Production of acetone-butanol-ethanol by Clostridium acetobutylicum using a spin filter perfusion bioreactor

Abstract

The performance of a custom-built cell perfusion bioreactor was investigated in the biosynthesis of acetone, butanol and ethanol by Clostridium acetobutylicum. In a continuous flow operating mode with total cell retention, i.e., when only the cell-free spent medium was removed, steady-state concentrations of acetone, butanol, ethanol, butyric acid, acetic acid and residual glucose and increasing biomass concentration were observed up to 49 g l −1 of glucose in the feed stream. The steady-state concentrations of acetone, butanol, ethanol, butyric acid and acetic acid were independent of the dilution rate and a function of the feed glucose concentration. Under these conditions a complete utilization of glucose with a maximum volumetric productivity of 1.14 g l −1 h −1 of total solvents was obtained. Increasing the feed glucose concentration to 58 and 63 g l −1 in total cell retention mode led to sustained undampened oscillations resulting from product inhibition. These oscillations were eliminated when a full harvest stream of cell containing spent medium was withdrawn in addition to the cell-free filtrate stream.