Decolorization of the benzidine-based azo dye Congo red by the new strain Shewanella xiamenensis G5-03

Shewanella xiamenensis G5-03 was observed to decolorize the azo dye Congo red in synthetic wastewater. The influence of some factors on the dye decolorization efficiency was evaluated. The optimal decolorization conditions were temperature 30-35 °C, pH 10.0, incubation time 10 h, and static condition. The kinetic of Congo red decolorization fitted to the Michaelis–Menten model (Vmax = 111.11 mg L-1 h-1 and Km = 448.3 mg L-1). The bacterium was also able to degrade benzidine, a product of azo bond breakage of the Congo red, which contributed to reduce the phytotoxicity. The ability of S. xiamenensis G5-03 for simultaneous decolorization and degradation of Congo red shows its potential application for the biological treatment of wastewaters containing azo dyes.

Preparation and Photocatalysis of CuO/Bentonite Based on Adsorption and Photocatalytic Activity

A CuO/bentonite composite photocatalyst was prepared to fully utilize the adsorption capacity of bentonite and the photocatalytic activity of CuO. CuO and bentonite were chosen as a photocatalyst due to the excellent optical property of CuO and large specific surface area of bentonite, together with their high stability and low production cost. The sample was characterized by XRD, SEM, and BET. The effects of several factors on degradation process were investigated such as dosage of H2O2, irradiation time, pH of the solution, and dosage of catalyst. The optimum conditions for decolorization of methylene blue solution by CuO/bentonite were determined. Under optimal conditions, the decolorization efficiency of methylene blue by a 1.4% CuO/bentonite (400 °C) composite photocatalyst under visible irradiation at 240 min reached 96.98%. The degradation process follow edpseudo-second-order kinetics. The photocatalytic mechanism is discussed in detail. This composite structure provides a new solution to the cycle and aggregation of the photocatalyst in water.

Biotransformation of congo red in a UASB reactor under salinity conditions using immobilized redox mediator in granular activated carbon

Azo dyes are susceptible to be treated by reductive biotransformation process under anaerobic conditions. The process can be accelerated by the addition of quinones and humic substances acting as redox mediators (RM). In this study, the anthraquinone-2-sulfonate (AQS) was immobilized on granular activated carbon (GAC) to evaluate the reductive biotransformation of congo red (CR) in an up-flow anaerobic sludge blanket reactor (UASB). The syudy was divided in five stages, where the reactors with immobilized RM and without RM were operated under different salinity levels (1% and 3%) and hydraulic retention times (HRT = 5 and 10 h). The reactor with immobilized RM (GAC-AQS) achieved a decolorization efficiency of 96.1% and substrate consumption of 98.8% with a HRT = 15 h and 1% of salinity. Nonetheless, with a salinity of 3% and the same HRT, the efficiency was similar (95.6%). The reactor provided with unmodified GAC achieved values below those observed in the reactor GAC-AQS, with decolorization efficiencies of 90.8% and 75.8%, and substrate consumption of 97.1% and 88.4%, for the stages IV and V, respectively. The microbial consortium sued was able to promote the biotransformation of azo dye and no inhibitory effects were identified.

Decolorization of mixture of UV/ TiO2 pre-treated azo dyes by using developed bacterial consortium – An excellent outcome

The degradation of the mixture of azo dyes by the developed bacterial consortium, photocatalytic process (TiO2/UV) and their combined effects were investigated in this study. The bacteria consortium was developed from waste disposal drains in the local textile dyeing industry. The consortium consists of two different bacteria which were identified as Stenotrophomonas pavanii and Bacillus licheniformis through 16S rDNA sequence alignment. The decolorization efficiency was estimated by spectrophotometry and it was observed that biological and photochemical methods alone could not effectively remove the dyes as the decolorization efficiency was low and the absorption peak in the UV region was not completely removed. After 5 days of incubation at 37°C, pH 7 and a dye concentration of 150 mg/L, the microbial dye degradation reached a decolorization efficiency of more than 55%. Additionally, the UV treatment alone was also able to decolorize the dye less than 20% at 45°C, pH 9 at 150 mg/L of dye. A two-step treatment process, namely, photocatalytic treatment followed by biological degradation, was assessed. Ultraviolet-Visible (UVVis) spectral analysis showed that the combined effects were most efficient in the dye degradation (97-98%) which involved a complex interaction of enzyme activity, biosorption and photocatalytic action. Here we also report the optimization of various operational parameters.

Graphite/NiO/Ni Electrode for Electro-oxidation of the Remazol Black 5 Dye

Graphite/NiO/Ni electrode had been fabricated for the electro-oxidation of remazol black 5 dye. The electrode was synthesized by electrodeposition method. Electro-oxidation of 100 ppm remazol black 5 dye was carried out at various concentrations of NaCl, 0.025; 0.05; 0.1; 0.25; and 0.5 M, variations in electro-oxidation time were 15, 30, 45, and 60 minutes, and pH variations were 4, 6, and 8. Cyclic voltammetry test revealed that graphite/NiO/Ni electrode had higher electrocatalytic capability compared to graphite electrode. The X-ray diffraction (XRD) patterns showed the decreasing value of 2θ from 44.6° for Ni to 43.5° for NiO. Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) showed that NiO/Ni deposited on the graphite surface in the form of solid grains and cracks, FTIR showed that δ(Ni−O) bond appeared at 582–511 cm−1. The decolorization efficiency of remazol black 5 for graphite/NiO/Ni electrode was 100% for 45 minutes of the electro-oxidation process, while the decolorization efficiency of remazol black 5 for graphite electrode was 99.74% for 60 minutes of the electro-oxidation process. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Photoelectrocatalytic Oxidation of Textile Industry Wastewater by RuO2/IrO2/TaO2 Coated Titanium Electrodes

Photoelectrocatalytic Oxidation (PECO) system prominently increases the migration of photoexcited charges, hinders the fast recombination of electron-hole, and increases the period of photogenerated holes. In this article, we constructed a novel PECO system to degrade textile industry wastewater by RuO2/IrO2/TaO2 coated titanium electrodes. The result shows that PECO treatment can effectively reduce the color and true color of the secondary pollutants present in the wastewater. It is confirmed that a synergistic effect exists between photocatalysis (PC) and electrocatalysis (EC). Moreover, we discussed the influence of pH, current density, electrolyte concentration, and stirring speed. The maximum decolorization efficiency of textile industry wastewater with a pH of 8.2 was found to be 96% under the optimum condition stirrer speed of 200 rpm, an electrolyte concentration of 0.05M, a current density of 15 mA.cm-2, and at a treatment time of 30 mins. The UV-Visible spectra confirm the degradation of textile industry wastewater.

Improved electrochemical oxidative degradation of Reactive Red 24 dye by BDD anodes coupled with nitrate: operating parameters, kinetics, and degradation pathways

The electrochemical oxidation (EO) process coupled with BDD anode and nitrate was used to improve Reactive Red 24 (RR24) removal efficiency in wastewater treatment. The effects of operating parameters on the decolorization efficiency of RR24 were discussed, and the optimal operating parameters were obtained as follows: 45 mA cm− 2, 100 mM SO42−, 7 mM NO3−, 60°C, pH 5.88, and 100 mg L− 1 RR24 initial concentration. The energy consumption for 100% decolorization within 15 min is 0.92 kWh m− 3, and the total organic carbon (TOC) reaches 51.35% within 90 min. Through the effect of quenchers on RR24 decolorization efficiency, various active species in the EO process were studied. It was found that •OH was closely related to the decolorization degradation of RR24, reaching a contribution rate of 99.47%. Finally, we propose the degradation pathways of RR24 by UV-Vis spectrum and LC-MS test. In summary, the proposed treatment process could be applied to treat RR24 dyes as an efficient method.

Biodegradation of azo dyes and dyes present in textile wastewaters using Bacillus sp. az28, obtained from industrial effluents

The bacterial isolate Bacillus sp. AZ28, obtained from industrial effluent, demonstrates a great capacity to degrade various azo dyes (methyl orange (MO), magneson I (MI), novacron dark blue (NDB), and novacron red FN 3GF (NRF3)), and azo dye-containing textile effluent (TE). The degradation was evident by decolorization of dyes, and the decolorization efficiency of 84-95% was achieved within 14-72 h under optimum conditions, such as 37˚C, pH 7, inoculation size 8%, 1% glucose, and 1% beef extract. The extent of decolorization of individual dye was determined by UV–Vis spectroscopy, and products of biodegradation were analyzed by FTIR spectroscopy and TLC analyses. Chemical analysis showed that the COD and BOD values were significantly reduced after treatment. Thus, the biodegradation ability under mild conditions suggests that Bacillus sp. AZ28 has potential in textile effluent treatment. J. Bangladesh Acad. Sci. 45(1); 117-122: June 2021

Three-Dimensional Electrochemical Oxidation of Recalcitrant Dye Using Green Iron Microparticles

This study evaluated the effect of the addition of green iron microparticles (Fe-MPs) as a three-dimensional electrode on efficiency of the electrochemical oxidation process. Polyphenols present in green tea extract act as a reducing and capping agent during green synthesis of the Fe-MPs. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis indicates that the average size of particles is 100 µm, with about ~47 wt % of Fe in oxide form. The addition of Fe-MPs as a third electrode in the conventional electro-oxidation (EO) process converts it into a three-dimensional (3D) catalytic EO process to enhance the decolorization efficiency. Green synthesized Fe-MPs function as several microelectrodes in the process. Adsorption study indicated that only 12% of decolorization is due to adsorption on the Fe-MPs surface. Moreover, improvement in generation of hydroxyl radicals was validated by applying dimethyl sulfoxide as scavenger, and it was observed that generation of hydroxyl radicals decreased with the addition of DMSO. Results showed that decolorization efficiency increased in the 3D EO process with Fe-MPs by about 24% compared to the conventional 2D process without the Fe-MPs dosing, and initial pH as well as the Fe-MPs dose has a significant effect on decolorization efficiency during the 3D process. It is observed that reaction works better at highly acidic pH (2-4), and decolorization efficiency improved with higher doses of Fe-MPs.

Biodegradation of Indanthrene Blue RS dye in immobilized continuous upflow packed bed bioreactor using corncob biochar

The current study describes the aerobic biodegradation of Indanthrene Blue RS dye by a microbial consortium immobilized on corn-cob biochar in a continuous up-flow packed bed bioreactor. The adsorption experiments were performed without microbes to monitor the adsorption effects on initial dye decolorization efficiency. The batch experiments were carried out to estimate the process parameters, and the optimal values of pH, temperature, and inoculum volume were identified as 10.0, 30 °C, and 3.0 × 106 CFU mL−1, respectively. During the continuous operation, the effect of flow rate, initial substrate concentration, inlet loading rate of Indanthrene Blue RS on the elimination capacity, and its removal efficiency in the bioreactor was studied. The continuous up-flow packed bed bioreactor was performed at different flow rates (0.25 to 1.25 L h−1) under the optimal parameters. The maximum removal efficiency of 90% was observed, with the loading rate varying between 100 and 300 mg L−1 day−1. The up-flow packed bed bioreactor used for this study was extremely useful in eliminating Indanthrene Blue RS dye using both the biosorption and biodegradation process. Therefore, it is a potential treatment strategy for detoxifying textile wastewater containing anthraquinone-based dyes.