In contrast to alkali-pretreated switchgrass, SSF of de-ashed
paper mill sludge (7.4% solid loading and 10 FPU) showed very
good ABE solvents yield (Fig. 2c). Specifically in the first 24 h, glucose
and xylose reached 10 and 6 g/L, respectively. Both acetic and
butyric acids reached 4.0 g/L, respectively. After 24 h, the glucose
concentration continued to increase and reached at 16.1 g/L at
48 h, then decreased gradually to 5.0 g/L at 120 h as SSF progressed.
The xylose concentration was kept at 6 g/L from 24 to
120 h. Butanol was steadily produced from 24 to 120 h and
reached 9.7 g/L at the end of fermentation. The total ABE solvent
concentration was 17.1 g/L, the solvent yield was 0.24 (g/g sugars)
and the productivity was 0.20 g/L/h. As comparing to the SSF of
Avicel, the total acids concentration (5.7 g/L) was significantly
higher than that in SSF of de-ashed sludge. Most likely, it is due