Continuous production of acetone and butanol by Clostridium acetobutylicum in a two-stage phosphate limited chemostat

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When Clostridium acetobutylicum was grown in continuous culture under phosphate limitation (0.74 mM) at a pH of 4.3, glucose was fermented to butanol, acetone and ethanol as the major products. At a dilution rate of D=0.025 h−1 and a glucose concentration of 300 mM, the maximal butanol and acetone concentrations were 130 mM and 74 mM, respectively. 20% of the glucose remained in the medium. On the basis of these results a two-stage continuous process was developed in which 87.5% of the glucose was converted into butanol, acetone and ethanol. The cells and minor amounts of acetate and butyrate accounted for the remaining 12.5% of the substrate. The first stage was run at D=0.125 h−1 and 37° C and the second stage at D=0.04 h−1 and 33° C. High yields of butanol and acetone were also obtained in batch culture under phosphate limitation.