Microbe could prove an economical, environmentally sound method of addressing stubborn dioxane co-contamination
A pair of industrial solvents associated with cosmetics and household cleaning products has been detected at thousands of aquifer sites nationwide, according to a new study published in Environmental Science and Technology Letters. The United States Environmental Protection Agency (EPA) considers 1,4-Dioxane (dioxane) and 1,1-Dichloroethylene (1,1-DCE) probable human carcinogens. The widespread nature of the contamination poses a cleanup problem that will be not only expensive, but also technically challenging with today’s remediation methods. On-site groundwater remediation is a difficult job in the best of circumstances, but the two chemicals have presented special challenges.
Treating groundwater with natural bacteria that target contaminants, a process known as bioremediation, is often the most efficient course of action. But some of dioxane’s properties — high solubility in water, a low Henry’s law constant, and its frequent co-occurrence with chlorinated solvents and other contaminants — make bioremediation difficult.
In groundwater, dioxane often occurs alongside 1,1 DCE, a chlorinated solvent that renders ineffective microbes that can break down dioxane, including Pseudonocardia and Mycobacterium. Together, the chemicals are extremely expensive to remove because of their very different properties: Each individual contaminant requires a completely different strategy for removal.
Now, a team of New Jersey Institute of Technology (NJIT) researchers has isolated a bacterium from an activated sludge sample that can break down coexistent dioxane and 1,1 DCE, potentially opening the door to bioremediation for the 80% of dioxane sites that are co-contaminated. The bacterium the team isolated, Azoarcus sp. DD4 (DD4), has a very promising profile in terms of future bioremediation.
Microorganisms used as bioremediators sometimes work naturally, but in other cases the process must be coaxed along by the addition of fertilizers, which increases bioavailability through a process known as biostimulation. During testing, the researchers found that they didn’t need to add other nutrients such as ammonia to test sites for the newly isolated DD4 to do its work.
Bacteria currently used in dioxane bioremediation — Pseudonocardia and Mycobacterium — are prone to vegetative growth and clumping behaviors that limit their use. This didn’t occur with DD4, which can co-oxidize dioxane and 1,1-DCE without forming clumps when propane is used as a primary substrate. Instead, the DD4 disperses into the water evenly, a promising characteristic.
Within 14 days of incubation in a sample of contaminated groundwater, the DD4 brought levels of dioxane down from 10.4 mg/L to <0.4 μg/L.
The NJIT research team, comprised of Daiyong Deng, Fei Li, Chen Wu, and Mengyan Li, is still conducting DD4 feasibility testing but hopes to conduct field demonstrations as soon as early 2019. Mengyan Li, assistant professor of chemistry and environmental science at NJIT, stated:
Biodegradation by DD4 is the first biological method we have found for treating both compounds concurrently, and it is also environmentally friendly and cost-efficient.