Enzymatic hydrolysis and detoxification of lignocellulosic biomass are not always necessary for ABE fermentation: The case of Panicum virgatum

Hemicellulosic hydrolysate of switchgrass, pre-treated with dilute sulfuric acid, was assessed for butanol production via acetone-butanol-ethanol (ABE) fermentation. Clostridium beijerinckii CECT 508 was selected among eight wild strains as the most efficient to produce butanol from glucose/xylose mixtures. The effects of inhibitory compounds from the acid hydrolysate on ABE fermentation were studied using model fermentation media, observing that the most harmful inhibitors were acetic acid > phenolic compounds > sulfate > furfural, while 5-HMF and levulic acid seemed to have no effect. Several detoxification treatments, including evaporation, overliming and activated charcoal adsorption, were evaluated to remove inhibitors from switchgrass acid hydrolysate. Although activated charcoal was the most effective method, there were no significant differences in butanol production between non-detoxified and detoxified hydrolysates. The non-detoxified switchgrass acid hydrolysate (containing 26 g L−1 xylose, 4 g L−1 glucose and 4 g L−1 arabinose) was successfully fermented by C. beijerinckii CECT 508, obtaining 4.00 ± 0.71 g L−1 butanol (yield 0.184 ± 0.032 g g−1). To the best of our knowledge, this is the first time that a hydrolysate obtained from switchgrass has been efficiently fermented to butanol without previous enzymatic hydrolysis or detoxification steps, using a non-genetically modified Clostridium strain.