Continuous Xylose Fermentation by candida shehatae in a two-stage reactor

Recent work has identified ethanol toxicity as a major factor pre­ venting continuous production of ethanol at the concentrations ob­ tainable in batch culture. In this paper we investigate the use of a con­ tinuous two-stage bioreactor design to circumvent toxic effects of ethanol. Biomass is produced via continuous culture in the first stage reactor in which ethanol concentrations are either absent or main­ tained at low levels. The freshly grown cells are fed into the second bioreactor in which high ethanol concentrations are produced. The steady influx of fresh cells and continuous removal of spent cells helps minimize the loss of fermentative activity that results from anaerobiosis and exposure to high ethanol concentrations. A final ethanol concentration of 37 g L-1 and overall yield of .32 g g-1 were obtained with the two-stage reactor as compared to corresponding values of 38 g L-1 and .32 g g-1 obtained in batch. The volumetric rate in the two-state process was .96 g L-1 as compared to .46 g L-1h-1 in batch. *Author to whom all correspondence and reprint requests should be addressed. †Maintained in cooperation with the University of Wisconsin-Madison. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the US Department of Agriculture of any product or service to the exclusion of others which