Environmental Engineering Reference
In-Depth Information
6.4
Application of Biosludge
as Metal Chelator
at the highest P concentration, the accumulation
was reduced to almost half. Therefore, P amend-
ment moderates the toxicity caused by the sup-
plied Cr in
R. sativus
. This finding can be utilized
to develop a novel technology for the ameliora-
tion of Cr stressed fields. Generally, Cr(VI) nega-
tively affected both the size and activity of soil
microbial biomass. Recently, Leita et al. (
2011
)
reported that with the addition of glucose in-
creased the reduction rate of Cr(VI) as it induced
soil microbial biomass size and activity with an
indirect role in the increased rate of Cr(VI) re-
duction, by promoting growth of indigenous mi-
crobial biomass.
Recently, National Environmental Engineering
Research Institute (NEERI), India has started
to develop cost-effective and ecofriendly tech-
nologies that use microorganisms and industrial
wastes for cultivation of petro-crops in lands
degraded due to metals (Juwarkar et al.
2006
).
Juwarkar et al. (
2008
) evaluated the effect of
different concentrations of As-, Cr-, and Zn-
contaminated soils, amended with biosludge and
biofertilizer on the growth of
Jatropha curcas,
which is a biodiesel crop. The study revealed
that biosludge alone and in combination with
biofertilizer significantly improved survival rates
and enhanced the growth of the plant. With the
amendments, the plant was able to grow and
survive up to 250 mg kg
− 1
of Cr-contaminated
soil. In absence of biosludge, heavy metal accu-
mulation in the plant increased with increasing
concentrations of heavy metals in soil, whereas
in soils amended with biosludge, a significant
reduction in the metal uptake in the plant was
observed. It was assumed that the organic mat-
ter present in the biosludge acted as a metal che-
lator, thereby reducing the toxicity of metals to
the plant. Findings suggest that plantation of
J.
curcas
may be promoted in metal-contaminated
soils, degraded soils, or wastelands suitably after
amending with organic waste. Role of other or-
ganic amendments, such as fermented compost,
has also been reported in the reestablishment
of vegetation on contaminated sites by decreas-
ing the bioavailability of heavy metals in soil
(Tordoff et al.
2000
; Walker et al.
2004
).
6.3.3
Effect of Biochar Application
on Soil Properties and Plant
Nutrient Uptake Under Cr
Toxicity
The addition of biochar increased soil pH, elec-
trical conductivity (EC), organic carbon, total
nitrogen, available P, cation exchange capacity
(CEC), and exchangeable cations of Cr-polluted
and Cr-unpolluted soils (Topoliantz et al.
2002
).
Uptake of nitrogen, P, and K were also increased
by addition of biochar. The presence of plant nu-
trients and ash in the biochar, high surface area
and porous nature of the biochar, and the capacity
of biochar to act as a medium for microorganisms
are identified as the main reasons for the increase
in soil properties and highest nutrient uptake at
biochar-treated soils (Verheijen et al.
2009
). The
increase in the availability of major plant nutri-
ents due to application of biochar was also re-
ported by Glaser et al. (
2002
) and Lehman et al.
(
2003
). Application of biochar on Cr-polluted
and Cr-unpolluted soils significantly (
p
< 0.01)
increased the mean values of soil organic C and
total N (Nigussie et al.
2012
). The increases in
organic carbon were observed in soils treated and
total nitrogen upon addition of biochar due to
presence of high amounts of carbon and nitrogen
in the maize stalk. High organic carbon in soils
treated with biochar has been also reported by
Lehmann (
2007
).
6.5
Bioremediation of Cr Using
Microbial Inoculants
The bioremediation is an approach to exploit the
naturally occurring biodegradative processes to
clean up contaminated sites. In situ, ex situ, and
intrinsic bioremediation are receiving increas-
ing attention as viable remediation alternatives.
The application of the bioremediation approach
depends on the type of pollutant or pollutant
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