Figure 4 . Kinetics of continuous fermentation with 50 g/L glucose and 4 g/L butyric acid at the dilution rate of 0.06 h-1. (a) Time course data of cell density (OD), glucose, solvents (acetone, butanol, and ethanol), and acids (acetic acid and butyric acid) in the reactor outlet stream; (b) Butanol and ABE yields and butanol productivity.