UC Berkeley

Biotechnological strategies for producing commodity chemicals from CO2 instead of fossil fuels have traditionally relied on sugars derived from staple crops such as corn and sugarcane. Although this method has been demonstrated at large scales, substantially replacing fossil fuel feedstocks with crop-derived sugars would require dedicating a significant amount of arable land to the chemical industry instead of food production.Anticipating abundant clean electricity generation from solar cells, wind turbines, or other renewable energy technologies in the near future, researchers have proposed that various electromicrobial production (EMP) processes could avoid the “food vs. fuel” conundrum of traditional bioprocessing strategies. Although nomenclature varies in the literature, I define EMP as any process that converts CO2 into a value-added product (i.e., contains some form of primary production), uses electricity as the primary source of energy driving that transformation, and uses microbes to produce the final product. In this thesis, I develop multiphysics models to analyze and evaluate a variety of EMP processes using a comprehensive life cycle assessment (LCA) framework. In Chapter 2, I apply this method to “mediated” EMP systems that rely on molecular hydrogen (H2), formic acid, and acetic acid as substrates for microbial growth and product formation. In these systems, electrolyzers produce the substrate molecules, which are then supplied to downstream bioreactors. This analysis indicated that all three EMP strategies could outcompete traditional bioprocessing if the electricity grid was sufficiently decarbonized and demonstrated that H2-mediated EMP systems outperformed the other options. The latter result is due mainly to the high performance of water electrolysis compared to earlier-stage CO2 electrolysis, so I also used the LCA framework to identify what performance metrics the CO2 electrolyzer system would need to reach. In Chapters 3, 4, and 5, I evaluate novel EMP strategies that integrate electrochemical and biochemical processes into a single reactor. In Chapter 3, I analyze formate-mediated EMP; In Chapters 4 and 5, I analyze EMP based on direct electron transfer from an electrode to the microbe. Based on current technology, neither of these strategies is able to outcompete their more well-established counterparts analyzed in Chapter 2. Therefore, I also discuss research avenues that may improve the performance of these strategies. EMP processes have applications beyond simply those on Earth. As a member of the Center for the Utilization of Biological Engineering in Space (CUBES), I also analyzed EMP technologies for their ability to support exploratory human missions to Mars. These, and other processes necessary to support a human habitat, require a substantial amount of power. Therefore, in Chapter 6, I evaluate energy generation and storage options on Mars that would supply power to EMP processes for in situ resource utilization. I demonstrate that both miniaturized nuclear fission reactors and photovoltaic panels would adequately support a human habitat, and that solar panels would outcompete nuclear energy over ~50% of the planet’s surface. The results of this thesis develop a roadmap for deploying EMP processes on both Earth and Mars and indicate that “electrifying” biotechnology may have a key role to play in sustainable commodity chemical production in the future.