The combined effect on initial glucose concentration and pH control strategies for acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum DSM 792

The use and depletion of fossil fuels raised the interest in biofuels like biobutanol. Clostridium acetobutylicum DSM 792 is capable of producing biobutanol through ABE fermentation. Butanol production can be influenced by low sugar concentrations, like those obtained after hydrolysis of pre-treated lignocellulosic biomass. This study aimed to evaluate the influence of the initial glucose concentrations (33, 66 and 100 g L⁻¹) and pH control strategies on biobutanol production and glucose consumption. Uncontrolled pH fermentation exhibited low butanol production due to either glucose exhaustion (33 g L⁻¹) or the phenomenon of acid crash (66 and 100 g L⁻¹), which was alleviated by the use of any of the minimum pH set-points (4.8; 5.0; 5.1 and 5.5). Fermentation at a pH_min of 5.1 gave the best performance in butanol production and glucose consumption rate. Fermenting with a pH_min of 5.1 with 33 g L⁻¹ of initial glucose caused acidogenic fermentation, while the use of 66 and 100 g L⁻¹ of glucose led to a ∼1.5 and ∼1.7-fold increase in butanol concentration over their counterparts without pH control respectively. By controlling the pH after the acidogenic phase 15.8 g L⁻¹ of butanol was obtained with 100 g L⁻¹ of glucose, which was ∼2-fold higher than without pH control. Different initial glucose concentrations therefore require different pH strategies to optimize butanol production.