Biodegradation of Near-Saturated Concentrations of TCE in Site Groundwater: Selection of Treatment Strategy

Margaret Findlay, Ph.D., Donna Smoler, Samuel Fogel, Ph.D. (Bioremediation Consulting Inc., Watertown MA)
Sami Fam, Innovative Engineering Solutions Inc.

One of BCI goals is to help its engineering clients biodegrade TCE at concentrations approaching saturation (~1,000 ppm). Our approach is focused on the development of special bioaugmenation cultures able to convert high concentrations of TCE to ethene while efficiently managing associated parameters of culture growth such as pH, mineral nutrient requirements, and molecular hydrogen formation. Results from two projects will be discussed. One project involves growing bioaugmentation culture for a Superfund pilot test in TX. A second project addresses a private sector client in OK.

As of July 2005, using one of BCI’s bioaugmentation cultures (BCIe), we successfully achieved reductive dechlorination of 100 ppm of TCE and 33 ppm cis-DCE to ethene in site groundwater. The ultimate goal for the Superfund site is to achieve complete transformation of 400 ppm TCE. A second project (OK) is being conducted in site groundwater in which microcosms have been constructed with TCE concentrations of 400 ppm and 800 ppm respectively. At these concentrations, transformation to cis-DCE occurred relatively rapidly, but the conversion to vinyl chloride was slow.

Factors influenceing the process of dehalorespiration at high concentrations of TCE are being systematically investigated, including: the selection of electron donor (whey, sodium lactate, corn syrup, vegetable oil), addition of co-factors such as vitamins and pH control. The role of specific members of the consortium are also being evaluated including sulfate reducing bacteria, fermentors, and methanogens.

Our results will be discussed from the standpoint of strategic approach on how to treat sites containing high concentrations TCE. Two approaches are considered, treatment from the outside of the dNAPL location toward the inside, and treatment from the inside where the concentrations are the highest. The advantages and disadvantages will be discussed.