Textile Dyes Degradation: A Microbial Approach for Biodegradation of Pollutants - Microbial Degradation of Synthetic Dyes in Wastewaters - page 184

synthetic dye was patented by Perkin in August 1856, as dye aniline purple and
after its success in France, it was renamed mauve (or mauveine), after the French
word for the purple mallow

ower (Susan 1982 ).
The coloring processes discharge huge quantities of dye ef uents, which pollute

local terrestrial habitat, rivers and others aquatic bodies. The untreated ef uents and

toxic chemicals, solid wastes nd their way to the ground water and rivers, causing

extensive damage to soil and water. In countries, such as India, China and Mauritius
discharge from a large number of the textile industries go straight into the rivers.
According to an annual report by Union Ministry of Environment and Forests
(MoEF), about 4.4 million tons of hazardous wastes are generated by 13,011 units
spread over 373 districts of the country (Ramaswamy 2003 ). The industrial process
produces wastewater containing about one tone of dyes daily.
Dyes are natural or synthetic colored organic compounds having the property of
imparting their color to the other substances, such as textile

bers. Synthetic dyes are
used extensively for textile dyeing, paper printing, leather dyeing, color photography
and as additives in petroleum products because of their ease and cost effectiveness in
synthesis, rmness, high stability to light, temperature, detergent and microbial attack

and variety in color as compared to natural dyes (Couto 2009 ). The dyestuff, textile,
paper and leather industries, the major users of dyes, produce ef

uents that are usually
very resistant to the biological treatment and hence, their industrial waste is a major
problem to the environment. The released wastewater from textile industries is a
complex mixture of many polluting substances, ranging from agro-based pesticides
to heavy metals associated with dye or the dye process. Approximately, 10,000
different dyes and pigments are used in different industries and their production
exceeds over 7 10 5 tonnes annually worldwide (Zollinger 1987 ). The textile

industry generates a large volume of wastewater, which if not properly treated, can
cause serious problems of environmental contamination (Kunz et al. 2002 ).
Many synthetic dyes are used in a number of industries, such as textiles, paper
printing, color photography and the food industries (Meyer 1981 ) and as additive in
petroleum products (Maynard 1983 ). The pigments used in printing ink, such as
carbon black, titanium dioxide and others organic pigments, which are rendered
insoluble by complexing with metal ions. Most of these pigments are prepared from
azo, anthraquinone and triarylmethane dyes, and phthalocyanines. Since 50 % of
dyes are used in the textile industry, azo dyes account for the largest proportion of
all synthetic dyes in terms of number and amount. Approximately 70 % of all
organic dyes that are currently available in the market are manufactured mainly in
China, India, Korea, Taiwan and Argentina. Azo dyes, one of the largest classes of
dyes used in textile industry, are released into the aquatic and terrestrial environ-
ments through the ef

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uents emanating from textile and dyestuff industries and are
normally not removed by conventional wastewater treatment system. The charac-
teristic chemical structure (such as

─ C ═ C ─ , ─ N ═ N ─ and ─ C ≡ N ─ ) of azo

dyes makes them recalcitrant to biological break down.
Biodegradation refers to the breakdown of complex molecules to mostly smaller
and simpler ones. The original complex molecules are often environmentally
objectionable. The biodegradation is a biological process by which environmental