Enhancing the Production of H₂ and Volatile Fatty Acids by Fungal Pretreatment of Invasive Macroalgae (<i>Rugulopteryx okamurae</i>) Followed by Dark Fermentation

The blue economy promotes the sustainable use of marine resources, such as algae, for socioeconomic development. This study aims to increase the production of hydrogen (H₂) and volatile fatty acids (VFA) through the dark fermentation of the invasive macroalga . Batch experiments were conducted to identify the optimal operating conditions, with the following parameters being varied: inoculum-substrate ratio (IS) (0.43, 0.25, and 0.11 v/v); initial pH (5.5, 6.5, and 7.5); and algal suspension concentration (4, 6, 8, and 10% w/v). Additionally, the impact of biological pretreatment using was assessed. This was performed via solid-state fermentation (SSF) at two fungal inoculum concentrations (10⁷ and 10⁸ cel/g_biomass) and two incubation times (5 and 8 days). The highest H₂ yield (9.49 mL_H₂ /g_biomass) was obtained after 8 days of pretreatment with 10⁷ cel/g_biomass, whereas the greatest TVFA production (213 mg of acetic acid equivalents/g_biomass) occurred after 5 days using 10⁸ cel/g_biomass. These results suggest that biological pretreatment can enhance the performance of dark fermentation and that the latter condition is most suitable for VFA-oriented biorefineries.