The yeast number and cell
activity in R3 was (9.8 ± 2.8) 108 cm3 and (9.2 ± 1.0)mm3 min1,
respectively (Figs. 8B and 7). In the continuous ethanol fermentation
at 30 C, the decreasing trend in ethanol concentration and
yeast cell viability disappeared (Fig. 8A and B) by feeding the fresh
yeast cells from R3 into R2. The yeast cell viability stabilized at 60%
to 70 %, and the number of viable yeast was (1.7 ± 0.4) 109 cm3
(Fig. 8B). Moreover, the cell activity was (3.8 ± 1.0) mm3 min1,
which was markedly higher than the activity without a fresh feed
(Fig. 7). The ethanol concentration in R2 was (80.1 ± 1.8) g L1
(Fig. 8A), corresponding to ethanol yield of 82.5% and productivity
of 8.8 g L1 h1. The concentration of VFA in each reactor was
relatively constant and at low level, indicating that no bacterial
contamination occurred