3.2. Simultaneous saccharification and fermentation of Avicel, alkalipretreated
switchgrass and de-ashed paper mill sludge
SSF of Avicel, alkali-pretreated switchgrass and de-ashed paper
mill sludge were compared and fermentation of mixed sugars (glucose
and xylose) was used as a control. Mixed sugars fermentation
showed both glucose and xylose were consumed and the final solvent
concentration reached 17.3 g/L (Fig. 1) and butanol was
10.4 g/L. At the end of fermentation (120), small amount of glucose
(3.3 g/L) and xylose (2.1 g/L) were not utilized. ABE fermentation of
mixed sugars gave a total solvent yield of 0.31(g/g sugars).
SSF of Avicel was performed with a solid loading of 5.8% (w/v)
and enzyme loading of 20 FPU/g-glucan (Fig. 2a). During the initial
24 h, glucose was quickly released to 12.0 g/L, and acetic and butyric
acids were accumulated to 2.9 and 3.2 g/L, respectively. After
that, glucose concentration decreased and more acids were reassimilated
to butanol, acetone and ethanol. Acetic and butyric
acids were stabilized at 1.9 and 1.2 g/L after 72 h. At the end of
SSF (120 h), ABE total solvents reached 16.8 g/L with 9.5 g/L of
butanol. The ABE solvent yield was 0.28 (g/g glucose) and the productivity
was 0.14 g/L/h.