A biorefinery approach to bioethanol and bioelectricity co-production from tropical seaweeds

The use of biomass in biofuel production is known to harness only a fraction of the entire biomass leading to the generation of large quantities of waste. This underutilisation of biomass has become a major challenge in the development of biofuels, such as bioethanol, as an economical and eco-friendly alternative to fossil fuels. In this study, the algae Ulva fasciata, Hydropuntia dentata and Sargassum vulgare harvested from Ghanaian coasts were used for the co-production of bioethanol and bioelectricity using an integrated biorefinery approach as a means to maximise substrate use. The study obtained ethanol yields of 5.1, 3.7 and 2.4 g (100 g)⁻¹ DM from U. fasciata, S. vulgare and H. dentata, respectively using Ambrosiozyma angophorae and various strains of Saccharomyces cerevisiae (SI17, C8T17, FT17 and PT17) as fermenting organisms. Seaweed bioethanol production residues obtained were used as substrates in microbial fuel cells to generate electric power densities of up to 0.50 W m⁻³, which were comparable to sodium acetate substrate by up to 52.6% with substantial substrate removal efficiencies of up to 46%. The novel co-production of bioethanol and bioelectricity from seaweeds successfully reduced waste generation to as low as 24.4% from a potential 69 to 79% from seaweed bioethanol production alone. The waste generated in the form of effluents from seaweed-residue-fed MFCs can be considered for soil amendment due to their ammonia content of up to 26%.