Ex-situ single-culture biomethanation operated in trickle-bed configuration: Microbial H kinetics and stoichiometry for biogas conversion into renewable natural gas.

Biomethanation converts carbon dioxide (CO) emissions into renewable natural gas (RNG) using mixed microbial cultures enriched with hydrogenotrophic archaea. This study examines the performance of a single methanogenic archaeon converting biogas with added hydrogen (H) into methane (CH) using a trickle-bed bioreactor with enhanced gas-liquid mass transport. The process in continuous operation followed the theoretical reaction of hydrogenotrophic methanogenesis (CO + 4 H → CH + 2 HO), producing RNG with over 99 % CH and more than 0.9 H conversion efficiency. The Monod constants of H uptake were experimentally determined using kinetic modelling. Also, a dimensionless parameter was used to quantify the ratio between the H mass transfer rate and the maximum attainable H consumption rate. Single-culture biomethanation averts the formation of secondary metabolites and bicarbonate buffer interferences, resulting in lower demands for H than mixed-culture biomethanation.