GeoSyntec, working with the University of Toronto (U of T), has isolated a stable, natural microbial consortia (referred to as KB-1) capable of stimulating rapid dechlorination of trichloroethylene (TCE) to ethene at groundwater contamination sites where this activity is otherwise deficient. Figure 1 shows the performance of KB-1 added to microcosms in which TCE dechlorination had stalled at cis-1,2-dichloroethylene (DCE), despite continued electron donor addition. Bioaugmentation of these microcosms with KB-1 (also referred to as dehalococcoides ethenogenes) immediately stimulated dechlorination of cis-1,2-DCE via vinyl chloride (VC) to ethene; cis-1,2-DCE was completely transformed to ethene in a matter of days. Development of these and similar microbial cultures now provides the ability to accelerate bioremediation of TCE and related chlorinated solvents at sites where complete dechlorination reactions do not otherwise occur. Furthermore, studies using KB-1 indicate that this culture can dechlorinate very high concentrations of TCE (in excess of 100 milligrams per liter [mg/L]) and its daughter products, suggesting that containment and/or treatment of source areas may be possible via bioaugmentation.

The initial phase of this project involved evaluating biodegradation of TCE at progressively higher concentrations, with the objective to demonstrate dechlorination at and above saturation concentrations (i.e., in the presence of a dense nonaqueous-phase liquid [DNAPL]). Various dechlorinating consortia were used for these experiments. Batch incubations were carried out to determine dechlorination rates at various chloroethene concentrations. Perchloroethylene (PCE) was dechlorinated up to its aqueous saturation limit. The results of the experiments indicate that the cultures can dechlorinate chlorinated ethenes at dissolved concentrations typically associated with their presence as DNAPL’s (i.e., hundreds of milligrams per liter). The cultures can convert 50 mg/L of PCE rapidly through TCE to DCE within 16 days, and all cultures could dechlorinate TCE up to 200 mg/L. The results of the laboratory studies indicated that the cultures would function in the DNAPL source zones and thus improve the dissolution rate and provide biological containment of DNAPL sources.

The primary objective of the second phase of this project is to enhance the dissolution of a DNAPL source via enhanced biological activities (i.e., electron donor amendment and bioaugmentation). In demonstrating this, we will show that controlled stimulation of microorganisms can be an effective means of containing the source area by rapidly degrading the highly concentrated dissolved phase emanating from DNAPL source area and/or enhancing the flux of dissolved DNAPL to reduce cleanup time by removing the DNAPL free-phase.

The study approach will consist of a field trial at NASA’s Launch Complex 34 on Cape Canaveral Air Force Station to demonstrate that there is a significant increase in the extent of dechlorination and the mass flux from a source zone when biological dehalorespiration activity is enhanced through nutrient addition and bioaugmentation. Predesign laboratory batch and column studies will be conducted to establish key design parameters for the pilot-scale field demonstration.

Key accomplishments:

• Laboratory testing of biological culture on DNAPL source zone.
• Field-scale design submission and approval by state and Federal regulators.
• Field-scale implementation of a bioaugmentation remedial action at a trichloroethylene DNAPL site.

Figure 2. Dehalococcoides Ethenogenes
(Thin-section electron micrographs showing coccoid and
elongated cells, courtesy of Steve Zinder, Cornell University)

Key milestones:

• 2001: Completed laboratory testing of biological culture on TCE DNAPL source contamination.
• 2002: Design approval by state and Federal regulators and initiate field-scale deployment of bioaugmention.
• 2003: Review data after steady-state conditions reached in the field.

Contact: Dr. J.W. Quinn (Jacqueline.Quinn-1@ksc.nasa.gov), YA-C3-C, (321) 867-8410
Participating Organization: GeoSyntec Consultants (Dr. D. Major and Dr. E. Hood)