Importance of agitation in acetone‐butanol fermentation

The specific rates of anaerobic solvent production by Clostridium acetobutylicum increased with increasing fermentor impeller speed from 190 to 340 rpm ( N Re = 3.93 × 10 4 ). The maximum values were 5.54, 3.85, and 0.8 mmol/h · g cell for butanol, acetone, and ethanol, respectively. Corresponding rates for respective gases produced were 11.60 and 15.88 mmol/h · g cell for H 2 and CO 2 . Further increases in agitation speed resulted in generally decreasing specific production rates to the point of inactive fermentation at 560 rpm. A competition observed between the cellular subsystems for butanol + butyric acid and biomass biosynthesis was evaluated through expressing the energetic yield coefficients. An imbalance between the production and outflux of the former metabolites is apparently further enhanced by a mechanical damage of the cells at high shear rates. A correlation was developed between the production of gases and solvents pointing at both H 2 ‐to‐solvent as well as CO 2 ‐to‐solvent ratios following the same pattern, peaking at 410 rpm.