Abstract
Isolated Enterococcus faecalis YZ 66 strain shows ability to decolorize various industrial dyes among which, it showed complete decolorization and degradation of toxic, sulfonated recalcitrant diazo dye Direct Red 81 (50 mg/L) within 1.5 h of incubation under static anoxic condition. The optimum pH and temperature for decolorization was 7.0 and 40°C, respectively. Significant induction in the activity of intracellular oxidoreductive enzymes suggested its involvement in the decolorization of Direct Red 81. The biodegradation of Direct Red 81 was monitored by UV-Visible, FT-IR spectroscopy and HPLC. The final products were characterized by GC-MS and possible pathway of the degradation of the dye was proposed. The phytotoxicity assay (with respect to plants Sorghum vulgare and Phaseolus mungo) revealed that the degradation of Direct Red 81 produced nontoxic metabolites. Finally E. faecalis was employed to decolorize actual industrial effluent showing decolorization (in terms of ADMI value) with moderate COD and BOD reduction. Moreover the result increases the applicability of the strain for the treatment of industrial wastewaters containing dye pollutants.Electronic supplementary materialThe online version of this article (doi:10.1186/s40201-014-0151-1) contains supplementary material, which is available to authorized users.
Highlights
Azo dyes are xenobiotic compounds characterized by the presence of one or more azo linkages and aromatic rings [1]
There was no abiotic loss of Direct Red 81 (DR 81) within 24 h incubation indicating that the decolorization of DR 81 was due to biological mechanism rather than adsorption
We propose that initially primary reductive cleavage in azo bond of Direct Red 81 results in the product such as, sodium-4-aminobenzenesulfonate, 1,4-benzenediamine and 7-benzylamino-3-dibenzyl-1-4hydroxy naphthalene-2-sulfonic acid
Summary
Azo dyes are xenobiotic compounds characterized by the presence of one or more azo linkages and aromatic rings [1]. They are the largest class of dyes with the greatest variety of colour. Among various applications of synthetic dyes about 30,000 tons of different dyestuffs are produced per year worldwide [3]. Among these synthetic dyes, azo dyes are the most widely used which account for over 60% of the total number of dyes known to be manufactured [4,5]. Some investigators reported that azo dyes and their metabolites are toxic, carcinogenic and mutagenic in nature which leads to the formation of tumors and allergies besides growth inhibition of bacteria, protozoan, algae, plants and different animals [6,7]
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