The continuous ethanol fermentation in the packed-bed reactor
was performed with a feed sugar concentration of 220 g/L at a dilution
rate of 0.04 h1over a 20-day period without breakage of the
carriers. The cell concentration data after 20 days of continuous
fermentation are shown in Table 2 and indicate that the yeast cells
were efficiently confined by the packed bed. Only 0.4–0.5 g/L of the
free cells were in the effluent, whereas almost all of the cells were
restrained in the packed bed reactor. After 20 days of continuous
fermentation, the average immobilized yield from the continuous
fermentation in the packed-bed reactor was 87.0%, which was
slightly lower than that of the repeated batch operation. The free
cells in the reactor appeared healthy and retained their normal
oval shape. The cells mostly flocculated in big groups of 50–200
cells, whereas the free cells in the effluent were suspended as single
cells or small groups of 3–5 cells (data not shown).