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_maxexpressed 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_maxfor
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.