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 (H 2 ) and endogenous carbon dioxide (CO 2 ) to methane (CH 4 ). The cost of renewable electrolysis-derived H 2 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 H 2 intermittently in times of low cost. This was tested at pilot-scale by dynamic injection of H 2 for 6–10 h and 20 h into a 31 m 3 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 H 2 was converted immediately after injection and correspondingly increased the CH 4 production rate (MPR). In contrast to the rapid H 2 uptake, H 2 injection impacted the bicarbonate system in the digestate, which affected the product gas composition. Intermittent operation with standby periods without H 2 injection allowed the system to stabilize and recover to baseline conditions without further mitigation steps needed, making it ideal to convert renewable dispatchable energy. • Injection-based in situ biomethanation was demonstrated at 31 m 3 reactor size. • Intermittent operation was demonstrated with increased CH 4 production rates. • Fast H 2 uptake kinetics favor intermittent operation of in situ biomethanation. • Slow CO 2 dynamics in the reactor liquid affected product gas quality.