Emerging Contaminants Summit

Spring 2020

StudentCompetitionrobelAlix Robel
Graduate Research Assistant
Oregon State University 

I am a third year Environmental and Molecular Toxicology PhD student working in Dr. Jennifer Field's Laboratory. The focus of my PhD work has been on Per- and Polyfluoroalkyl Substances in a number of matrices.



Pilot-Scale Application of Granular Activated Carbon for Removal of Per- and Polyfluoroalkyl Substances in Groundwater at a Military Site. 

Aqueous film-forming foams (AFFFs) have historically been applied to hydrocarbon-based fuel fires because of their unique, proprietary chemistries and, as a result, are used for both emergency response and fire-fighter training purposes.  Repeated use of AFFFs at fire-fighter training areas resulted in contamination of soils, aquifer sediments, and groundwater with PFASs including perfluoroalkyl carboxylates (PFCAs, e.g., PFOA) and sulfonates (PFSAs, e.g., PFOS) at concentrations above current health advisory levels. Granular activated carbon (GAC) is one remediation technology used to remove PFASs from groundwater.  At present, there are few data at pilot and full scale that describe the removal of PFASs by GAC.  With the focus primarily on the removal of PFOA and PFOS, there are few data that describe the removal of other PFASs by GAC, including precursors.  A pilot-scale system consisting of flow-through lead and lag vessels, each containing 91kg DSR-GAC, and was operated at a flow rate of approximately 9.5 liters per minute.  Weekly samples of influent and the effluents from the lead and lag vessel were analyzed for 16 individual PFASs including C4-C8 PFCAs, C4-C8 PFSAs, 4:2-8:2 fluorotelomer sulfonates, C6 and C8 perfluoroalkyl sulfonamides, and a cationic precursor.  Samples were also analyzed by the total oxidizable precursor (TOP) assay and by particle induced gamma ray emission (PIGE) spectrometry for total fluorine.  Individual PFASs that are oxidizable accounted for the production of PFCAs upon oxidation, thus closing the mass balance on PFASs in the influent groundwater.  Breakthrough curves were constructed to determine the efficacy for removal of the individual PFASs.  In addition, the relationship between the order of individual PFAS elution on analytical columns used in LC-MS/MS analysis was determined to be the same as the order of breakthrough on GAC. The relationship between elution and breakthrough could be used for predicting breakthrough of other precursors. Breakthrough curves were also generated from TOP assay and PIGE data.  Discussion will include the advantages and limitations of relying on TOP assay and PIGE data for total fluorine as an alternative or in addition to individual PFAS analysis by LC-MS/MS. 

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.

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