Here comes the sun: intermittent operation of hydrogen-based in situ biomethanation at pilot-scale

Injection-based in situ biomethanation is a promising energy conversion technology that was here investigated in a pilot-scale biogas reactor for microbial conversion of exogenous hydrogen (H2) and endogenous carbon dioxide (CO2) to methane (CH4). The cost of renewable electrolysis-derived H2 is dependent on electricity cost and will thus be highly dependent on the availability and associated cost of renewable energy. Technologies like in situ biomethanation should therefore be able to utilize H2 intermittently in times of low cost. This was tested at pilot-scale by dynamic injection of H2 for 6–10 h and 20 h into a 31 m3 bioreactor, simulating solar and wind intermittency, respectively. By monitoring various process parameters of the in situ biomethanation system it was found that 97.53 % of the exogenous H2 was converted immediately after injection and correspondingly increased the CH4 production rate (MPR). In contrast to the rapid H2 uptake, H2 injection impacted the bicarbonate system in the digestate, which affected the product gas composition. Intermittent operation with standby periods without H2 injection allowed the system to stabilize and recover to baseline conditions without further mitigation steps needed, making it ideal to convert renewable dispatchable energy.