Environmental Engineering Reference
In-Depth Information
Degradation of Azo Dyes by White-Rot
Fungi
Susana Rodr
guez-Couto
í
1 Introduction
The rst synthetic dye, mauveine, was discovered in 1856 by the English chemist
W.H. Perkin. Since then, natural dyes have been progressively replaced by synthetic
dyes (Cardon
2003
). Thus, around 800,000 tons of synthetic dyes are produced
annually worldwide, 40 % of which are produced in Europe (Hessel et al.
2007
).
Synthetic dyes are xenobiotic compounds, i.e. extraneous to the biosphere. Conse-
quently, they are resistant to biodegradation by the indigenous micro-organisms and,
therefore, they persist in the environment for a long time, causing serious detrimental
effects on ecosystems.
Synthetic dyes are used extensively in many industrial sectors, such as printing,
pharmaceutical, food, cosmetic and textile industries (McMullan et al.
2001
). These
industries generate large quantities of coloured wastewater containing about
2
60 % of the dyes used, depending on the type of dyes (Hessel et al.
2007
).
Among synthetic dyes, since azo dyes are the most widely used, they are mostly
found in industrial ef
-
uents. Azo dyes are characterised by the presence of one or
more azo groups (
) (monoazo, diazo, triazo, polyazo) linked to phenyl and
naphthyl radicals, which usually have some combinations of functional groups
including amino (
N=N
-
-
NH
2
), chlorine (
Cl), hydroxyl (
OH), methyl (
CH
3
), nitro
-
-
-
-
(
SO
3
Na) (Fig.
1
). They are designed to
have high photolytic stability and resistance towards the main oxidising agents
(Reife and Othmer
1993
).
-
NO
2
), sulphonic acid and sodium salts (
-
Search WWH ::
Custom Search