Graduate Thesis Or Dissertation
 

Experimental demonstration and modeling of aerobic cometabolism of 1,4-dioxane by isobutane-utilizing microorganisms in aquifer microcosms

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  • 1,4-dioxane, a probable human carcinogen at low (< 1ppb) concentrations, has emerged as a groundwater contaminant due to its historical use as a stabilizer for the chlorinated solvent 1,1,1-trichloroethane. Aerobic cometabolism, the use of a primary substrate to induce the production of microbial enzymes that fortuitously degrade other compounds, is a promising in situ treatment strategy for 1,4-dioxane because it has the potential to mineralize trace 1,4-dioxane concentrations to carbon dioxide. The effectiveness of biostimulation with isobutane (2-methylpropane) as a primary substrate and bioaugmentation with Rhodococcus rhodochrous strain ATCC 21198 was assessed in microcosms constructed with aquifer solids from Fort Carson, Colorado, a site with 1,4-dioxane and trichloroethene (TCE) co-contamination. Isobutane effectively stimulated native 1,4-dioxane-degrading microorganisms in the aquifer solids after a lag of approximately one week. Microcosms bioaugmented with 21198 showed immediate consumption of isobutane and cometabolism of 1,4-dioxane after isobutane was consumed below 0.15 mg L, indicating primary substrate inhibition. At a concentration of 200 μg L, TCE did not inhibit 1,4-dioxane degradation, however TCE was not readily cometabolized. 1,4-dioxane-cometabolizing microbial populations remained active in bioaugmented and biostimulated microcosms with repeated additions of isobutane over approximately 300 days, though transformation rates slowed without inorganic nutrient amendment. Modeling of simultaneous isobutane utilization, 1,4-dioxane degradation, and biomass growth according to Michaelis-Menten and Monod kinetics accurately simulated data from microcosms not experiencing inorganicnutrient limitation. Optimization of kinetic parameters yielded the following values: Kmax,1IB=2.58 mg mg day, Ks,IB=0.1 mg L, Kmax,14D=0.87 mg mg day, Ks,14D=4.35 mg L, KI=0.13 mg L, b=0.03 1 day, and Y=0.885 mg mg.
  • KEYWORDS: 1,4-dioxane, aquifermicrocosms, kinetics, isobutane, cometabolism, numerical modeling, trichloroethene (TCE)
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