Efficient bioconversion of whole sweet sorghum plant to acetone, butanol, and ethanol improved by acetone delignification

Acetone–butanol–ethanol (ABE) production from grains, bagasse, and juice of sweet sorghum was conducted by Clostridium acetobutylicum. Delignification with acetone, one of the ABE fermentation products, was evaluated as a pretreatment for the improvement of ABE production from bagasse. Different modes of hydrolysis and fermentation of “separate hydrolysis and fermentation (SHF)” (process I), “simultaneous saccharification and fermentation (SSF)” (process II), and “simultaneous saccharification and co-fermentation (SSCF)” (process III) were compared for ABE production from delignified bagasse. Direct ABE fermentation of stalks without juice extraction was also evaluated (process IV). Along with the stalks, the starchy grains of the sorghum plant were directly utilized in the ABE fermentation. Total concentration of acetone, butanol, and ethanol (ABE) of 10.6 g/L, containing 3.17 g/L acetone, 6.34 g/L butanol, and 1.06 g/L ethanol, was obtained through SSF process at pH 5.8 and 37 °C from the bagasse pretreated at 180 °C for 60 min. Through the SSCF process, solvents production was increased by 27–36% as compared to the SSF. From each kg sweet sorghum plant, 156, 136, 101, and 110 g total acetone, butanol, and ethanol (g ABE) was produced through process I, II, III, and IV, respectively. It was concluded that utilizing all parts of sweet sorghum plant, as an energy crop, is a promising approach for ABE production.