Environmental Engineering Reference
In-Depth Information
like wood, polyamide, silk and modi
ed aryl. Basic dyes are cationic compounds
that are used for dyeing acid-group containing
bers, usually synthetic
bers like
modi
ed poly aryl (van der Zee
2002
).
Dyes are usually aromatic and heterocyclic compounds and are often recalcitrant
in nature. A few of them are very toxic and even carcinogenic in nature (Vyas and
Mollitoris
1995
). They include a broad spectrum of different chemical structures,
primarily based on substituted aromatic and heterocyclic groups, such as the aro-
matic amine (C
6
H
5
-
NH
2
), which is a suspected carcinogen, phenyl (C
6
H
5
-
CH
2
)
and naphthyl (NO
2
-
OH). Common to all is their ability to absorb light in the visible
region (Rajamohan and Karthikeyan
2006
). Direct dyes lack fastness during
washing and so, they are popular for items which are unlikely to require fastness
during washing like paper. A direct diazo dye commonly used in the paper industry
is Congo red, which is intended primarily for the coloration of paper products. It is
a recalcitrant and also a well known carcinogen due to the presence of the aromatic
amine group (Cripps et al.
1990
; van der Zee
2002
; Rajamohan and Karthikeyan
2006
). Congo red is the sodium salt of benzidinediazo-bis-1-naphtylamine-4-sul-
fonic acid (C
32
H
22
N
6
Na
2
O
6
S
2
; mw: 696.66 g mol
−
1
). It is a secondary diazo dye.
2 Microbial Treatment
Various physical, chemical and biological pre-treatment, as well as main treatment
techniques have been reported to remove color from dye-containing wastewater
(van der Zee
2002
). Biological techniques include bacterial and fungal biosorption
and biodegradation in aerobic or anaerobic treatment processes. Over the last two
decades, a lot of work has been done with the purpose of using microorganisms as
bioremediation agents in the treatment of wastewater-containing textile dyes (Ra-
malho et al.
2004
).
Numerous studies have demonstrated the ability of bacteria in monoculture to
degrade dyes anaerobically and aerobically (Banat et al.
1996
). Dye decolorization
by bacteria has been observed under different conditions. Reductive cleavage of the
azo bond by a wide variety of microorganisms, sediments and sludges occurs
readily under anaerobic conditions (Stolz
2001
; Field and Brady
2003
). The
effectiveness of microbial decolorization depends on the adaptability and the
activity of selected microorganisms. Many microbes including bacteria, fungi and
yeast are capable of degrading azo dyes (Chen et al.
2003
). A highly alkali ther-
mostable Bacillus sp. strain SF isolated from the wastewater drain of a textile
nishing company was found capable of degrading an azo dye (Maier et al.
2004
).
An azo dye-reducing and endospore forming bacterium was isolated from textile
industry wastewater that can decolorize the azo dye Remazol Black B. The bac-
terium was found to be 92.1
95 % similar to Paenibacillus sp. based on 16S rDNA
sequence homology (Meehan et al.
2001
). Transformation of six industrial dyes by
manganese peroxidase from Bjerkandera adusta and Pleurotus eryngii was also
investigated (Hein
-
ing et al.
1998
).
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