Synthetic dyes are extensively used for textile dyeing,
paper printing, colour photography and as additives in
petroleum products. During the dyeing process, 10–15%
of dye is discharged in the effluent. Approximately a half
of all known dyes are azo dyes, making them the largest
group of synthetic colourants. Azo dyes and their pigments
are versatile and the most common synthetic
colourants released into the environment. They are also
typically amenable to structural modification and representative
azo dyes can be made to bind most synthetic
and natural textile fibers. Approximately 10,000 different
dyes and pigments are used for industries and
over 7 105 tons of these dyes are annually produced
worldwide (Zollinger, 1987).
Several amino-substituted azo dyes including 4-phenylazoaniline
and N-methyl- and N,N-dimethyl-4-