Abstract

The ethanol fermentation of concentrated food waste hydrolyzates by free and immobilized cells of S. cerevisiae H058 in a batch system was studied. The effect of initial reducing sugar and initial inoculum concentration on ethanol fermentation in both immobilized and free cell systems were studied. Parameters such as ethanol concentration, ethanol production rate, ethanol yield and sugar consumption rate were assessed and compared for both fermentation systems. In addition, repeated batch fermentations with the immobilized yeast cells were carried out for ethanol production. The result showed an optimal initial reducing sugar concentration of 180 g/L, inoculum concentration of 2% (v/v) and fermentation time of 60 h were determined for the free cell system. For the immobilized system, an optimal initial reducing sugar concentration of 200 g/L, inoculum concentration of 2% (w/v) and fermentation time of 48 h were selected. The immobilized cells were also proved to be reusable in 7 batches of fermentation. More than 98.5% reducing sugar was utilized during the 7 repeated batches by the same immobilized cells and overall ethanol concentration fluctuated around 94.24 g/L. The immobilized cell system was superior to the free cell system since lower substrate inhibition and less fermentation time and higher ethanol tolerance were realized.

Keywords:

Enzymatic hydrolysis, ethanol, fermentation, food waste, immobilization,

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