3.4. Simultaneous saccharification and fermentation
In order to measure conversion of cellulose to ethanol, bioabatement
was carried out on RHH without removal of fibrous
solids, which were then saccharified with cellulase enzymes
and fermented. Simultaneous saccharification and fermentations
(SSF) using E. coli FBR5 in unabated samples failed completely (i.e. no ethanol was produced) while SSF of bioabated
RHH proceeded after a 6.4 h 0.8 h lag and yielded 65%
of the theoreticalmaximum based on hydrolyzed glucose plus
xylose in the SSF (Fig. 3A). Fermentations using the conventional
yeast S. cerevisiae D5a are shown in Fig. 3B. Ethanol
yields were 36% and 41% of the theoretical maximum for
unabated and bioabated samples, respectively. The effect of
bioabatement in fermentations using D5a was also apparent
in the reduced lag time (3.0 0.7 h) observed for bioabated
samples compared to unabated samples, which averaged
9.1 4.0 h lag time. For the xylose-fermenting yeast YRH400
(Fig. 3C), ethanol yields were 49% and 51% of the theoretical
maximum for bioabated and unabated samples, respectively,
with a slightly reduced lag time associated with bioabatement
(2.4 0.5 h) compared to unabated samples (4.1 1.6 h). Fermentations
using YRH400 (Fig. 3C) were complete sooner than
those using D5a (Fig. 3B).