Anaerobic thermophilic trickle bed reactor as a promising technology for flexible and demand-oriented H-2/CO2 biomethanation

Increasing energy production from variable renewable sources, especially wind and solar photovoltaic, requires measures to maintain a stable electricity grid that balances power production and demand. Flexible conversion of excess renewable energy into a storable substitute natural gas via H-2/CO2 biomethanation may be a suitable approach for tackling this challenge. This study investigated the performance of an anaerobic thermophilic trickle bed reactor (ATTBR) during demand-oriented H-2/CO2 biomethanation. Different combinations of standby periods (SPs) varying from 1 to 8 days and standby temperatures (25 degrees C and 55 degrees C) as well as their repetitive effect on the biological gas conversion performance were systematically evaluated using a standardized restart procedure. The results revealed that the influence of the SP temperature on the restart performance by far outweighed the length of SP investigated. While the investigated ATTBR represents a robust system with a very good restart performance after 25 degrees C SPs, the repetitive effect of 55 degrees C SPs was in particular identified as a critical standby setting that causes deterioration of the restart performance. This may be attributed to increased inactivation rates for thermophilic hydrogenotrophic methanogens at 55 degrees C, which also influences volatile fatty acid transformation dynamics and leads to substantial propionate accumulation (similar to 3000 mg/L) during 55 degrees C SPs. For the application of ATTBR in dynamic energy conversion and storage scenarios, further research is required to reduce response times and enhance flexibility.