Determination of a Surrogate for Contaminants in the in-Situ Degradation of 1,4-Dioxane in Groundwater By Rhodococcus Rhodochrous

Determination of a Surrogate for Contaminants in the In-situ Degradation of 1,4-Dioxane in Groundwater by Rhodococcus rhodochrous.

Gillian Williams, Grant Kresge, Eileen Lukens, Hannah Rolston, Mohammad F. Azizian, Lewis Semprini

School of Chemical, Biological & Environmental Engineering; Oregon State University, Corvallis, OR, 97330

1,4-Dioxane is a carcinogenic chemical component found in degreasers, dyes, paint strippers, and many more products pertinent to industrial processes. The chemical was used primarily in the late 1960s and 70s as an industrial chemical stabilizer for chlorinated solvents such as 1,1,1-TCA (EPA 2014). The release of chlorinated solvents has correlated to the spread of 1,4-Dioxane in groundwater. One potential remediation strategy is bioremediation. The in-situ bioremediation of this contaminant utilizes the metabolic properties of bacteria to transform carcinogenic pollutants that contaminate our drinking water sources to non-toxic substances. A model microorganism, Rhodococcus rhodochrous, American Type Culture Collection 21198, degrades 1,4-Dioxane through cometabolism. 21198 is fed a primary growth substrate, isobutane, which induces the production of an enzyme that fortuitously oxidizes other compounds such as 1,4-Dioxane. The purpose of this study was to determine the suitability of propylene or isobutene as a less toxic surrogate to study the in-situ degradation of 1,4-Dioxane.

Degradation tests were conducted in 27-mL batch reactors to measure the rate at which 21198 transformed various quantities of propylene or isobutene. Each reactor contained 10 mL of mineral salts media, approximately 5 mg of active 21198 grown on isobutane, and a variable volume of propylene or isobutene. 21198 was quantified as cell dry weight through total suspended solid analysis. Using a gas chromatograph equipped with a flame ionization detector, the concentration of propylene or isobutene in the batch reactor was measured over time as it was cometabolically degraded. An initial linear rate for the transformation of propylene or isobutene was determined and used to develop a Monod curve that compares the initial liquid concentration of substrate (umol/L) to the rate of transformation (umol/mg TSS*day). Monod curves are utilized in order to determine the kinetic parameters of the culture’s maximum degradation rate (K_max) and half-saturation constant (K_s) of the contaminant.

The highest values of K_max expressed when degrading propylene and isobutene were 1.5 and 2 times greater than that of 1,4-Dioxane, respectively. The highest value of K_s expressed when degrading isobutene was twice that of 1,4-Dioxane. During degradation tests, 21198 was operating at or near K_max for the entire degradation of propylene, therefore the value of K_s for propylene was unable to be determined.

United States Environmental Protection Agency. Technical Fact Sheet – 1,4-Dioxane. January 2014.