Interaction between the production of ethanol and glycerol in fed-batch bioreactors

During alcoholic fermentation, most of the substrates supplied to the yeasts are converted into ethanol and carbon dioxide generating energy for cell maintenance. However, some of these substrates end up being diverted to other metabolic pathways generating by-products reducing the yield in ethanol production. Glycerol is the most important by-product quantitatively, and its production during fermentation is associated to the production of ethanol. The present study was carried out at a full scale in an industrial fermentation plant applied to sugar cane industry with bioreactors operated in fed-batch mode. Varying levels of the operating factors feeding time, temperature, and concentration of yeast were used in order to verify the interaction between ethanol and glycerol in the fermentative kinetics and how these factors can be optimized to increase ethanol production with reduced carbon losses during the formation of other products. The results obtained indicated that glycerol production is linearly associated with ethanol production and that this correlation is influenced by the process conditions. Feeding time had a significant effect and was inversely proportional to the glycerol/ethanol production ratio. Therefore, it can be said that a moderate feeding rate can reduce the production of glycerol in relation to the ethanol produced reducing losses and increasing the fermentation yield.