Molecular Soil Biology (online), 2013, Vol. 4 No.1, 1-6
ISSN 1925-2005
http://msb.sophiapublisher.com
4
Table 2 Constants and correlation coefficients for the Langmuir
and Freundlich isotherms
Adsorption parameters
Radial growth (mm)
Frenundlich
K
1.753
1/
n
1.09
r value
0.963
Langmuir
qmax
570.16
b
0.405
r value
0.945
Note: r: fitness values of adsorption isotherm; b: binding
energy; K: adsorption coefficient qmax: Adsorption maxima
Figure 2 Biosorption of Cr (VI) by
T. harzianum
at different pH
A gradual increase in pH demonstrated increased
metal removal capacity by
T. harzianum
.
Similar kind
of results was also noticed by other researchers (Tian–
Wei et al., 2004; Wuyep et al., 2007). The less
bioaccumulation capacity at lower pH is reported due
to the competition of hydrogen ion with metal ion on
the sorption sites (Congeevaram et al., 2007). It has
been reported that, sorption of heavy metals by the
fungi is strongly pH dependent and biosorption rate
increases with increase in pH (Lovely, 1995). Metal
removal was noticed between pH 3 to 5 in the present
study with the maximum metal removal in pH 4.
Several authors previously described an optimal pH
around 4 is an ideal condition for metal removal
(
Tobin et al., 1984; Tsezos and Volesky, 1981). At pH
value above 7, metals exist as hydroxide colloids and
precipitate at alkaline pH due to osmotic changes and
hydrolyzing effect (Nasseri et al., 2002), thus resulting
reduced uptake rate.
Temperature plays a significant role in the biosorption
of metal ions. An increase in temperature showed
increased metal removal to certain point. The
optimum temperature for maximum Cr (VI) removal
was noticed at 30
?
in the present study (Figure 3).
At this temperature, the metal removal was in the
range of 90%. Srivastava and Thakur (2006)
suggested that 30
?
was the ideal condition for
bioaccumulation of chromium in case of
Aspergillus
sp. The metal uptake was decreased beyond this
temperature. At 40
?
the metal removal was reduced
to 20% whereas, no absorption was noticed at 50
?
.
Similar report was suggested by Bai and Abraham
(2001),
where a decline in Cr (VI) biosorption was
noticed at 50
?
.
Though temperature plays an
important role for the growth of organisms, at elevated
level, it damages the organisms by denaturing
enzymes, transport carriers, integrity of cell membrane
(
Prescott et al., 2002), and also hinder compart-
mentalization of metal ions leading to reduced metal
uptake (Fartal et al., 2007). The present
in vitro
studies indicated that
Trichoderma harzianum
strain
was able to uptake substantial amount of Cr (VI) from
aqueous medium. A temperature of 30
?
and pH
range of 3 to 5 was perfect for the maximum metal
removal in the present study.
Figure 3 Biosorption of Cr (VI) by T. harzianum at different
temperature
Author’s Contributions
SS, AS and RP collected and systematized data, SS performed
the statistical analyses and the manuscript. All the authors have
read and approved the final manuscript.
Acknowledgements
The authors are thankful to Dr. N. Muraleedharan, Adviser and