In-situ biogas upgrading in thermophilic granular UASB reactor: key factors affecting the hydrogen mass transfer rate

Biological biogas upgrading coupling CO₂ with external H₂ to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H₂ to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO₂ in the biogas into CH₄, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H₂ was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H₂ through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO₂ content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH₄ content.