Objective

Chlorinated solvents such as 1,1,1-trichloroethane (1,1,1-TCA) have been widely used at many Department of Defense (DoD) installations. Cyclic ethers, including 1,4-dioxane, are added as stabilizers in commercial formulations of 1,1,1-TCA to extend the working life of the active chlorinated solvent. The concentration of stabilizers can significantly increase during normal solvent use and incorrect disposal of spent solvents can result in 1,4-dioxane becoming an important co-contaminant at solvent-impacted sites. Aerobic cometabolic biodegradation processes may be reliable and cost-effective in situ remediation approaches for 1,4-dioxane and its 1,1,1-TCA-derived co-contaminants. However, understanding of the microorganisms and substrates that can promote these processes is currently limited.

The overall aim of this project is to evaluate the two simplest branched hydrocarbons (isobutane [2-methylpropane] and isobutylene [2-methylpropene]) as stimulants for the cometabolic degradation of 1,4-dioxane and its co-contaminants, including 1,1,1-TCA and its degradation products. These hydrocarbons have not been previously recognized or examined for their abilities to support cometabolic processes for cyclic ethers or chlorinated hydrocarbons. However, these compounds potentially offer considerable specificity in the types of microorganisms and enzyme activities that they can stimulate. They can also be introduced into groundwater using well-established approaches used to promote cometabolic biodegradation of compounds like trichloroethene (TCE). Preliminary data show isobutane and isobutylene support rapid cometabolic 1,4-dioxane biodegradation in two model organisms, Mycobacterium vaccae JOB5 and Mycobacterium ELW1, respectively.