Description:

Enhanced Rhizosphere Biodegradation

Enhanced rhizosphere biodegradation takes place in the soil immediately surrounding plant roots. Natural substances released by plant roots supply nutrients to microorganisms, which enhances their biological activities. Plant roots also loosen the soil and then die, leaving paths for transport of water and aeration. This process tends to pull water to the surface zone and dry the lower saturated zones.

The most commonly used flora in phytoremediation projects are poplar trees, primarily because the trees are fastgrowing and can survive in a broad range of climates. In addition, poplar trees can draw large amounts of water (relative to other plant species) as it passes through soil or directly from an aquifer. This may draw greater amounts of dissolved pollutants from contaminated media and reduce the amount of water that may pass through soil or an aquifer, thereby reducing the amount of contaminant flushed though or out of the soil or aquifer.

Phyto-accumulation

Phyto-accumulation is the uptake of contaminants by plant roots and the translocation/accumulation (phytoextraction) of contaminants into plant shoots and leaves.

Phyto-degradation

Phyto-degradation is the metabolism of contaminants within plant tissues. Plants produce enzymes, such as dehalogenase and oxygenase, that help catalyze degradation. Investigations are proceeding to determine if both aromatic and chlorinated aliphatic compounds are amenable to phyto-degradation.

Phyto-stabilization

Phyto-stabilization is the phenomenon of production of chemical compounds by plant to immobilize contaminants at the interface of roots and soil.

Synonyms:

Vegetation-enhanced bioremediation.

Applicability:

Some plant species have the ability to store metals in their roots. They can be transplanted to sites to filter metals from wastewater. As the roots become saturated with metal contaminants, they can be harvested.

Hyper-accumulator plants may be able to remove and store significant amount of metallic contaminants.

Currently, trees are under investigation to determine their ability to remove organic contaminants from ground water, translocate and transpiration, and possibly metabolize them either to CO₂ or plant tissue.

Limitations:

• The depth of the treatment zone is determined by plants used in phytoremediation. In most cases, it is limited to shallow soils.
• High concentrations of hazardous materials can be toxic to plants.
• It involves the same mass transfer limitations as other biotreatments.
• It may be seasonal, depending on location.
• It can transfer contamination across media, e.g., from soil to air.
• It is not effective for strongly sorbed (e.g., PCBs) and weakly sorbed contaminants.
• The toxicity and bioavailability of biodegradation products is not always known.
• Products may be mobilized into ground water or bioaccumulated in animals.
• It is still in the demonstration stage.
• It is unfamiliar to regulators.

Data Needs:

Performance Data:

USAEC is also leading the team of experts from EPA, Tennessee Valley Authority (TVA) and the Waterways Experimental Station (WES) to successfully demonstrate phytoremediation of explosive contaminated sites in Milan Army Ammunition Plant in Milan, TN.

AFCEE is currently conducting several phytoremediation demonstrations, including the following:

A "mature tree" study has been completed at Cape Canaveral Air Station. Live Oak, Saw-tooth Palmetto and Scrub Oak species in the midst of a TCE plume were evaluated for TCE transpiration and TCE transformation rates. Evapotranspiration rates were also measured. Mature trees were used in this study to obviate the waiting period for whips to grow into mature trees.

An initial planting of 110 trees in 1998 was followed by 200 (early 2000) and 150 (spring 2000) additional trees at Travis AFB, CA. The plantings are being used as hydraulic control for a TCE plume. This is a long-term test of the ability of trees to control the movement of groundwater.

A similar study is taking place at Altus AFB, OK. One hundred ten non seed-bearing hybrid cottonwood trees were planted in the fall of 1998. The plantings are being used as hydraulic control for a TCE plume. Soil moisture, groundwater levels, climatic conditions and sap flow rates are monitored remotely in this demonstration. A report on the results of the study will be released in the summer 2001.

A new effort was launched in the summer 2000, with five large-scale plantings planned for Fairchild, Offutt, Hill and Whiteman AFBs. Plantings should be complete by early 2001.  More information can also be located at http://www.afcee.brooks.af.mil/er/ert/phytorem.htm. 

Cost:

The key cost driver information and cost analysis was developed in 2006 using the Remedial Action Cost Engineering and Requirements (RACER) software.

Key Cost Drivers 

·        Scale of effort

o       Area of contamination is the primary cost driver

·        Density of sampling

o       Primary cost driver of sampling cost; may be directed by regulatory requirements.

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply phytoremediation technology at sites of varying size and complexity.   A more detailed cost estimate table which includes specific site characteristics and significant cost elements that contributed to the final costs can be viewed by clicking on the link below.

 Detailed Cost Estimate 

References:

Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition, EPA 542-R-01-004

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Treatment Experiences at RCRA Corrective Actions, December 2000, EPA 542-F-00-020

Abstracts of Remediation Case Studies, Volume 4, June 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

Boyajian, G. E. and Devedjian, D. L., 1997. "Phytoremediation: It Grows on You", Soil & Groundwater Cleanup, February/March, pp. 22-26.

EPA, 1998. A Citizen's Guide to Phytoremediation, Technology Fact Sheet, EPA NCEPI, EPA/542/F-98/011.

EPA, 1996. A Citizen's Guide to Phytoremediation, Technology Fact Sheet, EPA NCEPI, EPA/542/F-96/014.

EPA, 1996. Recent Developments for In Situ Treatment of Metal Contaminated Soils, EPA/542/R-96/008.

Schnoor, J.L., L.A. Licht, S.C. McCutcheon, N.L. Wolfe, and L.H. Carreira. 1995. "Phytoremediation of organic and nutrient contaminants," Environ. Sci. Technol. 29:318A-323A.

USAEC, 1997. "Phytoremediation of Lead" in Innovative Technology Demonstration, Evaluation and Transfer Activities, FY 96 Annual Report, Report No. SFIM-AEC-ET-CR-97013, pp. 89-92.

U.S. DOE, 1995. "Bioremediation of High Explosives by Plants," in Technology Catalogue, Second Edition, Office of Environmental Management Office of Technology Development, DOE/EM-0235, pp. 169-172.

A comprehensive list of 850 references on phytoremediation are available at Remediation Technologies Development Forum (RTDF) Phytoremediation Action Team Web Site. Click to access

RTDF Phytoremediation Bibliography

• Trenton, NJ Site 
• Dearing, KS 
• Whitewood Creek, SD 
• Brookhaven National Laboratory 
• McCormick & Baxter SUPERFUND Site, Portland, OR (Wood treatment site)
• Argonne National Laboratory
• Craney Island Fuel Terminal, U.S. Navy, Portsmouth, VA
• EPA S.I.T.E. Program, Ogden, Utah
• Ohio (Former metal plating site)
• DOE Demo: Savannah River Site , SC
• DOE Savannah River Site, SC

General FRTR Agency Contacts

Government Web Sites

Non Government Web Sites

A list of vendors offering In Situ Biological Soil Treatment is available from EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

Government Disclaimer

To be added