Description:

Enhanced Rhizosphere Biodegradation

Enhanced rhizosphere biodegradation takes place in the soil surrounding plant roots. Natural substances released by plant roots supply nutrients to microorganisms, which enhances their ability to biodegrade organic contaminants. 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.

Hydraulic Control

Depending on the type of trees, climate, and season, trees can act as organic pumps when their roots reach down towards the water table and establish a dense root mass that takes up large quantities of water.

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-volatilization

Phyto-volatilization occurs as plants take up water containing organic contaminants and release the contaminants into the air through their leaves. Plants can also break down organic contaminants and release breakdown products into air through leaves.

Synonyms:

Vegetation-enhanced bioremediation.

Applicability:

Plants also produce enzymes, such as dehalogenase and oxygenase, which help catalyze degradation.

Limitations:

• It is limited to shallow soils, streams, and ground water.
• High concentrations of hazardous materials can be toxic to plants.
• It involves the same mass transfer limitations as other biotreatments.
• Climatic or seasonal conditions may interfere or inhibit plant growth, slow remediation efforts, or increase the length of the treatment period.
• 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.
• Phytoremediation will likely require a large surface area of land for remediation.
• The toxicity and bioavailability of biodegradation products is not always known. Products may be mobilized into ground water or bioaccumulated in animals. More research is needed to determine the fate of various compounds in the plant metabolic cycle to ensure that plant droppings and products manufactured by plants do not contribute toxic or harmful chemicals into the food chain or increase risk exposure to the general public.

Data Needs:

In addition, detailed information is needed to determine the kinds of soil used for phytoremediation projects. Water movement, reductive oxygen concentrations, root growth, and root structure all affect the growth of plants and should be considered when implementing phytoremediation.

Performance Data:

In Iowa, EPA demonstrated the usage of phytoremediation by planting poplar trees along a stream bank between a corn field and the stream. These trees acted as natural pumps to keep toxic herbicides, pesticides, and fertilizers out of the streams and ground water. After three years, while the nitrate concentration in ground water at the edge of the corn field was measured at 150 mg/L, the ground water among the poplar trees along the stream bank had nitrate concentration of only 3 mg/L.

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.

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

·        Tree size (maturity) is the secondary cost driver.

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

Remediation Technology Cost Compendium - Year 2000

Groundwater Cleanup: Overview of Operating Experience at 28 Sites, September 1999, EPA 542-R-99-006,

Potential Applicability of Assembled Chemical Weapons Assessment Technologies to RCRA Waste Streams and Contaminated Media, August 2000, EPA 542-R-00-004

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

Brownfields Technology Primer: Selecting and Using Phytoremediation for Site Cleanup, July 2001, U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response Technology Innovation Office

An Overview of the Phytoremediation of Lead and Mercury, August 2000, U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response Technology Innovation Office 

Phytoremediation Resource Guide, June 1999, U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response Technology Innovation Office

Phytoremediation Decision Tree, November 1999, The Interstate Technology and Regulatory Cooperation Work Group Phytoremediation Work Team

Phytoremediation of TCE in Groundwater using Populus, February 1998, U.S. EPA Technology Innovation

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

California Base Closure Environmental Committee (CBCEC), 1994. Treatment Technologies Applications Matrix for Base Closure Activities, Revision 1, Technology Matching Process Action Team, November, 1994.

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 Bioremediation, Technology Fact Sheet, EPA NCEPI, EPA/542/F-96/007.

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.

USAEC, 1997.Phytoremediation of Explosives in Groundwater Using Constructed Wetlands in Innovative Technology Demonstration, Evaluation and Transfer Activities, FY 96 Annual Report, Report No. SFIM-AEC-ET-CR-97013, pp. 155-156.

• Chevron, Ogden, UT 
• Aberdeen, MD
• Ogden, UT
• U.S Air Force Facility, Fort Worth, TX
• Milan Army Ammunition Plant (USAEC), TN
• DOE, Bear Creek, Oak Ridge National Laboratory, TN

General FRTR Agency Contacts

Government Web Sites

Non Government Web Sites

A list of vendors offering In Situ Biological 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