Co-production of solvents and organic acids in butanol fermentation by Clostridium acetobutylicum in the presence of lignin-derived phenolics

Co-production of solvents (butanol, acetone, and ethanol) and organic acids (butyrate and acetate) by Clostridium acetobutylicum using lignocellulosic biomass as a substrate could further enlarge the application scope of butanol fermentation. This is mainly because solvents and organic acids could be used for production of fine chemicals such as butyl butyrate, butyl oleate, etc. However, many phenolic fermentation inhibitors are formed during the pretreatment process because of lignin degradation. The present study investigated the effects of five typical lignin-derived phenolics on the biosynthesis of solvents and organic acids in C. acetobutylicum ATCC 824. Results obtained in 100mL anaerobic bottles indicated that butanol concentration was enhanced from 10.29 g L-1 to 11.36 g L-1 by the addition of 0.1 g L-1 vanillin. Subsequently, a pH-control strategy was proposed in a 5 L anaerobic fermenter to alleviate the acid crash phenomenon and improve butanol fermentation performance, simultaneously. Notably, organic acid concentration was enhanced from 6.38 g L-1 (control) to a high level of 9.21-12.57 g L-1 with vanillin or/and vanillic acid addition (0.2 g L-1) under the pH-control strategy. Furthermore, the butyrate/butanol ratio reached the highest level of 0.80 g g(-1) with vanillin/vanillic acid co-addition, and solvent concentration reached 13.85 g L-1, a comparable level to the control (13.69 g L-1). The effectiveness and robustness of the strategy for solvent and organic acid co-production was also verified under five typical phenolic environments. In conclusion, these results suggest that the proposed process strategy would potentially promote butanol fermentative products from renewable biomass.