It is well recognized there is a critical need to develop management strategies for 1,4-dioxane due to its widespread occurrence in groundwater. This chemical, a probable human carcinogen, was commonly used as a stabilizer in 1,1,1-trichloroethane formulations and is now frequently detected at sites where chlorinated solvents are present. A major challenge in addressing 1,4-dioxane impact in groundwater concerns chemical characteristics that result in migration and persistence. This research will examine the effectiveness of growth factors (in yeast extract) for sustaining growth and 1,4-dioxane biodegradation in mixed microbial communities. The overall objective of this project is to evaluate if minor modifications can be made for improved treatment and to investigate the importance of cometabolic and metabolic metabolism at low concentrations of 1,4-dioxane.

This research examines the impact of yeast extract as an amendment to improve microbial growth and biodegradation kinetics at low 1,4-dioxane concentrations. The work is based on previous evidence for the enhancement of 1,4-dioxane biodegradation by the addition of specific growth factors. The experimental design will include laboratory microcosms containing soil or sediment as well as media with various treatments. Each set of experiments will include triplicate sample microcosms, triplicate live control microcosms, and triplicate abiotic control microcosms. The first task will examine the effect of varying concentrations of yeast extract on removal kinetics. The second task will identify minimum threshold 1,4-dioxane concentrations for microbial growth for specific phylotypes in mixed microbial communities. Microorganisms will also be identified that derive a growth benefit at low 1,4-dioxane concentrations. Additionally, the functional genes and phylotypes associated with 1,4-dioxane biodegradation at low concentrations will be investigated using shotgun sequencing and 16S rRNA gene amplicon sequencing. Functional gene abundance will be correlated with biodegradation rates, results that could have implications for other chemicals of concern.

If this research is successful, the approach could be important for other groundwater chemicals of concern present at low levels. Further, if sustained biodegradation and growth at low concentrations can be demonstrated without substrate addition (e.g., propane), this could result in significant cost savings for site remediation. The research has the potential to provide a better understanding of the natural attenuation and degradation kinetics of 1,4-dioxane when present at low concentrations and should, in turn, lead to more efficient remedial design. As the majority of research on 1,4-dioxane biodegradation has been performed at higher concentrations, this research will fill an important knowledge gap for the bioremediation of this chemical. (Anticipated Project Completion – 2024)