Production From Cassava By Clostridium Acetobutylicum

Acetone-butanol-ethanol fermentation(ABE fermentation) is often performed in batch fermentation from grain crops such as corn. However, ABE fermentation from corn has the disadvantage of both competing for food with humans and lower productivity of batch fermentation. Therefore, we studied on the butanol fermentation form non-grain crops placed on the grain crops in this article. Original strain was selected from two industrial butanol- producing strains and fermentation characteristics with glucose, corn, molasses and cassava were investigated. The conditions of fermentation from cassava were optimized. Finally, according to the bacteria growth dynamics in the batch fermentation, the optimal dilution rates and a four stages cassava continuous fermentation system were established.Clostridium acetobutylicium A and Clostridium acetobutylicium T were compared in the effect of fermentation on various substrates. And C. acetobutylicium A was selected as the original strain because of the excellent starch fermented ablility. Then, its fermentation characteristics of glucose, corn, molasses and cassava were tested. The cassava fermentation conditions were optimized with C. acetobutylicium A. The influence of nitrogen sources, cassava content,α-amylase loading, initial pH of medium and stir were investigated. The optimal conditions were obtained as follows: fermentation medium composing of 120 g/L cassava and 6 g/L ammonium acetate; the cassava hydrolyzed at 90℃for 60 min with high-temperature amylase of 20 U/g and gelatinized for 30 min; as well as initial fermentation pH 6.0, the stir speed is 50 r/min. When fermentation was carried out in 5 L fermentor under these conditions for 96 h, the concentration of butanol and total solvents reached 13.6 g/L and 24.7 g/L, the solvent productivity was 0.24 g/(L·h), respectively. With the optimizing, the butanol and solvent production at were all improved from cassava fermentation compared with corn fermentation. Meanwhile, butanol fermentation from cassava behaved two acidogenesis stages and two solventogenesis stages.Mult-stages cassava continuous fermentation system was also preliminary studied. To control the quality of the seeding tank in the continuous fermentation, the bacteria cell growth dynamics in exponential phase of batch fermentation from cassava was calculated, which demonstrated that the optimal dilution rate is 0.1 h^-1. The dilutions of next three fermentors depended on their retention time. In the end, a four stages continuous fermentation system was established. The butanol and solvent production reached 12.38 g/L and 22.8 g/L, respectively after 100 h continuous fermentation. The dilution rates of four fermentors were 0.1 h^-1, 0.1 h^-1, 0.06 h^-1, 0.04 h^-1, respectively. The most butanol and solvent production in the latest fermentor was 13.2 g/L and 23.3 g/L respectively. The productivity reached 0.39 g/(L·h), and were increased by 63%, which reduced the fermentation times, increased the capacity utilization rate and reduced the labor intensity.