Developing distillery biorefineries through dark fermentation of whiskey production by-products: the effect of organic loading rate on decarbonisation pathways

Biorefinery approaches can be utilised at distilleries using dark fermentation to treat whiskey production by-products and provide decarbonisation opportunities. A biorefinery can convert residues to hydrogen, carbon dioxide and volatile fatty acids (VFAs). This study investigated the effect of organic loading rate (OLR) on the production of VFAs and biogas in dark fermentation. Similar yields of hydrogen (5.6–6.9 ml H₂. g^-1 VS), carbon dioxide (18.3–24.9 ml CO₂. g^-1 VS), and VFAs (141.7–155.0 mg VFA. g^-1 VS) were found for all OLRs. However, the composition of VFAs altered; higher caproic acid levels (1.2 g. L⁻¹) were observed at low OLRs and higher valeric acid levels at high OLRs (2.0 g. L⁻¹). The most prominent VFAs were butyric acid and acetic acid across the OLR range. The biogenic carbon dioxide and hydrogen offset potential was also assessed. A 50 million-litre whiskey distillery could satisfy approximately half of the carbon dioxide requirement of the Irish brewing industry. Biogenic hydrogen was found to be best suited as a transport fuel. The biorefinery supports the distillery's transition to circular production systems.