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Abstract
Bioethanol has attracting growing interest around the world in order to reduce greenhouse gas emission and reduce the dependence on petroleum fuels. The present work focused on the enhancement of ethanol productivity and yield in the fermentation system using sugar beet (Beta vulgaris) molasses as substrate for S. cerevisiae fermentation activity. Analysis of beet molasses revealed that it contains 55 % fermentable sugar. The adjustment of the operational conditions in the fermentation system indicated that submerged anaerobic batch fermentation technique, 18 h fermentation time, 30% molasses concentration and 200 rpm agitation rate were the most suitable ones for bioethanol, biomass, and sugar consumption by S. cerevisiae. Optimization of the cultural conditions for maximum production of ethanol was performed using the taguchi statistical design with investigating eight factors and 18 experimental media. After ANOVA analysis, it was found that inoculum size was the only significant factor for sugar consumption, while biotin, pH, and specific gravity were significant factors in bioethanol production. Ethanol production from beet molasses by S. cerevisiae under the optimized conditions revealed that medium (16) was the optimum for sugar consumption (100 %), fermentation efficiency (99.61), degree of attenuation (62%), bioethanol yield (Y p/s =0.508 g/g ), bioethanol productivity (Q p =1.966 g/500ml/h) and remaining sugar (0.00 g/500ml). Ethanol production by Ca-alginate immobilized S. cerevisiae revealed that it allowed three reuse cycles, after cycle three a significant rupture of beads was observed with stopping of fermentation. The immobilized yeast cells were significantly more tolerant to changes in pH and temperature in the fermentation system, compared with free cells