Biogas Upgrading by Hydrogenotrophic Methanogens: An Overview

Hydrogenotrophic methanogens play a key role in methane (CH₄) production during various wastes’ anaerobic digestion (AD). The metabolism of hydrogenotrophic methanogens involves Wolfe-cycle to reduce carbon dioxide (CO₂) to CH₄ using hydrogen as feed. Hydrogenotrophic methanogenesis is a potential process for up-gradation of biogas and renewable power intermittency. This review focuses on enhancing hydrogenotrophic methanogenesis for the up-gradation of biogas and, more importantly, a hybrid system that couples both in-situ and ex-situ approaches in one unit. Upgradation of biogas by hydrogenotrophic methanogenesis is advantageous for achieving a higher concentration of CH₄ and removing trace elements and CO₂ from biogas. This approach helps to decrease the cost of upgrading biogas to natural gas quality. Using microbial electrolysis cells coupled with AD could be a potential alternative to increase the CH₄ production yield and remove CO₂ from biogas. The exploitation of the hydrogen gas and integration of the available technologies on a large scale could be explored in future work and help in realizing the production of clean CH₄ in an industrial set-up. This review summarizes the metabolic background of hydrogenotrophic methanogens and their efficient utilization towards methane production. Limited works are available in public domain covering this aspect and thus a review article is important for the readers to update their understanding and research work in light of recent findings. Graphical Abstract: [Figure not available: see fulltext.]