Performance studies on the immobilized yeast reactor for ethanol production

Abstract

Studies were carried out to develop the process for ethanol production using immobilized living whole cell of $\mbox{\underline{Saccharomyces}}$ $\mbox{\underline{cerevisiae}}$ SC 4126. Immobilized yeast cell was prepared by entrapping the low concentration of cell within calcium alginate gels. This immobilized yeast pellet was activated by incubation in complete medium to obtain maximum fermentative activity. The gel incubated for 40 hours was shown that the maximum specific metabolic activity, 0.320 g glucose/ml gel/hr. To achieve more efficient ethanol production, the performance of packed column reactor and continuous stirred reactor by $CO_2$ gas recycle were compared. As a result, packed column reactor system showed more efficient performance than continuous reactor by $CO_2$ gas recycle. This result was due to mainly decrease the specific metabolic activity of gels by vigorous mixing in continuous stirred reactor system. Moreover, to design the most efficient packed column reactor for ethanol production, the effect of reactor geometry (H/D ratio) on production of ethanol was investigated. The rate of ethanol production was independent of the column dimension over a range of H/D ratios from 1.6 to 11.9. During the operation of packed bed reactor, the effect of residence time, substrate concentration on ethanol productivity were investigated. The highest ethanol concentration, 98 g/l could be obtained at a residence time of 3.82 hours in a medium containing 250 g/l glucose. And it was found that 100\% of theoretical conversion which could be obtained was a problem of residence time. In ethanol fermentation substrate as well as product inhibits the rate of ethanol production. The effect of substrate and product was investigated using an immobilized cell differential reactor system. The results represented the typical substrate inhibition mode and the related apparent kinetic constant (Vm, Ks, Kis) were 0.345 g glucose/ml gel/hr, 41.7 g/l, 132.6 g/l respecti...