2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
cells often exceeds the amount predicted using information
about the charge density of the cell surface 9,25 .
bioprecipitation. Sulfate reduction is an example for
the precipitation of metals ions in solution. Sulfate-reducing
bacteria form metal sulfides that are insoluble. The stability
of these sulfides depends on maintenance of anoxic conditions
7,24 , and nutrients are also inevitable. Stimulating sulfate
reducion can increase pH also and form metal hydroxides and
oxides that precipitate and do not migrate in soil and groundwater
7 .
biooxidation, bioreduction. Microorganisms are also
known to oxidize and reduce metal contaminants. Mercury
and cadmium can be oxidized while arsenic and iron can
be reduced by microorganisms. Cr(VI) can be oxidized to
Cr(III) that is less mobile and toxic. Bacteria such as Bacilus
subtilis and SRB in the presence of sulfur can perform this
reaction 7 .
bioremediation Technologies
According to the site, bioremediation technologies are
divided to:
in-situ – are carried out at the place of the contamination,
ex-situ – the contaminated matter is taken off from the
natural locality and it is consequently processed26 •
•
.
Ex situ bioremediation is usually realized on the specific
revised place or in the reactor. The pre-treating of contaminated
matter increases the efficiency of this process 26 . Ex-situ
methods have been around longer and are better understood,
and they are easier to contain, monitor, and control. However,
in-situ bioremediation has several advantages over ex-situ
techniques. In-situ treatment is useful for contaminants that
are widely dispersed in the environment, present in dilute
concentrations, or otherwise inaccessible (e.g., due to the presence
of buildings or structures). This approach can be less
costly and less disruptive than ex-situ treatments because no
pumping or excavation is required. Moreover, exposure of
site workers to hazardous contaminants during in-situ treatment
is minimal 27 .
Broadly, bioremediation strategies can be further divided
into natural attenuation, biostimulation, and bioaugmentation
strategies 27 .
bioaugmentation presents an addition of microorganisms
or their products, such as biosurfactants or enzymes28.
Thus, inoculation of ‘specialized’ biomass may allow for
an increased biodegradation of target pollutants as well as a
more effective detoxification of the solid matrix 29 . Another
common result of bioaugmentation is the dramatic reduction
of remediation times 30,31 . Indigenous or exogenous, standard
or modified microorganisms are used 32,33 . Generally, they
present mixed cultures of microorganisms, but it could be
also pure bacterial strains adapted onto the aimed contaminant
in the laboratory 34,35 .
biostimulation can be aggressive or passive, in that
electron donors, electron acceptors, and trace nutrients can
s455
be injected into the environment to stimulate indigenous
organisms to increase biomass or activity to affect the contaminant.
Passive biostimulation techniques include simple
infiltration galleries or simply spreading fertilizer on surface
without any pumping or mixing 25,27 .
Natural attenuation relies on the intrinsic bioremediation
capabilities of that environment. Environments high
in organic carbon and energy sources, low contaminant concentrations,
and without significant nutrient deficiencies may
be able to degrade or transform the contaminants of concern
without any intervention 27 .
Conclusions
Environmental biotechnologies with applications of
bacteria are eco-friendly and cost effective. They present
natural technologies for treatment of toxic metals from soil.
The following development is desirable, because of the high
specificity and the time-consuming of biological processes
and because of the difficulty to control them.
Acknowledgement (This work has been supported by
Slovak Academy of Science No. VEGA 2/0049/08
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