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 product recovery techniques, such as extractive fermentation. In this work, the hydrolyzed cellulose from organosolv pre-treated beech wood ( L.) was fermented by CECT 508 and compared with synthetic P2 medium in conventional and extractive fermentation processes. The conventional control fermentation yielded 9.12 g l of ABE with 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.