Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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- All Subjects: Environmental engineering
Description
Water is a vital resource, and its protection is a priority world-wide. One widespread threat to water quality is contamination by chlorinated solvents. These dry-cleaning and degreasing agents entered the watershed through spills and improper disposal and now are detected in 4% of U.S. aquifers and 4.5-18% of U.S. drinking water sources. The health effects of these contaminants can be severe, as they are associated with damage to the nervous, liver, kidney, and reproductive systems, developmental issues, and possibly cancer. Chlorinated solvents must be removed or transformed to improve water quality and protect human and environmental health. One remedy, bioaugmentation, the subsurface addition of microbial cultures able to transform contaminants, has been implemented successfully at hundreds of sites since the 1990s. Bioaugmentation uses the bacteria Dehalococcoides to transform chlorinated solvents with hydrogen, H2, as the electron donor. At advection limited sites, bioaugmentation can be combined with electrokinetics (EK-Bio) to enhance transport. However, challenges for successful bioremediation remain. In this work I addressed several knowledge gaps surrounding bioaugmentation and EK-Bio. I measured the H2 consuming capacity of soils, detailed the microbial metabolisms driving this demand, and evaluated how these finding relate to reductive dechlorination. I determined which reactions dominated at a contaminated site with mixed geochemistry treated with EK-Bio and compared it to traditional bioaugmentation. Lastly, I assessed the effect of EK-Bio on the microbial community at a field-scale site. Results showed the H2 consuming capacity of soils was greater than that predicted by initial measurements of inorganic electron acceptors and primarily driven by carbon-based microbial metabolisms. Other work demonstrated that, given the benefits of some carbon-based metabolisms to microbial reductive dechlorination, high levels of H2 consumption in soils are not necessarily indicative of hostile conditions for Dehalococcoides. Bench-scale experiments of EK-Bio under mixed geochemical conditions showed EK-Bio out-performed traditional bioaugmentation by facilitating biotic and abiotic transformations. Finally, results of microbial community analysis at a field-scale implementation of EK-Bio showed that while there were significant changes in alpha and beta diversity, the impact of EK-Bio on native microbial communities was minimal.
ContributorsAltizer, Megan Leigh (Author) / Torres, César I (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Rittmann, Bruce E (Committee member) / Kavazanjian, Edward (Committee member) / Delgado, Anca G (Committee member) / Arizona State University (Publisher)
Created2020
Description
Groundwater contamination is of environmental and human health concern. Bioremediation is a nature-based method for contaminant treatment. Bioremediation, which relies on the ability of microorganisms to destroy or transform contaminants, must be reliable and cost-competitive in comparison to more traditional treatment methods. Two hurdles must be overcome to enhance bioremediation’s effectiveness and competitiveness: i) being able to degrade recalcitrant compounds, and ii) being able to control the growth rate and location of microorganisms involved in bioremediation in the subsurface. My dissertation adds foundational knowledge and engineering application on how to biodegrade recalcitrant emerging and legacy halogenated compounds. Generating biotransformation knowledge on the recalcitrant emerging contaminants called per- and polyfluoroalkyl substances (PFAS) may lead to solutions for protecting both people and the planet. In my dissertation, I analyzed PFAS biotransformation and microbial defluorination literature via meta-analytical and bibliometric methods to identify unexplored topics and experimental conditions. The metanalytical work identified trends in PFAS microbial biotransformation science to inform future experimental design.
The second hurdle which must be overcome is being able to control bacterial growth in the subsurface. During bioremediation implementation microbial overgrowth may clog injection wells and the subsurface, leading to reduced porosity and treatment efficacy. Contaminant treatment schemes based on aerobic cometabolism frequently exhibit overgrowth at subsurface injection points for O2 (the electron acceptor) and a labile hydrocarbon (e.g., propane). My dissertation work experimentally evaluated acetylene as a microbial inhibitor for use in controlling microbial overgrowth during trichloroethene (TCE) aerobic cometabolism. I demonstrated that acetylene reduces the likelihood of microbial overgrowth of TCE-degrading microorganisms in soil-free microcosms and aquifer soil columns while retaining TCE degradation capacity. Cumulatively, my dissertation provides foundational knowledge for academics and bioremediation practitioners to develop robust and reliable bioremediation technologies.
ContributorsSkinner, Justin Paul (Author) / Delgado, Anca G. (Thesis advisor) / Rittmann, Bruce E (Committee member) / Chu, Min Ying Jacob (Committee member) / Arizona State University (Publisher)
Created2023