Process development for simultaneous starch saccharification and ethanol fermentation by Zymomonas mobilis

Various simultaneous starch saccharification and ethanol fermentation (SSSF) processes were developed and evaluated on batch, semibatch and continuous modes of fermentation in laboratory and pilot scale fermentors using Zymomonas mobilis. Compared with a two-step process involving separate saccharification and fermentation stages, the SSSF reduced the total process time by half. In order to produce ethanol from sago starch economically, the immobilization of amyloglucosidase and Z. mobilis cells was studied. Among the various immobilization methods tested, a co-immobilized system using chitin and sodium alginate appeared most promising with respect to ethanol productivity and operational stability. In order to scale-up the SSSF process, large scale SSSF processes were studied in batch and semibatch fermentation modes. In pilot scale SSSFs, the kinetic results were found to be similar to those from laboratory scale fermentation. Finally, a mathematical model was described for the SSSF process. Simulations of glucose concentration and other fermentation parameters agreed closely with experimental results.ope