CO2 to green fuel converter: Photoautotrophic-cultivation of microalgae and its lipids conversion to biodiesel

Abstract

This research focused on utilizing photoautotrophically-cultivated microalgae as efficient converters of CO2 into high-quality renewable biodiesel. This study investigated the feasibility of capturing CO2 from the atmosphere (0.04 % CO2) and simulating industrial sources (20–40 % CO2) for utilization as a simulated waste carbon source for the growth and biodiesel feedstock accumulation of three photoautotrophically-cultivated microalgae species, including Chlorella sp. AARL G049, Tetradesmus obliquus AARL G090, and Desmodesmus opoliensis AARL G085. The results demonstrated that all the tested microalgae are promising CO2-to-fuel converters due to their ability to efficiently convert CO2 into lipid-rich biomass, which can subsequently be processed into biodiesel. All three strains of microalgae displayed remarkable CO2 capture capabilities as well as significant biomass production and lipid accumulation, with the highest performance observed under a 20 % CO2 concentration. The microalgae demonstrated CO2 fixation rates ranging from 0.020 to 0.072 g-CO2/L/day, leading to significant improvements in both biomass productivity, which ranged from 0.011 to 0.040 g/L/day, and lipid accumulation, which ranged from 0.22 to 3.39 mg/L/day. Additionally, the lipid content varied between 5.04 % and 14.75 %. Interestingly, changes in CO2 concentration, ranging from 0.04 % to 40 %, significantly influenced the composition of fatty acids, leading to elevated levels of C16–C18 fatty acids. Nevertheless, these alterations had a minimal impact on the overall quality of biodiesel. The estimated fuel characteristics of the produced biodiesel complied with global specifications for biodiesel, providing better oxidative stability (≥6 h), high heating value (≥39 MJ/kg), and cetane number (≥47). Therefore, this study emphasizes sustainable CO2 capture and the potential of microalgae as a renewable source of economically viable biodiesel.