Theme: 14. Emerging Contaminants

Topic Area: 14b. Advances in 1,4-Dioxane Biological Treatment Technologies

Formatted Title:

Microbial Degradation of 1,4-Dioxane in Groundwater

Background/Objectives:

1,4-Dioxane is most likely a human carcinogen and is highly prevalent, primarily as a groundwater contaminant. Its high mobility in water allows dioxane plumes to be dilute and vast (<100 µg/L). On the basis of a one-in-one million cancer risk assessment, the U.S. EPA has established a Health Reference Level (HRL) for dioxane of 0.35 μg/L. Treatment of dilute dioxane plumes to this low concentration presents a significant challenge and financial burden for many stakeholders. This is because of high capital and operating costs for aggressive ex situ technologies (e.g., pump and treat, advanced oxidation processes) which are the only remedy for large dilute plumes. Therefore, ongoing research has aimed to develop low-cost in situ technologies, such as bioaugmentation, for dioxane-contaminated groundwater. There is a state-of-the art in this area with organisms that have both metabolic and co-metabolic degradation pathways, but there is room for improvement. Allonnia has identified two microbes that have demonstrated metabolic degradation of 1,4-dioxane. They have been designated as Strain ALL22_0001 (1,4 D-Stroy) & ALL22_0048 (CB1190). Here we describe the laboratory characterization of 1,4-dioxane degradation by 1,4 D-Stroy under varied conditions including low starting concentrations of 1,4-dioxane (sub 100 ppb). We also compared the ability of the organism to perform in presence or absence of additional carbon sources. We also characterized 1,4 D-Stroy’s ability to degrade 1,4-dioxane in the presence of chlorinated solvents. We further constructed columns to understand this organism’s transport characteristics in relevant conditions. This complete data package allows us to better facilitate in situ degradation of 1,4-dioxane using 1,4 D-Stroy.

Approach/Activities:

Under lab conditions, 1,4 D-stroy was grown in synthetic media supplemented with as low as 100 ppb of 1,4-dioxane. Samples were harvested after 72-h incubation and the amount of residual 1,4-dioxane was measured. Similar experiments were conducted by exposing 1,4 D-Stroy to various chlorinated solvents like cis-1,2-DCE, vinyl chloride and 1,4-dioxane. Columns measuring 7.8 cm in diameter and 32 cm in length were constructed from PVC pipe and end fittings, with three sampling ports evenly distributed along the column’s length. Vertically oriented columns were packed with Accusand (50/70 mesh) and operated in a fully saturated, up-flow configuration, with influent being delivered by a peristaltic pump at flowrates relevant to typical subsurface conditions. The two-field trials utilized separate injection processes. One was a direct injection into points 5 ft upstream of a monitoring well (shallow and deep screen). The setup included an onsite drill team, four buckets containing uncontaminated groundwater and a small amount of culture. The other was similar to our previous reported field trial where after aerating each well, a small amount of the culture was added along with a nutrient mix to facilitate growth. Dilution in the well was minimal. Equipment setup included a large mixing tank containing uncontaminated water, one aeration pump and stone, one peristaltic pump, one Horiba multiparameter meter and flow through cell, silicone and HDPE tubing, and a water level meter.

Results/Lessons Learned:

Under lab conditions using synthetic media, we have observed that both strains can degrade 1,4-dioxane at very low starting concentrations (100 ppb). We tested 1,4 D-Stroy for ability to degrade 1,4-dioxane in the presence of chlorinated solvents and demonstrated positive degradation ability under the conditions tested. This was the first instance of demonstrating this strain’s ability to successfully degrade 1,4-dioxane in the presence of chlorinated solvents. For the field study, wells will be monitored for a duration of 6 months with regular sampling events to track the microbial load and 1,4-dioxane concentration.

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Patrick Leggieri