STUDIES ON BIODEGRADATION OF SELECTED AZO DYE
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Date
2010
Authors
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Publisher
IARI, DIVISION OF MICROBIOLOGY
Abstract
Synthetic dyes and pigments are widely used nowadays in textile, paper printing, food, cosmetics and pharmaceutical industries. These dyes are released into the environment from two major sources, the textile and the dye manufacturing industries. Contamination of surface water with dyes from these textile and dye manufacturing industries represents a serious ecological problem. World wide 7×105 metric tonnes of the dyes and pigments are produced out of which azo dye represents 70%. Azo dyes are the largest group of man made chemicals since aromatic azo and sulfo groups are not synthesized in nature and hence azo dyes are considered to be xenobiotics.
In the present investigation, biodegradation of sulfonated diazo dye Red HE7B by Bacillus sp. Azo1, isolated from textile dyeing mill effluent contaminated soil, was studied. Numerical prevalence of the dye decolourizer present in contaminated sample soil collected from various sites was estimated by most probable number technique. Highest number of dye decolourizer was found in the soil sample collected from textile mill effluent contaminated field soil left barren followed by rice field adjacent to main drainage carrying effluent. Out of the six isolates, Azo1 and Azo5 showed remarkably good decolourization ability during initial screening, but further study showed that decolourization potential of Azo5 was quite variable and hence rest of the experiments were conducted with Azo1. This isolate decolourized 100% of the dye at 50mg/l and 71% at 200mg/l dye concentrations at 300C. Decolourization of dye was recorded from pH 5 to 9 with maximum declourization observed at pH 7. Among various carbon sources tested, citric acid proved to be the best followed by starch. Least decolourization was observed when glucose was used as a carbon source. Effect of aeration on decolourization of Red HE7B was negative and best decolourization was observed under static condition.
Biodegradation of the dye was confirmed by TLC and HPLC. High levels of induction in activities of key enzymes like azoreductase and laccase was suggestive of involvement of these enzymes in biodegradation of Red HE7B. Mass spectra of degradation product obtained by GCMS showed formation of a number of products, some of which were identified and a tentative pathway of degradation was worked out. Phytotoxicity study of Red HE7B and its degradation product showed reduction in root length, shoot length and fresh weight of seedling with more effect on root length of
wheat, radish and mustard in presence of dye. Biodegradation product of the dye did not cause any significant effect on these parameters indicating it as to be nonphytotoxic. Hence biodegradation of the dye Red HE7B by Bacillus sp. Azo1 can be economic and ecofriendly option for textile mill caused pollution.
Description
T-8373
Keywords
colourants, concentrates, productivity, enzymes, liquid wastes, bacteria, biodegradability, acidity, processed products, irrigation