A novel immobilized visible light-active photocatalyst (TiO₂/polyvinyl alcohol after thermal treatment (T-PVA)/cordierite honeycomb (CHC)) was successfully prepared by a simple and convenient method combining sol–gel and thermal treatment using tetrabutyl titanate (TBOT) as the titanium source, polyvinyl alcohol (PVA) as the precursor of conjugated polymer, and CHC as the support. The synthesized photocatalyst was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, and field emission scanning electron microscopy. The results showed that PVA was dehydrated to produce conjugated unsaturated T-PVA. The T-PVA not only extended the response spectrum of TiO₂ to visible light region, but also strengthened the adhesion of TiO₂ to CHC. The TiO₂/T-PVA/CHC showed both outstanding adsorption properties and excellent photocatalytic performance under visible light on the decolorization of Rhodamine B. Over eight cycles, the photocatalyst continued to maintain perfect photocatalytic activity, showing good stability.

The growth of white-rot fungus Pleurotus eryngii F032 in a suitable medium can degrade an azo dye Reactive Black 5 (RB5), because of its ability to produce ligninolytic enzymes such as lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase that able to degrade and transform the complex structure of the dye into a less toxic compound. The effect of environmental factors such as initial concentration of Reactive Black 5, pH, temperature of growth medium, surfactant (Tween 80), and agitation were also investigated. The productions of ligninolytic enzymes were enhanced by increasing the white-rot fungi growth in optimum conditions. The decolorization of Reactive Black 5 were analyzed by using UV–vis spectrophotometer at the maximum absorbance of 596 nm. The white-rot fungus, P. eryngii F032 culture exhibited 93.56 % decolorization of 10 mg/L RB5 within 72 h of incubation in dark condition with agitation. The optimum pH and temperature for the decolorizing activity was recorded at pH 3 and 40 °C, respectively. The addition of surfactant (Tween 80) increased the decolorization to 93.57 % and agitation of growth medium at 120 rpm enhanced the distribution of nutrients to the fungus thus optimized the enzymatic reaction that resulted maximum decolorization of RB5 which was 93.57 %. The molecular docking studies were performed using Chimera visualization software as to analyze the decolorization mechanism of RB5 at molecular level.

Dual-effects of adsorption and photodegradation over titania, silica embedded titania, silica and commercial Degussa P-25 samples were studied for the decolourization of methylene blue in aqueous medium. Silica embedded titania and silica were prepared using inexpensive polymeric version of ethyl silicate as a source of silica. Catalysts were characterized by X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy and low temperature (77 K) nitrogen adsorption measurements. Among all the catalysts, silica embedded titania has exhibited faster decolourization of methylene blue solution on account of the enhancement of adsorption followed by degradation. An amount of the catalyst and the initial dye concentration of MB solution were found to influence the decolourization activity. Compared to titania catalyst, silica embedded titania and Degussa P-25 have shown the red shift in their UV-Vis spectrum. The experimental data of the reaction fitted well to the pseudo first order kinetic model. In present studies, the adsorption mechanism for the decolourization of MB solution was found to be applicable for an intra particle diffusion model. © 2013 Springer Science+Business Media Dordrecht.

Pyrite, FeS₂, is the most common sulfide mineral. The aim of this work was to assess the oxidative ability of H₂O₂ in presence of natural pyrite by employing reactive black 5, acid red GR, and cationic red X-GRL as model pollutants. The effects of H₂O₂ dosage, pyrite loading, and initial pH on reaction were investigated. The results reveal that natural pyrite-promoted H₂O₂ has a great activity in the decoloration of azo dyes. About 85 % of reactive black 5 and acid red GR can be removed within 10 min when 0.3 mM H₂O₂ and 0.3 g/L pyrite are used with initial pH values ranging from 6.32 to 6.96. The discoloration efficiencies are demonstrated to be less sensitive to the initial solution pH value. Approximately 90 % of discoloration for reactive black 5 and acid red GR can be achieved when initial pH value ranges from 2 to 10. Ion leaching experiments show that high levels of ferrous iron and sulfate can be detected when natural pyrite is added to dye solution alone. To gain an understanding of the reaction mechanism and the role of natural pyrite takes in these processes, techniques including scanning electron microscope, X-ray diffraction, and X-ray photoelectron were employed to characterize the solid sample and ion leaching experiments were also carried out. Results indicate that the determined high levels of ions have resulted from the dissolution of FeSO₄·H₂O formed on the surface of pyrite and the homogeneous Fenton reaction initiated by ferrous iron in presence of H₂O₂ is mainly responsible for the observed fast color removal rate.

The decolorization and degradation of anionic sulphonated azo dye (Reactive orange 16 (RO16)), which is suspected to be carcinogenic, were investigated using ozone. The decolorization process of the reactive dye was carried out by bubbling ozone at the bottom of a bubble column reactor containing the dye solution. The effect of pH, reaction time, dye concentration, ozone concentration, and decolorization time was studied. Also, degradation products and possible degradation mechanism were investigated. The results showed that ozonation was a highly effective way to remove color from wastewater. The color of a synthetic waste solution containing water-soluble reactive dye was reduced to 69.69 % under the basic condition (pH 12), with complete RO16 degradation occurring in 8 min. Ozone consumption continued for a further 16 min after which time most of the degradation reactions were complete. Kinetic studies showed that direct ozonation of the aqueous dyes represented a pseudo-first-order reaction with respect to the dye. The apparent rate constant increased with both the applied ozone dose and higher pH values and declined logarithmically with the initial dye concentration. Intermediates such as 6-acetylamino-3-aminonaphthalene-2-sulfonic acid, 2-(4-nitrosophenyl) sulfonylethyl hydrogen sulfate, and 6-acetamido-4-hydroxy-3-nitroso naphthalene-2-sulfonic acid were detected by gas chromatograph coupled with mass spectrometry in the absence of pH buffer, while nitrate and sulfate ions and formic, acetic, and oxalic acids were detected by ion chromatography.

Large quantities of pollutants such as phthalocyanine which are difficult to degrade by conventional techniques are discharged by the textile industry. Advanced oxidation processes have been shown to be capable of degrading organic compounds and removing colour from the industrial wastewater. In this research, the hydrogen peroxide (H2O2)/UV process under different operative variables has been checked using a photoreactor lab plant to analyse its behaviour in the removal of colour and chemical oxygen demand of synthetic textile wastewater with a pigment named phthalo blue 36:3 (C.I. PB15:3). Different pH and H2O2 concentrations were tested to find the better conditions for the UV/H2O2 process suitable for this kind of pollution; this was carried out as an initial study of the operative variables for the scale-up of this technology. The research has shown that with pH 7 and 5 g/L of H2O2, this process can get an organic matter removal higher than 89 % and a colour removal near 70 %. Different kinetic models of organic matter removal have been checked to analyse and predict the influence of time on the process to model similar conditions of pollution. The high correlation between empirical and theoretical data model was pseudofirst order (R 2 = 0.989 ± 0.007). © 2013 Springer Science+Business Media Dordrecht.

A novel dye degrading bacterium capable of decolorizing and mineralizing four different dyes (Methyl red, Orange II, Direct red 80, and Direct blue 71) was isolated from textile industrial wastewater using the selective enrichment technique. The bacterium was identified as Pseudomonas aeruginosa. More than 80 % decolorization of Direct red 80 was obtained under microaerophilic conditions in 48 h, whereas only 10 % color removal was obtained under oxic conditions at the same time. Subsequent aeration of the decolorized medium resulted in the mineralization of the metabolic intermediates generated after azo bond cleavage by P. aeruginosa as confirmed by total organic carbon content and high-performance liquid chromatography analyses. The degradation products were characterized by Fourier transform infrared spectrometer and nuclear magnetic resonance techniques whereas the biotoxicity profile of the samples were evaluated using the brine shrimp lethality test assay. Data from this study provide evidence of dye mineralization and detoxification by a monoculture of P. aeruginosa in successive microaerophilic/oxic stages. © 2013 Springer Science+Business Media Dordrecht.

Textile dye Victoria Blue-B (VB-B) was approached in two different ways: one to get rid of the color for its easy disposal to the environment, and the other is to reuse the decolorized water for coloring the same dye. Shewanella decolorationis (MBTD16) isolated from Dona Paula Bay, identified by 16S rRNA gene and its action over decolorization was monitored by Fourier transform infrared spectroscopy, UV–Vis spectrum, and a color scanner. Dye removal index increased L*, a*, and b* to 91.585, −2.856, and −0.132 against 62.29, −4.93, and −20.75 within 42 h as a first report. A maximum extent of decolorization (94.83 %) could be achieved with minimum dye concentration of 50 mg L⁻¹. The colored water treated by free and immobilized bacterial cells tested to reuse (VB-B dye) could give 35–50 % more color than the original. Process parameters optimized to achieve maximum decolorization indicated pH 7, temperature 32 ± 2 °C, inoculum size 8 % with co-substrates of glucose and yeast extract 5 g L⁻¹ for its supremacy. Synthesis of lignin peroxidase and tyrosinase augmented in strain S. decolorationis only after being exposed into the dye signifies the enzymes in decolorization, and it was confirmed through one-way ANOVA. Results obtain by this work could suggest that S. decolorationis can be used very well to decolorize the textile dye, and the same water could be recycled to get back its original color by adding around half the quantity of dye. Thus, by the use of water, dye and pollution levels could be minimized.

A total of three fungal isolates from samples collected at spent wash disposal area were screened for their ability to degrade melanoidin. Distillery molasses spent wash was decolorized, and its chemical oxygen demand (COD) was reduced in immobilized fungal bioreactor (IFB) in the absence of carbon and nitrogen source using fungal mycelia of Aspergillus oryzae MTCC 7691. Fungal mycelia immobilized on baggase packed in a glass column under a batch-wise mode (1) effected removal of 75.71 +/- 0.12 % color, 51.0 +/- 0.13 % biological oxygen demand (BOD), 86.19 +/- 2.56 % COD, and 49.0 +/- 0.12 % phenolic pigments of distillery spent wash up to 25 days at 30 degrees C, while free fungal mycelia resulted in removal of 63.1 +/- 0.16 % color, 27.74 +/- 0.14 % BOD, 76.21 +/- 1.62 % COD, and 37.32 +/- 0.17 % phenolic pigments of distillery spent wash using shake flask, (2) manganese peroxidase (MnP) activity was highest (1.55 +/- 0.01 U ml(-1) min(-1)) in immobilized fungi, followed by lignin peroxidase (0.65 +/- 0.01 U ml(-1) min(-1)) and laccase activity (0.9 +/- 0.01 CU ml (1) min (1)), (3) accumulative MnP activity was highly correlated with (r=0.9216) spent wash decolorization and (r=0.7282) reduction of phenolic pigments, suggesting the presence of MnP activities in bioremediation of spent wash and (4) degradation of spent wash was confirmed by high-performance thin layer chromatography and gas chromatography-mass spectrometry analysis. Measurement of chlorophyll a content of Chlorella species cultivated on treated spent wash effluent obtained from immobilized fungal bioreactor was 5.16 +/- 0.71 mu g ml(-1) compared with 1.306 +/- 0.017 +/-mu g ml(-1) obtained with untreated spent wash. Thus, this work may provide a reasonable alternative for cost-effective bioremediation of distillery spent wash using immobilized A. oryzae on baggase fibers.

Wastewater released from textile industries causes water pollution, and it needs to be treated before discharge to the environment by cost effective technologies. Solar photocatalysis is a promising technology for the treatment of dye wastewater. The Ag@TiO nanoparticles comprising of Ag core and TiO shell (Ag@TiO) have unique photocatalytic property of inhibition of electron-hole recombination and visible light absorption, which makes it a promising photocatalyst for use in solar photocatalysis and with higher photocatalytic rate. Therefore, in the present work, the Ag@TiO nanoparticles synthesized by one pot method with postcalcination step has been used for the degradation of Acid Yellow-17 (AY-17) dye under solar light irradiation. The Ag@TiO nanoparticles were characterized using thermogravimetric-differential thermal analysis, X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray analysis. The catalyst has been found to be very effective in solar photocatalysis of AY-17, as compared to other catalysts. The effects of pH, catalyst loading, initial dye concentration, and oxidants on photocatalysis were also studied. The optimized parameters for degradation of AY-17 using Ag@TiO were found to be pH 3, dye/catalyst ratio of 1:10 (g/g), and 2 g/L of (NH)SO as oxidant. Efficient decolorization and mineralization of AY-17 was achieved. The kinetics of color, total organic carbon, and chemical oxygen demand removal followed the Langmuir-Hinshelwood model. Ag@TiO catalyst can be reused thrice without much decline in efficiency. The catalyst exhibited its potential as economic photocatalyst for treatment of dye wastewater.