Development of dissolved carbon dioxide-driven-and-controlled repeated batch fermentation process for ethanol production

We previously observed that as glucose is completely exhausted during ethanol fermentation, the dissolved carbon dioxide (DCO₂) level in the fermenter will suddenly decline. This observation was implemented to design and develop a DCO₂-driven-and-controlled repeated batch fermentation process for ethanol production. The process was tested at four different glucose concentrations (~150 g/L, ~200 g/L, ~250 g/L, and ~300 g/L), and each glucose concentration was controlled under three respective DCO₂ control levels (without DCO₂ control, and DCO₂ controlled at either 1000 mg/L or 750 mg/L). The results show that reported process features complete glucose utilization and is self-driven. For glucose concentration less than 200 g/L, ~41%-50% of fermentation time per batch was saved during the repeated batch operation. It took 12.1 ± 1.1 hours-14.9 ± 1.9 hours to complete a batch with glucose feed at ~250 g/L and 21.7 ± 6 hours-31.5 ± 7 hours to complete a batch with glucose feed at ~300 g/L. The reported process is time saving and stable, but the ethanol yield is ~20% lower than the operation without DCO₂ control. Dissolved CO₂ control became essential for glucose concentrations greater than 250 g/L if zero glucose discharge in each batch during the operation is desired.