Biorefinery concept comprising acid hydrolysis, dark fermentation, and anaerobic digestion for co-processing of fruit and vegetable wastes and corn stover

A new biorefinery conceptual process is proposed for biohydrogen and biomethane production from a combination of fruits and vegetable wastes (FVW) and corn stover (CS). The objective of this work was to perform the acid hydrolysis (HCl 0.5% v/v, 120 °C, 2 h) of the FVW and CS at 3:1 dry basis ratio, and to process its main physical phases, liquid hydrolyzates (LH) and hydrolyzed solids (HS), by mesophilic dark fermentation (DF) and anaerobic digestion (AD), respectively. In DF of LH as carbon source, hydrogen was produced at maximum rate of 2.6 mL H₂/(g_glucose h) and maximum accumulation of 223.8 mL H₂/g_glucose, equivalent to 2 mol H₂/mol_glucose, in a butyric-pathway-driven fermentation. HS were digested to methane production assessing inoculum to substrate ratios in the range 2–4 g_inoculum/g_VS. The main results in AD were 14 mmol CH₄/g_vs. The biorefinery demonstrated the feasibility to integrate the acid hydrolysis as pretreatment and subsequently use the LH for hydrogen production, and the HS for methane production, with an energy yield recovery of 9.7 kJ/g_vs, being the energy contribution from anaerobic digestion 8-fold higher than of dark fermentation.