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

Abstract

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 Rugulopteryx okamurae. 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 Aspergillus awamori was assessed. This was performed via solid-state fermentation (SSF) at two fungal inoculum concentrations (10^7 and 10^8 cel/gbiomass) and two incubation times (5 and 8 days). The highest H2 yield (9.49 mLH2/gbiomass) was obtained after 8 days of pretreatment with 10^7 cel/gbiomass, whereas the greatest TVFA production (213 mg of acetic acid equivalents/gbiomass) occurred after 5 days using 10^8 cel/gbiomass. 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.