Butanol Fermentation From Cane Molasses And Straw Hydrolyzates

Butanol is an important chemical organic solvent and a potential biofuel. ABE (acetone-butanol-ethanol) production from non-grain substrate can not only reduce substrate cost, but also accord with new energy policy of china, and is important for the energy regeneration from renewable resources.In this study, C. saccharobutylicum DSM 13864, a sugar strain, was chose for ABE fermentation with cane molasses and lignocellulosic hydrolysates from 8 ABE strains preserved in our laboratory.Under optimum conditions (including cane molasses 6%, CaCO3 3.2 g/L, (NH₄)2SO₄ 2 g/L, K2HPO₄ 0.5 g/L, corn steep powder 20 g/L, MnSO₄·H2O 0.01 g/L, pH 6.0, 37℃), total solvent reached 19.80 g/L after 72 h of fermentation in shake flask, including 13.40 g/L butanol, 5.01 g/L acetone, 1.39 g/L ethanol. In a 5-L bioreactor, total solvent of 17.88 g/L was attained after 36 h of fermentation, the ABE productivity and yield were 0.50 g/L/h and 0.33 g ABE/g sugar consumption, respectively. In semi-continuous fermentation, the process could be steadily operated for over 8 days (205 h, 26 cycles) with average productivity (stage II) of 1.05 g/L/h and cell concentration (stage I) of 7.43 OD660, respectively. And the average batch fermentation time (stage I and stage II) could be reduced to 21-25 h with an average total solvent of 15.27 g/L. In continuous fermentation, the solvent production could be steadily operated at around 160 h, the average total solvent and productivity were 12.41 g/L, 0.25 g/L/h, respectively.Using corn stover hydrolyzate as substrate, the medium composition was optimized by orthogonal method as follows: CaCO3 2.0 g/L, (NH₄)2SO₄ 1.0 g/L, K2HPO₄ 0.5 g/L, corn steep powder 15 g/L, and MnSO₄·H2O 0.01 g/L. In a 3-L bioreactor, total solvent of 16.1 g/L (butanol 10.59 g/L) was reached after 40 h of fermentation, and the productivity and yield were 0.40 g/L/h and 0.33 g ABE/g sugar consumption, respectively. Batch fermentation process using temperature-shifting demonstrates that lower temperature was beneficial to the solvent accumulation. Compared with temperature-constant process (37℃), total solvent was increased from 17.01 g/L to 19.98 g/L. The temperature-shifting continuous fermentation process was operated for 269 h at dilution rate of 0.1 h-1, and the solvent production entered a stable phase at around 80 h. The average solvent during the stable solvent-production stage was 12.28 g/L (including 8.50 g/L butanol), and the average solvent productivity was 0.25 g/L/h. The maximum total solvent was up to 15.29 g/L (including 10.82 g/L butanol).