Alcohol production from sterilized and non-sterilized molasses by Saccharomyces cerevisiae immobilized on brewer's spent grains in two types of continuous bioreactor systems

In this work an integrated cost effective system for continuous alcoholic fermentation of a cheap raw material (molasses) is described, involving yeast immobilized by a simple method on brewer's spent grains, able to ferment in the temperature range 30-40 degrees C, and two types of bioreactors, a Multistage Fixed Bed Tower (MFBT) and a Packed Bed reactor (PB). The MFBT bioreactor gave better results regarding ethanol concentration, productivity and conversion. Furthermore, the use of sterilized and non-sterilized molasses, fed in two similar MFBT bioreactors, showed that ethanol concentration (kg m(-3)) was significantly (p < 0.05) affected by the sterilization process as well as temperature alteration. Higher ethanol concentrations were obtained in the case of non-sterilized molasses (47.4-50.6 kg m(-3)at 35 degrees C and 44.2-48.2 kg m(-3) at 40 degrees C), compared to sterilized molasses, where ethanol concentration ranged from 35.6 to 46.6 kg m(-3) at 35 degrees C and 30.8-44.2 kg m(-3)at 40 degrees C. During 32 days of continuous operation using non-sterilized molasses no contamination was observed. Industrialization of the proposed system seems to have a potential, mainly due to its high fermentation efficiency and the obtained high operational stability. (c) 2012 Elsevier Ltd. All rights reserved.