Theme: 01. Remediation Technology Innovations

Topic Area: 01b. Bioremediation: Advances in Amendment Formulations

Formatted Title:

Development of New Bacterial Consortium for Enhanced Biodegradation of 1,1-Dichloroethane and Chloroethane

Background/Objectives:

Biological degradation of 1,1,1-trichloroethane (1,1,1-TCA) results in accumulation of daughter products including 1,1-dichloroethane (1,1-DCA) and chloroethane (CA). The USEPA characterizes 1,1-DCA as a possible human carcinogen, and some studies indicate that CA is an animal carcinogen. 1,1-DCA has been found in at least 673 of the 1,699 National Priorities List (NPL) sites, and CA has been detected in at least 282 of these sites. Based on current data, Dehalobacter spp. play a critical role in the transformation of 1,1,1-TCA to 1,1-DCA and CA. However, the biodegradation rates of 1,1-DCA and CA are typically much slower than for 1,1,1-TCA, making them more persistent in groundwater. Moreover, the presence of 1,1-DCA can inhibit the complete degradation of chlorinated ethenes such as 1,1-dichloroethene (1,1-DCE) and vinyl chloride (VC). The objective of this work is the development of a bioaugmentation consortium capable of rapid degradation of 1,1-DCA and CA.

Approach/Activities:

To develop a new consortium, aquifer solids and groundwater were collected from a 1,1,1-TCA and 1,1-DCA contaminated site in New Jersey. Samples of the aquifer material were sequentially transferred in reduced anaerobic mineral medium with 1,1-DCA as the sole electron acceptor and sodium lactate as the electron donor. Rates of 1,1-DCA biodegradation were measured over time during the transfers. The resulting consortium, TCA-20B, was then sequentially grown in a 3 L fermenter, followed by a 20 L fermenter and then a 750 L fermenter to define conditions required for large-scale growth. Batch bottle studies were also conducted to quantify biodegradation rates under different conditions.

Results/Lessons Learned:

The TCA-20B culture exhibited rates of 1,1-DCA degradation in fermenters that were as high as 18-20 milligrams per liter per day (mg/L/day). The culture also degraded CA with an average rate of nearly 3 mg/L/d during growth in the fermenters. This result is surprising, because many cultures and consortia capable of degrading 1,1,1-TCA and 1,1-DCA produce CA as a terminal product. Batch bottle assays confirmed degradation of CA by TCA-20B, but the rate of degradation was appreciably lower compared to when the culture was grown in fermenters with continuous feed of 1,1-DCA. Molecular analysis of the consortium revealed the presence of bacteria from many different dechlorinating genera including Dehalobacter, Dehalococcoides, Desulfitobacterium, Dehalobium and Desulfuromonas. Despite the growth of TCA-20B consortium on 1,1-DCA, the most common gene mediating this process, the 1,1-DCA dehalogenase DcrA was not detected, but a gene known to dehalogenate chloroform, CfrA, was present. During this presentation, we will provide data concerning the characterization, growth and degradation kinetics of the TCA-20B consortium. We will also provide information concerning the activity of this culture when combined with a traditional chlorinated ethene consortium (SDC-9^TM) as an approach for complex sites with chlorinated ethenes and 1,1-DCA.

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Simon Vainberg