Bioaugmentation and phytoremediation to treat 1,4-Dioxane-contaminated groundwater

1,4-Dioxane (dioxane) is a probable carcinogen and persistent groundwater pollutant often found comingled with chlorinated solvents (e.g., trichloroethylene, dichloroethylene, and trichloroethane). Because of dioxane’s high mobility in groundwater, dioxane plumes tend to be large and dilute. State-issued clean-up guidelines for dioxane are on the order of 1 µg/L and sometimes less. Reaching these low clean-up guidelines through remediation has proven to be particularly difficult and costly. Utilizing aggressive pump-and-treat and ex-situ technologies such as advanced oxidation (AO) on dilute dioxane plumes is often prohibitively expensive. This work evaluated bioaugmented phytoremediation, a promising, cost-effective clean-up strategy for dioxane-contaminated groundwater. This work confirmed phytoremediation by hybrid poplar removed dioxane to health advisory levels (~1 µg/L) in bench-scale experiments. In addition, bioaugmenting the rhizosphere of poplar plants with archetype dioxane-degrading strains Pseudonocardia dioxanivorans CB1190 and Mycobacterium sp. PH-06 significantly increased the rate of dioxane removal. This work also identified Rhodococcus ruber 219 as a promising candidate for field bioaugmentation. With the addition of B-vitamins, the strain can sustain growth in dilute dioxane concentrations (<100 µg/L) and degrade dioxane to risk-based health advisory levels (~0.35 µg/L). This work demonstrated that bioaugmented phytoremediation is a promising treatment alternative for dioxane-contaminated groundwater to achieve low concentrations (<1.0 µg/L). While challenges remain, the successful implementation of this strategy offers a cost-effective and green solution to a widespread threat to human health.