Molecular Soil Biology (online), 2013, Vol. 4 No.1, 1-6
ISSN 1925-2005
http://msb.sophiapublisher.com
3
1.6
Effects of pH and temperature on Cr (VI)
removal
To study the effect of different pH and temperature on
Cr (VI) removal, CDB was amended with known
concentration of Cr (VI) solution and adjusted to
different pH (2,3,4,5 and 6) by using 0.1N HCl and
0.1
N NaOH.
T. harzianum
strain was inoculated in
the medium and incubated at different temperature
(10
?
~40
?
).
Measurement of Cr (VI) content in the
growth medium was measured as mentioned above.
2
Results and Discussion
Influence of Cr (VI) on mycelial development of
T.
harzianum
strain is presented on Table 1. A
progressive increase in percent inhibition was
observed with increase in initial concentration of Cr
(
VI). Among the different concentrations of Cr (VI)
tested, 40 mg/L was the most lethal, where the growth
inhibition was 94%, followed by 30 mg/L (91%).
Metal removal capacity of
T. harzianum
strain is given
in figure 1. It was noticed that the metal removal to a
certain extent was time dependent process. A
progressive increase in Cr (VI) absorption was noticed
with an increase in incubation days. At 7
th
day
incubation, the metal uptake was maximum (90.2%).
Further incubation did not change the capacity of
metal removal significantly. This may be due to the
saturation of the fungal mycelia in metal uptake.
Previous studies reported that metal-ion uptake of
biosorbent increases as long as the biosorbent is not
saturated (Fourest and Roux, 1992).
Table 1 Sensitivity/Tolerance of
T. harzianum
strain to Cr (VI)
Cr (VI) Conc. (mg /L)
Radial growth (mm)
5
41.5 (4.60)
a
10
34.2 (21.37)
20
19.2 (55.80)
30
3.75 (91.00)
40
2.25 (94.00)
Control
b
43.5
c
CD at 5%
0.60
Note:
a
Radial growth on PDA medium after 5days incubation
on the treated plates. Values in the parenthesis indicate percent
inhibition of the mycelial growth compared to the control plates;
b
Radial growth on PDA medium after 5 days incubation on
control plates;
c
Critical difference
Figure 1 Biosorption of Cr (VI) by
T. harzianum
at different
days
The adsorption of hexavalent chromium followed the
typical Freundlich and Langmuir isotherm pattern
(
Table 2). In the case of Freundlich adsorption
isotherms the plot made between log x / m verses log
C was found to be straight line for Cr (VI). The
Freundlich coefficient ‘K’ is regarded as the
hypothetical index of heavy metal sorbed from a
solution having unit equilibrium concentration
(
Ghosal et al., 2003). Hypothetical index was found to
be 1.753 in the present study. Considering the fit value
(96%),
it is suggested that the adsorption of heavy
metals by
T. harzianum
can use Freundlich adsorption
isotherm to evaluate the adsorption characteristics. In
case of Langmuir adsorption isotherm, the plot made
between C/ (x/m) and C was found to be straight line.
In general, Langmuir adsorption isotherms were
having fit value 94% in the present study. Therefore
this isotherm can also be used to predict the metal
adsorption characteristics of
T. harzianum.
In case of
adsorption maxima and binding energy, the value was
higher (570.16 and 0.405 respectively) which
indicated the metal adsorption and retaining capacity
of
T. harzianum
was superior in case of Cr (VI).The
mycelium after the study were re suspended in water
to observe any leakage of the adsorbed metals to the
surroundings. No residues were detected in the water
up to 10 days, which indicated the binding tendencies
of the
T. harzianum
mycelium towards the tested
chromium metal (data not shown).
The effect of different pH on metal removal is
presented in Figure 2. At lowest pH tested in the
present study (pH 2), no metal removal was observed.