Date of Award
Master of Science
Terry C. Hazen
Frank Loeffler, Jill Mikucki
The utilization of native microbial communities to remediate and immobilize hazardous contaminants has been a common practice for decades. One technique commonly employed to enhance this process is biostimulation, where limiting nutrients are added to a contaminated system in order to stimulate favorable reducing conditions for specialized microorganisms. Many biostimulation applications have been conducted using emulsified vegetable oil (EVO), which stimulates growth of indigenous microbial communities and favorable reducing conditions. However, this practice is sometimes known to cause a lag phase before degradation can occur, lessening the overall efficiency of this practice. The studies described herein aim to reduce the lag phase of degradation by taking advantage of a history-dependent adaptation, called the microbial memory response. This is a novel concept which hypothesizes that a microbial community which has been exposed to a substrate in the past will be able to degrade it more rapidly upon a second or subsequent exposure. To do this, two experiments were designed—one laboratory scale microcosm experiment and one secondary in situ injection of EVO. Both experiments focus on Area 2 of the Oak Ridge Field Research Center (ORFRC), which underwent a subsurface injection of EVO in 2009. The microcosm experiment included groundwater and sediment collected from two sites: one which had been exposed to EVO before and one which had not. Both types of microcosms were amended with a small amount of EVO and monitored for changes in geochemical parameters and the microbial community. Results from this study indicated that the microbial response to EVO was similar in both types of microcosms. The in situ secondary injection was conducted at Area 2 in December 2017 and was monitored for 134 days for changes in geochemical parameters and microbial community. Results from this study indicated that while a distinct community of microbes responded to the EVO injection, the rate at which it was degraded was similar to the primary injection. Overall, neither of the studies showed strong conclusive evidence for the presence of a memory response but did potentially elucidate the limited duration and magnitude of the memory response.
McBride, Kathryn R., "Microbial Memory Response: Observing History-Dependent Adaptation to Repeated Exposures of Emulsified Vegetable Oil in a Contaminated Aquifer. " Master's Thesis, University of Tennessee, 2018.