Fossil fuels are still major energy sources, but the search for renewable energy sources has been encouraged. Bioethanol has been recognized as an alternative to fossil fuels and nowadays it represents more than 90% of the global biofuel production. Bioethanol production from raw sugar beet cossettes as a semi-solid substrate was studied. The study was carried out in the horizontal rotating tubular bioreactor (HRTB) with Saccharomyces cerevisiae as a microbial production strain. The impact of different combinations of HRTB operational parameters such as, rotation speed (5-15 min-1), rotation type [constant or interval (3-15 min h-1)] and working volume (ratio V W/V T = 0.2-0.7) on the bioethanol production was examined. In this study, the highest bioprocess efficiency parameters ([Formula: see text] = 0.47 g g-1, E = 87.36% and Pr = 0.618 g L-1 h-1) were observed at 0.20 V W/V T, interval rotation of 12 min h-1 and rotation speed of 15 min-1. It has to be pointed out that bioethanol production efficiency in the HRTB was on the similar level as observed by bioethanol production from the raw sugar beet juice. Naturally present microorganisms of sugar beet could have a significant impact on bioethanol production. Higher yeast inoculation rate could reduce contaminant activities and, consequently, the bioethanol production efficiency would be improved.
Keywords: Bioethanol; Different HRTB operational conditions; Horizontal rotating tubular bioreactor (HRTB); Raw sugar beet cossettes.