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Biogas, a gaseous effluent from the anaerobic digestion of organic waste, is considered an important source of energy, since it has a composition mainly of methane (CH 4 ; 55-75%) and CO 2 (20-60%). Today, CO 2 from biogas is an excellent carbon source to induce high microalgal biomass production; however, each microalga strain can have different optimal CO 2 concentrations for maximizing their bio-refinery capacity as well as different ability to endure stressful conditions of industrial effluents. This study assessed the bio-refinery capacity of Chlorella sp. and Scenedesmus sp., native of Lago de Chapala, Mexico, from biogas, as well as the effect of high CO 2 and methane concentrations on the physiological performance to grow, capture CO 2 and biochemical composition of both microalgae cultured under different biogas compositions. The results show that both microalgae have the biotechnological potential to endure biogas compositions of 25% CO 2 -75% CH 4 . Under this condition, the biomass production attained by Chlorella sp. and Scenedesmus sp. was 1.77 ± 0.32 and 2.25 ± 0.20 g L -1 , respectively, with a biochemical composition mainly of carbohydrates and proteins. Overall, this study demonstrates that both microalgae have the ability to endure the stressful biogas composition without affecting their physiological capacity to capture CO 2 and biosynthesize high-value metabolites. Moreover, it is worth highlighting the importance of screening wild-type microalgae from local ecosystems to determine their physiological capacity for each biotechnological application.

Microalgae are considered as a promising biotechnological strategy to capture CO 2 from biogas, producing biomass with valuable energetic compounds. This study has evaluated the biotechnological potential to fix CO 2 from biogas and biomass production by Scenedesmus obliquus cultured in four different formulations of culture media, C30, Bristol, Bold 3N, and C30+M, as well as the effect of methane (CH 4 ) of biogas during CO 2 fixation and biomass production. The results obtained showed that different nutrient composition and concentration of culture media, mainly micronutrient and vitamin concentrations, induced different patterns of CO 2 fixation from biogas and biomass production in S. obliquus. The highest CO 2 fixation (23.03 ± 0.24%) and biomass production (4.63 ± 0.31 g L -1 ) were attained in the microalgae growing in C30+M medium, accumulating mainly proteins. Moreover, these results demonstrated that the CH 4 of biogas did not affect CO 2 fixation from biogas and biomass production by S. obliquus. Overall, these results demonstrated that a culture medium with a balanced nutrient supply is crucial to increasing the biotechnological potential of microalgae to fix CO 2 from biogas.

In the present study, the capacity of the cyanobacterium Leptolyngbya sp. CChF1 to remove CO 2 from real and synthetic biogas was evaluated. The identification of the cyanobacterium, isolated from the lake Chapala, was carried out by means of morphological and molecular analyses, while its potential for CO 2 removal from biogas streams was evaluated by kinetic experiments and optimized by a central composite design coupled to a response surface methodology. Results demonstrated that Leptolyngbya sp. CChF1 is able to remove CO 2 and grow indistinctly in real or synthetic biogas streams, showing tolerance to high concentrations of CO 2 and CH 4 , 25 and 75%, respectively. The characterization of the biomass composition at the end of the kinetic assays revealed that the main accumulated by-products under both biogas streams were lipids, followed by proteins and carbohydrates. Regarding the optimization experiments, light intensity and temperature were the studied variables, while synthetic biogas was the carbon source. Results showed that light intensity was significant for CO 2 capture efficiency (p = 0.0290), while temperature was significant for biomass production (p = 0.0024). The predicted CO 2 capture efficiency under optimal conditions (27.1 °C and 920 lx) was 93.48%. Overall, the results of the present study suggest that Leptolyngbya sp. CChF1 is a suitable candidate for biogas upgrading.