Sequential biofuel production from seaweeds enhances the energy recovery: A case study for biodiesel and bioethanol production

Summary In the present study, eight seaweeds (five red, two brown and one green) were collected and evaluated for dual biodiesel and/or bioethanol production. The highest significant lipid and carbohydrate contents were recorded in the brown seaweed Dilophus fasciola (4.92 and 37.97%dw, respectively). Three routes were investigated, namely R1 and R2 for direct production of biodiesel and bioethanol, respectively, from the whole biomass, in addition to R3 representing the sequential biodiesel and bioethanol production. D. fasciola showed a biodiesel yield of 35.04 mg g−1 dw, composed mainly of C16‐C18 fatty acids with a high saturation degree. All biodiesel characteristics complied with the recommended values of international standards. The maximum reducing sugar content (37.2 g L−1) and bioethanol productivity at 72 hours (0.165 g L−1 h−1) were recorded in the lipid‐free biomass (R3), which were 16.3% and 27.9%, respectively, higher than that of R2. Therefore, a maximum estimated total energy output of 9.96 MJ kg−1 was recorded in R3, which represented 6‐times and 28.3% higher than R1 and R2, respectively. Dilophus fasciola showed a biodiesel yield of 35.04 mg g‐1 dw. Lipid‐free biomass showed the maximum reducing sugar content (37.2 g L‐1) and bioethanol productivity at 72 h (0.165 g L‐1 h‐1), which were 16.3% and 27.9%, respectively, higher than that from the whole biomass. Therefore, the maximum estimated total energy output (9.96 MJ kg‐1) was recorded using the suggested sequential route.