Hydrogen and Fatty Acid Production by Dark Fermentation of Sweet Sorghum Stalks as an Efficient Pre-treatment for Energy Recovery Before Their Bioconversion into Methane

Hydrogen, volatile fatty acids (VFAs), and methane coproduction from sweet sorghum stems using bacterial consortium was investigated as an efficient and sustainable pre-treatment strategy to improve energy recovery. Integrated two-stage dark fermentation and methanization approach aimed to reduce fractionation, juice extraction, and pre-treatment steps to improve the efficiency and sustainability of stalks energy bioconversion. Stems biomass loading did not significantly influence hydrogen and VFAs productivities. Energy recovery yields were (7.07) and (10.01) MJ/kg dry matter (DM), respectively, for raw stem single dark fermentation (DF) and methanization processes, corresponding to 41.22% and 58.37% of raw stalk energy potential. Methanogenic potential increase of 31.9% and energy bioconversion yield of 13.21 MJ/kg DM were reached for solid residues from DF (80.75% of their energy content), suggesting that bacterial consortium efficiently pre-treated sorghum stalk fibers. Coupling process led to 88.74% net biomass energy recovery yield, corresponding respectively to 57.38% and 40.23% more than single DF and methanization. Fiber degradation ability of DF bacterial consortium significantly contributed to improve sorghum stalk energy recovery efficiency and cost-competitiveness.

Graphical Abstract