Ãngel Alejandro Ramos-Garcia is a PhD student at the Environmental Engineering & Earth Science Department at Clemson University in Clemson, South Carolina. Ãngel is currently working on his research on regard biodegradation of 1,4-dioxane in groundwater, specifically on how microbes that degrade 1,4-dioxane mobilize through aquifers to enhance the bioaugmentation process.
Modeling Microbial Transport in Response to Bioaugmentation for In Situ Bioremediation of 1,4-Dioxane
Microbes have been identified that are capable of aerobically biodegrading 1,4-dioxane through metabolic and cometabolic pathways. However, at many sites it appears that the necessary microbes are either lacking or present at very low densities. In such instances, bioaugmentation may be required. Although injection of microbial cultures into aquifers has gained wide acceptance, the practice is largely empirical. Models to predict the movement of bioaugmented microbes in porous media are lacking. Several studies have evaluated the role of various physical, chemical and biological factors on microbial transport and removal in natural subsurface environments, but little has been done to model migration through soil in response to bioaugmentation. Pseudonocardia and Rhodococcus are examples of microbes that are being considered for use in bioaugmentation. Transport of Pseudonocardia poses interesting challenges, since they tend to clump together when grown to high densities, a property that may inhibit their movement in aquifers.
The primary objectives of this study were to characterize a new isolate obtained from a 1,4-dioxane-contaminated site capable of metabolizing the contaminant, and to develop a model that can predict the transport of microbes through soil, with a specific focus on bacteria capable of biodegrading 1,4-dioxane.
A strain capable of using 1,4-dioxane as it sole carbon and energy source was isolated from a contaminated site in the southeastern U.S. Further identification and characterization of the strain is underway, including whole genome sequencing. Although it shares many characteristics with Pseudonocardia, it does not tend to clump like CB1190. An evaluation of its intrinsic kinetic parameters (yield, maximum specific growth rate, decay rate, half saturation constant, and affinity for dissolved oxygen) is also underway. The results will be compared to the characteristics of other microbes capable of growing on 1,4-dioxane, including CB1190.
A proposed model for microbial transport of 1,4-dioxane degraders (via metabolism and cometabolism carried out by propanotrophs) will be presented. The model takes into account advection and dispersion, growth, decay, attachment, detachment, and chemotaxis. An experimental design for bench-scale columns to evaluate the transport model will also be presented. Transport of microbes that metabolize or cometabolize 1,4-dioxane will be compared. Once validated, the transport model will be integrated into a groundwater transport model. This will facilitate a comparison of metabolism and cometabolism and help delineate which approach is more advantageous under a variety of conditions, including the concentration of 1,4-dioxane in the contaminant plume.