Butanol production from waste figs through sequential mesophilic and thermophilic consolidated fermentation

The increasing demand for energy leads to the intensive use of fossil fuels, resulting in the rapid depletion of these resources and the emergence of significant environmental problems. Among renewable energy sources, biomass-based biofuels are a strong alternative to fossil fuels. Among renewable energy sources, biomass-based biofuels stand out as strong alternatives to fossil fuels, and within this group, biobutanol has been gaining increasing importance due to its superior properties. In this study, butanol production was carried out from aflatoxin‑containing waste dried figs using sequential mesophilic (MF) and thermophilic (TF) consolidated fermentation. In the MF stage, the Box–Wilson experimental design was applied to optimize process parameters, and various parameters were evaluated in three different experimental sets. As a result of the experiments, the optimum conditions were determined as: 1 bar CO₂ pressure, 22.5 g/L fig concentration, 5% MF inoculum percentage, 88 hours MF retention time, a 250 C/N ratio and a 950 C/P ratio. Under these optimum conditions, a butanol concentration of 0.78 g/L was obtained. In the TF stage, studies conducted using Thermoanaerobacterium thermosaccharolyticum DSM 571 employed the Taguchi experimental design, and various parameters were examined across three different experimental sets. According to the results obtained, the optimum conditions were determined as: 1 day TF retention time, 1% TF inoculum ratio, 0.8 bar H₂ pressure, 5 mg/L Mo, 15 mg/L W, 15 mg/L Fe, 500 mg/L L-cysteine·HCl, 30 mg/L Zn, pH 7 and a temperature of 50 °C. In the fermentation carried out under these optimum conditions, 1.15 g/L butanol was obtained. The obtained results indicate that waste figs can be used for butanol production through sequential mesophilic and thermophilic fermentation processes, and that this method contributes to the utilization of waste for energy generation.