1,4-Dioxane (1,4-D), a potential carcinogen and persistent chemical, is a common co-occurring chemical of chlorinated solvents in groundwater. Because of its high mobility in groundwater, 1,4-D plumes tend to be large and dilute (less than 100 µg/L). It is now recognized that the conventional in situ bioremediation technologies usually do not work for 1,4-D because the 1,4-D concentration at these sites are too low to sustain continuous metabolism of 1,4-D by the microorganisms isolated or enriched to date. Thus, there are a number of projects that focus on adding primary substrates such as an alkane to stimulate the growth of the 1,4-D-degrading microbes through co-metabolism.

This research project will develop an alternative in situ bioremediation technology based on metabolism instead of co-metabolism; this approach eliminates the need for adding a primary substrate. The project team will study the fundamental science that guides the selective enrichment of cultures able to metabolize 1,4-D at low concentrations (< 100 µg/L). The project team will also combine the enriched cultures with low-cost adsorbents, which are already used in chlorinated solvents remediation. The project team expects the in situ bioremediation approach will meet the U.S. Environmental Protection Agency’s health-based reference level for 1,4-D and require less ongoing maintenance than co-metabolism-based approaches in general.

This project builds on preliminary experiments in which five bioaugmented continuous flow columns successfully metabolized 1,4-D from 25 to <0.5 µg/L for over a year. This is the first report of a continuous-flow bioreactor able to metabolically degrade 1,4-D to below the health-based reference level. The four tasks include:

• Task 1: Development of methods for enriching mixed cultures that are able to continuously metabolize 1,4-D at low concentrations;
• Task 2: Characterization of the enriched mixed cultures that have the best performance;
• Task 3: Proof of concept for the combined remedy approach; and
• Task 4: Evaluation of environmental factors affecting the treatment performance.

Currently, limited approaches are available to deal with the generally large and dilute 1,4-D plumes. Often, that leads to the need for costly advanced oxidation treatment combined with pump-and-treat. This project will develop an in situ remediation method based on metabolic degradation that can be easily implemented. Compared to the co-metabolism-based approach, this method is potentially effective, but eliminates the need for periodic injection of chemicals to support the continuous biodegradation process. (Anticipated Project Completion - 2026)