Continuous xylose fermentation byCandida shehatae in a two-stage reactor

Abstract

Recent work has identified ethanol toxicity as a major factor preventing continuous production of ethanol at the concentrations obtainable in batch culture. In this paper we investigate the use of a continuous 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 maintained 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⁻¹ h⁻¹ in batch.