Potential applications of the oxidoreductive enzymes in the decolorization and detoxification of textile and other synthetic dyes from polluted water: a review

Recently, the enzymatic approach has attracted much interest in the decolorization/degradation of textile and other industrially important dyes from wastewater as an alternative strategy to conventional chemical, physical and biological treatments, which pose serious limitations. Enzymatic treatment is very useful due to the action of enzymes on pollutants even when they are present in very dilute solutions and recalcitrant to the action of various microbes participating in the degradation of dyes. The potential of the enzymes (peroxidases, manganese peroxidases, lignin peroxidases, laccases, microperoxidase-11, polyphenol oxidases, and azoreductases) has been exploited in the decolorization and degradation of dyes. Some of the recalcitrant dyes were not degraded/decolorized in the presence of such enzymes. The addition of certain redox mediators enhanced the range of substrates and efficiency of degradation of the recalcitrant compounds. Several redox mediators have been reported in the literature, but very few of them are frequently used (e.g., 1-hydroxybenzotriazole, veratryl alcohol, violuric acid, 2-methoxy-phenothiazone). Soluble enzymes cannot be exploited at the large scale due to limitations such as stability and reusability. Therefore, the use of immobilized enzymes has significant advantages over soluble enzymes. In the near future, technology based on the enzymatic treatment of dyes present in the industrial effluents/wastewater will play a vital role. Treatment of wastewater on a large scale will also be possible by using reactors containing immobilized enzymes.     

Peroxidase mediated decolorization and remediation of wastewater containing industrial dyes: a review

In this article an effort has been made to review literature based on the role of peroxidases in the treatment and decolorization of a wide spectrum aromatic dyes from polluted water. Peroxidases can catalyze degradation/transformation of aromatic dyes either by precipitation or by opening the aromatic ring structure. Peroxidases from plant sources; horseradish, turnip, tomato, soybean, bitter gourd, white radish and Saccharum uvarum and microbial sources; lignin peroxidases, manganese peroxidases, vanadium haloperoxidases, versatile peroxidases, dye decolorizing peroxidases have been employed for the remediation of commercial dyes. Soluble and immobilized peroxidases have been successfully exploited in batch as well as in continuous processes for the treatment of synthetic dyes with complex aromatic molecular structures present in industrial effluents at large scale. However, recalcitrant dyes were also decolorized by the action of peroxidases in the presence of redox mediators.     

Remediation and treatment of organopollutants mediated by peroxidases: a review

In this paper an effort has been made to review the literature on the role of peroxidases in the remediation and treatment of a wide spectrum of aromatic pollutants. Peroxidases can catalyse degradation/transformation of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, organochlorines, 2,4,6-trinitrotoluene, phenolic compounds and dyes. These enzymes are also capable of treating various types of recalcitrant aromatic compounds in the presence of redox mediators. Immobilised peroxidases from plant and fungal sources have been used for the remediation of such types of industrial pollutants on a large scale.     

Oxidoreductases for the remediation of organic pollutants in water – a critical review

Water contamination by various recalcitrant organic aromatic compounds is an emerging environmental issue that is increasingly attracting the attention of environmental scientists. A great majority of these recalcitrant pollutants are industrial wastes, textile dyes, pharmaceuticals, hormones, and personal care products that are discharged into wastewater. Not surprisingly, various chemical, physical, and biological strategies have been proposed and developed to remove and/or degrade these pollutants from contaminated water bodies. Biological approaches, specifically using oxidoreductase enzymes (such as peroxidases and laccases) for pollutant degradation are a relatively new and a promising research area that has potential advantages over other methods due to their higher efficiency and the ease of handling. This review focuses on the application of different classes of oxidoreductase enzymes to degrade various classes of organic pollutants. In addition to classifying these enzymes based on structural differences, the major factors that can affect their remediation ability, such as the class of peroxidases employed, pH, molecular structure of the pollutant, temperature, and the presence of redox mediators are also examined and discussed. Interestingly, a literature survey combined with our unpublished data suggests that “peroxidases” are a very heterogeneous and diverse family of enzymes and have different pH profiles, temperature optima, thermal stabilities, requirements for redox mediators, and substrate specificities as well as varying detoxification abilities. Additionally, remediation of real-life polluted samples by oxidoreductases is also highlighted as well as a critical look at current challenges and future perspectives.     

Use of bitter gourd (Momordica charantia) peroxidase together with redox mediators to decolorize disperse dyes

In this study, salt fractionated bitter gourd (Momordica charantia) peroxidase was used for the decolorization of water-insoluble disperse dyes; Disperse Red 17 and Disperse Brown 1. Effect of nine different redox mediators; bromophenol, 2,4-dichlorophenol, guaiacol, 1-hydroxybenzotriazole, m-cresol, quinol, syringaldehyde, violuric acid, and vanillin on decolorization of disperse dyes by bitter gourd peroxidase has been investigated. Among these redox mediators, 1-hydroxybenzotriazole was the most effective mediator for decolorization of both the dyes by peroxidase. Bitter gourd peroxidase (0.36 U/mL) could decolorize Disperse Red 17 maximally 90% in the presence of 0.1 mM 1-hydroxybenzotriazole while Disperse Brown 1 was decolorized 65% in the presence of 0.2 mM 1-hydroxybenzotriazole. Maximum decolorization of these dyes was obtained within 1 h of incubation at pH 3.0 and temperature 40°C. The application of such enzyme plus redox mediator systems may be extendable to other recalcitrant and water insoluble synthetic dyes using novel redox mediators and peroxidases from other new and cheaper sources.     

Redox-mediated decolorization of Direct Red 23 and Direct Blue 80 catalyzed by bioaffinity-based immobilized tomato (Lycopersicon esculentum) peroxidase

The aim of this study was to investigate the role of concanavalin A (Con A)-cellulose-bound tomato peroxidase for the decolorization of direct dyes. Cellulose was used as an inexpensive material for the preparation of bioaffinity support. Con A-cellulose-bound tomato peroxidase exhibited higher efficiency in terms of dye decolorization as compared to soluble enzyme under various experimental conditions. Both Direct Red 23 and Direct Blue 80 dyes were recalcitrant to the action of enzyme without a redox mediator. Six compounds were investigated for redox-mediating property. Immobilized peroxidase decolorized both dyes to different extent in the presence of all the used redox mediators. However, 1-hydroxybenzotriazole emerged as a potential redox mediator for tomato peroxidase catalyzed decolorization of direct dyes. These dyes were maximally decolorized at pH 6.0 and 40 degrees C by soluble and immobilized peroxidase. The absorption spectra of the untreated and treated dyes exhibited a marked difference in the absorption at various wavelengths. Immobilized tomato peroxidase showed a lower Michaelis constant than the free enzyme for both dyes. Soluble and immobilized tomato peroxidase exhibited significantly higher affinity for Direct Red 23 compared to Direct Blue 80.     

Differential decolorization of textile dyes in mixtures and the joint effect of laccase and cellobiose dehydrogenase activities present in extracellular extracts from Funalia trogii

The largest part of the bio-decolorization investigations have been performed to date on a single dye without exploring the behavior in complex mixtures as the real dyeing baths. Therefore, mixtures of dyes belonging to azo and anthraquinonic classes, chosen among the most utilized in textile wool dyeing, were employed for comparative enzymatic decolorization studies using the extracellular extracts from the white rot fungus Funalia trogii, to understand how the concomitant presence of more than one dye could influence their degradation course and yield.Fungal extracts containing laccase activity only were capable to partially decolorize dyes mixtures from the different classes analyzed. The deconvolution of the decolorization with time allowed to monitor the degradation of the single dyes in the mixtures evidencing a time dependent differential decolorization not observed for the singles alone. Some dyes in the blend were in fact decolorized only when the most easily converted dyes were largely transformed. These experiments would allow to help the dyeing factories in the selection of the most readily degraded dyes.Since F. trogii grown on different media and activators shows diverse levels of expression of the redox enzymes laccase and cellobiose dehydrogenase (CDH), the dyes mixtures recalcitrant to decolorization by laccase activity alone, were subjected to the combined action of extracts containing laccase and CDH. The use of CDH, in support to the activity of laccase, resulted in substantial decolorization increases (>84%) for all the refractory dyes mixtures.     

Partially purified bitter gourd (Momordica charantia) peroxidase catalyzed decolorization of textile and other industrially important dyes

The aim of this study was to evaluate the enzymatic action of partially purified bitter gourd peroxidase for the degradation/decolorization of complex aromatic structures. Twenty-one dyes, with a wide spectrum of chemical groups, currently being used by the textile and other important industries have been selected for the study. Here, for the first time we have shown peroxidases from Momordica charantia (300 EU/gm of vegetable) to be highly effective in decolorizing industrially important dyes. Dye solutions, containing 50-200 mg dye/l, were used for the treatment with bitter gourd peroxidase (specific activity of 99.0 EU/mg protein). M. charantia peroxidases were able to decolorize most of the textile dyes by forming insoluble precipitate. When the textile dyes were treated with increasing concentration of enzyme, it was observed that greater fraction of the color was removed but four out of eight reactive dyes were recalcitrant to decolorization by bitter gourd peroxidase. Step-wise addition of enzyme to the decolorizing reaction mixture at the interval of 1h further enhanced the dye decolorization. The rate of decolorization was enhanced when the dyes were incubated with fixed quantity of enzyme for increasing times. Decolorization of non-textile dyes resulted in the degradation and removal of dyes from the solution without any precipitate formation. Decolorization rate was drastically increased when the textile and other industrially important non-textile dyes were treated with bitter gourd peroxidase in presence of 1.0 mM 1-hydroxybenzotriazole. Complex mixtures of dyes were prepared by taking three to four reactive textile and non-textile dyes in equal proportions. Each mixture was decolorized by more than 80% when treated with the enzyme in presence of 1.0 mM 1-hydroxybenzotriazole. Our data suggest that the peroxidase/mediator system is an effective biocatalyst for the treatment of effluents containing recalcitrant dyes from textile, dye manufacturing, dyeing and printing industries.     

Comparison of the potential of Ficus sycomorus latex and horseradish peroxidases in the decolorization of synthetic and natural dyes

The aim of this study was to compare the potential of Ficus sycomorus latex peroxidase (POL) and horseradish peroxidase (HRP) in the decolorization of a wide spectrum of eight synthetic dyes and two natural dyes, hibiscus flower color and pomegranate juice. We study for the first time the decolorization of natural dyes enzymatically. The highest decolorization percent was reported at 20 mg/l for all dyes treated with POL and HRP. Both the enzymes had lower decolorization % for azo-carmin (30–33%). During decolorization treatment, both natural dyes and titan yellow formed precipitates which settled down and were removed by centrifugation. The enhancement of the decolorization % of the most tested dyes by treatment with POL and HRP was reported in the presence of some redox mediators. The rate of decolorization was enhanced by increasing the time and the most significant changes were observed during the first 6 h of incubation. One hundred percent enhancement in decolorization was reported for azo-carmine in the presence of histidine and α-naphthol as redox mediators. A few of redox mediators caused no significant effect or decreases the decolorization % for a little number of tested dyes. The decolorization of dyes by POL and HRP in the presence of redox mediators appeared without the formation of precipitate. A similar decolorization % for all the tested dyes by POL and HRP was detected. The data suggested that the peroxidase/mediator system was an effective biocatalyst for the decolorization of synthetic and natural dyes, and POL could be used as a potential option for the application of dye decolorization.     

Decolorization of textile dyes by enzymatic extract and submerged cultures of <Emphasis Type="Italic">Pleurotus sajor-caju</Emphasis>

Pleurotus sajor-caju PS2001 was screened in Petri dish plates to assess the dye-decolorizing ability of industrial textile dyes. P. sajor-caju PS2001 was also cultivated in solid-state fermentation containing sawdust of Pinus sp. and wheat bran to obtain the enzymatic extract, showing laccase and manganese-peroxidase activity, which was used to test the capacity to degrade the textile dyes. Additional tests of decolorization were performed in liquid cultures. Anthraquinone-type textile dyes proved to be substrates for the enzymatic system of P. sajor-caju PS2001. Cultures in Petri dish plates showed that the anthraquinone dye Reactive Blue 220 can act as a redox mediator for the enzymatic reactions involved in the decolorization process, and enables the azo dye degradation. Reactive Blue 220 and Acid Blue 280 were completely decolorized in 30 min and 60 min, respectively, during the tests with precipitated enzymatic extract, while the azo dyes showed resistance to degradation. Additionally, in submerged cultures with dyes, veratryl alcohol oxidases and lignin peroxidase activities were observed. These results suggest that the strain P. sajor-caju PS2001 has great potential for use in the bioremediation technology of recalcitrant pollutant such as textile effluents.     

Potential of Trametes trogii culture fluids and its purified laccase for the decolorization of different types of recalcitrant dyes without the addition of redox mediators

Trametes trogii BAFC 463 culture fluids (containing 110 U ml⁻¹ laccase; 0.94 U ml⁻¹ manganese peroxidase), as well as its purified laccase were capable of decolorizing azoic, indigoid, triphenylmethane, anthraquinonic and heterocyclic dyes, in the absence of redox mediators. Six dyes: RBBR, Indigo Carmine, Xylidine, Malachite Green, Gentian Violet and Bromophenol Blue were almost completely degraded (more than 85% decolorization after 1 d) by either laccase or T. trogii itself in culture, proving the role of the enzyme in dye decolorization. The purified laccase also decolorized 65% of Fast Blue RR and 30% of Azure B and Methylene Blue after 24 h. The use of redox mediators significantly increased the decolorization rates (90% decolorization of Azure B after 1 h). 1-hydroxybenzotriazole resulted the best redox mediator, but the natural mediator p-hydroxybenzoic acid also demonstrated its efficiency for dye decolorization. Due to their ability to decolorize recalcitrant dyes without addition of redox mediators, high laccase activities, high thermostability and efficient decolorization at 70 °C and pH 7.0, even in the presence of high concentrations of heavy metals (100 mM Cu⁺², Pb⁺² or Cd⁺²) or in a synthetic dyebath, T. trogii culture fluids could be effectively used to decolorize synthetic dyes from effluents.     

Fungal laccase, cellobiose dehydrogenase, and chemical mediators: combined actions for the decolorization of different classes of textile dyes

Dyes belonging to the mono-, di-, tri- and poly-azo as well as anthraquinonic and mono-azo Cr-complexed classes, chosen among the most utilized in textile applications, were employed for a comparative enzymatic decolorization study using the extracellular crude culture extracts from the white rot fungus Funalia (Trametes) trogii grown on different culture media and activators able to trigger different levels of expression of oxidizing enzymes: laccase and cellobiose dehydrogenase. Laccase containing extracts were capable to decolorize some dyes from all the different classes analyzed, whereas the recalcitrant dyes were subjected to the combined action of laccase and the chemical mediator HBT, or laccase plus cellobiose dehydrogenase. Correlations among the decolorization degree of the various dyes and their electronic and structural diversities were rationalized and discussed. The utilization of cellobiose dehydrogenase in support to the activity of laccase for the decolorization of azo textile dyes resulted in substantial increases in decolorization for all the refractory dyes proving to be a valid alternative to more expensive and less environmentally friendly chemical treatments of textile dyes wastes.     

Decolorization and detoxification of textile dyes using a versatile Streptomyces laccase-natural mediator system

Currently, there is increasing interest in assessing the potential of bacterial laccases for industrial and environmental applications especially in harsh conditions. The environmental impact of the textile industry requires novel and effective technologies to mitigate the presence of dyes in wastewaters before discharging into the environment. Dyes usually remain stable in the presence of a variety of chemicals, light and are recalcitrant to microbial degradation. Among available technologies the biological treatments offer environmentally friendly strategies for decolorizing and detoxifying these compounds. The recent discovery of versatile laccases in streptomycetes opens up new opportunities for their commercial application. The aim of this study is to assess the potential of a novel bacterial laccase SilA produced by Streptomyces ipomoeae CECT 3341 active over wide temperature and pH ranges for use as an eco-friendly, biological treatment for the degradation of textile dyes. Insights into the enhancement of the oxidative action of this enzyme through the use of natural redox mediators are presented together with an assessment of the potential toxicity of the degradation products. Our results confirm that the combination of the laccase and natural mediators such as acetosyringone and methyl syringate enhanced the decolorization and detoxification of a variety of textile dyes up to sixfold and 20-fold, respectively. Mediator concentration was found to have a significant effect (p < 0.05) on dye decolorization at 60 °C; thus, the decolorization of Acid Orange 63 increased from 6 to 70-fold when the mediator concentration was increased from 0.1 to 0.5 mM. Further, the toxicity of tartrazine decreased 36-fold when the SilA-MeS system was used to decolorize the dye. The thermal properties of the SilA coupled with the stability of SilA at high pH suggest a potential commercial application for use in the decolorization of textile wastewaters which generally are performed at high temperature (>55 °C) and salinity and neutral pH, conditions which are unfavourable for conventional fungal laccases.     

Rapid decolorization of azo dyes by crude manganese peroxidase from Schizophyllum sp. F17 in solid-state fermentation

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.     

Immobilization of horseradish peroxidase onto Purolite® A109 and its anthraquinone dye biodegradation and detoxification potential

Horseradish peroxidase (HRP) is a highly specific enzyme with great potential for use in the decolorization of synthetic dyes. A comprehensive study of HRP immobilization using various techniques such as adsorption and covalent immobilization on the novel carrier Purolite® A109 with a special focus on enzymatic decolorization and toxicity of artificially colored wastewater. The immobilized preparations with an activity of 156.21 ± 1.41 U g⁻¹ and 85.71 ± 1.62 U g⁻¹ after the HRP adsorption and covalent immobilization, respectively, were obtained. Stability and reusability of the immobilized preparations were also evaluated. A noteworthy decolorization level (~90%) with immobilized HRP was achieved. Phytotoxicity testing using Mung bean seeds and acute toxicity assay with Artemia salina has confirmed the applicability of the obtained immobilized preparation in industrial wastewater plants for the treatment of colored wastewater.     

Lignin degrading system of white-rot fungi and its exploitation for dye decolorization

With global attention and research now focused on looking for the abatement of pollution, white-rot fungi is one of the hopes of the future. The lignin-degrading ability of these fungi have been the focus of attention for many years and have been exploited for a wide array of human benefits. This review highlights the various enzymes produced by white-rot fungi for lignin degradation, namely laccases, peroxidases, aryl alcohol oxidase, glyoxal oxidase, and pyranose oxidase. Also discussed are the various radicals and low molecular weight compounds that are being produced by white-rot fungi and its role in lignin degradation. A brief summary on the developments in research of decolorization of dyes using white-rot fungi has been made.     

Azo Dye Biodecolorization Enhanced by Echinodontium taxodii Cultured with Lignin

Lignocellulose facilitates the fungal oxidization of recalcitrant organic pollutants through the extracellular ligninolytic enzymes induced by lignin in wood or other plant tissues. However, available information on this phenomenon is insufficient. Free radical chain reactions during lignin metabolism are important in xenobiotic removal. Thus, the effect of lignin on azo dye decolorization in vivo by Echinodontium taxodii was evaluated. In the presence of lignin, optimum decolorization percentages for Remazol Brilliant Violet 5R, Direct Red 5B, Direct Black 38, and Direct Black 22 were 91.75% (control, 65.96%), 76.89% (control, 43.78%), 43.44% (control, 17.02%), and 44.75% (control, 12.16%), respectively, in the submerged cultures. Laccase was the most important enzyme during biodecolorization. Aside from the stimulating of laccase activity, lignin might be degraded by E. taxodii, and then these degraded low-molecular-weight metabolites could act as redox mediators promoting decolorization of azo dyes. The relationship between laccase and lignin degradation was investigated through decolorization tests in vitro with purified enzyme and dozens of aromatics, which can be derivatives of lignin and can function as laccase mediators or inducers. Dyes were decolorized at triple or even higher rates in certain laccase–aromatic systems at chemical concentrations as low as 10 µM.     

Induction of a white laccase from the deuteromycete Myrothecium verrucaria NF-05 and its potential in decolorization of dyes

Myrothecium verrucaria NF-05 is a deuteromycete fungus capable of producing a white laccase. The optimal concentration of Cu²⁺ for laccase production by this strain is 0.2 mM (43.23 ± 1.16 U mL^{? 1}). A comprehensive investigation of the induction demonstrated that NF-05 laccase production could be synergistically enhanced by various inducers, including aromatic phenols, amines and recalcitrant dyes, in the presence of 0.2 mM Cu²⁺. Sixteen phenols, fourteen amines and four dyes exhibited significant inductive effects on laccase production. The best inducer was 3, 3’-dimethylbenzidine, which increased laccase production to 258.1 ± 11.1 U mL^{? 1}. These results suggest that M. verrucaria NF-05 is a promising industrial laccase producer. Based on the increased production, purified NF-05 laccase was used to decolorize dyes of various structural types in the presence of six redox mediators. Among the 26 tested dyes, the decolorization rate of six azo dyes, chromotrope 2R, orange G6, Congo red, Ponceau S, amaranth and reactive yellow 135 and two arylmethane dyes, fast green 3 and neutral red, were significantly increased by each of the six mediators. These results demonstrate the potential use of the NF-05 laccase for the decolorization of recalcitrant dyes in dye bleaching and effluent detoxification.     

The new incorporation bio-treatment technology of bromoamine acid and azo dyes wastewaters under high-salt conditions

The accelerating effect of quinones has been studied in the bio-decolorization processes, but there are no literatures about the incorporation bio-treatment technology of the bromoamine acid (BA) wastewater and azo dyes wastewaters under high-salt conditions (NaCl, 15%, w/w). Here we described the BA wastewater as a redox mediator in the bio-decolorization of azo dye wastewaters. Decolorization of azo dyes was carried out experimentally using the salt-tolerant bacteria under the BA wastewater and high-salt conditions. The BA wastewater used as a redox mediator was able to increase the decolorization rate of wastewater containing azo dyes. The effects of various operating conditions such as dissolved oxygen, temperature, and pH on microbial decolorization were investigated experimentally. At the same time, BA was tested to assess the effects on the change of the Oxidation–Reduction Potential (ORP) values during the decolorization processes. The experiments explored a great improvement of the redox mediator application and the new bio-treatment concept.