Improvement Of Cassava Based Butanol Fermentation Performance By Shortening Phase-shift Delay

In the recent years, food crisis, energy security and low-carbon economy have become the three major issues subject to great concerns/attentions all over the world. Cassava is very attractive in bio-butanol production for its natures of cheap, high productivity, and no competition with the foods for arable land. In this dissertation, bio-butanol fermentations were conducted in a 7 L static/anaerobic fermentor using cassava based medium as the raw material, aiming to provide some useful and important data for cassava-based bio-butanol industrial production. The major contents and results of the dissertation were summarized as follows:1) Performance of cassava-based bio-butanol production was much lower than that of corn-based production in both traditional and extractive fermentations. The major problems include severe delay or complete failure in phases shifting from acidogenic phase into solventogenic phase, long fermentation time, low butanol productivity, etc.2) Addition of 1% urea in the initial cassava-based medium could promote the accumulation of butyrate and acetate in the early fermentation stage. However, under this condition, fermentation eventually ended at acidogenesis phase.3) Addition of 1% urea in the initial cassava-based medium and supplementing 2.5 g/L yeast extract when phases-shifting delay appears, could stimulate phase shift from acidogenesis phase into solventogenesis phase and shorten the phase-shifting time for about 10～30 hours. Compared with corn-based bio-butanol fermentation, butanol productivity in cassava-based traditional fermentation reached a level of 0.267 g/(L?h) which is 33% higher than that obtained with the relevant corn-based fermentation; and butanol productivity in cassava-based extractive fermentation using olyel alcohol reached a level of 0.340 g/(L?h) which is equivalent with that obtained with the corn-based extractive fermentation.4) Real-time PCR measurements indicated that CoA-transferase encoding ctfAB gene was activated and the transcriptional level of ctfAB was largely enhanced after yeast extract was added during the fermentation. Under this condition, the major metabolic routes including acetone and butanol synthesis routes were activated, and butyrate/acetate accumulated were re-utilized and consumed rapidly.