Biomethanation on demand: Continuous and intermittent hydrogen supply on biological CO2 methanation

Achieving carbon neutrality in Europe hinges on the exploitation of renewable energy resources. Although these resources seem plentiful, critical challenges emerge from the excess energy that cannot be effectively stored or from insufficient electricity production. A promising approach to sustaining a balanced electricity network that aligns production with demand involves integrating the transformation of surplus energy into biomethane through a two-stage process. The surplus energy is utilized to produce hydrogen through water electrolysis, followed by the biological methanogenesis of hydrogen and carbon dioxide to synthesize biomethane. Investigating energy undersupply scenarios is crucial to understanding the resilience of biological processes, requiring evaluation of intermittent hydrogen supply modes and their microbial impacts. The present study focused on simulating actual demand-driven operational conditions by intermittently halting the supply of input gas, thereby inducing disruptions within the biological processes. Various sequences of consecutive starvation and regular operation phases, spanning one to five weeks, were assessed. The experimental framework was executed in two thermophilic Trickle Bed Reactors under anaerobic conditions, each utilizing distinct packing materials; specifically, activated carbon pellets and polyethylene K1 Media Raschig rings. The objective was to scrutinize the influence of these materials on the composition of the output gas, process stability and resilience of the microbial community. Remarkably, in both reactors, the biomethanation process demonstrated high adaptability, with capabilities to cease and recommence almost instantaneously, even following a five-week starvation period, effectively returning the process performance to its optimal pre-starvation state.