Decolorization Of Reactive Black 5 Research Articles

Comparing biofilm reactors inoculated with Shewanella for decolorization of Reactive Black 5 using different carrier materials.

This study assessed the performance of biofilm reactors inoculated with azo dye degrading Shewanella for the decolorization of Reactive Black 5 (RB5), using three different carrier materials, namely almond shell biochar, moving bed biofilm reactor (MBBR), and polypropylene carrier (PPC). The reactors were fed with low-nutrient artificial wastewater containing RB5, and all three carriers showed good RB5 decolorization performance, with varying efficiencies. Liquid Chromatography-Mass Spectrometry analysis revealed distinct RB5 degradation pathways associated with each carrier, influenced by carrier materials and microbial communities. The MBBR carrier exhibited good stability due to its rough surface and microbial aggregates. Sequencing results highlighted differences in the microbial community structures among the carriers. Shewanella predominated the functional bacteria in the MBBR and PPC carriers, while the biochar carrier fostered highly efficient degrading microbial communities. The physicochemical properties of carrier materials significantly influenced the microbial community and RB5 degradation efficiency. These findings provide valuable insights for optimizing biofilm reactors for dye-containing wastewater treatment.

Anaerobic biodegradation of azo dye reactive black 5 by a novel strain Shewanella sp. SR1: Pathway and mechanisms

The efficiency of microbial populations in degrading refractory pollutants and the impact of adverse environmental factors often presents challenges for the biological treatment of azo dyes. In this study, the genome analysis and azo dye Reactive Black 5 (RB5) degrading capability of a newly isolated strain, Shewanella sp. SR1, were investigated. By analyzing the genome, functional genes involved in dye degradation and mechanisms for adaptation to low-temperature and high-salinity conditions were identified in SR1. The addition of co-substrates, such as glucose and yeast extract, significantly enhanced RB5 decolorization efficiency, reaching up to 87.6%. Notably, SR1 demonstrated remarkable robustness towards a wide range of NaCl concentrations (1–30 g/L) and temperatures (10–30 °C), maintaining efficient decolorization and high biomass concentration. The metabolic pathways of RB5 degradation were deduced based on the metabolites and genes detected in the genome, in which the azo bond was first cleaved by FMN-dependent NADH-azoreductase and NAD(P)H-flavin reductase, followed by deamination, desulfonation, and hydroxylation mediated by various oxidoreductases. Importantly, the degradation metabolites exhibited reduced toxicity, as revealed by toxicity analysis. These findings highlighted the great potential of Shewanella sp. SR1 for bioremediation of wastewaters contaminated with azo dyes.

Alkaline-thermal hydrolysate of waste activated sludge as a co-metabolic substrate enhances biodegradation of refractory dye reactive black 5

Aromatic azo dyes possess inherent resistance and are known to be carcinogenic, posing a significant threat to human and ecosystems. Enhancing the biodegradation of azo dyes usually requires the presence of co-metabolic substrates to optimize the process. In addressing the issue of excessive waste activated sludge (WAS) generation, this study explored the potential of utilizing alkaline-thermal hydrolysate of WAS as a co-metabolic substrate to boost the degradation of reactive black 5 (RB5) dyes. The acclimated microbial consortium, when supplemented with the WAS hydrolysate obtained at a hydrolysis temperature of 30 °C, achieved an impressive RB5 decolorization efficiency of 90.3% (pH = 7, 35 °C) with a corresponding COD removal efficiency of 45.0%. The addition of WAS hydrolysate as a co-substrate conferred the consortium with a remarkable tolerance to high dye concentration (1500 mg/L RB5) and salinity levels (4–5%), surpassing the performance of conventional co-metabolic sugars in RB5 degradation. 3D-EEM analysis revealed that protein-like substances rich in tyrosine and tryptophan, present in the WAS hydrolysate, played a crucial role in promoting RB5 biodegradation. Furthermore, the microbial consortium community exhibited an enrichment of dye-degrading species, including Acidovorax, Bordetella, Kerstersia, and Brevundimonas, which dominated the community. Notably, functional genes associated with dye degradation and intermediates were also enriched during the RB5 decolorization and biodegradation process. These findings present a practical strategy for the simultaneous treatment of dye-containing wastewater and recycling of WAS.

Adsorption and decolorization study of reactive black 5 by immobilized metal-organic framework of UiO-66 and Gloeophyllum trabeum fungus.

This study aimed to investigate immobilized metal-organic framework (MOF) UiO-66 and brown-rot fungus Gloeophyllum trabeum (GT) in PVA-SA matrices for adsorption and decolorization of reactive black 5 (RB5). Furthermore, UiO-66/GT@PVA-SA composite was successfully fabricated and obtained by immobilizing UiO-66 and GT mycelia into a mixture of PVA-SA. This composite demonstrated a decolorization ability of 80.12% for RB5 after 7 days. The composite's reusability was assessed for three cycles; at last, it only achieved 21%. This study reported that adsorption of RB5 by the composite followed a pseudo-second-order kinetic model with a correlation coefficient (R2) of 0.9997. The Freundlich model was found to be suitable for the isotherm adsorption. The process was also spontaneous and feasible, as indicated by the negative ΔG value. Subsequently, four metabolite products resulting from decolorization of RB5 by UiO-66/GT@PVA-SA composite were proposed, namely: C24H19N5Na2O13S4 (m/z = 762), C10H13N2O8S2- (m/z = 353), C12H9N4O7S2- (m/z = 384), and C10H13O8S2- (m/z = 325).

Study of kinetic parameters related to dyes oxidation in ascorbic acid-mediated Fenton processes

Ascorbic acid (AA) is a natural reducer that has been used as a prooxidant additive to improve dyes oxidation via Fenton processes (Fe2+/H2O2 and Fe3+/H2O2). In the present work, low concentration of AA (10 μmol L1) enhanced Bismarck Brown Y (BBY), Safranin T (ST), Rhodamine B (RB), and Reactive Black 5 (RB5) decolorizations in solution, mainly in reactions initially containing Fe3+ as a catalyst (Fe3+-reactions), e.g., Fe3+/H2O2 decolorization of RB5 was increased from 54 % to 73 % after 60 min due to added AA. Decolorization increased from 0 up to 60–90 μmol L−1 of added reducer. At higher concentrations, AA did not improve decolorization. The dyes were decolorized below 10 % when incubated with 1 % tert-butanol, indicating that HO• radical is the main oxidant involved in the reactions. The kinetic analysis showed that the 1st- and 2nd-order kinetic models fitted well to both Fe2+- and Fe3+-reaction data. The BMG kinetic model also fitted well to the Fe2+-reactions (with and without AA), along with Fe3+/H2O2/AA. Based on these kinetic models, we verified that reaction rate constants were increased due to added AA. There was a decrease in activation energy (Ea) in decolorizing ST from added AA by varying the reaction temperatures. For example, Ea decreased from 111.6 to 81.8 kJ mol−1 for Fe3+-reactions and from 72.6 to only 69.3 kJ mol−1 for Fe2+-reactions. The AA/H2O2 system was least effective in decolorizing ST since Ea was 130 kJ mol−1. In summary, ascorbic acid decreases the energy barrier to improve Fenton-based ST oxidation.

Fabrication of metal-organic framework Universitetet i Oslo-66 (UiO-66) and brown-rot fungus Gloeophyllum trabeum biocomposite (UiO-66@GT) and its application for reactive black 5 decolorization

Many various industries use synthetic dyes as their raw materials. These dyes have triggered environmental problems because of the occurring effluents, and one of the environmentally safe solutions for this problem is biodegradation through microorganisms. Reactive Black 5 (RB5) dye degradation was performed by utilizing a metal-organic framework Universitetet i Oslo-66 (UiO-66) and Gloeophyllum trabeum (GT) fungus biocomposite. The UiO-66@GT composite was fabricated by inoculating the fungal culture in flasks with the PDB medium that contained UiO-66. This biocomposite was applied to decolorize and degrade RB5 dye, while pure GT culture can decolorize about 36.47% in five days. The percentage of RB5 decolorization was shown to be increased with the addition of UiO-66; the composite could decolorize RB5 up to 72.55% after five days incubation period. Moreover, the optimum conditions for the 100% targeted rate of RB5 decolorization found by the Response Surface Methodology (RSM) are: initial RB5 concentration (72.54 mg L -1 ), pH (6.53), and temperature (38.06 °C). Two novel metabolites from RB5 decolorization by the composite were detected based on LCMS-QTOF analysis and were used to propose a degradation pathway: 6-((1-amino-7,8-dihydroxy-6-sulfonaphthalen-2-yl) diazinyl) cyclohexa-2,4-dien-1-ide ( m / z = 360) and 3,4-diamino-5,6-dihydroxy-1,2,7,8-tetrahydronaphthalene-2,7-disulfonic acid ( m / z = 354).

Catalytic activation of peroxymonosulphate with manganese and cobalt coated micro sand particles for the treatment of Floor-wash containing Reactive Black 5 (RB5) dye

Reactive Black 5 (RB5) is an azo dye widely used in various industries. This work is focused on treating Floor wash wastewater, which is one of the most voluminous and coloured streams emerging from RB5 manufacturing units. It is possible to reuse this water if it is efficiently decolorized. Water containing RB5 dye is hard to treat using conventional treatments due to its high stability and solubility. In this work, decolorization of simulated Floor-wash was investigated using peroxymonosulphate (PMS) and heterogeneous catalyst. The simulated floor-wash containing 100 mg/L of RB5 was prepared using tap water. The synthesis of manganese and cobalt-coated micro sand (MnCoMS) particles was done to efficiently activate peroxymonosulphate (PMS). The operational parameters such as catalyst dosage, PMS concentration, initial pH, reaction time, and reusability of MnCoMS were investigated. Under optimum conditions: 200 mg/L PMS, 10 g/L MnCoMS, and initial pH 9.5, 97.8 % of initial 100 mg/L RB5 was decolorized at the end of 60 min reaction time. RB5 decolorization was slightly slower at initial pH near neutral (7–7.8) as compared to that at acidic (4.5) or alkaline (9.5) pH values. The rate and extent of RB5 decolorization increased with an increase in PMS concentration from 50 mg/L to 200 mg/L. Similarly, the increase in MnCoMS concentration from 5 to 25 g/L increased the rate of RB5 decolorization. However the %RB5 decolorization at the end of 60 min was almost constant for MnCoMS concentration of 10 g/L and above. Experiments conducted in the presence of scavengers revealed that sulphate and hydroxyl radicals played important role in RB5 decolorization. The MnCoMS catalyst demonstrated excellent reusability with > 80 % RB5 decolorization achieved till the sixth use. Overall, PMS activation by heterogeneous catalyst MnCoMS is an efficient method for rapid decolorization of floor-wash containing RB5 dye.

Decolorization of Reactive Black 5 Using N-Doped TiO2

Decolorization of Reactive Black 5 (RB5) was investigated by heterogeneous photocatalysis using N-doped TiO2. N-doped TiO2 photocatalysts were synthesized by means of a sol-gel process. X-ray diffraction performed the characterization of synthesized samples, scanning electron microscopy and X-ray photoelectron spectroscopy measurements. Photocatalytic activity of N-doped TiO2 samples was assessed by following decolorization and degradation efficiency of RB5. N-TiO2(3) sample yielded the highest decolorization efficiency. The apparent first-order rate constants for decolorization of RB5 with N-TiO2(X) samples followed the order of N-TiO2(3) > N-TiO2(2) > N-TiO2(4) > N-TiO2(1). Improvement of decolorization efficiency of TiO2 was observed doping with nitrogen. The effect of actual sunlight on decolorization efficiency was also investigated. 96% and 49% of decolorization efficiency levels were attained within 60 minutes of reaction time with outdoor sunlight and fluorescent daylight lamps, respectively.

Optimization of reactive black 5 decolorization by the newly isolated Saccharomyces cerevisiae X19G2 using response-surface methodology.

In the current investigation, the capacity of different yeast strains to decolorize reactive black 5 (RB-5) was assessed. A comparative study between the different strains demonstrated that Saccharomyces cerevisiae X19G2 exhibited the highest decolorization rate (69.20 ± 1.16%) after 48h of incubation. This strain was selected to optimize the medium components' concentrations for maximum RB-5 decolorization. Response-surface methodology (RSM) was tested for the most significant parameters (glucose, yeast extract and RB-5 dye concentrations) that were previously determined by Plackett-Burman design. A dye decolorization rate of 99.59 ± 0.24% was achieved within 48h using a maximum RB-5 concentration (0.15g/L) with glucose and yeast extract concentrations equalling to 10.5g/L and 1g/L, respectively. Experimental data results proved to fit well with the pseudo-second order kinetics model.The phytotoxicity assessment was carried out using Raphanus sativus seeds to determine the toxicity of RB-5 before and after treatment by S. cerevisiae. Results suggested that germination rate and the length of seeds radical irrigated with 0.15g/L of RB-5 decreased by 30 and 53%, compared to those irrigated with treated solution. Therefore, metabolites derived from decolorization of RB-5 by S. cerevisiae X19G2 were significantly less toxic than the original dye.

Microbial fuel cells as an electrical energy source for degradation followed by decolorization of Reactive Black 5 azo dye

The problem of wastewater has long been ubiquitous and has great consequences for the environment and its inhabitants. Microbial fuel cells (MFCs) have enormous potential for the treatment of wastewaters polluted with azo dyes. The amount of energy that can be produced from a single-chamber MFC is sufficient to perform decolorization and degradation of such dyes, which are widely used in the textile industry. This study on the azo dye, reactive black 5 (RB5), provides an alternative method through three parallel-connected MFCs to obtain electricity that directly serves for the dye’s electrochemical degradation. We examined degradation followed by decolorization of RB5 using Fe and Pt electrodes, together with H2O2, to achieve the electro-Fenton process. The amount of voltage produced (295 mV), the current density (276 mA m−3) and the power density (50 mW m−3) were sufficient to degrade 25 mg L-1 RB5 dye with 0.5 mM H2O2 in just 2 h. The dye degradation mechanism was investigated using UV–VIS, FT-IR and HPLC-MS/MS. The ecotoxicity of the degradation products was assessed using a bacterial model, Aliivibrio fischeri. These tests showed that there was successful degradation of the dye to products whose toxicity is less than that of RB5.

Reactive Black 5 decolorization using immobilized Brown-rot fungus Gloeophyllum trabeum

Reactive Black 5 (RB5) is one of the most common synthetic reactive dyes that requires treatment due to its effect on the water ecosystems and human health (e.g., cancer), therefore, it needs to be treated. This study aimed to decolorize RB5 dye using the immobilized brown-rot fungus, Gloeophyllum trabeum, on sodium alginate (SA). The immobilized beads involved two variations, living and dead fungus (biomass), entrapped into 2% (w/v) SA and solidified by chilled CaCl2. The result showed that the immobilized G. trabeum biomass exceeded the abilities of the living fungus after 7 days of incubation. Using the spectrophotometric method, the RB5 decolorization percentages by immobilized living and dead fungus were 13.35% and 53.08%, respectively. The decolorization abilities were affected by several factors, such as dye concentration, temperature, pH, and static or agitated conditions. Optimum conditions for decolorizing RB5 by dead fungus G. trabeum beads were incubation time 7 days, initial dye concentration 50 mg/L, pH 7.0, temperature 40 ˚C, and under shaking conditions. Meanwhile, for living fungus G. trabeum beads, the initial concentration was 50 mg/L, pH 3.0, temperature 25 ˚C, and under static conditions. In addition, the isothermal adsorption kinetics of RB5 by the dead and living fungus beads followed the Langmuir and Freundlich model, respectively.

Factors Affecting the Simultaneous Removal of Nitrate and Reactive Black 5 Dye via Hydrogen-Based Denitrification

Textile wastewater (TW) contains toxic pollutants that pose both environmental and human health risks. Reportedly, some of these pollutants, including NO3−, NO2− and reactive black 5 (RB-5) dye, can be removed via hydrogen-based denitrification (HD); however, it is still unclear how different factors affect their simultaneous removal. This study aimed to investigate the effect of H2 flow rate, the sparging cycle of air and H2, and initial dye concentration on the TW treatment process. Thus, two reactors, an anaerobic HD reactor and a combined aerobic/anaerobic HD reactor, were used to investigate the treatment performance. The results obtained that increasing the H2 flow rate in the anaerobic HD reactor increased nitrogen removal and decolorization removal rates. Further, increasing the time for anaerobic treatment significantly enhanced the pollutant removal rate in the combined reactor. Furthermore, an increase in initial dye concentration resulted in lower nitrogen removal rates. Additionally, some of the dye was decolorized during the HD process via bacterial degradation, and increasing the initial dye concentration resulted in a decrease in the decolorization rate. Bacterial communities, including Xanthomonadaceae, Rhodocyclaceae, and Thauera spp., are presented as the microbial species that play a key role in the mechanisms related to nitrogen removal and RB-5 decolorization under both HD conditions. However, both reactors showed similar treatment efficiencies; hence, based on these results, the use of a combined aerobic/anaerobic HD system should be used to reduce organic/inorganic pollutant contents in real textile wastewater before discharging is recommended.

Decolorization and detoxification of different azo dyes by Phanerochaete chrysosporium ME-446 under submerged fermentation.

Azo dyes are widely used in the textile industry due to their resistance to light, moisture, and oxidants. They are also an important class of environmental contaminant because of the amount of dye that reaches natural water resources and because they can be toxic, mutagenic, and carcinogenic. Different technologies are used for the decolorization of wastewater containing dyes; among them, the biological processes are the most promising environmentally. The aim of this study was to evaluate the potential of Phanerochaete chrysosporium strain ME-446 to safely decolorize three azo dyes: Direct Yellow 27 (DY27), Reactive Black 5 (RB5), and Reactive Red 120 (RR120). Decolorization efficiency was determined by ultraviolet-visible spectrophotometry and the phytotoxicity of the solutions before and after the fungal treatment was analyzed using Lactuca sativa seeds. P. chrysosporium ME-446 was highly efficient in decolorizing DY27, RB5, and RR120 at 50 mg L-1, decreasing their colors by 82%, 89%, and 94% within 10 days. Removal of dyes was achieved through adsorption on the fungal mycelium as well as biodegradation, inferred by the changes in the dyes' spectral peaks. The intensive decolorization of DY27 and RB5 corresponded to a decrease in phytotoxicity. However, phytotoxicity increased during the removal of color for the dye RR120. The ecotoxicity tests showed that the absence of color does not necessarily translate to an absence of toxicity.

Synthesis and Characterization of Fe-TiO2 Nanomaterial: Performance Evaluation for RB5 Decolorization and In Vitro Antibacterial Studies.

A photocatalytic system for decolorization of double azo reactive black 5 (RB5) dye and water disinfection of E. coli was developed. Sol gel method was employed for the synthesis of Fe-TiO2 photocatalysts and were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and Brunauer–Emmett–Teller (BET) analysis. Results showed that photocatalytic efficiency was greatly influenced by 0.1 weight percent iron loading and 300 °C calcination temperature. The optimized reaction parameters were found to be the ambient temperature, working solution pH 6.2 and 1 mg g−1 dose to completely decolorize RB5. The isotherm studies showed that RB5 adsorption by Fe-TiO2 followed the Langmuir isotherm with maximum adsorption capacity of 42.7 mg g−1 and Kads 0.0079 L mg−1. Under illumination, the modified photocatalytic material had higher decolorization efficiency as compared to unmodified photocatalyst. Kinetic studies of the modified material under visible light irradiation indicated the reaction followed the pseudo-first-order kinetics. The illumination reaction followed the Langmuir-Hinshelwood (L-H) model as the rate of dye decolorization increased with an incremental increase in dye concentration. The L-H constant Kc was 1.5542 mg L–1∙h–1 while Kads was found 0.1317 L mg–1. The best photocatalyst showed prominent percent reduction of E. coli in 120 min. Finally, 0.1Fe-TiO2-300 could be an efficient photocatalyst and can provide a composite solution for RB5 decolorization and bacterial strain inhibition.

Microbially mediated cleavage of Reactive Black 5 in attached growth bioreactors with immobilized Shewanella indica strain on different carriers

Decolorization and removal of contaminants in textile wastewater are essential for pollution control. This study investigated the potential application of a halophilic and halotolerant Shewanella indica (S. indica) strain as immobilized biofilm in two attached growth bioreactors with moving bed bioreactor carrier and polyurethane porous gel carrier, respectively. Under optimized operation conditions, both bioreactors had high tolerance for Reactive Black 5 (RB5) concentration fluctuation and could decolorize RB5 effectively and stably (97% on average) for over 6 months. The decolorization of RB5 in bioreactors was mainly due to microbially mediated cleavage of the azo dye, though adsorption by biofilm and carrier (contribution of different carriers varied) also contributed to the process. However, the azo dye was barely mineralized, and the toxicity remained after decolorization. Overall, this study demonstrated the viability and sustainability of the bioreactors incubated with S. indica in decolorizing RB5. Nevertheless, further technologies need to be explored to detoxify the degradation metabolites.

Photocatalytic Decolorization and Biocidal Applications of Nonmetal Doped TiO2: Isotherm, Kinetic Modeling and In Silico Molecular Docking Studies.

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO2 against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO2 with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO2. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m2 g−1 specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g−1 with Kads of 0.113 mg−1. The LH model yielded a higher coefficient KC (1.15 mg L−1 h−1) compared to the adsorption constant KLH (0.3084 L mg−1). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol−1) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Enhancing the decolorization activity of Bacillus pumilus W3 CotA-laccase to Reactive Black 5 by site-saturation mutagenesis.

Reactive Black 5 (RB5) is a typical refractory azo dye. Widespread utilization of RB5 has caused a variety of environmental and health problems. The enzymatic degradation of RB5 can be a promising solution due to its superiority as an eco-friendly and cost-competitive process. Bacterial CotA-laccase shows great application prospect to eliminate hazardous dyes from wastewater. However, efficient decolorization of RB5 CotA-laccase generally requires the participation of costly, toxic mediators. In the present study, we modified the amino acids Thr415 and Thr418 near the type 1 copper site and the amino acid Gln442 at the entrance of the substrate-binding pocket of Bacillus pumilus W3 CotA-laccase to boost its RB5 decolorization activity based on molecular docking analysis and site-saturation mutagenesis. Through the strategies, two double site mutants T415D/Q442A and T418K/Q442A obtained demonstrated 43.94 and 52.64% RB5 decolorization rates in the absence of a mediator at pH10.0, respectively, which were about 3.70- and 4.43-fold higher compared with the wild-type CotA-laccase. Unexpectedly, the catalytic efficiency of the T418K/Q442A to ABTS was enhanced by 5.33-fold compared with the wild-type CotA-laccase. The mechanisms of conferring enhanced activity to the mutants were proposed by structural analysis. In summary, the mutants T415D/Q442A and T418K/Q442A have good application potentials for the biodegradation of RB5. KEY POINTS: • Three amino acids of CotA-laccase were manipulated by site-saturation mutagenesis. • Decolorization rate of two mutants to RB5 was enhanced 3.70- and 4.43-fold, respectively. • The mechanisms of awarding enhanced activity to the mutants were supposed.

Efficient bacterial isolate from roots of cactus degrading Reactive Black 5

Abstract The current study aimed at azo dye degradation using a facultative anaerobe. A bacterial strain capable of decolorization and degradation of RB5 under static conditions was isolated from root nodules of Cactus. The strain efficiently degraded Reactive Black 5 (RB5) with metabolites detected by GC–MS. The strain was identified as Proteus mirabilis and placed in phylogenetic position through 16S rRNA gene analysis. The degradation increased with time to achieve up to 90 % after 72 h incubation at 37 oC and pH value of 7. Variations of C source did not affect the process while yeast extract was effective. The effective degradation was achieved at 100 ppm of dye. The GC–MS detected metabolites included; acetaldoxime, oxirane trimethyl, acetic acid-2-propenyl ester, acetaldehyde semi carbazone, 2-pentanone, 4-hydroxy-4-methyl, hydrazine, 1-5-hexenyl-1-methyl and enanthamide Protox and phytotoxicity results showed fewer toxic ranges of these metabolites as compared to products of benzene and amines. The isolated strain can be useful in the bioremediation of azo dyes contaminated environments.

Green Synthesis of Kaolin-Supported Nanoscale Zero-Valent Iron Using Ruellia tuberosa Leaf Extract for Effective Decolorization of Azo Dye Reactive Black 5

Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract of Ruellia tuberosa was used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe0, indicating that Fe0 nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV–Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.

Ecofriendly biodegradation of Reactive Black 5 by newly isolated Sterigmatomyces halophilus SSA1575, valued for textile azo dye wastewater processing and detoxification

A total of seven yeast strains from 18 xylanolytic and/or xylose-fermenting yeast species isolated from the wood-feeding termite Reticulitermes chinenesis could efficiently decolorize various azo dyes under high-salt conditions. Of these strains, a novel and unique azo-degrading and halotolerant yeast, Sterigmatomyces halophilus SSA1575, has been investigated in this study. This strain could significantly decolorize four combinations of a mixture of dyes. It showed a high capability for decolorizing Reactive Black 5 (RB5) even at 1,500 mg L−1. The strain SSA1575 still showed a high capability for decolorizing a 50 mg L−1 RB5 with a salt mixing at a NaCl concentration of up to 80 g L−1. It also exhibited significant ability to decolorize repeated additions of dye aliquots, with a reduction in time of up to 18 h. Most of the tested carbon and nitrogen sources could significantly enhance a RB5 decolorization. However, this process was inhibited by the addition of sucrose and sodium nitrate. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase were determined as the key reductase and oxidase of S. halophilus SSA1575. Finally, strain SSA1575, can effectively detoxify RB5 into non-toxic products. Overall, S. halophilus SSA1575, might be a promising halotolerant yeast valued for the treatment of various textile effluents with high salinity.