Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides: 2. Field Research on Bioremediation of Metals and Radionuclides Page: 3 of 30
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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. 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. Ideally, the most cost effective and
efficient approach to treat most large contaminant plumes is to use more aggressive approaches,
e.g. bioaugmentation or even excavation and removal, at the source, grading into natural
attenuation at the leading edge, or over time as the contaminant concentration declines. There
are no bioaugmentation candidates yet for metals and radionuclides that we are aware of. Rarely
is a single remediation approach completely effective or cost efficient. Indeed, combining
aggressive physical and chemical treatment techniques like chemical oxidation/reduction,
thermal desorption with bioremediation can provide advantages to some types of contaminants
and allows bioremediation to be an effective polishing or sentinel strategy for the cleanup.
1.1 BIOREMEDIATION STRATEGIES FOR METALS AND RADIONUCLIDES
Over the past few years, interest in bioremediation has increased. It has become clear that many
organic contaminants such as hydrocarbon fuels can be degraded to relatively harmless products
like CO2 (the end result of the degradation process). Wastewater managers and scientists have
also found that microorganisms can interact with metals and convert them from one chemical
form to another. Laboratory tests and ex situ bioremediation applications have shown that
microorganisms can change the valence, or oxidation state, of some heavy metals (e.g.,
chromium and mercury) and radionuclides (e.g., uranium) by using them as electron acceptors.
In some cases, the solubility of the altered species decreases and the contaminant is immobilized
in situ, e.g., precipitated into an insoluble salt in the sediment. In other cases, the opposite
occurs -the solubility of the altered species increases, increasing the mobility of the
contaminant and allowing it to more easily be flushed from the environment. Both of these kinds
of transformations present opportunities for bioremediation of metals and radionuclides -either
to lock them in place, or to accelerate their removal. Microorganisms can do much more than
biotransform contaminants. They can also influence contaminant behavior by changing the
acidity of the system in the immediate vicinity of the contaminant, or by altering the form of
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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/m1/3/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.