Alcohol production from sterilized and non-sterilized molasses by Saccharomyces cerevisiae immobilized on brewerʹs 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 brewerʹs spent grains, able to ferment in the temperature range 30–40 °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−3at 35 °C and 44.2–48.2 kg m−3 at 40 °C), compared to sterilized molasses, where ethanol concentration ranged from 35.6 to 46.6 kg m−3 at 35 °C and 30.8–44.2 kg m−3at 40 °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.