Decolorization and degradation of azo dyes by the thermal and heavy metal tolerant bacterial consortium BPA-1.

Electrochemical characteriztion of the bioanode during simultaneous azo dye decolorization and bioelectricity generation in an air-cathode single chambered microbial fuel cell

Bioaugmentation of Azo Dyes.- Biodegradation of Azo Dyes Under Anaerobic Condition: Role of Azoreductase.- Biodegradation of Azo Dyes in Anaerobic-Aerobic Sequencing Batch Reactors.- Decolorization of Azo Dyes by Immobilized Bacteria.- Decolorization and Degradation of Azo Dyes by Redox Mediator System with Bacteria.- Bioreactors for Azo-Dye Conversion.- Treatment of Azo Dye-Containing Wastewater Using Integrated Processes.- Decolorization of Azo Dyes by White Rot Fungi.- Decolorization of Azo Dyes by Immobilized Fungi.- Decolorization of Azo Dyes by Yeasts.- Factors Affecting the Complete Mineralization of Azo Dyes.

White-rot basidiomycetes such as Lentinus crinitus produce laccases with potential use in dye biodegradation. However, high productivity and enzymes with specific properties are required in order to make viable laccase production. We aimed to produce laccase from Lentinus crinitus grown in sugarcane bagasse for dye decolorization. Solid state cultivation medium had sugarcane bagasse added with a nutrient solution of 10g/L glucose, 1g/L KH2PO4, 0.5g/L MgSO4, 0.001g/L FeSO4, 0.01g/L ZnSO4, and 0.01g/L MnSO4. The addition of different nitrogen sources (peptone, urea, or peptone plus urea) and different nitrogen concentrations (0, 0.4, 0.6, 0.8, 1.0, and 1.2g/L) were evaluated. Enzymatic extract was used in the decolorization of azo dyes, reactive blue 220 (RB220) and reactive black 5 (RB5), and anthraquinone dye, Remazol brilliant blue R (RBBR). The greatest laccase activity (4800U/g dry mass) occurred when the peptone and urea mixture was added to the solid state cultivation medium. When the nitrogen concentration was 1g/L, the laccase activity increased to 6555U/g dry mass. The laccase activity peak occurred on the 10th day, and the maximum decolorization within 24h was observed with enzymatic extracts obtained on different cultivation days, i.e., 6th day for RB220, 10th day for RB5, and 9th day for RBBR. Manganese and lignin peroxidases were not produced when nitrogen was added to the cultivation medium. The crude enzymatic extract was more effective in the decolorization of azo dyes (RB220 and RB5), more than 90% of decolorization, than anthraquinone dye with 77% decolorization.

The production of ligninolytic enzymes by the fungus Schizophyllum sp. F17 using a cost-effective medium comprised of agro-industrial residues in solid-state fermentation (SSF) was optimized. The maximum activities of the enzymes manganese peroxidase (MnP), laccase (Lac), and lignin peroxidases (LiP) were 1,200, 586, and 109 U/L, respectively, on day 5 of SSF. In vitro decolorization of three structurally different azo dyes by the extracellular enzymes was monitored to determine its decolorization capability. The results indicated that crude MnP, but not LiP and Lac, played a crucial role in the decolorization of azo dyes. After optimization of the dye decolorization system with crude MnP, the decolorization rates of Orange IV and Orange G, at an initial dye concentration of 50 mg/L, were enhanced to 76 and 57%, respectively, after 20 min of reaction at pH 4 and 35°C. However, only 8% decolorization of Congo red was observed. This enzymatic reaction system revealed a rapid decolorization of azo dyes with a low MnP activity of 24 U/L. Thus, this study could be the basis for the production and application of MnP on a larger scale using a low-cost substrate.

Shewanella xiamenensis BC01 (SXM) was isolated from sediment collected off Xiamen, China and was identified based on the phylogenetic tree of 16S rRNA sequences and the gyrB gene. This strain showed high activity in the decolorization of textile azo dyes, especially methyl orange, reactive red 198, and recalcitrant dye Congo red, decolorizing at rates of 96.2, 93.0, and 87.5%, respectively. SXM had the best performance for the specific decolorization rate (SDR) of azo dyes compared to Proteus hauseri ZMd44 and Aeromonas hydrophila NIU01 strains and had an SDR similar to Shewanella oneidensis MR-1 in Congo red decolorization. Luria-Bertani medium was the optimal culture medium for SXM, as it reached a density of 4.69 g-DCW L(-1) at 16 h. A mediator (manganese) significantly enhanced the biodegradation and flocculation of Congo red. Further analysis with UV-VIS, Fourier Transform Infrared spectroscopy, and Gas chromatography-mass spectrometry demonstrated that Congo red was cleaved at the azo bond, producing 4,4'-diamino-1,1'-biphenyl and 1,2'-diamino naphthalene 4-sulfonic acid. Finally, SEM results revealed that nanowires exist between the bacteria, indicating that SXM degradation of the azo dyes was coupled with electron transfer through the nanowires. The purpose of this work is to explore the utilization of a novel, dissimilatory manganese-reducing bacterium in the treatment of wastewater containing azo dyes.

It is widely accepted that the addition of redox mediators increases the decolorization rates of azo dyes by bacterial strains under anaerobic conditions. However, little information exists about whether quinoid redox mediators can enhance the performance of aerobic azo dye decolorization. In the present study, quinone-mediated decolorization of different azo dyes by whole cells and cell extracts from the Escherichia coli strain CD-2 under aerobic conditions were investigated. The results demonstrated that reduction rates of different azo dyes were greatly increased when quinone compounds were used as redox mediators. Compared with menadione, 2-hydroxy-1,4-naphthoquinone (lawsone) was more effective at aiding azo dye degradation and the optimum concentration for lawsone is 0.1mM. Strain CD-2 and the anthraquinone were co-immobilized by entrapment in different polymeric matrices. The co-immobilized beads exhibited good catalytic activity for azo dye degradation and kept stable during successive repeated experiments. The mechanism of the quinone-mediated reduction showed that although whole cells incubated with quinones could significantly increase the rate of decolorization of azo dyes, the quinone compounds did not directly promote azoreductase activity. According to the survey, this is the first report to confirm that the addition of quinoid redox mediators to bacteria increased decolorization under aerobic conditions.

Aerobic decolorization and degradation of azo dyes by suspended growing cells and immobilized cells of a newly isolated yeast Magnusiomyces ingens LH-F1

Chapter 19 - Enzymatic decolorization and degradation of azo dyes

Decolorization and degradation of azo dye – Reactive Violet 5R by an acclimatized indigenous bacterial mixed cultures-SB4 isolated from anthropogenic dye contaminated soil

Biodecolorization of synthetic wastewater containing azo dyes, Direct Red-80 (DR-80) and Mordant Blue-9 (MB-9), both individually and together, using immobilized Phanerochaete chrysosporium in a batch-operated rotating biological contactor (RBC) reactor was investigated. Following initial startup of the RBC reactor, which took almost 1 month, results on dye decolorization and enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) by the fungus were obtained. From experiments involving the individual dyes, decolorization efficiencies were found to be in the range of 94−100%, and from experiments in which the dyes were added together, the decolorization efficiencies of the dye mixture were between 77% and 97% at the end of 24 h. Results of LiP and MnP activities by the fungus revealed a strong role played by the enzymes in the dye decolorization process. As compared to the previous results obtained in batch shake flasks, the results in the present study revealed excellent performance of...

Kinetic study approach of remazol black-B use for the development of two-stage anoxic–oxic reactor for decolorization/biodegradation of azo dyes by activated bacterial consortium

Azo dyes are the largest and the most diverse group of synthetic dyes widely used in many industries, which are generally recalcitrant to biodegradation due to their xenobiotic nature. The effective treatment of azo dye wastewaters has been a big challenge, and up to now there is no single and economically attractive treatment that can effectively decolorize dyes. However, notable achievements have been conducted to explore the accelerating effects of different redox mediators during the anaerobic decolorization and degradation of azo dyes over the last two decades. The accumulated evidence suggest that redox mediators play a major role of electron shuttles in the reductive decolorization of azo dyes, both by chemical and biological mechanisms. This review is focused on the bacterial decolorization and degradation of azo dyes catalyzed by redox mediators and the further investigation to enhance the applicability of redox mediators on the bio-transformation of azo dyes.

Synthetic azo dyes are widely used in the textile industry; however, their use often poses environmental challenges. Here, we characterized the compost bacterium Bacillus subtilis strain CKCC for the decolorization of various azo dyes, including Congo Red, Reactive Black 5, Reactive Green 19, Reactive Red 120, and Reactive Blue 4. The application of strain CKCC exhibited high decolorization efficiency by utilizing various extracellular enzymes, including azoreductase and ligninolytic enzymes such as laccase, lignin peroxidase, and manganese peroxidase, which are essential for the decolorization of azo dyes. Fourier transform infrared spectroscopy (FTIR) analysis revealed structural changes during decolorization, consistent with the degradation of key functional groups. This transformation was attributed to the cleavage of azo linkages by azoreductase, with ligninolytic enzymes functioning on phenolic and aromatic moieties. While FTIR confirmed these structural changes, our findings only provided insights at the functional-group level, and the presence or absence of specific decolorized metabolites, such as aromatic amines, requires additional analytical techniques. In this study, the phytotoxic metabolites positively affected the germination and growth of Vigna radiata, confirming that decolorization using strain CKCC significantly reduced the toxic properties of the metabolites produced during dye decolorization. Hence, our isolated strain CKCC offers a potentially effective and environmentally sustainable method for treating azo-dye effluent in the textile industry.

Detoxification of synthetic dyes is one of the main challenges in clearing textile industry wastes. Biodegradation of azo-dyes using Phanerochaete chrysosporium is one the most environmentally friendly methods available. The main enzymes responsible for mycodecolorization process are lignin and manganese peroxidases. Here, optimization of expression conditions has been carried out with manipulating culture condition and nutrient sources. Therefore, the effects of buffer and temperature as well as nitrogen source on lignin peroxidase and manganese peroxidase production were investigated at two levels and four levels, respectively. For this purpose, P. chrysosporium RP78 based on Taguchi design of experiment has been applied. Maximum lignin and manganese peroxidase activities of 182 ± 2.5 U/L and 850 ± 41 U/L were obtained under predicted optimum conditions, respectively. Thereby, about 100 % decolorization was achieved after 24 h for two most widely used groups of azo dyes in textile industry consisting reactive and acidic. The physical adsorption of the azo dyes by mycelia was not significant which indicated that the enzymatic degradation of the dyes was occurred. Time profile of these enzymes showed that manganese peroxidase was peaked on 9 th day while lignin peroxidase peaked on 13 th. day and remained stable in the culture. The extracellular expression profiles of both were studied by 2 dimensional gel electrophoresis to partially characterize the enzymes.

Ligninolytic enzymes, including laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP), have attracted much attention in the degradation of contaminants. Genes of Lac (1827 bp), MnP (1134 bp) and LiP (1119 bp) were cloned from Aspergillus sp. TS-A, and the recombinant Lac (69 kDa), MnP (45 kDa) and LiP (35 kDa) were secretory expressed in Pichia pastoris GS115, with enzyme activities of 34, 135.12 and 103.13 U l−1, respectively. Dyes of different structures were treated via the recombinant ligninolytic enzymes under the optimal degradation conditions, and the result showed that the decolourization rate of Lac on Congo red (CR) in 5 s was 45.5%. Fourier-transform infrared spectroscopy, gas chromatography–mass spectrometry analysis and toxicity tests further proved that the ligninolytic enzymes could destroy the dyes, both those with one or more azo bonds, and the degradation products were non-toxic. Moreover, the combined ligninolytic enzymes could degrade CR more completely compared with the individual enzyme. Remarkably, besides azo dyes, ligninolytic enzymes could also degrade triphenylmethane and anthracene dyes. This suggests that ligninolytic enzymes from Aspergillus sp. TS-A have the potential for application in the treatment of contaminants.