Integrative assessment of biohydrogen and biomethane production from Brittany and Caribbean Sargassum (Ochrophyta, Fucales)

Dark fermentation (DF) and anaerobic digestion (AD) are promising approaches for energy recovery and waste management, yet the process performance and operational feasibility of Caribbean Sargassum under semi-continuous conditions remain uncertain. This study provides a holistic evaluation of the biochemical hydrogen potential (BHP) and biochemical methane potential (BMP) of two brown algae species: Sargassum muticum from Brittany and a mixture of Caribbean Sargassum species. Batch tests showed that S. muticum exhibited the highest hydrogen yield (32 NL H 2 ·kg VS −1 ), while methane yields across all samples ranged from 57 to 140 NL CH 4 ·kg VS −1 . HCl-assisted pretreatment enhanced energy recovery in Caribbean biomass, with gains of 66.6 % for beached samples. For the first time, semi-continuous DF–AD was implemented in 2 L bioreactors with powdered Brittany and Caribbean Sargassum as substrates. Under these conditions, S. muticum produced four times more hydrogen (12.7 vs. 3.0 NL H 2 ·kg VS −1 ) and twice as much methane (59.9 vs. 29.5 NL CH 4 ·kg VS −1 ) compared with Caribbean biomass. These findings demonstrate the limited suitability of Caribbean Sargassum for hydrogen production alone but confirm its viability for methane recovery, providing new insights for the valorization of invasive seaweed through integrated bioenergy systems. • Comprehensive evaluation of energy potential from Brittany and Caribbean Sargassum. • Batch tests: HCl pretreatment increased methane yield of beached Caribbean biomass by 64 %. • Semi-continuous DF–AD: S. muticum showed 4 × higher H 2 yield and 2 × higher CH 4 yield. • PCA revealed a strong correlation (r = 0.93) between R m and BHP 0 .