Production of ethanol with Saccharomyces cerevisiae in a continuous reactor. Note III: an experimental, kinetic study with suspended, recycled biomass

By way of comparison with the kinetic investigation of the continuous production of ethanol in a tubular reactor with immobilized yeasts, a study was carried out of continuous fermentation in a stirred reactor, with final separation and recycling of the microorganisms. Flocculation with potassium ferrocyanide and zinc sulphate was used to separate the biomass. The maintenance of the metabolic activity was assessed. Next, discontinuous fermentation at various substrate and biomass concentrations was performed to determine the kinetics of glucose-ethanol transformation by flocculated and reinoculated Saccharomyces Cerevisiae. Once again, the kinetic expression was a Michaelis-Menten equation, with un-competitive inhibition of the substrate and linear inhibition of the product. The values observed for the various parameters were not very different from those for a biomass immobilized on an inert support or for a free biomass. Finally, the productivities of several types of reactor are compared.