Pilot-scale fermentation of 300 t/a total solvents from sweet sorghum stalk juice

Abstract

Solvent production from non-grain crops as the substrate via microbial fermentation has been projected to replace highly polluting and unsustainable chemical production methods in fossil oil refinery. Although a promising process pilot-scale studies, the prerequisite for production at industrial scale, are rare. This study reports a complete pilot test process using sweet sorghum stalk juice as feedstock, including the acquisition of sweet sorghum stalk juice, laboratory screening of suitable strains, optimization of industrial conditions, and a pilot-scale test at Yuanxing Bioenergy Co., ltd., China. Strain CIBT S0031 (Clostridium saccharobutylicum DSM13864) performed exceptionally in sweet sorghum stalk juice fermentation compared to other solventogenic clostridia tested. Furthermore, a simple and reliable non-anaerobic inoculation method applicable to extensive industrial solvent fermentation was developed. The optimal minimal medium was adapted for pilot scale fermentation, containing only sweet sorghum stalk juice diluted with industrial water, 1.5 g/L ammonium sulfate, and 1 g/L calcium carbonate. The solvent titers of single batch fermentation (2.36 m3), fed-batch (2.28 m3), and semi-continuous fermentation (7.14 m3) reached 16.5 g/L, 19.29 g/L, and 18.39 g/L, respectively, which replicated the laboratory results at the ton-scale. In the multi-stage process for continuous fermentation (total of 48.3 m3, chained with one breeding tank and three fermenters of 16 m3), 800 kg of solvents was produced with a yield of 0.45 g /g, comparable to corn-based fermentation. This study verified the effectiveness of the tested strain and the pilot process, thus laying a solid foundation for the large-scale production of solvents from a non-grain crop.