Graduate Thesis Or Dissertation
 

Evaluation in a Physical Aquifer Model the Long-Term Performance of a Permeable Reactive Bio-Barrier Packed with Co-encapsulated Gellan Gum Beads for the Bioremediation of Chlorinated Compounds and Co-Contaminants

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5999nb67p

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  • Chlorinated solvents are a class of widespread groundwater contaminants that are toxic, carcinogenic, and difficult to remediate at low concentrations. 1,4-dioxane, a suspected carcinogen, is often a co-contaminant found in mixtures of chlorinated solvent plumes. In-situ bioremediation methods of degrading these chemicals through aerobic cometabolism have shown promise. Permeable Reactive Bio-barriers (PRBBs) use the passive movement of groundwater through a reactive media to degrade or entrap contaminants and are a less invasive technology than conventional pump and treat remediation methods. In this study, a cometabolic PRBB was evaluated in a physical aquifer model (PAM). The PRBB was constructed as follows. A ~500g mixture of previously developed gellan gum beads co-encapsulated with Rhodococcus rhodochrous ATCC 21198 and a 1-butanol producing slow release growth substrate (SRC) was packed into a 500 mL column (RB1) within a 50 L effective volume rectangular sand packed PAM. The PAM simulated a homogenous confined aquifer and operated continuously with a synthetic groundwater flow of 2.88 L/day and an estimated hydraulic retention time of ~6.9 days. Experimentation lasted over 300 days after packing. A funnel-and-gate structure was placed at the front of the column containing gellan gum beads (RB1) to direct groundwater flow into the reactive column. After initial packing of RB1 low dissolved oxygen (DO) and 1-butanol concentrations inside the PAM, and specifically in RB1, indicated microbial activity. Isobutene, a surrogate for 1,4-dioxane, was injected into the PAM at concentrations ~38 μg/L. Isobutene transformation into isobutene oxide indicates aerobic cometabolism. Spatial samples were taken at 8 different locations inside the PAM. Isobutene oxide was measured in groundwater samples from RB1 for ~55 days during continuous isobutene injection. Isobutene concentrations inside RB1 were consistently below the detection limit during this period, suggesting rapid transformation into isobutene oxide. Isobutene was detected at sampling locations adjacent to RB1, indicating some of the flow bypassed the constructed PRBB. Isobutene oxide was also measured at lower concentrations downstream of RB1. 1,2-Dichloroethane (1,2-DCA), a common groundwater pollutant, was injected into the PAM at concentrations ~100 μg/L to determine chlorinated solvent transformation capability. Over the course of the 1,2-DCA injection, it is estimated that the PRBB treated at least 26% of influent 1,2-DCA with at least 65% of the 1,2-DCA entering RB1 transformed. The lowest concentrations of 1,2-DCA, ~15 μg/L, were observed inside RB1. 1,2-DCA was observed bypassing the constructed PRBB. Based on mixing estimations, the PRBB received ~42-47% of the groundwater flow, despite the funnel and gate and RB1 structure taking up ~67% of the PAM’s cross-sectional area. Bromide added as a conservative tracer indicated no significant changes in the PAM groundwater flow through and around the PRBB for over 100 days of tracer addition. The study demonstrated the metabolic and cometabolic activity of the gellan gum beads for over 300 days after their emplacement in the PAM. Further studies and modeling of the groundwater flow would support the viability of a similarly constructed PRBB for in-situ application.
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  • Pending Publication
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  • 2022-08-31 to 2023-03-29

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