Environmental Engineering Reference
In-Depth Information
nitrogen sources, like sodium or ammonium salts, are used for microbial growth
and dye decolorization, since the use of organic nitrogen supplementation is cost-
intensive (Radha et al.
2005
; Kumar et al.
2012
). An increased dose of nitrogen
source inhibited decolorization of Congo red (Tatarko and Bumpus
1998
), while
nitrogen supplementation had no effect on dye decolorization by Cyathus bulleri
(Vasdev et al.
1995
). It is well established in P. chrysosporium that under condi-
tions of carbon or nitrogen limitation, the ligninolytic enzyme production for dye
decolorization is much more effective (Zhen and Yu
1998
), while Bjerkandera
adusta produced more lignin peroxidase and manganese peroxidase in nitrogen-
suf
cient media (Hein
ing et al.
1998
). In the case of ef
uents, the presence of
usable nitrogen sources may cause rapid dye degradation.
3.4 Other Media Components
Many research studies have used various growth factors. From an economic per-
spective, it is not imperative to use them for developing decolorization technolo-
gies. All microbes have certain requirements of mineral nutrients for growth and
decolorization. For example, the white-rot fungi need trace metal salts of iron,
copper and manganese. They can be present in the efuent or must be supplemented
to the medium to affect better dye biotransformation. Different oxidizing mediators,
like veratryl alcohol, tryptophan and aromatics, e.g. phenol and aniline, can act as
low molecular mass redox mediators of ligninolytic activities and therefore, pro-
mote the decolorization process (Rodriguez Couto and Toca-Herrera
2007
).
3.5 pH
Most of the research studies on growth and decolorization have been performed in
batch cultures, usually without the pH control during the cultivation. Indeed, culture
pH mainly in
uences many enzymatic processes and transport of various compo-
nents across the cell membrane. Depending on the type of substrates used the pH
changes during cultivation. The growth on carbohydrate supplemented media
generally causes acidi
cation of the media, which depends on the carbon source
and therefore requires buffering. However, majority of
lamentous fungi along with
white-rots grow optimally at acidic pH. It was earlier reported that different fungi
favoured textile dye removal within an optimum pH ranging between pH 4 and 6
which depends on the medium composition and the dye present in the decolor-
ization medium (Jadhav and Govindwar
2006
; Parshetti et al.
2006
; Asgher et al.
2008
). Since Malachite green is a cationic dye, the optimal initial pH was alkaline
which favored adsorption of dye on to the algal surface, which increased decol-
orization ef
ciency (Kumar et al.
2005
; Daneshvar et al.
2007
; Khataee et al.
2009
).
The medium pH mainly in
uences the solubility of the dye and the ionization state
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