ESTCP Project #1011, Rhizosphere
Alaska Department of Environmental Conservation requested information on this technology to
address remediating former storage tank pads at a number of villages.
6.3 End-User Issues
End users at each site participated largely by agreeing to allow a technology demonstration to be
conducted at their site. Due to more knowledgeable staff, changed attitudes, more experience,
and resource constraints, regulators in some areas, including Alaska, are more open to low-cost
approaches in recent years.
Although we have shown that this technology is more effective than the controls or than adding
only fertilizer, we are still unable to predict the time necessary for a site to reach target
concentration goals. We have shown that rhizosphere-treatment will proceed faster than non-
rhizosphere and fertilizer alone treatments. Our data from these and other sites show that
rhizosphere related processes are more effective than non-rhizosphere processes and fertilizer
additions alone in reducing more recalcitrant petroleum compounds.
These data have been provided to the EPA-RTDF working group on Phytoremediation of
6.4 Specifics for Implementing Rhizosphere-Enhanced Remediation at
The plant has to grow. Although there may be exceptionally good and exceptionally poor plants
for enhancing petroleum degradation, they have not all been identified. Extensive plant screening
is difficult and costly, and results probably vary with many other conditions such as temperature,
the nature of the petroleum, soil conditions, rainfall, and other conditions not yet understood or
identified. The University of Saskatchewan has developed a database, PhytoPet
(http://www.phytopet.usask.ca/mainpg.php), to catalogue plants for petroleum phytoremediation.
PhytoPet was originally developed as an inventory of plants that have demonstrated ability to
either phytoremediate or tolerate soils contaminated with petroleum hydrocarbons. As with much
phytoremediation information, the database is changing and allows for user interaction. There
also are molecular-based efforts that are attempting to screen plants by looking for specific genes
in plants and matching these to contaminant degradation pathways, but this research is not yet to
the application stage.
Petroleum degradation is well characterized, and for rhizosphere-enhanced remediation the
process is a root-surface phenomenon, rather than one centered in the plant. From CRREL's
experience, grasses do well for petroleum. This is most likely due to their fibrous root system
that explores a large volume of soil fairly completely and, in a sense, provides pseudo-mixing. In
various field studies at other sites, we also have used annual ryegrass (Lolium multiflorum), tall
fescue (Festuca arundinaceae), and winter rye (Secale cereale L.). We have seeded at rates