Pilot-scale ethanol fermentation by Zymomonas mobilis from simultaneously saccharified sago starch

Abstract

A simultaneous saccharification of sago starch and ethanol fermentation (SSF), by an enzyme, amyloglucosidase, and a bacterium, Zymomonas mobilis, was studied at pilot-scale. Various SSF processes were performed in batch and semi-batch modes. In the batch SSF processes using a 72 litre stirred-tank fermentor, the final ethanol concentration obtained from 20% (w/w) sago starch was 92.6g litre-1 with 97.4% of the theoretical ethanol yield. In 100 and 500 litre airlift fermentors equipped with systems for self-mixing by C02 recycle the fermentation kinetics were similar to those obtained from the stirred-tank fermentor. Semi-batch SSF processes using a cell-recycle system by ultrafiltration gave about 80% increase of ethanol productivity compared with batch SSF processes.