Features of a Staged Acidogenic/Solventogenic Fermentation Process to Improve Butanol Production from Rice Straw

This study introduced an innovative two-stage fermentation process to maximize sugar utilization and biobutanol production from alkaline-pretreated rice straw. The new bioconversion process was composed of an acidogenic fermentation process followed by an acetone-butanol-ethanol (ABE) fermentation process. A sugar-rich hydrolysate (90.4 g/L reducing sugar) and a high acid content fermentation broth (33.9 g/L butyric acid), both produced from rice straw, were mixed together to increase the yield of the biofuels in the ABE fermentation process. Butyric acid and acetic acid generated from the acidogenic fermentation process play a critical role in the ABE fermentation process, which was confirmed by gene expression analysis of five messenger RNAs. Compared with the conventional process, this unique strategy increased the final butanol concentration from 6.2 to 15.9 g/L with 3-fold lower cellulase loading. Furthermore, an enhanced production of 149 g butanol and 36 L hydrogen gas from 1 kg rice straw was achieved, which is approximately equivalent to the energy contained in 124 and 15 g gasoline, respectively. Thus, the novel two-stage fermentation process was an effective and economic new approach for energy generation from lignocellulosic biomass.