Ethanol fermentation by S. cerevisiae in a bioreactor packed vertically with ceramic rods

Abstract

A conventional randomly packed bed reactor of immobilized whole cell has much disadvantages, such as plugging and channeling, to reduce the productivity of a biological reactor. In this research, a new fixed biofilm reactor has been employed to improve the productivity of the reactor. $\mbox{\underline{Saccharomyces}}$ $\mbox{\underline{cerevisiae}}$ was chosen as a microorganism and fixed on the ceramic rods with diameter of 3.7 mm and length of 45 cm. The ceramic rods were coated with gelatin crosslinked by glutaraldehyde and then packed vertically into the column of the reactor with inside diameter of 3 cm and length of 50 cm. The temperature of this fixed-biofilm reactor and feed pH were fixed at 25$^\circ$C and 4.0 respectively. As a basic study, batch and continuous experiments were carried out. In batch experiment, the limiting glucose concentration was 25 g/l and the cell yield from glucose, the product yield from glucose, the product yield from cell were 0.106, 0.38, 3.58 respectively. If the initial substrate concentration presented higher than 33 g/l, the specific growth rate was inhibited. In the continuous experiment using continuous stirred tank reactor (CSTR), the washout rate was 0.25 $hr^{-1}$, and the maximum productivity was obtained 1.82 g/l/hr at the dilution rate of 0.185 $hr^{-1}$ and the values of maximum specific rate of product formation and maximum growth rate were determined as 0.917 $hr^{-1}$ and 0.278 $hr^{-1}$, respectively. In the fixed-biofilm reactor, for a given initial concentration of glucose, the production of ethanol changed rapidly with dilution rate in low flow rate region, but slowly in high flow rate region. When the initial concentration was 30 g/l, the maximum productivity was 12.5 g/l/hr which is much higher than 7.4 g/l/hr of others. This higher productivity may be due to reduction of the carbon dioxide hold up. Especially when the initial substrate concentration was 150 g/l, the maximum productivity was obtained 2...