CO2 from biogas: valorisation, economic and environmental impacts in circular carbon systems

Abstract The production of biogas through anaerobic digestion (AD) of organic-renewable feedstocks is recognized as a viable solution within the renewable energy sector. Biogas typically contains a methane concentration ranging from 60 to 70%, presenting a significant opportunity for energy generation. However, the co-generated carbon dioxide (CO 2 ), which constitutes approximately 30–40% of biogas, poses challenges to overall energy efficiency, thus necessitating the implementation of purification methods to enhance methane concentrations. It is noteworthy that the production of one ton of biomethane results in the generation of approximately two tons of biogenic CO 2 . This reality opens avenues for carbon capture, storage, and valorization strategies. The biogas industry is beginning to recognize CO 2 not merely as a byproduct to be discarded, but as a valuable resource for the synthesis of biomethane, chemicals, fuels, and even building materials. There is a growing interest in utilizing biogenic CO 2 as a climate-friendly feedstock, with “bio-Carbon Capture and Utilization” (bio-CCU) practices facilitating the development of sustainable fuels, chemicals, and materials. The article extends to various methods of valorization for biogenic CO 2 , providing an analysis of techniques for separating and upgrading CO 2 derived from biogas. This assessment encompasses both physical and biological methodologies within the carbon capture, utilization, and storage (CCUS) framework. The article further demonstrates both in-situ and ex-situ processes, including biological methodologies that employ microorganisms for CO 2 conversion, as well as thermo-physicochemical processes that transform CO 2 into biobased products. Additionally, the article demonstrates the economic and environmental advantages associated with the strategic utilization of biogenic CO 2 . Repurposing this resource is vital for achieving sustainability goals, particularly in renewable energy sectors, where it can significantly enhance energy efficiency and reduce waste. Finally, the article emphasizes the importance of these practices in climate change mitigation, advocating for a circular economy that prioritizes carbon reuse over atmospheric emissions, thus contributing to the advancement of a sustainable future.