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4-30 TYPICAL CO-METABOLIC BIOREMEDIATION SYSTEM (IN SITU) FORCONTAMINATED GROUNDWATER

4.30 CO-METABOLIC PROCESSES

Description: Co-metabolism is one form of secondary substrate transformation in whichenzymes produced for primary substrate oxidation are capable of degrading thesecondary substrate fortuitously, even though the secondary substrates do notafford sufficient energy to sustain the microbial population. An emergingapplication involves the injection of water containing dissolved methane and

oxygen into groundwater to enhance methanotrophic biological degradation.This class of microorganisms can degrade chlorinated solvents, such as vinylchloride and TCE, by co-metabolism.

Applicability: Target contaminants for co-metabolic processes are VOCs and SVOCs. The processmay also have some effectiveness in treating fuels and pesticides. As with otherbiological treatments, treatability is highly dependent upon the biodegradability of thecontaminants.

Limitations: Factors that may limit the applicability and effectiveness of the process include:

• This technology is still under development.

• Where the subsurface is heterogeneous, it is very difficult to circulate themethane solution throughout every portion of the contaminated zone.Higher permeability zones are cleaned up much faster becausegroundwater flow rates are greater.

• Safety precautions (such as removing all ignition sources in the area)must be used when handling methane.

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IN SITU WATER TREATMENT TECHNOLOGIES

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Data Needs: A detailed discussion of these data elements is provided in Subsection 2.2.2(Data Requirements for Groundwater, Surface Water, and Leachate).

Characteristics that should be addressed prior to system design include aquifer

permeability, site hydrology, dissolved oxygen content, pH, and depth, type,concentration, and biodegradability of contaminants.

PerformanceData: While ex situ bioreactors for methanotrophic TCE biodegradation are being

used in full-scale remediation, in situ application has not yet been demonstratedat a practical scale. A field demonstration project has been conducted at DOD'sMoffett Naval Air Station, and another is being conducted at DOE's SavannahRiver site.

The DOE pilot-scale demonstration was performed at the Savannah River site'sabandoned seepage basin and process sewer line employed for disposal of 

solvents used to degrease nuclear fuel target elements. Contamination is mostlyTCE and PCE with concentrations of 10,000 ppb in soil and 1,000 ppb ingroundwater. Extensive soil and groundwater monitoring has demonstrated thatwhen methanotroph densities increased five orders of magnitude, TCE and PCEconcentrations declined to less than 2 ppb.

Cost: For the DOE Savannah River demonstration, capital investment costs were$150K and 200 manhours for site preparation, setup, and assembly. Theoperation is low maintenance, requiring only one technician at 25% time (10hours per week); other operational costs are for electricity, natural gas, andequipment maintenance.

O&M costs can be significant because a continuous source of methane solutionmust be delivered to the contaminated groundwater.

References: EPA, 1993.  In Situ Bioremediation: Biodegradation of Trichloroethylene and 

Tetrachloroethylene by Injection of Air and Methane, Innovative RemedialTechnology Information Request Guide.

DOE, 1991. "Modeling Bioremediation Experiments at SRS ID," FY92

Technical Task Description, TTP No. AL 1211-02.

DOE, 1992. "SRS Integrated Demo: Remediation Tasks," FY92 Technical Task 

 Description , TTP Reference Number: SR 1211-06.

DOE-SR, 1993. Technical Name: Methanotrophic In Situ Bioremediation

Using Methane/Air and Gaseous Nutrient Injection Via Horizontal Wells,Technology Information Profile, Rev. 2, DOE ProTech Database, TTPReference Number: SR-1211-06.

DOE, 1991. "VOCs in Non-Arid Soils Integration Demonstration, Analysis,and Evaluation Task," FY92 Technical Task Summary/Description, TTPReference Number: SF 2111-01.

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4.30 CO-METABOLIC PROCESSES

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Site Information:

Site Name Contact Summary Levels Attained Costs

Beginning Levels

Tinker AFB Alison Thomas Ex situ methanotrophic

and ORNL AL/EQW-OL bioreactor

139 Barnes Drive NA NA NATyndall AFB, FL 32403(904) 283-6303

DOE Savannah Terry C. Hazen Methane and air injected TCE/PCE $150K capRiver Site Westinghouse Savannah into seepage basin by <2 ppb

Aiken, SC River Co. horizontal wells NAP.O. Box 616

Bldg. 773-42AAiken, SC 29802

(803) 725-5178

Bendix CERCLA Lead Predesign - TCE, DCE, DCA,

Corp./Allied NA anaerobic cycle to treat VCAutomotive TCE NA NA

St. Joseph, MI

Note: NA = Not Available.

Points of Contact:

Contact Government Agency Phone Location

Ronald Lewis EPA RREL (513) 569-7856 26 West M.L. King Dr.

Fax: (513) 569-7620 Cincinnati, OH 45268

Technology USAEC (410) 671-2054 SFIM-AEC-ETDDemonstration and Fax: (410) 612-6836 APG, MD 21010-5401

Transfer Branch

Kurt Gerdes DOE (301) 903-7289 EM-551, Trevion II

Washington, DC 20585