This project aims to treat 1,4-dioxane, a probable carcinogen and persistent groundwater pollutant often found comingled with chlorinated solvents (e.g., trichloroethene, dichloroethene, and trichloroethane). Because of dioxane’s high mobility in groundwater, 1,4-dioxane plumes tend to be large and dilute. Proposed health advisory guidelines for 1,4-dioxane are as low as 0.35 μg/L. Reaching this low concentration through remediation has proven to be particularly difficult and costly. The objective of this project is to demonstrate that bioaugmented phytoremediation offers a reliable and cost-effective treatment solution for 1,4-dioxane-contaminated Department of Defense (DoD) sites. The project team expects that this treatment strategy will meet the Environmental Protection Agency risk assessment guideline for 1,4-dioxane of 0.35 μg/L.

Phytoremediation with poplar and willow trees is an attractive and cost-effective treatment strategy for dilute 1,4-dioxane plumes due to its exceedingly low energy demand. Phytoremediation has also been shown as an effective treatment for chlorinated solvents, allowing for the treatment of comingled plumes. During the work on SERDP project ER-2719, Utilizing the Plant Microbiome and Bioaugmentation to Degrade 1,4-Dioxane and Co-Contaminants, the project team demonstrated bioaugmenting the poplar rhizosphere with metabolic dioxane-degrading bacteria speeds the treatment of 1,4-dioxane to ~1 μg/L. The project team also confirmed that known dioxane-degrading bacterium Pseudonocardia dioxanivorans CB1190 utilizes root exudates as an auxiliary carbon source, thus reducing challenges associated with low 1,4-dioxane concentrations and metabolic degraders.

During this demonstration, the project team will implement bioaugmented phytoremediation to treat 1,4-dioxane-contaminated groundwater. The demonstration will be conducted in Phyto Attached Growth Reactors (PhAGR®), one-year old poplar or willow trees rooted in 300-gallon bags filled with either perlite or soil. These PhAGRs will provide a near field-scale demonstration of the technology without the added cost and space requirements of a large plantation. In addition, PhAGRs will offer a controlled system where bioaugmentation candidate strains can be thoroughly evaluated. The system will allow for optimization of parameters, including irrigation flow rates and hydraulic residence times.

Throughout the project, 1,4-dioxane-contaminated groundwater will be distributed onto the bioaugmented PhAGRs by sub-surface irrigation. System performance will be observed by analyzing influent and effluent 1,4-dioxane concentrations as well as 1,4-dioxane metabolite formation. In addition, strain viability will be tracked using quantitative polymerase chain reaction and microbial community analyses. Finally, in-planta analyses will be used to quantify rhizospheric transformation as well as 1,4-dioxane uptake and translocation by trees.

1,4-Dioxane plumes are found at many DoD sites and present a formidable cost for remediation. Utilizing aggressive pump-and-treat and ex situ technologies such as advanced oxidation on dilute 1,4-dioxane plumes are often prohibitively expensive. The goal of this project is to demonstrate the effective treatment of 1,4-dioxane-contaminated groundwater using bioaugmented phytoremediation. Phytoremediation has also been shown to treat common chlorinated solvent co-contaminants to below health-advisory levels. If validated, bioaugmented phytoremediation has the potential to provide significant cost savings for DoD.