Exploring microalgae species for integrated bioenergy Production: A Multi-Fuel cascade valorisation approach

• Four microalgae species were evaluated for their potential in biofuel production. • Aurantiochytrium sp. demonstrated the highest biodiesel and bioethanol yields. • Maximum biodiesel purity of 59 wt% and bioethanol yield of 36 mg/g were obtained. • Biodiesel, bioethanol and biogas were produced through cascade valorisation. • Bioethanol and biogas yields decreased by 30% and 60% using the cascading route. The present study aims to evaluate the cascade valorisation of microalgae for bioenergy production after defining the most promising species between Aurantiochytrium sp., Scenedesmus obliquus , Nannochloropsis oceanica , and Nannochloropsis sp.. For selection, biodiesel (after hexane lipid extraction coupled with cell-disruption methods) and bioethanol (after acid hydrolysis) were produced from raw biomass. Aurantiochytrium sp. achieved the highest oil and FAME contents (21 ± 1 wt% and 58.9 ± 0.6 wt%, respectively), as well as the highest bioethanol concentration (5.4 ± 0.3 g/L). The integrated production of biodiesel, bioethanol and biogas led to a decrease in bioethanol and biogas production efficiency compared to raw biomass (around 30 % and 60 %, respectively). However, it allows multiple product outputs, potentially improving economic and environmental outcomes. The current study highlights the potential of using microalgae species such as Aurantiochytrium sp. for bioenergy production, in a zero-waste approach.