1,4-dioxane (14D) is a groundwater contaminant and a common solvent stabilizer, which has been detected along with 1,1,1-trichloroethane and other chlorinated solvents in groundwater and surface water across the United States. 14D is highly soluble and mobile in groundwater, and is resistant to natural attenuation, resulting in extended dilute concentration plumes. Several pure and mixed cultures are known to transform14D, via aerobic cometabolism. 14D is effectively cometabolized by the isobutane-metabolizing bacteria, R. rhodochrous (ATCC 21198), and in-situ treatment might be achieved using these bacteria. The effects of substrate inhibition (isobutane) on 14D cometabolism needs to be better understood in order to design effective in-situ treatment systems. In this study, the kinetic parameters; maximum transformation rates (kmax) and half-saturation coefficient (Ks) were determined for R. rhodochrous grown on isobutane. In order to obtain rate versus concentration data, rate tests of 14D transformation were performed in batch reactors as a function of 14D concentration, both in the absence and presence of isobutane. Nonlinear fits to the Monod equation and the linearized Lineweaver-Burk plots were used to obtain estimates of kmax and Ks in the absence of isobutane and apparent kmax and Ks values in the presence of isobutane. Both methods fit closely to the Monod model for the isobutane consumption rate and the cometabolic transformation of 14D. Results showed increased inhibition of 14D transformation with increasing isobutane concentrations. The 14D apparent kmax decreased from 9.84 to 7.97 and 6.29 μmol/mg TSS*day with increasing isobutene concentrations from 0 to 70 and 140 umol/L, respectively, while the apparent Ks values increased from 353, to 659 and 1049 uM. The results indicate isobutane is exhibiting mixed inhibition behavior, with both competitive and noncompetitive inhibition being expressed. Values of the inhibition constants are being determined and a modeling analysis is being performed to simulate the results of the time dependent rate tests of 14D transformation in the presence of isobutane.

Inhibition of the cometabolic transformation of 1,4-dioxane by Rhodococcus rhodochrous 21198 grown on isobutane

253rd National Meeting (2017)

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