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Fungi, Laccaria fraterna and Pleurotus ostreatus are potential microorganisms for the degradation of azodye (congored) in this study. Dye was demonstrated by their decolorization in the culture medium. Heat killed mycelium of Pleurotus ostreatus showed 35% dye absorption but treated mycelium degraded the congored up to 95% on 7th day itself. On the 14th day, except a small peak at UV region, the entire chromatophoric peak was removed due to fungi. Heat killed mycelium of L. fraterna exhibited 40% absorption, while treated mycelium showed 92% degradation on 7th day. On the 14th day and 21st day, 94-96% degradation was effected due to the fungal mycelium and their extracellular enzymes.
At present, over 10,000 dyes are commercially available and about 7×105 tons of dye stuffs
are being produced annually; inefficiency in the dyeing process results 10-15% of dyestuff being
directly let into waste waters which will consequently pollute the environment (Zollinger, 1987).
It is known that 90% of reactive textile dyes entering activated sludge sewage treatment plants
will pass through unchanged and will be discharged to rivers (Pierce, 1994). Contamination
of surface water with dyes from the textile—and dyestuff industry represents a serious ecological
problem (Mateja et al., 2006). Most of the azo dyes are either inert or non-toxic, but they
become toxic, mutagenic and carcinogenic upon their biotransformation.
The toxic products
are usually aromatic amines (Baughaman and Perenich, 1988). However, physical and chemical
treatment methods like ultraviolet, ion exchange and lime precipitation are expensive, and hence,
alternative eco-biotreatment processes are being explored.
Synthetic dyes are extensively used in paper, textile, photography, pharmaceutical, food,
cosmetics and other industries (Saratale et al., 2006). Biological decolorization of
triphenylmethane dyes has been widely reported using red yeasts, Rhodotorulae rubra andRhodotorulae sp (Kwasniewska, 1985); Cyathus bulleri can decolorize crystal violet, malachite
green and bromophenol blue (Vasdev et al., 1995). Based on the chemical source of the chromophoric group, synthetic dyes are described as azo dyes, anthraquinone dyes,
triarylmethane dyes, etc. Azo dyes constitute the largest of these groups used in industry.
The characteristic chemical structures of azo dyes (the azo linkage and aromatic groups) make
them recalcitrant to biological breakdown (Zollinger, 1987). |
