Towards the development of a biobutanol production process for local fig producers: Nutrient optimization in sequential mesophilic and thermophilic fermentation

Abstract

This study tests the hypothesis that raw fig waste can be utilized for thermophilic butanol production without pretreatment and that optimizing carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios can enhance fermentation performance. The research is significant for addressing challenges such as food waste valorization, reducing fossil fuel dependency, and contributing to carbon-neutral goals. Economic feasibility is achieved by eliminating costly pretreatment steps and lowering raw material costs. In the mesophilic stage, mixed acidogenic sludge was used for selective butyrate production, followed by butanol synthesis in the thermophilic stage using Thermoanaerobacterium thermosaccharolyticum DSM 571. The effect of external nitrogen and phosphorus supplementation was evaluated using a Box–Wilson experimental design, with C/N (10–400) and C/P (50–2000) ratios as variables. The highest butanol concentration (0.78 g L⁻¹) was obtained at C/N 250 and C/P 950, while the optimum C/N/P ratio was determined as 100/0.4/0.105, increasing butanol production by 30% compared with the control. These findings introduce a new approach in biobutanol production and highlight the industrial potential for integrating agricultural waste into sustainable energy systems.