Ethanol Production by Saccharomyces cerevisiae Immobilized in Calcium Alginate
<p>Glucose and ethanol diffusion coefficients in calcium alginate were measured in a diffusion cell using the lag time method. The diffusion coefficients decreased as the alginate concentration increased. Glucose and ethanol concentrations had no effect on the diffusion coefficients. Also the...
| Summary: | <p>Glucose and ethanol diffusion coefficients in calcium alginate were measured in a diffusion cell using the lag time method. The diffusion coefficients decreased as the alginate concentration increased. Glucose and ethanol concentrations had no effect on the diffusion coefficients. Also the presence of 20% dead yeast cells had no effect on the diffusion coefficients.</p>
<p>Experiments were conducted under anaerobic conditions to determine the intrinsic, specific rates of growth, glucose uptake, and ethanol production for <i>Saccharomyces cerevisiae</i> immobilized in calcium alginate. The simultaneous processes of diffusion and reaction were analyzed in an alginate membrane to determine the intrinsic, specific growth and reaction rates from glucose and ethanol concentration measurements made outside the alginate phase. Under anaerobic conditions, the specific growth rate of immobilized <i>S. cerevisiae</i> decreased by 20% compared to the growth rate for suspended cells. The specific glucose uptake rate and specific ethanol production rate increased by a factor of four (4) compared to suspended cells. The ethanol yield remained the same and the biomass yield decreased to one-fifth (1/5) the yield for suspended cells.</p>
<p>Further experiments were conducted under aerobic conditions to investigate the effects of dissolved oxygen concentration on the specific rates of growth, glucose uptake, and ethanol production of immobilized <i>S. cerevisiae</i>. Oxygen appears to affect immobilized cells similarly to the way it affects suspended cells.</p>
<p>A mathematical model was developed to quantify the effects of oxygen, glucose, and ethanol on the intrinsic, specific rates of growth, glucose uptake, and ethanol production of immobilized cells. The model was tested using <i>S. cerevisiae</i> immobilized in calcium alginate beads in a well-mixed batch reactor. The mathematical model accurately predicts the bulk fluid glucose and ethanol concentrations.</p>
<p>The mathematical model for intrinsic, specific rates of growth, glucose uptake, and ethanol production was used to simulate the behavior of a continuous plug flow reactor and a continuous stirred tank reactor for ethanol production by <i>S. cerevisiae</i> immobilized in calcium alginate beads. Unsteady-state reactor operation was considered. The effects of bead size, feed glucose concentration, residence time, and dissolved oxygen concentration on reactor performance were investigated.</p>
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