Synergistic Reductive Dechlorination of 1,1,1-Trichloroethane and Trichloroethene and Aerobic Biodegradation of 1,4-Dioxane

Dr. Bruce Rittmann | Arizona State University



This proof-of-concept research project aims at improving the ability to treat mixed contaminants of concern in groundwater. Biological processes have been widely tested for trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and 1,4-dioxane removal due to their low cost, but their application has been very limited due to two challenges. First, the degradation daughter products of TCE and TCA may accumulate and are much more toxic than TCE and TCA. Second, the biological removal rate of 1,4-dioxane is very low due to its low concentration in typical groundwater. To address these challenges, a novel biodegradation approach that exploits a synergy between anaerobic biological removal of TCA and TCE and aerobic biological removal of 1,4-dioxane will be tested. The overall objectives of this project are to demonstrate proof-of-concept of this novel synergistic platform and to explore strategies to optimize this synergy.

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Technical Approach

The concept begins with the hydrogen-based membrane biofilm reactor (MBfR) to anaerobically convert TCA and TCE to ethane by reductive dechlorination. The ethane is then used in a following biological activated carbon (BAC) reactor as the primary electron-donor substrate to stimulate dioxane-degrading bacteria that can remove dioxane through co-metabolism under aerobic condition. The daughter products of TCE and TCA, if accumulated in the MBfR, are biologically oxidized in the BAC column. This synergistic platform addresses the two challenges associated with biological removal of TCE, TCA, and dioxane.

Bench-scale experiments will be conducted to maximize the reduction of TCE and TCA to ethane in the MBfR and the co-metabolism of 1,4-dioxane in the BAC. The experiment will focus on strategies to minimize the daughter products of TCE and TCA in the MBfR so that daughter products do not need to be biologically oxidized in the BAC and more end product (i.e., ethane) can be used to stimulate the growth of 1,4-dioxane-degrading bacteria. The strategies will be understood by exploring changes in the microbial community structure in the reactors and generalizing the experimental data using a mathematical multi-species biofilm model. The generalized data will be used to guide pilot-scale or field-scale study in the future. A cost analysis will be conducted, with the objective to provide data for end users to consider this novel synergistic platform.

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This project is strongly driven by the pressing needs of many DoD sites that are contaminated by 1,4-dioxane and TCE and/or TCA. One example application is a site in which a GAC-adsorption system already is in place for TCE and/or TCA removal; then, the novel system may be able to retrofit the GAC adsorber to be part of this biodegradation-based system. The proposed platform is for ex situ treatment, but the principles of the synergy can be adapted for in situ treatment. This research also will contribute to understanding of the fundamental factors controlling reductive dechlorination and the co-metabolic biodegradation of 1,4-dioxane, processes that occur during in situ and ex situ groundwater treatment settings.

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Points of Contact

Principal Investigator

Dr. Bruce Rittmann

Biodesign Institute at ASU

Phone: 480-727-0434

Fax: 480-727-0889

Program Manager

Environmental Restoration