Degradation of Azo Dyes by Trametes villosa Laccase over Long Periods of Oxidative Conditions

Abstract

Trametes villosa laccase was used for direct azo dye degradation, and the reaction products that accumulated after 72 h of incubation were analyzed. Liquid chromatography-mass spectrometry (LC-MS) analysis showed the formation of phenolic compounds during the dye oxidation process as well as a large amount of polymerized products that retain azo group integrity. The amino-phenol reactions were also investigated by 13 C-nuclear magnetic resonance and LC-MS analysis, and the polymerization character of laccase was shown. This study highlights the fact that laccases polymerize the reaction products obtained during long-term batch decolorization processes with azo dyes. These polymerized products provide unacceptable color levels in effluents, limiting the application of laccases as bioremediation agents.The chemical structure of dyes is comprised of a conjugated system of double bonds and aromatic rings. The major classes of dyes have antroquinoid, indigoid, and azo aromatic structures. All of these structures allow strong -* transitions in the UV-visible (UV-Vis) area, with high extinction coefficients that allow us to consider these structures dye chromophores. Of all of these structures, the azo aromatic one is the most widespread dye class in the industry. The main drawback of this class of dyes is that they are not easily degraded by aerobic bacteria, and with the action of anaerobic or microaerobic reductive bacteria, they can form toxic and/or mutagenic compounds such as aromatic amines (9, 10, 34). There is a great environmental concern about the fate of these dyes, with special emphasis on reactive dyeing of cellulosic fibers, where large amounts of unbound dye are discharged in the effluent (24).Laccases have been extensively studied for their degradation of azo dyes (1,5,8,17,19,21,23,33). These enzymes are multicopper phenol oxidases that decolorize azo dyes through a highly nonspecific free radical mechanism forming phenolic compounds, thereby avoiding the formation of toxic aromatic amines (8,35). Over long periods of time, there can be a coupling between the reaction products, and even polymerization. It is known that laccases can catalyze the polymerization of various halogen-, alkyl-, and alkoxy-substituted anilines (15). In the literature, there is a large number of papers reporting on the decolorization of azo dyes; however, the fate of the products of azo dye laccase reactions and their possible polymerization have been ignored (7,16,25,28). Therefore, the purpose of this work was the study of azo dye degradation products in the presence of laccase. Direct azo dye laccase degradation and amino-phenol polymerization were performed for several days. The formed soluble products were studied by liquid chromatography-mass spectrometry (LC-MS), and the polymerized insoluble products were studied by 13 C-nuclear magnetic resonance ( 13 C-NMR). MATERIALS AND METHODSDyes, reagents, and enzymes. The investigated dyes, 3-(4-dimethylamino-1-phenylazo) benzenesulfonic acid (dye I) and 3-(2-hydroxy-1-naphthyl...

Laccase-conjugated amino-functionalized nanosilica for efficient degradation of Reactive Violet 1 dye

“…Thus, analytical studies revealed RV 1 degradation yielded low-molecular-weight compounds using oxidative mechanism of laccase nanoparticles. Similar results were reported by Zille et al [40], who studied degradation pathway of azo dyes, 3-(4-dimethylamino-1-phenylazo) benzenesulfonic acid (dye I) and 3-(2-hydroxy-1-naphthylazo) benzenesulfonic acid (dye II) using Trametes villosa laccase.…”

Decolourization of Congo Red by Ganoderma lucidum Laccase: Evaluation of Degradation Products and Toxicity

“…Laccases present wide substrate specificity, are tolerant to pollutants at high concentrations and can be produced in large quantities through fermentative processes. For these reasons, they have attracted growing attention in many industrial and environmental fields, including textile dye decolourization (Zille et al 2005;Michniewicz et al 2008;Majeau et al 2010;Manavalan et al 2013).…”

Degradation of Synthetic Azo Dyes of Textile Industry: a Sustainable Approach Using Microbial Enzymes

“…2 Mechanism of reduction of azo dyes by azoreductase [28,36] Fig . 3 Proposed mechanism of laccase in degradation of an azo compound, 3-(2-hydroxy-1-naphthylazo) benzenesulfonic acid [28,37] sulfophenyldiazene gets oxidized to phenyldiazene radical, followed by readily loss of molecular nitrogen producing sulfonyl radical and ultimately producing sulfophenyl hydroperoxide, scavenged by oxygen [5] (Fig. 3).…”