Development of Hydrogen-Assisted Gas Fermentation Technology to Convert Carbon Dioxide Emissions into Renewable Natural Gas Using Methanogenic Archaea
Creators: name: Ale Enriquez, Fuad
Publisher: name: Washington State University
Year: 2025
Subjects: Carbon capture
Hydrogen
Methanogenic archaea
Renewable natural gas
Genomics
Molecular Biology
Proteomics

description: Climate change is the defining issue of our time. The carbon dioxide that is emitted from the combustion of fossil fuels is the main contributor to climate change. Despite the projected efforts to transition to carbon-negative fuels in the following decades, the demand of fossil natural gas is expected to remain constant at least until 2050. Therefore, the development of cost-effective carbon capture technologies is a priority to counteract the contributions of fossil fuels on climate change. Gas fermentation takes advantage of chemolithotrophic microorganisms to fix carbon dioxide and convert it into renewable value-added products, including methane and acetic acid. The microorganisms involved in gas fermentation use hydrogen as electron donor in anaerobic conditions to catalyze the reduction of carbon dioxide. Gas fermentations can be operated at mild temperature conditions, do not generate hazardous waste, and are compatible with the existing elements in the water-waste-energy nexus worldwide. It makes sense that hydrogen-assisted gas fermentations emerge as a solution for both carbon capture and renewable fuel production, however this technology is limited by three primary elements; the low solubility of hydrogen in water, the relatively high costs associated to cultivation of chemolithotrophic microorganisms in an industrial setting, and the uncertainty about the robustness of non-model chemolithotrophs. In this work, new gas fermentation technology was developed to mitigate these limitations. First, a comprehensive set of strategies to overcome the mass transport limitations of hydrogen were methodically identified in the literature. This knowledge was used to build a continuous lab-scale bioreactor with enhanced gas-liquid mass transport. Later, a novel methanogenic strain with minimum nutritional demands was adapted and isolated in the laboratory. The phenotype and the genome of the new strain were characterized using microbiology principles and genomics. The study of the genome revealed evolutionary adaptations that explained the ability of the strain to grow with ammonium as only nitrogen source. Furthermore, the possibility to use wastewater as alternative low-cost medium for cultivation was demonstrated. The new strain was used to seed the bioreactor with enhanced gas-liquid mass transport, and a series of experiments were conducted to evaluate the performance of the new strain to convert biogas into renewable natural gas. The results showed an outstanding hydrogen conversion efficiency of &gt;0.98 and a final methane titer of &gt;99%. The bioreactor study also provided new insights to improve the performance of biogas upgrading and stablished a stepping stone for upscaling single-culture biogas upgrading technology. The use of the developed microbial strain in biogas upgrading and carbon capture was subject to a provisional patent application. In a last study, the new methanogenic strain was challenged with temperature changes, oxygen contamination, nutrients depletion, and hydrogen starvation during batch cultivation. The robustness of the cellular functions under these perturbations was measured, using a descriptive statistics approach. The measurement of robustness was used to find the perturbations that affected the most the performance of the microbe, providing a starting point for future improvement of the strain. The explanatory power of global proteomics was used to provide a mechanistic framework of what proteins are involved in the stress response and adaptation in methanogens, when exposed to relevant process perturbations. This last study also helped in the identification of genetic engineering targets in methanogens that could further lead to improved performance and robustness.