Complete Decolorization Research Articles

Co-metabolic decolorization of a textile reactive dye by Aspergillus fumigatus

In the present study, a widely used reactive dye, Color Index (C.I.) Reactive Blue 268 was utilized for mycoremediation by Aspergillus fumigatus isolated from textile effluent. Complete decolorization of the test dye (0.1 g L−1) was recorded within 6 days of static incubation at 27 °C in Czapek Dox broth (CDB). However, the isolate was unable to utilize the dye as a sole source of energy in Czapek Dox agar and CDB in absence of sucrose and obligate requirement of a labile carbon source, i.e., sucrose needed for induction of decolorization. Biosorption seems to play the pivotal role in decolorization as evident by coloring of the fungal biomass as that of dye color. The optimal conditions for the highest decolorization were found at 30 °C and pH 6.0 with 6-day-old inoculums supplemented with sucrose (10 g L−1) and ammonium chloride (2 g L−1) as a carbon and nitrogen source, respectively. The response of the isolate to increasing dye concentrations was found to be growth inhibitory. Surprisingly, about 65 % of dye decolorization was recorded with heat-inactivated biomass powder within 6 days of static incubation supporting the fact of fungal biosorption. Results of this study have established the candidature of the isolate for biotechnological removal of dyes from disreputable dying effluents.

Sono-dispersion of CuS-CdS over TiO2 in one-pot hydrothermal reactor as visible-light-driven nanostructured photocatalyst

Hybrid CuS-CdS/TiO2 photocatalyst was synthesized via on-pot hydrothermal method for the sake of enhancing the charge separation and extending the absorption response of TiO2 into visible region in the photocatalytic degradation of azo dye. To explore the effectiveness of ternary CuS-CdS/TiO2 system, CuS/TiO2 and CdS/TiO2 dual nanocatalysts were synthesized. The synthesized samples were characterized by XRD, FESEM, EDX, TEM, BET, FTIR, PL and DRS analysis. The degradation efficiency was found to be 85.2, 100, 100 and 44.9% for TiO2, CdS(10)/TiO2, CuS(5)CdS(5)/TiO2 and CuS(10)/TiO2, respectively at reaction time of 100min. The effect of initial pH, photocatalyst dosage and initial dye concentration on degradation efficiency and reusability of photocatalysts were evaluated. The results showed that CuS(5)CdS(5)/TiO2 owing to its good structural properties and increasing the life time of charge carriers can reach to complete decolorization in short time. Therefore, CuS(5)CdS(5)/TiO2 nanoparticles can be used as a promising photocatalyst for degradation of organic pollutants under visible light illumination.

Electrochemical oxidation of RB-19 dye using a highly BDD/Ti: Proposed pathway and toxicity

In this work, the electrolysis of Reactive Blue 19 (RB-19, a toxic textile dye with a high half-life) using a highly non-commercial boron-doped diamond film on titanium substrate (BDD/Ti) was studied. The BDD film with a B/C ratio of 15,000ppm, a doping level around 1019cm−3 and higher content of sp3 (diamond) than sp2 (graphite) was produced with high quality and stability. Under appropriate conditions, the electrode promoted complete decolorization of RB-19, together with 99% of TOC removal and a significant decrease in toxicity against V. fischeri. Furthermore, benzene rings, aromatic amines and naphthalene could be removed also during the electrodegradation. The decay in dye concentration followed pseudo-first order kinetics and the values of the apparent rate constant increased with increasing current density applied. In addition, the main intermediates compounds of RB-19 degradation on BDD/Ti based on HPLC–MS analysis were amino-anthraquinone, tautomers keto-enolic, hydroquinone and benzoquinone, benzoic acid, phenol and acid aliphatic, such as oxalic acid. It is concluded that electrochemical oxidation using a BDD/Ti anode represents a satisfactorily method for the removal of RB-19 in aqueous solutions.

ZnO<sub></sub>/VNC Material for UV-Photodegradation of Methylene Blue

ZnO materials act as a Photocatalytic reaction and it leads to partial or complete mineralization or decolorization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze undergoes redox reactions in presence of air/O2 and water. In the present study Zinc oxide (ZnO) was doped with activated carbon prepared from the stem of the plant material by chemical activation namely, Vitexnegundo stem carbon (VNC). The decolourisation and degradation study of a dye namely, methylene blue (MB) was carried out to find out the efficiency of catalytic property of ZnO/VNC. The reaction was performed at 20, 40, 60 ppm of dye solution with ZnO/VNC material at 10 min interval of time. It found that the prepared ZnO / VNC composite exhibits an enhanced Photocatalytic activity for MB degradation under visible light irradiation and its photo catalysis efficiency was analyzed in specific 663 nm λ max using a UV–vis-spectrophotometer. The surface morphology and functional group present in the ZnO / VNC material was characterized by using FT-IR, SEM and XRD. The result reveals that the ZnO/VNC structure consists of irregular aggregates with rough surfaces and high photodegradation activities of ZnO/VNC on MB solutions are found to be at 20ppm. The ZnO/VNC may be used as an alternative adsorbent to remove MB from aqueous solutions.Keywords: Methylene blue (MB), ZnO / VNC, FT-IR, SEM, XRD

Application of porous boron-doped diamond electrode towards electrochemical mineralization of triphenylmethane dye

The aim of this study is to investigate the electrochemical degradation and decolorization of triphenylmethane dyexylenol orange (XO) on boron-doped diamond (BDD) electrodes. A series of parameters, including electrode materials, current density, initial dye concentration and electrolyte composition, are examined to discuss the effect of these factors in terms of chemical oxygen demand (COD) removal, current efficiency and decolorization rate. Complete decolorization and mineralization of XO could be realized on BDD electrodes while the oxidation is mass transfer controlled, and the degradation progress performs better performance in case of porous BDD electrode comparing with flat BDD electrode. The enhancement of effectiveness is highly correlated to the structure of electrode material, where porous BDD film provides more active sites for hydroxyl radicals. The presence of Cl− in the solution promotes the COD and color removal due to the formation of active chlorine. Porous Ti/BDD electrode presents the excellent potential in electrochemical decolorization and mineralization of triphenylmethane dye.

Minimizing the interference of carbonate ions on degradation of SRF3B dye by Fe0-aggregate-activated persulfate process

Abstract Carbonate ions in wastewater can interfere with the reactions in advanced oxidation processes. In the present study, the effects of carbonate ions on the degradation of a polyazo direct dye, the Sirius® Red F3B (SRF3B), using persulfate (PS) oxidation catalyzed by Fe 0 aggregates (PS/Fe 0 ) was investigated. Results of this study indicated that the oxidation power of the PS/Fe 0 process was inhibited in the dye solutions containing carbonates, and the efficiency of SRF3B decolorization decreased with increasing concentration of Na 2 CO 3 . A short period of ultrasound (US) irradiation can significantly enhance the destruction of dye molecules. Complete decolorization of a 25 mg/L SRF3B solution containing 1 × 10 − 3 M carbonate, 5 × 10 −3 M PS, and 1.5 g/L Fe 0 was achieved within 5 min in a PS/Fe 0 /US system augmented with 5 min of US irradiation (60 kHz, 106 W/cm 2 ). The operating cost to complete removal of the dye was estimated at 2.79 USD/m 3 . Higher PS dosage and US power further minimized the interference from carbonate ions. A two-step reaction model, including a slow surface heterogeneous and a fast homogeneous aqueous reactions was proposed for the system. The presence of Fe 2+ and Fe 3+ ions identified using X-ray photoelectron spectroscopy, suggests a direct oxidation of the dye on the surface of the Fe 0 aggregates.

ZnO<sub></sub>/VNC Material for UV-Photodegradation of Methylene Blue

ZnO materials act as a Photocatalytic reaction and it leads to partial or complete mineralization or decolorization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze undergoes redox reactions in presence of air/O2and water. In the present study Zinc oxide (ZnO) was doped with activated carbon prepared from the stem of the plant material by chemical activation namely,Vitexnegundostemcarbon (VNC). The decolourisation and degradation study of a dye namely, methylene blue (MB) was carried out to find out the efficiency of catalytic property of ZnO/VNC. The reaction was performed at 20, 40, 60 ppm of dye solution with ZnO/VNC material at 10 min interval of time. It found that the prepared ZnO / VNC composite exhibits an enhanced Photocatalytic activity for MB degradation under visible light irradiation and its photo catalysis efficiency was analyzed in specific 663 nm λ max using a UV–vis-spectrophotometer. The surface morphology and functional group present in the ZnO / VNC material was characterized by using FT-IR, SEM and XRD. The result reveals that the ZnO/VNC structure consists of irregular aggregates with rough surfaces and high photodegradation activities of ZnO/VNC on MB solutions are found to be at 20ppm. The ZnO/VNC may be used as an alternative adsorbent to remove MB from aqueous solutions.Keywords: Methylene blue (MB), ZnO / VNC, FT-IR, SEM, XRD

Decolorization of azo dye methyl red by suspended and co-immobilized bacterial cells with mediators anthraquinone-2,6-disulfonate and Fe3O4 nanoparticles

In this study, the decolorization and degradation of methyl red (MR) by suspended and immobilized cells of Aeromonas jandaei strain SCS5 under anaerobic and aerobic conditions have been investigated. The complete decolorization of MR at a concentration of 100 mg L−1 by A. jandaei strain SCS5 was obtained within 6 h for both anaerobic and aerobic suspended cultures, where the decolorization rate was faster in acidic conditions than basic conditions. The decolorization efficiency under 6 h increased with increasing cell mass of inoculation and decreased with increasing initial dye concentrations. Immobilized cells of A. jandaei strain SCS5 could decolorize MR, and the decolorization rate was significantly enhanced by cells immobilized with mediators such as anthraquinone-2,6-disulphonate and magnetic Fe3O4 nanoparticles compared to immobilized cells only. Moreover, the immobilized bacterial beads with mediators retained high decolorization activity up to more than 10 repeating cycles. UV–visible spectra (200–800 nm) and gas chromatography-mass spectrometry analysis demonstrated that MR was degraded by A. jandaei strain SCS5 through reductive cleavage of azo bond. MR degradation products showed less phytotoxicity against Triticum aestivum and Phaseolus mungo compared to untreated MR. This study has demonstrated that A. jandaei strain SCS5 could be a promising microbiological agent for the removal of azo dyes from the environment.

Simulation and Experimental Study for Degradation of Organic Dyes Using Dual pin‐to‐plate Corona Discharge Plasma reactors for Industrial Wastewater Treatment

AbstractThis work researches the possibility of increasing the dye removal efficiency from wastewater using nonthermal plasma. A study for the optimal air gap distance between dual pin and surface of Acid Blue 25 dye solution and thickness of ground plate is carried out using 3D‐EM simulator to find maximum electric field intensity at the tip of both pins. The consequences display that the best gap for corona discharge is approximately 5 mm using 15 kV source. In addition, the optimum plate thickness is 0.1 mm. These distance and thickness were mentioned are constant during the study of other factors. Dual pin‐to‐plate high‐voltage corona discharge plasma system is presented to investigation experimentally the gap distance, thickness of ground plate, initial dye concentration, pH solution and conductivity on the amount of Acid Blue 25 dye color removal efficiency from wastewater. There is a large consensus among the simulation and experimental work in the air gap and thickness of ground plate. Where the decolorization for air gap 5 mm is 95.74 at time 35 min compared with 91% and 17% for 1 mm and 20 mm gap distance respectively. Also, the discharge energy at each air gap are calculated. Measurement results for the impact of thickness of an Aluminum ground plate on color removal competence showed color removal efficiencies of 86.3%, 90.78% and 98.06%, after treatment time 15 min for thicknesses of 2, 0.5 and 0.1 mm respectively. The decolorization behavior utilizing dual pin‐to‐plate corona discharge plasma system display 82% pigment evacuation proficiency inside 11min. The complete decolorization was accomplished within 28min for distinctive examined introductory color focuses 5 ppm up to 100 ppm. Likewise, the impacts of conductivity by utilizing diverse salts as AlCl3, CaCl2, KCl and NaCl and with distinctive focuses have been explored. The rising of the solution conductivity leads to the reduction of decolorization efficiency. The decolorization efficiency and discharge energy are calculated at different concentration molarity for AlCl3, CaCl2, KCl and NaCl. It was observed that the presence of salts at the same concentration level substantially decreased the rate and the extent of decolorization. The results indicate that the optimum pH for the decolorization of Acid Blue 25 dye is in the range between 3 and 6. Furthermore the conductivity and discharge energy were measurement at each value of pH. Energy yield for decolorization and Electrical Energy per Order (EE/O) under different initial pH value were calculated. A kinetic model is used to define the performance of corona discharge system under different value of pH. The model of pseudo ‐zero, pseudo‐first order, and pseudo‐second order reactions kinetic are utilized to investigate the decolorization of Acid Blue 25 dye. The rate of degradation of Acid Blue 25 dye follows the pseudo‐first order kinetics in the dye concentration. Energy consumption requirements for decolorization was considered. The outcomes will be useful for designing the plasma treatment systems suitable for industrial wastewaters. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effective degradation of rhodamine B by electro-Fenton process, using ferromagnetic nanoparticles loaded on modified graphite felt electrode as reusable catalyst: in neutral pH condition and without external aeration.

Polytetrafluoroethylene/ferromagnetic nanoparticle/carbon black (PTFE/MNP/CB)-modified graphite felt (GF) was successfully applied as cathode for the mineralization of rhodamine B (RhB) in electro-Fenton (EF) process. The modified cathode showed high decolorization efficiency for RhB solution even in neutral pH condition and without external aeration, achieving nearly complete decolorization and 89.52% total organic carbon (TOC) removal after 270-min oxidation with the MNP load 1.2g at 50A/m(2). Moreover, the operational parameters (current density, MNP load, initial pH, and airflow rate) were optimized. After that, adsorption isotherm was also conducted to compare the absorption quantity of CB and carbon nanotube (CNT). Then, the surface morphologies of MNPs were characterized by transmission electron microscope (TEM), energy-dispersive X-ray detector (EDX), and Fourier transform infrared spectroscopy (FTIR); and the modified cathode was characterized by SEM and contact angle. Finally, the stability and reusability of modified cathode were tested. Result uncovered that the PTFE/MNP/CB-modified cathode has the potential for industrial application and the solution after treatment was easily biodegradable.

Multi-walled carbon nanotubes/TiO2 thin layer for photocatalytic degradation of organic pollutant under visible light irradiation

This paper is based on preparation of MWCNT/TiO2 photoactive thin layer deposited on glass substrate using the sol–gel dip-coating technique. The thin layer consists of TiO2 coupled with different amount of per-noncovalent functionalized multi-walled carbon nanotubes (MWCNTs). The optimum MWCNTs/TiO2 weight ratio in the thin film was found to be 1.75 % under the experimental conditions investigated. The MWCNT/TiO2 film was characterized by a range of analytical techniques including: scanning electron microscopy, atomic force microscopy, X-ray diffraction, photoluminescence spectra, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. The photoactivity of the prepared films, under visible light irradiation, was evaluated by decoloration of methyl orange (MO). Complete decoloration of MO was observed only in 2 h under visible light irradiation. Furthermore, we used chemical oxygen demand (COD) method to determine the degradation efficiency of the MWCNT/TiO2 thin layer. 42 % reduction in COD value of treated MO solution shows substantial degradation of MO by photoactive film. According to the results of MO removal experiment, the excellent activity of the photoactive film can be attributed to the strong interaction between TiO2 particles and MWCNT bundles and the high electron acceptability of CNTs network.

Treatment of textile wastewater using sequential sulfate-reducing anaerobic and sulfide-oxidizing aerobic membrane bioreactors

This study aims at evaluating the performance of sequential sulfate-reducing anaerobic and sulfide-oxidizing aerobic membrane bioreactors (MBRs) for the treatment of synthetic textile wastewater. The process performance was evaluated under varying concentrations of COD (1000–2000mg/L), NaCl (500–1000mg/L), and sulfate (500–1500mg/L), but keeping dye (Remazol Brilliant Violet 5R) concentration constant at 200mg/L. In sulfate reducing anaerobic MBR (AnMBR), COD removal efficiency remained between 80% and 85%. The sulfate reduction efficiency was directly related with COD/sulfate ratio. Almost complete decolorization was attained in the AnMBR, whereas slight recolorization was observed in the AeMBR due to autooxidation of aromatic amines. EDS analyses illustrated that cake layer in AnMBR contained much higher amounts of S, Fe and Cu due to formation of metal–sulfide precipitates, whereas Ca and P were the major inorganic elements in AeMBR. In the cake layers of both MBRs, high molecular weight soluble organics were observed by gel permeation chromatographic analyses together with the identification of proteins and polysaccharides by the FT-IR analyses. Capillary suction time, specific resistance to filtration and supernatant filterability tests illustrated that AnMBR sludge had less filterability and stable operation was possible with a flux of around 5LMH.

Photocatalytic Decolorization of Dye Effluent Using Radiation Developed Polymeric Nanocomposites

In this study [acrylic acid/p(N-vinyl-2-pyrrolidone)] (AAc/PVP) hydrogel was prepared using gamma irradiation technique. The prepared hydrogel was used as a template for in situ preparation of ZnO photocatalyst up to three deposition cycles. The structure, the thermal property, and the surface morphology of (AAc/PVP/ZnO) nanocomposite were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscope (TEM) and scanning electron microscope (SEM) techniques. The photocatalytic activity of the obtained nanocomposite was tested for the degradation of methyl blue dye (MB) in the aqueous medium using UV-light. The effect of operational parameters on the degradation of MB such as UV irradiation time, pH, and initial dye concentration were examined. It was found that complete decolorization of MB dye was achieved after 45 min at pH 4. The degradation rate fitted the pseudo-first-order model and the rate of the photocatalytic reaction of the first preparation cycle of ZnO was higher than that of the third preparation cycle.

COD removal from petrochemical wastewater by UV/hydrogen peroxide, UV/persulfate and UV/percarbonate: biodegradability improvement and cost evaluation

The petrochemical industry has been highly considered by environmentalists since it can affect the environment through the production of high strength wastewater. This study investigates chemical oxygen demand (COD) removal from petrochemical wastewater by ultra violet (UV)/oxidant systems with varying dosages of oxidants, initial pH values and reaction time. Hydrogen peroxide (H2O2), persulfate (PS) and percarbonate (PC) were used as oxidants. The results showed that pH = 3.0 was suitable for H2O2 and PC, while PS had the best performance at pH = 7.0. The presence of ferrous ions improved the removal efficiency, especially in the case of UV/PC. However, COD removal efficiencies of UV/PS and UV/H2O2 were more effective than that of the UV/PC system. The biochemical oxygen demand (BOD)/COD ratio achieved >0.4 by UV/PS/Fe2+, UV/H2O2 and UV/H2O2/Fe2+ systems. Complete decolorization occurred for all the UV/oxidant systems after only 30 min reaction time. Besides the effective performances of PS and H2O2 in COD removal, PC was considered as an inexpensive oxidant. The order of total costs based on kg COD removed was: UV/PS/Fe2+ > UV/PS > UV/H2O2/Fe2+ > UV/H2O2 > UV/PC/Fe2+ > UV/PC. In conclusion, UV/H2O2 displayed an effective, applicable and clean process for petrochemical wastewater treatment.

Acid blue 29 decolorization and mineralization by anodic oxidation with a cold gas spray synthesized Sn–Cu–Sb alloy anode

The elevated cost of anodic materials used in the anodic oxidation for water treatment of effluents undermines the real application of these technologies. The study of novel alternative materials more affordable is required. In this work, we report the application of Sn–Cu–Sb alloys as cheap anodic material to decolorize azo dye Acid Blue 29 solutions. These anodes have been synthesized by cold gas spray technologies. Almost complete decolorization and COD abatement were attained after 300 and 600 min of electrochemical treatment, respectively. The influence of several variables such as supporting electrolyte, pH, current density and initial pollutant concentration has been investigated. Furthermore, the release and evolution of by-products was followed by HPLC to better understand the oxidative power of Sn–Cu–Sb electrodes.

Tubular carbon nanotube-based gas diffusion electrode removes persistent organic pollutants by a cyclic adsorption – Electro-Fenton process

We report a novel tubular electrochemical cell which is operated in a cyclic adsorption – electro-Fenton process and by this means overcomes the drawbacks of the traditional electro-Fenton process. A microtube made only of multi-walled carbon nanotubes (MWCNT) functions as a gas diffusion electrode (GDE) and highly porous adsorber. In the process, the pollutants were first removed electroless from the wastewater by adsorption on the MWCNT-GDE. Subsequently, the pollutants are electrochemically degraded in a defined volume of electrolyte solution using the electro-Fenton process. Oxygen was supplied into the lumen of the saturated microtubular GDE which was surrounded by a cylindrical anode made of Ti-felt coated with Pt/IrO2 catalysts. For the proof of concept the model pollutant Acid Red 14 (AR14), an azo dye, was used. The decomposition of AR14 was studied at different applied current densities and initial concentrations of ferrous iron in the electrolyte solution. At optimal conditions, complete regeneration of the adsorption capacity of the MWCNT-GDE, complete decolorization and TOC and COD removal rates of 50% and 70% were achieved, respectively. The MWCNT-GDE is regenerated and again available for adsorption. This approach allows water treatment independent of its composition, thus does not require any addition of chemicals to the wastewater.

Application of non-thermal plasma reactor for degradation and detoxification of high concentrations of dye Reactive Black 5 in water

Degradation and detoxification efficiency of high concentrations of commercially available reactive textile dye Reactive Black 5 solution (40, 80, 200, 500, 1000 mg L-1), were studied. Advanced oxidation processes in water falling film based dielectric barrier discharge as a non-thermal plasma reactor were used. For the first time, this reactor was used for the treatment of high concentrations of organic pollutants such as reactive textile dye Reactive Black 5 in water. Solution of the dye is treated by plasma as thin water solution film that is constantly regenerated. Basically, the reactor works as a continuous flow reactor and the electrical discharge itself takes place at the gas-liquid interphase. The dye solution was recirculated through the reactor with an applied energy density of 0-374 kJ L-1. Decolorization efficiency (%) was monitored by UV-VIS spectrophotometric technique. Samples were taken after every recirculation (~ 22 kJ L-1) and decolorization percent was measured after 5 min and 24 h of plasma treatment. The efficiency of degradation (i.e. mineralization) and possible degradation products were also tracked by determination of the chemical oxygen demand (COD) and by ion chromatography (IC). Initial toxicity and toxicity of solutions after the treatment were studied with Artemia salina test organisms. Efficiency of decolorization decreased with the increase of the dye concentration. Complete decolorization, high mineralization and non-toxicity of the solution (<10 %) were acomplished after plasma treatment using energy density of 242 kJ L-1, while the initial concentrations of Reactive Black 5 were 40 and 80 mg L-1.

Photocatalytic degradation of azo dye using nano-ZrO2/UV/Persulfate: Response surface modeling and optimization

Dyes have always been considered in the context of recalcitrant organic pollutants in water. The present research has focused on the decolorization of Direct Blue 71 (DB71) using photocatalysis process of nano-ZrO2/UV/ Persulfate. Response surface method with central composite design was applied to determine the effects of four main factors (time, ZrO2 dosage, persulfate dosage and pH) on decolorization of DB71. The results indicated that the obtained quadratic model had a high R-squared coefficient based on the analysis of variance (ANOVA). Time had the highest effect (45.5%) on decolorization of DB71. The optimum condition predicted for complete decolorization was pH=7, 0.4 g ZrO2, 0.75 mM persulfate and 40 min reaction time. Verification experiments confirmed that there was good agreement between the experimental and predicted responses. The studied photocatalytic process could oxidize and destruct the structure of the DB71, and average oxidation state (AOS) significantly increased from −1.5 to +1.33, indicating the presence of more oxidized by-products and, consequently, improvement of biodegradability. The quenching tests showed that sulfate radical was the major agent in DB71 decolorization. It can be concluded that nano-ZrO2/ UV/Persulfate is a very effective process for decolorization of colored wastewater.

Linkage of iron elution and dissolved oxygen consumption with removal of organic pollutants by nanoscale zero-valent iron: Effects of pH on iron dissolution and formation of iron oxide/hydroxide layer.

The iron elution and dissolved oxygen (DO) consumption in organic pollutant removal by nanoscale zero-valent iron (nZVI) was examined in the range of solution pH from 3.0 to 9.0. Their behaviors were linked with the removal of organic pollutant through the dissolution of iron and the formation of iron oxide/hydroxide layer affected strongly by solution pH and DO. As an example of organic pollutants, azo-dye Orange II was chosen in this study. The chemical composition analyses before and after reaction confirmed the corrosion of nZVI into ions, the formation of iron oxide/hydroxide layer on nZVI surface and the adsorption of the pollutant and its intermediates. The complete decolorization of Orange II with nZVI was accomplished very quickly. On the other hand, the total organic carbon (TOC) removal was considerably slow and the maximum TOC removal was around 40% obtained at pH 9.0. The reductive cleavage of azo-bond by emitted electrons more readily took place as compared with the cleavage of aromatic rings of Orange II leading to the degradation to smaller molecules and subsequently the mineralization. A reaction kinetic model based on the Langmuir-Hinshelwood/Eley-Rideal approach was developed to elucidate mechanisms for organic pollutant removal controlled by the formation of iron oxide/hydroxide layer, the progress of which could be characterized by considering the dynamic concentration changes in Fe(2+) and DO. The dynamic profiles of Orange II removal linked with Fe(2+) and DO could be reasonably simulated in the range of pH from 3.0 to 9.0.

Dissimilatory azoreduction of Orange I by a newly isolated moderately thermophilic bacterium, Novibacillus thermophilus SG-1

Dye wastewater normally is discharged at high temperature, but thermophilic bacteria capable of decolorizing azo dyes have rarely been isolated. Here we report a newly isolated moderately thermophilic bacterium, Novibacillus thermophilus SG-1, which had a remarkable ability to decolorize the azo dye Orange I by utilizing a large variety of organic substrates as electron donors. When Orange I served as the sole electron acceptor, almost complete decolorization occurred at 50oC and pH 8.0 with acetate as the electron donor after anaerobic incubation of strain SG-1 for 24 h. The decolorization process followed the pseudofirst- order kinetics. The complete reduction of 0.3 mM Orange I was accompanied by a stoichiometric consumption of 0.17 mM acetate over time. The measured molar ratio (1.76) of Orange I reduced to acetate oxidized was close to the theory value of 2.0, suggesting that most of the electrons released by acetate had been transported to Orange I. Simultaneously energy generated from the electron transfer process was used to support cell anaerobic growth, which meant that azoreduction by strain SG-1 is an azorespiration process. To our knowledge, this is the first report of a thermophilic bacterium capable of azorespiration, which increases the limited number of bacteria for treating hightemperature azo dye wastewater.