Bioethanol production by Saccharomyces cerevisiae from molasses under high gravity fermentation / Heba Elsayed Mohammed Elsayed ; Supervised Amira Mohammed Abutaleb , Tarek Elsayed Mazeed

Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Botany and Microbiology

The use of high and very high gravity fermentation of sugarcane molasses in bioethanol production has a lot of advantages including the lower energy required for the distillation process and the high yield and low cost of bioethanol production. However, using high gravity fermentation is faced with many challenges such as increasing osmotic stress and viscosity.The fermentation processunder five different molasses specific gravities, 1.090, 1.100, 1.130, 1.145, and 1.160, for bioethanol production by Saccharomyces cerevisiae was studied. One of these specific gravities (1.090) was used by El- Hawamdia distillation factories in Egypt. It was found that increasing specific gravity, was accompanied by a decrease in fermentation efficiency.Two stages of sequential optimization strategy were performed in this investigation. The first stage was carried out using the Plackett-Burman design. Eight factors were investigated at three molasses specific gravities (1.130, 1.145, and 1.160). Four factors were found to be significant model terms and had positive effects on bioethanol production.These factors included urea, wheat bran, soy flour, and inoculum size. When a validation test was performed using the predicted conditions, a more than two-fold increase in fermentation efficiency was achieved (83%) at specific gravity 1.130, compared to the basal condition

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