Biobutanol production from pentose-hexose sugar mixtures

The Acetone-Butanol-Ethanol (ABE) fermentation is receiving renewed interest as a way to upgrade renewable resources into valuable base chemicals and liquid fuels (Cascone, 2008). Abundance and un-competitiveness with food sources are desired features of potential feedstocks. These features are fulfilled by lignocellulosic biomass. This contribution is about the characterization of the ABE fermentation by Clostridium acetobutylicum DSM 792 using sugars representative for hydrolysis products of lignocellulosic biomass: glucose, mannose, arabinose, and xylose. Preliminary tests (according to Napoli et al., 2009) were carried out adopting each single sugar as carbon source to investigate the ability of the microorganism to convert them. Batch fermentation tests with mixtures of two sugars were carried out in order to assess the possible combined effects of the investigated sugars on the fermentation performances. The tests had also the aim of assessing the ability of C. acetobutylicum to simultaneously metabolize different sugars. Investigated sugar mixtures were: glucose/mannose (GM), glucose/arabinose (GA), glucose/xylose (GX), mannose/arabinose (MA), and arabinose /xylose (AX). The total initial sugar concentration was set at 60 g/L and the mass ratio between the two sugars was set at 1:1. The conversion process was characterized as a function of time in terms of biomass, acids and solvents concentrations as well as pH and total organic content. Data were evaluated to assess sugars conversion and the kinetics of cell growth and of the ABE production. The yields for cells, acids and solvents on the carbon source were also assessed.