Biological decolorization of industrial dyes by Candida tropicalis and Bacillus firmus

Abstract

Disperse dyes are chiefly used by textile industries for the coloration of polyester and cellulose triacetate and their blended fibres. Their extensive use and recalcitrant nature, high tinctorial strength renders the voluminous textile effluents intensively colored and causes environmental concerns. Decolorization of representative members of Dianix CC and Dianix S brands (DyStar Pvt. Ltd.) of disperse dyes were tested with Candida tropicalis and Bacillus firmus isolated respectively from contaminated soil samples and sludge of a domestic sewage drain. While both the cultures efficiently remove color from the aqueous solutions of the dyes, the yeast culture was found to decolorize most of the tested disperse dyes through biotransformation, the bacterial culture showed color removal mainly by adsorption on the cell pellets. Formation of cleavage products such as p-nitroaniline was observed in the case of Dianix Orange E-3R, indicating reductive cleavage of the azo linkage of the dye.