Zero-waste biorefinery of oleaginous microalgae as promising sources of biofuels and biochemicals through direct transesterification and acid hydrolysis. (August 2020) - Mandik, Yohanis Irenius
Graphical abstract: Highlights: Oleaginous microalgae are promising for pigments, biodiesel, sugar and protein. Zero-waste biorefinery concept for oleaginous microalgal biomass was proposed. Sequential extractions contribute to efficient recovery of high-value biochemicals. Effective biodiesel and sugar production from microalgal biomass were established. Abstract: Oleaginous microalgae are considered as promising sources of biofuels and biochemicals due to their high lipid content and other high-value components such as pigments, carbohydrate and protein. This study aimed to develop an efficient biorefinery process for utilizing all of the components in oleaginous microalgae. Acetone extraction was used to recover microalgal pigments prior to processes for the other products. Microalgal lipids were converted into biodiesel (fatty acid methyl ester, FAME) through a conventional two-step process of lipid extraction followed by transesterification, and alternatively a one-step direct transesterification. The comparable FAME yields from both methods indicate the effectiveness of direct transesterification. The operating parameters for direct transesterification were optimized through response surface methodology (RSM). The maximum FAME yield of 256 g/kg-biomass was achieved when using chloroform:methanol as co-solvents for extracting and reacting reagents at 1.35:1 volumetric ratio, 70 °C reaction temperature, and 120 min reaction time. The carbohydrate content in lipid-free microalgal biomass residues (LMBRs) was subsequently acid hydrolyzed into sugars under optimized conditions from RSM. The maximum sugar yield obtained was 44.8 g/kg-LMBRs and the protein residues were recovered after hydrolysis. This biorefinery process may contribute greatly to zero-waste industrialization of microalgae based biofuels and biochemicals.