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promoting bacteria (PGPB) can be lyophilized and stirred at high density for the extended peri-
ods of time, making this method appealing for field-scale and commercial use (Reed and Glick,
2005). Alginate beads are also thought to offer protection to the PGPB in harsh environment by
acting as a time-release coating that slowly disintegrates and releases PGPB to the germinating
plants (Bashan
et al
., 2002). While studying the capacity of alignate encapsulation of PGPB for
revegetation in mine tailing, Grandlic
et al
. (2009) observed that encapsulation was an effective
way to inoculate PGPB. However, the feasibility of this approach at the field scale is limited by the
amount of carriers required to reach acceptable degradation (Owsianiak
et al
., 2010). The field
trials are required to evaluate and validate bioaugmentation with immobilized microorganism
(encapsulated) as a remediation strategy for As-contaminated soils and to determine the required
amount of carriers to be introduced into soil (Leung
et al
., 1995). Examples of bioaugmentation
by microbes in soil for some plants are shown in
Table 6.4
for the remediation of As.
6.6
CONCLUSIONS
In-situ
bioremediation of As contaminated soils shows great potential for future developments
due to its environmental compatibility. It relies on microbial activities to reduce, mobilize or
immobilize As through biosorption, biomethylation, complexation, oxidation-reduction, and bio-
volatilization processes. Bioremediation is widely accepted and cost-effective applied technology.
Full-scale field demonstrations are required along with assessment of cost-effective analysis.
Strategies like use of bio-surfactants, and other suitable nutrients and organics to reduce As
bioavailability should be investigated. The As tolerance, accumulation and biotransformation
capabilities of microbes may be improved through genetic engineering strategies. One major
limitation of
in-situ
bioremediation is its application in natural environments, where uncharacter-
ized microorganisms exist. Further, the environmental conditions are also varying with respect
to habitats, climate and hydro-geo dynamics. Compilation of database, taking the results of As-
contaminated sites and its bioremediation techniques, including the ecological risk assessment is
also essential for developing a site-specific bioremediation scheme.
ACKNOWLEDGEMENTS
Authors are thankful to Director, CSIR-National Botanical Research Institute, for providing
institutional support. Financial supports from Department of Biotechnology, Government of
India (BT/PR13147/BCE/08/780/2009) and Council of Scientific and Industrial Research are
thankfully acknowledged. Shubhi Srivastava is thankful to CSIR for providing Senior Research
fellowship (CSIR-SRF).
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