Effect of Air Sparging on Ethanol Production from Xylose and Glucose in Continuous Chemostat Fermentation Process Utilizing High Cell Density of Candida intermedia 4-6-4T2

Reducing fermentation periods and increasing ethanol productivity are cost effective for ethanol production from lignocellulosic biomass. Increasing the density of cells for fermentation typically increases ethanol productivity, but also increases the concentration of dissolved carbon dioxide (dCO2) in the fermented broth. Such accumulated dCO2 sometimes reduces ethanol production. The Continuous Chemostat Fermentation (CCF) process utilizing high density of Candida intermedia 4-6-4T2 with and without air sparging was evaluated for the effect on ethanol production and rapid fermentation using 24-h cycles. Synthetic fermentation solution without nitrogen sources containing 20 g/L xylose and 30 g/L glucose plus 5 g/L acetic acid as fermentation inhibitor was supplemented into a culture vessel at 15 mL/h, and fermented broth was recovered from the same flask at 15 mL/h. Various conditions were tested to reduce the accumulated dCO2 in the fermented broth, but air sparging at 0.056 vvm was the most effective for ethanol production in the CCF process. For the 24-h startup-batch and 6-cycle CCF process (144 h), the ethanol yield was 0.4 g/g and the cell density of the used C. intermedia 4-6-4T2 for one cycle was one-third compared to that of sequential batch fermentation.