Optimizing trickle-bed reactor performance for hydrogenotrophic methane production in power-to-methane systems

Biomethanation is a process enabling both power-to-methane and biogas upgrading by using methanogenic archaea to convert hydrogen and carbon dioxide to methane. This study describes the long-term operation of a lab-scale mixed culture ex-situ biomethanation trickle bed reactor (TBR) under varying operating conditions such as medium feeding rate, gas loading rate, temperature, pressure, and pH. Additionally, nutrient medium variations with a focus on trace elements were examined. Community analysis of the TBR startup revealed that the fraction of archaeal taxa increased from 0.24% to 5.1% and a stable archaeal consortium was established within 21 days after inoculation. Despite this, switching to thermophilic conditions after 239 days of mesophilic operation did not impair reactor performance. Nutrient starvation caused rapid drops in productivity which could be alleviated by higher medium dosing without long adaptation periods. Elevated sodium/potassium ratio and additional trace elements (zinc, boron, calcium, copper, manganese) significantly increased the methane production in batch culture, but this could not be replicated in the TBR. The final TBR methane evolution rate after 388 days of operation was 6.06 ± 0.04 m 3 /m 3 /d at 96.1% ± 2.8% CH 4 . These results represent an addition to the growing body of operational data for TBR biomethanation.