This tuber is of considerable interest not only for ethanol production but also to produce glucose syrup, and it is available in tropical countries. The ethanol yield from the whole manioc is equivalent to the ethanol produced from cereals using dry milling methods. The only known lies in that the manioc has to be processed 3-4 days after it was harvested. To avoid such lengthy processing times, the manioc is first sliced and then left to dry in the sun. The waste water produced in the process can be treated by means of anaerobic digestion to produce bio gas.

1.4 Spruce (picea abies)

This tree has attracted a great deal of attention as a raw material for ethanol production because it is a lignocellulose material mainly composed of hexose sugars, which are more readily convertible than pentose sugars.

1.5 Willow (salix)

This is a member of the Angiosperm family and is consequently characterized by a hard wood. In this species, a fraction of the xylose units is acetylated. Some of the OH groups of the xylose carbons C2 and C3 are replaced by O-acetyl groups. With pretreatment, these groups release acetic acid that, in high enough concentrations, inhibits the yeasts involved in the fermentation process, according to some studies (Sassner et al., 2008a). It was recently demonstrated (Sassner et al., 2008b) that, by pretreating willow with sulfuric acid before the enzymatic hydrolysis process, and then simultaneously performing saccharification and fermentation, they succeeded in obtaining a global ethanol yield of 79%.