3.3. Simultaneous saccharification and fermentation of the two-step
treated rice straw to ethanol
The ultimate objective of pretreatment of RS is to produce ethanol. In order to evaluate the suitability of the two-step treated RS
for ethanol production, the SSF of the two-step treated RS was
investigated. Fig. 4 shows the time course of the SSF of the
two-step treated RS for ethanol production. As shown in Fig. 4,
the time curves of ethanol, fermentable sugars, glucose and xylose
all had the typical characteristic of the SSF process. For ethanol, its
concentration increased with time until it remained almost
unchanged. As for glucose, there was a slight net build up in the
early part of the fermentation process and its concentration was
close to zero eventually because it was consumed to produce ethanol. As regard to xylose, its concentration kept increasing steadily
during the fermentation process. For fermentable sugars, it was
similar with glucose at early stage of the fermentation process,
but it was similar with xylose at the last stage. The fact that ethanol concentration remained almost constant while the fermentable
sugars and xylose had still relatively high concentration at the last
stage of the fermentation process suggests that the yeast used in
this study have low ability to produce ethanol from xylose. After
the SSF of the two-step treated RS for 72 h, the ethanol concentration and its yield reached 40.6 g L
1
and 86.4% respectively. It suggests the two-step pretreatment process was an efficient RS
pretreatment method for its ethanol production.
The aim of this work is to improve the ethanol production economy and decrease the ethanol production cost from RS by fully utilizing its components.Fig. 5shows the overall mass balance of our