Assessing two-phase anaerobic digestion systems for demand-driven electricity and biobutanol transport fuel at a large distillery

Decarbonisation of industry will necessitate innovative technological solutions that allow for both reduced carbon footprint and security of supply. Biogas systems can allow electricity production on-demand. This study evaluated and compared different two-phase anaerobic digestion systems for continuous volatile fatty acid (VFAs) production and demand-driven biogas production at a whiskey distillery using by-products as feedstock. The systems analysed were a two-phase continuously stirred tank reactor (CSTR) and a leach bed-expanded granular sludge bed reactor (LBR-EGSB) system. Both systems exhibited continuous VFA production (up to 10.4 g. L⁻¹_VFA made up of primarily butyric acid and acetic acid) and rapid biogas production, achieving peak flow rates within 30 min. The peak biogas production from the demand-driven EGSB was 3.1 L. L⁻¹_reactor. d⁻¹ compared to the CSTR, which recorded 1.8 L. L⁻¹_reactor. d⁻¹. Three kinetic models of both systems were assessed, which were able to describe the cumulative biogas production. A theoretical evaluation of processing butyric acid into biobutanol, to be blended with diesel, could produce a more sustainable transport fuel than diesel, reducing distillery-associated transport emissions by 16%.