This work deals with the utilization of soybean molasses (a low cost byproduct) to produce
ethanol, an important biofuel, using the microorganism Zymomonas mobilis NRRL 806,
a gram negative bacterium. At the first part of the work, laboratorial scale tests, using
125 mL flasks were performed to evaluate the effect of three variables on ethanol
production: soybean molasses concentration (the sole carbon and nitrogen source), pH and
period of previous aerobial phase. The optimal soybean concentration was around 200 g L-1
of soluble solids, pH between 6.0 and 7.0, and the period of previous aerobial phase did not
provide significant effect. At the second part, kinetic tests were performed to compare the
fermentation yields of Zymomonas mobilis NRRL 806 in flasks and in a bench scale batch
reactor (it was obtained respectively 78.3% and 96.0% of the maximum theoretical yields,
with productions of 24.2 and 29.3 g L-1 of ethanol). The process with a reactor fermentation
using Saccharomyces cerevisiae LPB1 was also tested (it was reached 89.3% of the theoretical
maximum value). A detailed kinetic behavior of the molasses sugars metabolism for
Z. mobilis was also shown, either in reactor or in flasks. This work is a valuable tool for
further works in the subject of ethanol production from agro-industrial by-products.