazardous dyes from wastewater. However, most laccases require the participation of mediators for efficient decolorization of indigo carmine. Here we describe the improvement of the decolorization ability of a bacterial laccase through site-directed mutagenesis. A D501G variant of Bacillus amyloliquefaciens laccase was constructed and overexpressed in Escherichia coli. The laccase activity in the culture supernatant achieved 3374 U·L−1 for the mutant. Compared with the wild-type enzyme, the D501G exhibited better stability and catalytic efficiency. It could decolorize more than 92% of indigo carmine without additional mediators in 5 h at pH 9.0, which was 3.5 times higher than the wild-type laccase. Isatin sulfonic acid was confirmed to be the main product of indigo carmine degradation by UV-vis and LC-MS analyses.

Effective photocatalytic decolorization of indigo carmine dye in Moroccan natural phosphate–TiO2 aqueous suspensions

Heterogeneous photocatalysis is a significant green technology for application in water purification. In this study, the photocatalytic activity of NP–TiO2 based on Moroccan natural phosphate (NP) doped by titanium dioxide TiO2 was evaluated by photocatalytic decolorization of indigo carmine (IC) dye in aqueous solution as a model pollutant under UV light. The NP–TiO2 catalyst was characterized by XRD, FTIR and surface area. The effect of the calcination temperature of NP–TiO2, catalyst concentration, initial concentration of the IC, initial pH, initial hydrogen peroxide H2O2 concentration and coexisting ions on the photocatalytic decolorization of IC was investigated. The NP–TiO2 showed a significantly higher rate of degradation of IC, when compared to TiO2. After 125min of irradiation using a low intensity of UV-lamp (15W∗3 lamps=45W), 99% of IC solution (20mgL−1) was decolorized with 0.5gL−1 of the NP–TiO2 calcined at 600°C at pH=11. Therefore, this process can be developed as an economically feasible and environmentally friendly method to decolorize or treat dye wastewater using sunlight.

Reductive decolorization of indigo carmine dye with Bacillus sp. MZS10

Decolorization of indigo carmine (IC) dye with strain Bacillus sp. MZS10 and its mechanism was evaluated in the present study. The decolorization ratio of 87.31 ± 2.04% was achieved after cultivation of IC (0.1 g L−1) with Bacillus sp. MZS10 for 15 h in a 5 L stirred-tank fermenter. In the process of decolorization, metabolites derived from IC decolorization were analyzed by ultraviolet–visible spectroscopy, mass spectroscopy, and Fourier transform infrared spectroscopy, respectively. Based on the analyses of metabolites, a novel mechanism of decolorization of IC was suggested as follows: the CC and CO bonds of IC were broken and –CH bonds were generated via a reductive process. Then an indoline derivative, indoline sulfonic acid was produced during biotransformation of IC. Decolorization efficiency and mechanism shown by the strain provides insight on its potential application for the bioremediation of IC and production of indoline derivative.

Manganese peroxidase production from cassava residue by Phanerochaete chrysosporium in solid state fermentation and its decolorization of indigo carmine

Bioconversion of lignocellulosic wastes to higher value products through fungal fermentation has economic and ecological benefits. In this study, to develop an effective strategy for production of manganese peroxidase (MnP) from cassava residue by Phanerochaete chrysosporium in solid state fermentation, the stimulators of MnP production were screened and their concentrations were optimized by one-at-a-time experiment and Box–Behnken design. The maximum MnP activity of 186.38nkat·g−1 dry mass of the sample was achieved after 6days of fermentation with the supplement of 79.5mmol·L−1·kg−1 acetic acid, 3.21ml·kg−1 soybean oil, and 28.5g·kg−1 alkaline lignin, indicating that cassava residue is a promising substrate for MnP production in solid state fermentation. Meanwhile, in vitro decolorization of indigo carmine by the crude MnP was also carried out, attaining the ratio of 90.18% after 6h of incubation. An oxidative mechanism of indigo carmine decolorization by MnP was proposed based on the analysis of intermediate metabolites with ultra-high performance liquid chromatography and gas chromatography tandem mass spectrometry. Using the crude MnP produced from cassava residue for indigo carmine decolorization gives an effective approach to treat dyeing effluents.

Enhanced expression of an industry applicable CotA laccase from Bacillus subtilis in Pichia pastoris by non-repressing carbon sources together with pH adjustment: Recombinant enzyme characterization and dye decolorization

In this study, protease-deficient Pichia pastoris strain SMD1168H was selected for heterologous expression of the CotA laccase from Bacillus subtilis. Four non-repressing carbon sources were individually applied to facilitate the recombinant laccase production. An up to 76-fold increase in laccase activity was achieved through sorbitol addition in combination with pH adjustment. Recombinant CotA (rCotA) demonstrated a remarkable stability under alkaline conditions, the enzyme retained 637% and 94.37% of its initial activity after 10-day incubation at pH 9.0 and 10.0, respectively. The rCotA laccase showed an outstanding thermostability and exhibited higher tolerance towards organic solvents than the spore laccase. The Km and kcat values of rCotA laccase for ABTS were of 146.4±2.7μM and 14.4±0.1s−1 and for SGZ of 12.7±2.6μM and 6.9±0.6s−1, respectively. A repeated-batch decolorization experiment was carried out at pH 10.0, 40°C to evaluate the capacity of rCotA for repetitive decolorization of indigo carmine under alkaline conditions. During the first six repeated cycles, more than 95% decolorization was observed in 10min and total color was removed within one hour. The decolorization efficiency stayed above 90% after twenty decolorization cycles.

Degradation of Indigo Carmine and Reactive Black 5 Dyes with Sb2O5-Doped Ti/RuO2-ZrO2 DSA in a Parallel-Plate Flow Reactor Via Active Chlorine

Wastewater from the textile industry is highly colored and of a complex and variable nature. The substantial amount of dyestuffs used in the dyeing stage of textile manufacturing processes represents an increasing environmental danger due to their refractory nature [1]. The treatment of textile wastewater by conventional methods such as biological and chemical processes or their combination are in common practice but have several drawbacks, e. g. inefficient color removal and/or the formation of toxic by-products [2]. On the other hand, electrochemical oxidation is a very promissory process for refractory pollutants degradation since no chemical reagents are needed and no secondary wastes are formed.In the present study, electrochemical degradation experiments were conducted to degrade a textile dyes namely indigo carmine (IC) and reactive black 5 (RB). A FM01-LC reactor was used to investigate the effect of various operating parameters using a dimensionally stable anode (DSA, Sb2O5-doped Ti/RuO2-ZrO2). The oxidation of IC and RB takes place in the bulk solution with electrolytically generated active chlorine (chlorine, hypochlorite ion and hypochlorous acid). Figure 1 shows the normalized color decay. For the indigo carmine decolorization occurs in 80 min, whereas for the reactive black it takes 2 h. The difference in the time of decolorization is due to the structure of each dye the structure of reactive black 5 is larger than that of indigo carmine.[1] Balcioglu I.A., Arslan I. and Sacan T. Homogenous and heterogenous advances oxidation of two commercial reactive dyes, Environment technology, 22 (2001), pp. 813-822.[2] Rajkumar D., Joo Song B. and Guk Kim J., Electrochemical degradation of Reactive Blue 19 in chloride medium for the treatment of textile dyeing wastewater with identification of intermediate compounds, Dyes and Pigments, 72 (2007), pp. 1-7.

Effect of oxygen gas on the decomposition of dye by pulsed discharge in water droplet spray

AbstractThe effect of O2 on the decolorization of indigo carmine and on the production of dissolved species such as \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} , \mathrm{NO}_{3}^{-} $ \end{document}, O3, and H2O2 in the treatment water by pulsed discharges in a water droplet spray was investigated by controlling the O2/N2 ratios as carrier gases in the reactor. The decolorization rate gradually increased with a rise in the O2 ratio, which reached a constant value in the range of 50 to 90% for the O2 ratio and decreased in pure O2. The maximum value was about two times that of 20% for the O2 ratio. The decolorization efficiency was not affected by the gas flow rate in the range of 4 to 50 L/min. \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} $ \end{document} in the treatment water was detected only in pure N2, but \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{3}^{-} $ \end{document} was produced in O2/N2. \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} $ \end{document} added to the treatment water was not oxidized in pure N2, but was perfectly converted to \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{3}^{-} $ \end{document} in O2/N2. These results implied that the hydroxyl radicals produced in the gas phase do not directly contribute to the oxidation of substances in water. The O3 concentration gradually increased with a rise in the O2 ratio, whereas the H2O2 concentration decreased. In the range of 50 to 80% for the O2 ratio, the O3 and H2O2 concentrations stayed at approximately constant values, similar to the trend of the decolorization rate. The rate constants for various gas mixing ratios for O2/N2 were determined from a kinetic study. These results suggest that hydroxyl radicals produced in the treatment water by the chain reactions of O3 and hydroperoxy radical (HO2·) play an important role in the decomposition of molecules in water. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 10–23, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22284