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Microbial Processes Influencing the Attenuation and Impacts of Fuel

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Microbial Processes Influencing the Attenuation and Impacts of Fuel Copyright Jie Ma December 3, 2013 Abstract Microbial processes influencing the attenuation and impacts of ethanol blend fuel releases By Jie Ma Fuel releases that impact groundwater are a common occurrence, and the growing use of ethanol as a transportation biofuel is increasing the likelihood of encountering ethanol in such releases. Therefore, it is important to understand how such releases behave and affect public safety and environmental health, and how indigenous microorganisms respond and affect their migration, fate, and overall impacts. Vapor intrusion risk (i.e., methane explosion and enhanced fuel hydrocarbon vapor intrusion) associated with ethanol blend releases is a potential concern. Using both experimental measurements and mathematical model simulations, this thesis shows that methane is unlikely to build up to pose an explosion hazard (5% v:v) if diffusion is the only mass transport pathway through the unsaturated zone. However, if methanogenic activity near the source zone is sufficiently high to cause advective gas transport, the methane indoor concentration may exceed the flammable threshold. As a group of widely distributed microorganisms, methanotrophs can significantly attenuate methane migration through the vadose zone, and thus alleviate the associated explosion risk. However, methane biodegradation could consume soil oxygen that i would otherwise be available to support biodegradation of volatile hydrocarbons, and increase their vapor intrusion potential. The release of an ethanol blend solution (10 % v:v ethanol solution mixed with 50 mg/L benzene and 50 mg/L toluene) experiment into a pilot-scale (8 m3) aquifer tank produced a large amount of volatile fatty acids (VFAs). The accumulation of VFAs (particularly butyric acid) exceeded the secondary maximum contaminant level value for odor, which represents a previously unreported aesthetic impact. After the release was shut off, ethanol anaerobic degradation was temporarily stimulated when the dissolved ethanol concentration decreased below its toxicity threshold (~2,000 mg/L for this system). Methane generation persisted for more than 100 days after the disappearance of dissolved ethanol. The persistent methane was likely generated from ethanol degradation byproducts (e.g., acetate) and solid organic carbon in aquifer materials. Ethanol blend releases stimulate the microbial growth and increased the organic carbon content in the aquifer. Microorganisms play a critical role in the fate of ethanol-blended fuel releases, often determining their region of influence and potential impacts. This thesis used advanced molecular tools including 454 pyrosequencing and real-time PCR (qPCR) to characterize changes in structure of indigenous microbial communities in response to 1) a pilot-scale ethanol blend release and to 2) the shut-off of such release. This thesis shows that the ethanol blend release stimulated microbial growth and significantly changed the microbial community structure by enriching microbial groups involved in the fermentative degradation process. The growth of putative hydrocarbon degraders and commensal anaerobes, and increases in degradation rates ii suggest an adaptive response that increases the potential for natural attenuation of ethanol blend releases. After the release was shut off, the microbial community returned towards the pre- contaminated state; however, restoration was relatively slow and far from complete even one year later. Overall, this thesis advanced current understanding of vapor intrusion risks and groundwater quality impacts associated ethanol blend releases and microbial ecology in the impacted aquifer. The integration of this knowledge with site-specific information on pertinent hydrogeological processes will undoubtedly enhance engineering practices such as site investigation, risk assessment, and bioremediation implementation and maintenance to deal with releases of current and future biofuel blends. iii Acknowledgements I would like to thank my advisor Dr. Pedro Alvarez for his unwavering support, unconditional trust and outstanding example of how to become a good scientist. I wish to thank Dr. Bill Rixey for his long-term collaborations and constant help in this study. My thanks also go to other members of my dissertation committee, Dr. Qilin Li and Dr. George Bennett for their valuable inputs and suggestions on the development of this dissertation. My research collaborators Yi Zhang, Dr. Carlos W. Nossa, Dr. George DeVaull, Dr. Hong (Emma) Luo and Dr. Brent Stafford provide a lot of time and effort on this study. I wish to thank Dr. Qiyou Jiang for his help with the shared computing facilities at Rice University and Dr. .Jan Hewitt for her help on the dissertation revisions. My office mate Dr. Zongming Xiu gave me a lot of guidance in doing research and beyond. I am also grateful to all other labmates and colleagues who helped make my time at Rice. Most importantly, I wish to thank my parents, who have always supported and loved me. This work was funded by the American Petroleum Institute. I also received a stipend from the China Scholarship Council. iv Based on this research, the following papers are published or submitted or in preparation: Ma, J., Xiu, Z., Monier, A., Mamonkina, I., Zhang, Y., He, Y., Stafford, B., Rixey, W. and Alvarez, P. (2011) Aesthetic Groundwater Quality Impacts from a Continuous Pilot-Scale Release of an Ethanol Blend. Ground Water Monitoring & Remediation 31(3), 47–54. Ma, J.,Rixey, W.G., DeVaull, G.E., Stafford, B.P. and Alvarez, P.J.J. (2012) Methane bioattenuation and implications for explosion risk reduction along the groundwater to soil surface pathway above a plume of dissolved ethanol. Environmental Science & Technology 46(11), 6013–6019. Ma, J., Rixey, W.G., and Alvarez, P.J.J. Microbial processes influencing the transport, fate and groundwater impacts of fuel ethanol releases. Current Opinion in Biotechnology 24(3): 457-466. Ma, J., Nossa, C.W., Xiu, Z., Rixey, W.G. and Alvarez, P.J.J. Adaptive changes in microbial community structure in response to a continuous pilot-scale release of an ethanol blend. Environmental Pollution 178(0): 419-425. Ma, J., Luo, H., DeVaull, G.E., Rixey, W.G.,Alvarez, P.J.J.A numerical model investigation for potential methane explosion and benzene vapor intrusion associated with high-ethanol blend releases. Environmental Science & Technology (minor revision) Ma, J., et al., Response to the shut-off of a pilot-scale ethanol blended release: increased ethanol degradation activities and persistent methanogenesis. (in preparation) Ma, J., et al., Pyrosequencing-based investigation for microbial response to a 2-years ethanol blended release and the shut-off of such release. (in preparation) v Table of Contents Abstract ..................................................................................................................................... i Acknowledgements ...................................................................................................................... iv List of Figures ............................................................................................................................... xi List of Tables ............................................................................................................................... xv Chapter 1 Introduction................................................................................................................... 1 1.1 Problem statement ................................................................................................................. 1 1.2 Objectives and hypothesis ..................................................................................................... 4 1.3 Dissertation outline ............................................................................................................... 6 1.4 Significance and potential benefits of this study ................................................................... 9 Chapter 2 Literature Review ....................................................................................................... 10 2.1 Physical behavior of ethanol-blended fuel releases ............................................................ 10 2.2 Biodegradation of ethanol-blended fuel .............................................................................. 12 2.3 How would ethanol affect BTEX degradation? .................................................................. 14 2.3.1 Gene expression ............................................................................................................ 16 2.3.2 Metabolic flux dilution ................................................................................................. 17 2.3.3 Thermodynamic inhibition ........................................................................................... 17 2.3.4 Cell physiology ............................................................................................................. 18 2.3.5 Community structure .................................................................................................... 19 2.3.6 Overall effect of ethanol on BTEX plume dynamics ................................................... 22 2.4 Existing knowledge gaps ..................................................................................................... 25 2.4.1 Methane explosion risk ................................................................................................. 25 2.4.2 Enhanced
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