| סיכום: | The ethanol fermentation efficiency of sweet sorghum stem juice (SSJ) under a very high gravity (VHG) condition (250 g/L of sugar) was improved by immobilized <i>Saccharomyces cerevisiae</i> SSJKKU01, using a stirred tank bioreactor (STR) coupled with a column bioreactor (CR). Dried rattan pieces (as carriers for cell immobilization) at 50% of the working volume of the CR were suitable for use in a batch ethanol fermentation. The average ethanol concentration (<i>P<sub>E</sub></i>) and ethanol productivity (<i>Q<sub>P</sub></i>) of repeated-batch fermentation in the CR for eight successive cycles were 109.85 g/L and 1.88 g/L⋅h, respectively. Then an STR coupled with a CR was applied for repeated-batch ethanol fermentation in two systems. System I was an STR (1.8 L working volume), and System II was an STR (1 L) coupled with a CR, referred to as a CR-F (0.8 L). Both systems were connected to a new CR, called CR-I, containing sterile dried rattan pieces at 50% of its working volume. Active yeast cells were inoculated only into the STR, and the medium circulation rate between bioreactors was 5.2 mL/min. The results showed that at least eight successive cycles could be operated with an average <i>P<sub>E</sub></i> of 108.51 g/L for System I and 109.44 g/L for System II. The average <i>Q<sub>P</sub></i> and <i>SC</i> values of both systems were also similar, with values of 1.87 to 1.88 g/L⋅h and 93 to 94%, respectively. The morphology of the carriers with and without immobilized cells before and after the fermentation was investigated. The obtained results demonstrated that a repeated-batch fermentation by immobilized cells on rattan pieces, using an STR coupled with a CR, was successfully used to produce high levels of ethanol from SSJ under a VHG condition.
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