starts decreasing at 44 h (around 29 g/L ethanol) for
S. cerevisiae RWB222, and at 25 h (around 23 g/L ethanol)
for Z. mobilis 8b. The viable cell growth curves of both
S. cerevisiae RWB222 and Z. mobilis 8b shown in Figure 4
were similar to those in the paper sludge SSCF’s shown in
Figure 1. This indicates that mass transfer limitations
associated with an initially viscous feedstock and any inhibitors
present in paper sludge are not responsible for the
observed loss of cell viability.
No soluble glucose or cellobiose was detected in Avicel
SSF by Z. mobilis 8b at 378C after 24 h as shown in
Figure 4B, while about 3.5 g/L glucose accumulated at the
end of fermentation in paper sludge SSCF by Z. mobilis 8b
under similar conditions as shown in Figure 1B. This
difference suggests that although Z. mobilis cell viability is
not affected by paper sludge, some component of paper
sludge inhibits the ability of Z. mobilis to consume glucose.