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

University of Minho, Department of Textile Engineering, 4800-058 Guimarães, Portugal,¹ University of Applied Sciences Cologne, Institute of Chemical Engineering and Plant Design, Betzdorfer Str. 2, D-50679 Cologne, Germany²

Received 19 April 2005/ Accepted 23 June 2005

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 ¹³C-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.