Abstract

Biogas upgrading via CO2 conversion to CH4 offers a promising pathway to recover renewable energy from organic waste while reducing greenhouse gas emissions. This dissertation advances both the fundamental understanding and practical implementation of H2-assisted biological methanation and complementary CO2 capture strategies, with a focus on brewery wastewater as a representative high-strength industrial effluent. First, a meta-analysis of 46 publications established the most comprehensive quantitative benchmark to date for biological biogas upgrading via hydrogenotrophic methanogenesis. The analysis confirmed a strong positive relationship between the H2:CO2 ratio and methane content, and showed that, near the stoichiometric 4:1 ratio, ex-situ reactors consistently achieved higher CH4 purities (~92%) than in-situ systems (~85%), while temperature and operation mode had no statistically significant effects on biological biogas upgrading. Building on these insights, a three-phase upflow biogas upgrading reactor with gas-permeable membrane H2 delivery was developed to overcome gas-liquid mass-transfer limitations. With continuous H2 supply, the reactor produced upgraded biogas containing ~92% CH4 at an optimal H2:CO2 ratio of 4.4, and up to ~95% CH4 at higher ratios, while maintaining >90% organic removal and enriching hydrogenotrophic methanogens in the membrane-supported biofilm. To further couple CO2 conversion with electrochemical H2 generation, a membrane electrochemical cell was integrated with an anaerobic digester treating brewery wastewater to produce hythane (CH4/H2 mixtures). Under optimized conditions, the system generated hythane containing ~71% CH4, ~27% H2, and ~2% CO2, achieved >90% CO2 removal and >99% H2S removal, and increased net energy output by more than 50% relative to raw biogas. Finally, a membrane-integrated anaerobic system was combined with a downstream adsorption column to produce pipeline-quality renewable natural gas (RNG) from brewery wastewater. By optimizing H2 dosage, mixing intensity, and hydraulic retention time, the integrated process reliably delivered upgraded biogas with >90% CH4, and a polished RNG stream exceeding 97% CH4 while meeting stringent H2S limits. Complementary work on flame spray pyrolysis of MgO nanoparticles demonstrated a scalable route to high-surface-area sorbents and elucidated trade-offs between pellet strength, porosity, and CO2 uptake, informing the design of solid sorbents for compact polishing units. Collectively, this work provides a multi-scale framework: from global data synthesis to reactor design and sorbent engineering, for converting organic waste streams into high-purity RNG and hythane, and outlines pathways for integrating renewable H2 and modular upgrading systems into future low-carbon energy infrastructure.

Committee Chair

Zhen (Jason) He

Committee Members

Arpita Bose; Benjamin Kumfer; Fangqiong Ling; Yinjie Tang

Degree

Doctor of Philosophy (PhD)

Author's Department

Energy, Environmental & Chemical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

12-19-2025

Language

English (en)

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Available for download on Friday, December 18, 2026

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