Turning waste CO2 into value-added biorefinery co-products using cyanobacterium Leptolyngbya sp. KC45 as a highly efficient living photocatalyst

Currently, there has been an increase in greenhouse gases, primarily atmospheric CO2 content, from both anthropogenic and non-anthropogenic sources, leading to global warming and climate change. To achieve the goal of climate recovery, biochemically mediated CO2 capture and utilization have been shown to be particularly promising, with the added benefit of repurposing the biomass created by the process. In this study, a promising and feasible approach to mitigate waste CO2 from the atmosphere, flue gas, and biogas was proposed using the cyanobacterium Leptolyngbya sp. KC45 as a highly efficient living photocatalyst. Through photoautotrophically cultivated Leptolyngbya, >1875 kg-CO2 were photocatalytically transformed into one ton of Leptolyngbya biomass with its huge amounts of fluorescent pigments (9.3-40.2 % w/w) and lipids (2.6-11.5 % w/w). With the biorefinery co-products processing, the antioxidative and anticancer fluorescent pigment was firstly extracted, yielding 93-402 kg/ton-biomass. After fluorescent pigment extraction, Leptolyngbya lipids from fluorescent pigment-free cyanobacterial biomass residues were recovered and then transesterified to high-quality green biodiesel, providing 25-112 kg-biodiesel/ton-biomass. The majority of the recovered lipids (>93 %) were made up of C16-C18 fatty acids, and their fuel characteristics were acceptable in accordance with the worldwide specifications for biodiesel. Therefore, cyanobacterium Leptolyngbya sp. KC45 has the potential to function as a living photocatalyst for the efficient conversion of waste CO2 of varying concentrations into value-added biorefinery co-products. This proved that cyanobacteria-mediated CO2 capture and biorefinery could greatly contribute to sustainable development goals, leading to a sustainable and happy society.