Potential of Acrocomia aculeata Pulp Waste for Fermentative Hydrogen Production and the Impact of Hydrothermal Pretreatment

This study provides the first comprehensive evaluation of the biochemical hydrogen production (BHP) potential of Acrocomia aculeata pulp waste, a residue abundantly generated during fruit processing in Latin America. The valorization of this underused biomass is essential to promote circular bioeconomy strategies and expand renewable energy sources in the region. The fermentative hydrogen potential of untreated pulp and of fractions obtained after subcritical water pretreatment was assessed under mesophilic conditions to quantify hydrogen yields and elucidate the energy distribution between solid and liquid phases. Pretreatments were performed at 150, 200, and 250 °C, and both fractions were individually tested. The untreated pulp achieved the highest BHP (125.1 NmL H2/g VS fed), while pretreated solids showed decreasing values of 118.1, 71.6, and 41.6 NmL H2/g VS fed at 150, 200, and 250 °C, respectively. The liquid fractions yielded 107.2, 79.4, and 76.0 NmL H2/g COD fed, showing a similar decline with increasing severity. A mass-energy balance revealed that 1 ton of residual pulp could produce up to 104 m3 H2, equivalent to 15 GJ/ha-year, while the combined solid plus liquid fractions from pretreatment at 150 °C recovered a comparable 14.5 GJ/ha-year, with 65% of hydrogen energy originating from the liquid phase. More severe conditions led to up to 40% lower total energy yields. These findings demonstrate that A. aculeata pulp waste inherently exhibits high fermentative hydrogen potential without requiring hydrothermal pretreatment, highlighting its direct applicability as a renewable substrate for sustainable biohydrogen production.