Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides: 2. Field Research on Bioremediation of Metals and Radionuclides Page: 5 of 30
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Thus U bioreduction for immobilization of U(IV) is expected to be more sustainable under
slightly acidic conditions. The trade off is that the U(VI) sorption is weaker and U(IV) is soluble
at pH <4.
1.3 CHARACTERIZATION AND MONITORING CONSIDERATIONS
The success of any bioremediation application will be highly dependent on the characterization
and monitoring that is done before and during the field deployment. For any field remediation,
the first step is to form a conceptual model of the contaminant plume in the environment and
how that environment effects that plume. The uncertainties in this conceptual model provide the
drivers for the characterization and monitoring needs. For example, characteristics of the aquifer
will have a profound impact on the remediation strategy (Table 1). The largest part of the
expense of any remediation project is the characterization and monitoring. Hydraulic
conductivities can have a severe effect on your ability to deliver nutrients to the subsurface
(Table 2) and can be the most limiting part of the environment. However, as discussed above if
bioreduction was the strategy for a metal contaminated site and the site had a hydraulic
conductivity of only 10-8 cm/sec with very high nitrate and sulfate levels and high pH it may not
be cost effective to use bioreduction at this site. These issues also suggest why bioaugmentation
has not lived up to its hope. Though bioaugmentation promises 'designer biodegraders', it has
not proven to be better then biostimulation in repeated field trials over the last 2 decades.
Indeed, there is only one bacterium that has demonstrated that it can perform better then
biostimulation in situ on some occasions, Dehalococcoides ethenogenes for dehalorespiration of
chlorinated solvents. At least two products are commercially available and have been widely
used in the U.S. that are proprietary strains of this organism (Regenesis and Geosyntec). We
suspect the reason that this microbe has been successful is that it is a strict anaerobe, chlorinated
solvent dehalorespiration requires established methanogenic redox potentials, and the organism
is very small irregular coccus (0.5 pm) so it can penetrate the subsurface more easily (LOFFLER
et al. 2000). Patchy distributions of this organism in nature are also common, so
bioaugmentation may provide a couple of advantages. Fortunately, new advances in geophysics
and hydraulic push technology (Geoprobe) has enabled us to characterize sites in a fraction of
the time and cost. Once we have established the hydrology and basic geochemistry at the site
and used that data to refine our conceptual model, a base line characterization of the5
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Hazen, Terry C. & Tabak, Henry H. Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides: 2. Field Research on Bioremediation of Metals and Radionuclides, article, March 15, 2007; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc893696/m1/5/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.