| Currently, researchers are investigating processes to produce ethanol from biomass using plants and crop residues. Ethanol, a clean and renewable fuel, can be used for transportation and is less polluting to the atmosphere. Corn stover is broken down into sugars, such as glucose and xylose, by acid hydrolysis and enzymes and Zymomonas mobilis uses these sugars to produce ethanol during fermentation.; Fermentations were carried out in a 3.0 L bioreactor and 250 ml Erlenmeyer flasks utilizing a 20 percent (w/w) solids concentration. Fermentations were carried out at temperatures of 25°C, 30°C, and 35°C, agitation rates of 200 rpm, 400, rpm, and 600 rpm (100, 200, and 400 rpm for the flasks), and initial cell optical densities of 0.25, 0.5, and 1.0 (initial bacterial cell concentrations of 0.0075, 0.015, and 0.03 g dry cell mass/L).; Both fermentations in 250 ml flasks and the 3.0 L reactor produced the same results. Variation in initial bacterial cell concentration generated the largest differences in ethanol produced. A concentration of 0.3 g dry cell mass per liter produced the most ethanol. Temperature and agitation had minimal effect on the fermentation performance. Only about 2.8 to 4 g/L of ethanol was produced, which occurred during the first 3--6 hours of fermentation.; An inhibitor, other than acetic acid, was determined to be in the hydrolyzate media. This inhibitor was found to negatively affect cellulase activity and Zymomonas mobilis metabolization of the sugar to ethanol. Because of this, the fermentations were not successful in producing a large amount of ethanol. |
