Microalgal biomass as a biorefinery platform for biobutanol and biodiesel production

•We present a biorefinery approach for dual biofuel production from microalgae.•Biobutanol production was achieved with both raw and hydrolysed biomass.•Biodiesel extraction was enhanced by increased cell disruption treatments.•ABE process was optimized by supplementing butyric acid to the fermentation medium. Microalgal biorefineries have recently emerged as a potentially economically viable option for the co-production of value-added products and fuels, such as biodiesel (via the transesterification of lipids) and biobutanol (via the fermentation of carbohydrates). Whilst microalgal biodiesel has been studied extensively, microalgal biobutanol has received less attention due to the low product yields of the biochemical process from which biobutanol is obtained: the Acetone-Butanol-Ethanol (ABE) fermentation. In this work, we evaluate the potential of a microalgae-based biorefinery by: i) quantifying biobutanol production via ABE fermentation of microalgae (raw and hydrolysate form) using a medium optimised via surface response analysis (SRA) methodology; ii) quantifying biodiesel (fatty acid methyl esthers, FAMEs) production via transesterification of microalgae (raw, hydrolysed, and fermented form). Using SRA-optimised medium, butanol fermentation yields of 10.31% (g g−1 cdw) and 10.07% (g g−1 glucose) were attained by microalgae in raw and hydrolysate form, respectively. Meanwhile, the raw, hydrolysed, and fermented microalgae yielded up to 0.92%, 3.82% and 3.29% (g g−1 cdw) biodiesel, respectively. Results highlight the importance of pre-treatment methods and further support the development of microalgal biorefineries for dual biofuel production.