A high rate upflow anaerobic polyfoam-based bioreactor (UAPB) was developed for lab-scale in-situ biogas upgrading. The use of a porous diffuser, alongside high gas recirculation, led to a higher H ₂ liquid mass transfer, and subsequently to a better uptake for high CH ₄ content (up to 90%). Although our attempts to optimize both operational parameters (H ₂ flow rate and gas recirculation ratio) were not successful, at a very high recirculation ratio (32) and flow rate (54 mL/h), a significant improvement of the hydrogen consumption was achieved. These operational conditions have in turn driven the methanogenic community towards the dominance of Methanosaetaceae, which out-competed Methanosarcinaceae. Nevertheless, a highly stable methane production rate was observed despite the methanogenic turnover. During the different applied operational conditions, the bacterial community was especially impacted, resulting in substantial shifts of taxonomic groups. Notably, Aeromonadaceae was the only bacterial group positively correlated with increasing hydrogen consumption rates. The capacity of Aeromonadaceae to extracellularly donate electrons suggests that direct interspecies electron transfer (DIET) enhanced biogas upgrading. Overall, the proposed innovative biological in-situ biogas upgrading technology using the UAPB configuration shows promising results for stable, simple and effective biological biogas upgrading.