Bioethanol production from rapeseed straw by SSF at high dry matter

Rapeseed straw is currently considered as an abundant lignocellulosic residue that can be used as a low cost material and an environmental friendly feedstock without food competition. This agricultural residue can be used for bioethanol production because of its high carbohydrate content (>50%). The biochemical conversion, including pretreatment, enzymatic hydrolysis and fermentation, is the most promising option for ethanol production from these carbohydrates. The main goals of this process are to obtain high yields of sugar conversion and high ethanol concentrations.

In this work, different simultaneous saccharification and fermentation experiments for bioethanol production from steam exploded rapeseed straw were investigated using pretreated solids obtained under optimal conditions (215ºC, 7.5 min) as a substrate. Solid concentrations as high as 30% (w/v) were used in SSF experiments, since the use of high substrate loadings is essential to make the overall ethanol process more viable from an economic point of view as the cost of the subsequent distillation step can be reduced. Enzyme loadings of 20 and 40 FPU/g substrate and cell concentrations of 0.25, 2 and 5 g/L were used.

The results obtained from these different approaches showed a complete consumption of glucose as well as high ethanol concentrations, above 55 g/L after 72 h SSF in all experiments. Enzyme and inoculum dosages in the SSF process were not influential in the assayed ranges. Thus, the best results were reached at 20 FPU/g substrate and 0.25 g/L cell concentration, resulting in 72% of the theoretical ethanol yield after 72h.