Studies of decolorization of azo dyes by ascomycete yeasts

Abstract

Azo dyes are the most widely used colored materials in textile industries and its biodegradability is, therefore, an important issue in the biological treatment of dye-containing wastewater. However, these treatments are not totally effective in removing color of textile dye wastewater since dyes are typically resistant to oxidative degradation. Most biodegradation studies on azo dyes involve bacterial species, and anaerobic or microaerophylic conditions are usually refered to as being favorable to a reduction step producing colorless amines. Our group has succeeded in isolating a number of yeast species, which revealed an interesting potential in the color removal of azo dyes in aerated culture media. Three of these species (UM2, UM41 and UM45), where used in the present work. The tested dyes included several sulphonic and carboxylic monoazo dyes, and several reactive textile dyes. The results which will be described refer to (i) the conditions and time-course of the decolorization process, (ii) the optimization of the decolorization medium, aiming at the reduction in yeast extract concentration, (iii) the identification of dye reduction products formed in the course of the decolorization process and (iv) the effect of those reduction products on yeast specific growth rates.