Organosolv pretreated beech wood as a substrate for acetone butanol ethanol extractive fermentation

Acetone-butanol-ethanol (ABE) fermentation has a high potential for industrial application in lignocellulose-based biorefinery. Nevertheless, strong end-product inhibition is a severe limitation of this process, which can be partially solved by in situ product recovery techniques, such as extractive fermentation. In this work, the hydrolyzed cellulose from organosolv pre-treated beech wood (Fagus sylvatica L.) was fermented by Clostridium beijerinckii CECT 508 and compared with synthetic P2 medium in conventional and extractive fermentation processes. The conventional control fermentation yielded 9.12 g l−1 of ABE with C. beijerinckii CECT 508, while ABE overproduction of 40% was observed with cellulose hydrolysate as a substrate. After extractive batch fermentation based on 2-butyl-1-octanol as extractant, the final ABE titer was doubled in the P2 control medium over the conventional batch, with respective increases of 50, 190, and 140% for butanol (B), acetone (A) and ethanol (E). In the case of ABE as a hydrolysate medium, the total production increased by 10% with liquid extraction, while mainly B was responsible for this improvement. The total productivity was nevertheless gradually decreased in extractive fermentation, with a significantly slower production rate and the microbial growth compared to conventional fermentation. Moreover, solvent production and sugar consumption stopped, although the aqueous B concentration was below the inhibition threshold. The mid-term toxicity of the extraction solvent 2-butyl-1-octanol seems responsible for these results and this issue should be considered in future research.