Increasing the yield of volatile fatty acids from pilot scale biorefining of steel‑making syngas using recursive membrane extraction

Rising steel demand and blast furnace production pathways are incompatible with decarbonisation. Alternatives including electric arc furnaces also emit carbon, cannot exploit iron ore, and require scrap steel. Volatile fatty acids (VFAs) are valuable commodities largely refined from petrochemicals however fossil fuel dependency requires curtailing. CO comprises 20–30 % of blast furnace syngas (BFG) emissions and is converted to VFAs via the Wood-Ljungdahl metabolic pathway during fermentation. In this pathway, VFAs are ATP yielding intermediates, which are reduced into solvents to maintain redox balances. Fermentation research shows that VFA extraction enhances intermediate VFA yields and suppresses the yields of reduced products. Here, a mixed culture fermentation of the CO fraction of industrial BFG is studied at pilot scale within a commercial steel plant. Solvent production dominated before VFA extraction began. VFA extraction, comprising filtration, pervaporation and electrodialysis, subsequently supressed solventogenesis and increased VFA yields from 49 to 390 mg vfa L co −1 utilising 63 L co day −1 . For the first time a novel, integrated solids separation and VFA analysis platform (VFASENSE) provided live VFA production and extraction data, and informed maintenance schedules. This is also the first report of a technologically feasible method to utilise BFG for VFA production. Future research should focus on optimising VFA yields and CO utilisation. • First demonstration of pilot scale acidogenic fermentation of steelmaking syngas. • Volatile fatty acids (VFA) continuously extracted via pervaporative-electrodialysis. • Novel analyser provided live bioreactor VFA concentrations for the first time. • Solventogenesis initially dominated and suppressed VFA yield to 49 mg vfa L co −1 . • VFA extraction supressed solventogenesis and enhanced VFA yield to 390 mg vfa L co −1 .