Continuous ethanol production by cell-holding culture of yeasts

Abstract

A new apparatus for continuous ethanol production with internal separation of yeast cells is described. The removal of cell-free medium is accomplished by cake filtration through a thin layer of diatomaceous earth. By using a feeding pump connected with a level meter, fresh medium is supplied at the same rate at which the culture solution filtered off. Continuous operation with stepwise increases in glucose concentration in the feed medium resulted in steady states of cell density in accordance with the glucose concentration in the medium. A high density of yeast cells, more than 109/ml of culture broth, was maintained in the reactor with a loss of cells of the order of 104–105 during continuous filtration. Maximum ethanol productivity obtained in this cell-holding culture of commercial baker's yeast was 26 g/l/h when 10% glucose was supplied with a retention time of 1.7 h. The ethanol productivity in continuous operation was increased in proportion to the glucose concentration in the feed medium when growing Saccharomyces cerevisiae IFO 2363 cells were used. At any given glucose concentration, the conversion rate of glucose to ethanol achieved was 96% of the maximum theoretically obtainable.