Butanol Production From Hydrolysate Of Jerusalem Artichoke Juice

Butanol is a promising biofuel. Currently, the key factor that effected the development of biobutanol was the economic viability. As the cost of the raw material made up about 60% of the overall cost, the most important economic factor was the cost of the substrate. In order to make the process economically viable, the using of an abundant and low-cost substrate was essential. Jerusalem artichoke was a cheap substrate, and it was not the food ration. Thus the fermentation of Jerusalem artichoke would not contest the plough with the grain and the food with human. The using of Jerusalem artichoke as the substrate of acetone-butanol fermentation met the development needs of our country's energy strategy. However, the result of Jerusalem artichoke fermentation was not good. The residual sugar concentration was too high, and the butanol production was too low. At the end of Jerusalem artichoke fermentation using the initial pH of 5.5 without pH regulation, as high as 14.78 g/L sugars were remained unconverted, and the butanol concentration was just 6.69 g/L. The hydrolysate of Jerusalem artichoke was a mixture of glucose and fructose. In order to solve these problems during Jerusalem artichoke fermentation, some researches had been conducted with the mixture of glucose and fructose as the substrate.The simulative Jerusalem artichoke fermentation with glucose/fructose 1:4 had the similar result as Jerusalem artichoke fermentation. Fermentation using the simulative substrate without pH regulation appeared to terminate early, and the residual sugar concentration was 23.26 g/L, and butanol production of 5.51 g/L were obtained. After the fermentation of the mixed sugars with different ratios of glucose/fructose, we found there was also carbon catabolite repression in the mixture of fructose and glucose. During the mixed sugars fermentation, Clostridium acetobutylicum first utilized glucose, and the metabolism of fructose was started after the concentration of glucose dropped to a certain value. Then we observed that properly improving the ratio of glucose/fructose would solve the problems during mixed fructose-glucose fermentation. The residual sugar concentration was just 2.13 g/L, and the butanol concentration went up to 9.63 g/L during the mixed sugars fermentation with glucose/fructose 1:2.Compared with either glucose or fructose fermentation, the early termination of simulative Jerusalem artichoke fermentation might be caused by toxic organic acids and the low pH. When the pH of the fermentation system was controlled at higher levels, it was found that sugars utilization was facilitated, but less butanol was produced due to the over-accumulation of organic acids. On the other hand, when the pH was controlled at lower levels, more sugars were remained unconverted, although butanol production was improved. Based on these experimental results, a stage-wise pH regulation strategy, e.g., controlling the pH of the fermentation system at 5.5 untill the OD620 reached 1.0, and then the pH control was removed, was developed, which significantly improved the fermentation performance of the system. Using this strategy, the residual sugar dropped to 2.05 g/L and the sugar utilization increased from 57.30% to 96.55%, while butanol concentration reached 10.48 g/L, achieving an increase of 90.20%.In order to further solve the problems during Jerusalem artichoke fermentation, we also carried out the pH regulation during fermentation. However, the results showed the stage-wise pH regulation strategy was not fit for solving the residual sugar problem during Jerusalem artichoke fermentation. On the contrary, the butanol concentration decreased after the stage-wise pH regulation. The fermentation with the lower initial pH had increased the butanol production and decreased the concentration of butyrate and acetate, but the residual sugar was still too much. The pH regulation that pH controlled at late stage had significantly increased the concentration of butanol and decreased the residual sugar concentration during Jerusalem artichoke fermentation. The fermentation which pH controlled 4.8 at late stage had improved the butanol concentration to 8.25 g/L, achieving an increase of 23.32%.