ESTCP Project #1011, Rhizosphere
Final Report
ownership. Low-cost, effective, and applicable treatment technologies are needed for all of these
situations.
1.1.2 The Technology. Phytoremediation is an umbrella term that describes varied uses
of plants for the purpose of remediating soil or groundwater. Phytoremediation has shown
potential for several applications, all based on plant-driven processes but mechanistically
different. These include, but are not limited to, enhancing microbially driven degradation in the
rhizosphere, exudation of contaminant analogs by roots and stimulation of specific microbial
degradation pathways, and using trees either to control the hydrology, or to take up and degrade
trichloroethylene (TCE), or both.
Rhizosphere-enhanced remediation is based on root exudation of excess plant-produced carbon
compounds, which stimulate the soil microbial population near root surfaces, which in turn
stimulates bioremediation. The technology consists primarily of adding appropriate seeds and
nutrients to the contaminated soil to grow plants that, in turn, stimulate rhizosphere activity. It
thus requires minimal equipment and costs for setup, operation and maintenance, or shut down.
Our demonstrations include seeding and fertilization of cold-tolerant grasses and legumes in
POL-contaminated soils at three locations in Alaska.
1.1.3 The Benefits. The expected benefits of implementing rhizosphere-enhanced
bioremediation are:
1. Costs may be reduced dramatically in treating sites that are remote from infrastructure
such as roads, power, and transportation.
2. Rhizosphere-enhanced treatment can be used at active installations, releasing scarce
cleanup resources for more urgent contaminated sites.
3. The technology avoids the mechanical problems caused by freezing temperatures.
4. Human and environmental risks related to POL-contaminated soils will be reduced at
these sites.
The ultimate application is to be able to add appropriate nutrients and seed to a contaminated site
and have reasonable assurance, based on defensible data, of the treatment rates and endpoints.
For sites in cold regions, implementing rhizosphere-enhanced treatment may significantly
increase treatment rates, thereby reducing treatment times. The degree of improvement likely
depends on the growing season length and the recalcitrance of the compound. Although we have
demonstrated relatively short treatment times of one to three summers in some situations, in
other situations the benefit may be that significant treatment is accomplished in five to ten years
rather than not at all.
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