Honors College Thesis
 

Encapsulation of Rhodococcus rhodochrous ATCC 21198 in gellan gum at high densities and with a slow-release substrate for the in-situ bioremediation of contaminant mixtures from groundwater

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https://ir.library.oregonstate.edu/concern/honors_college_theses/gf06g963r

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  • As access to potable water grows scarce, there is an increasing reliance on alternative drinking water sources, namely groundwater (WHO, 2018). Chlorinated solvents, such as 1,1,1-trichloroethane (TCA) and 1,2-cis-Dichloroethene (cisDCE) are some of the most ubiquitous groundwater contaminants spread throughout the US. 1,4-dioxane (1,4D) was used primarily in the late 1960s and 70s as an industrial chemical stabilizer for chlorinated solvents. TCA, cisDCE and the co-contaminant 1,4D have been listed as groundwater contaminants of concern by the US DOD (EPA, 2014). Aerobic bioremediation of groundwater contaminants using microbes including American Type Culture Collection ATCC 21198 (ATCC 21198) is a method of interest for remediating contaminants of concern (COCs). Encapsulation of ATCC 21198 in gellan gum is advantageous for many reasons including: protection from ambient environmental stressors such as changes in pH and temperature, reduced rates of cell washout, and possible shielding from the toxic effects of COCs. ATCC 21198 may be co-encapsulated with slow-release compounds (SRSs), such as the orthosilicate T2BOS that produces alcohols, to sustain microbial activity required to transform COCs. The broad objectives of this thesis were to investigate the long-term resting cell transformation ability of gellan gum beads encapsulated with high densities of isobutane-grown R. rhodochrous of COC mixtures. In addition, the efficacy of co-encapsulating R. rhodochrous in gellan gum beads with a slow release substrate for the transformation of COC mixtures in groundwater aquifers was also investigated. Co-metabolic activity was observed in encapsulated cell reactors for over 70 days, transforming multiple additions of COC mixtures. Encapsulated cells outperformed suspended cell reactors in transforming multiple additions of COCs, maintaining more activity than suspended cell reactors. O2 consumption and CO2 production remain similar between suspended and encapsulated cells, therefore cells are not consuming the encapsulation matrix. Activity towards co-metabolism was observed for over 80 days in reactors containing groundwater and sediment mixtures. Lower oxygen uptake in reactors containing ATCC 21198 encapsulated with SRS T2BOS when compared to those encapsulated without SRS suggests utilization of T2BOS as a substrate. Collected data suggest that cells encapsulated in gellan gum beads at high cell densities with the slow release substrate T2BOS may be a viable method to solve some issues with current bioremediation methods.
  • Key Words: bioremediation, co-metabolism, encapsulation, chlorinated aliphatic hydrocarbons, chlorinated solvents, slow-release compounds, volatile organic compounds, transformation
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