Sustainability Assessment of Biomethane Production from Hydrogen-mediated Syngas Fermentation

Abstract

Syngas-derived biomethane production is an approach to treat recalcitrant lignocellulosic and fibrous materials that cannot be converted in anaerobic digesters. A coupled system, still at a demonstration level, of gas fermentation, gasification and water electrolysis aims to valorize biomass residues, by producing natural gas quality biomethane, as well as dealing with surplus renewable energy. While laboratory studies and process simulation data support the efficiency of this system in a trickle-bed reactor, comprehensive sustainability assessment is limited. This work has aimed to fill this gap by conducting a detailed Life Cycle Assesment for the trickle bed reactor, focusing on a functional unit of 1 MWh methane production for natural gas grid integration. The study has evaluated a cradle to gate model for the prospective LCA using proxy data and manual calculations for a 1.241m3 reactor. Results indicate that hydrogen-mediated syngas biomethanation is potentially more environmentally friendly, but that the source of hydrogen does not create an appreciable difference in the environmental profile. Future research should work on incorporating process simulation and uncertainty analysis to improve data quality and inventory completeness as well as study reliability.