Coupling biogas upgrading with biopolymers accumulation through cyanobacteria CO2 fixation

Biogas, primarily composed of carbon dioxide (CO 2 ) and methane, requires upgrading to biomethane by removing the CO 2 to improve its usability, making it suitable for direct injection into gas grid and serving as a renewable alternative to fossil-derived methane. This study investigates the potential of the recently isolated cyanobacterial strain Synechocystis sp. B12, selected for its robustness and tolerance to high light intensity, in biogas upgrading. Synechocystis sp. B12 demonstrated exceptional tolerance to high CO 2 concentrations as in the biogas, utilising it for photosynthetic growth without any detrimental effects from CH 4 or other contaminants. This establishes it as a promising candidate for biogas upgrading applications. The strain successfully fixed over 99 % of the CO 2 present both in synthetic gas mixture and industrial biogas. Moreover, Synechocystis sp. B12 converted the captured CO 2 into polyhydroxybutyrate, a biodegradable bioplastic compound, achieving productivities of approximately 80 mg L −1 . This approach provides the dual advantage of enhancing biogas quality while simultaneously transforming CO 2 into valuable bioproducts. • Synechocystis sp. B12 tolerates high CO 2 and CH 4 concentrations. • Synechocystis sp. B12 fixes over 99 % of biogas CO 2 upgrading it to biomethane. • Captured CO 2 is converted into biodegradable polyhydroxybutyrate. • This process produces biomethane and valuable bioplastics simultaneously.