Effect of medium composition and PH control strategies on butanol fermentation with Clostridium acetobutylicum

The medium composition and the fermentation pH significantly affect the performance of biobutanol fermentation. In this study, sodium bicarbonate, ammonium acetate, acetate buffer, and calcium carbonate were added into medium for pH control to enhance the butanol production. When the ammonium acetate was added into the medium at a concentration of 6 g/l, the butanol concentration increased from 2.0 g/l to 3.6 g/l since the acetate was the precursor of butanol metabolism. Acetate buffer with a concentration of 100 mM was used to maintain the pH at a constant level and also provides the precursors for ABE fermentation, exhibiting a marked increase in the butanol concentration from 2.0 g/l to 9.8 g/l. Calcium carbonate is shown to be effective in controlling the pH of the ABE fermentation. When the concentration of calcium carbonate was greater than 8 g/l, the pH value could be maintained at higher than 4.8, which is an appropriate pH for ABE fermentation. Finally, the pH of ABE fermentation was controlled via auto-T itration method. Controlling at pH 4.5 was the most suitable condition. Although batch mode operation of butanol fermentation gave high ABE production, continuous fermentation was preferred to achieve higher butanol productivity. The butanol yield and productivity obtained while operating on the continuous mode at a HRT of 24 h were 0.18 g-butanol/ g-glucose and 0.36±0.10 g/l/h, respectively. In the integrated process of continuous fermentation combined with in-situ butanol removal by vacuum membrane distillation, the butanol yield and productivity were further elevated to 0.21±0.04 g-butanol/ g-glucose and 0.51±0.09 g/l/h, respectively.