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Concentrating lignocellulosic hydrolysate by evaporation and its fermentation by repeated fedbatch using flocculating Saccharomyces cerevisiae
University of Borås, School of Engineering.
2008 (English)Independent thesis Advanced level (degree of Master (One Year))Student thesis
Abstract [en]

In order to obtain a sugar concentration of more than 100g.l-1of fermentable sugars, a spruce wood hydrolysate was subjected to high pressure and vacuum concentration and the fermentability of each hydrolysate was assessed by fermentation experiments with flocculating S. cerevisiae. The hypothesis that high pressure evaporated hydrolysate (evaporation carried out at 108°C and 1.3 bar) would be more difficult to ferment than vacuum evaporated hydrolysate (evaporation carried out at 80°C and 0.5 bar) was not confirmed by the results. Minor amount of cells lost their flocculating ability after fermentation which their ratio and their viability and vitality was assessed. By vacuum and high pressure concentration, the fermentable sugars (defined as the concentration of glucose, mannose and galactose) in the hydrolysates reached to 120g.l-1 and 129g.l-1 respectively. Compared to the initial hydrolysate the concentration factor represented a 3-fold increase of fermentable sugars. Furfural was evaporated in both trials and its concentration reached to 0.03g.l-1 and 0.1g.l-1 after vacuum and high pressure evaporation respectively. Fermentation with both 0.14h-1and 0.22h-1 initial dilution rates was possible, while more than 96% of furfural and to less extent formic and acetic acids disappeared from the hydrolyzates. However, HMF and levulinic acid remained in the hydrolyzates and concentrated proportionally. More than 84% of the fermentable sugars present in VEH were fermented by fed-batch cultivation using 12g.l-1 yeast and initial dilution rate (ID) of 0.22h-1, and resulted into 0.40±0.01g.g-1 ethanol in 21h. Fermentation of HPEH was as successful as VEH and resulted into more than 86% of the sugar consumption at the corresponding conditions. With an ID of 0.14h-1, more than 97% of the total fermentable sugars were consumed, and ethanol yielded 0.44±0.01g.g-1. A viability and vitality determination from the supernatant of fermentation liquor represented that about 76% of the cells which lost their flocculating ability kept their vitality. Cultivation of yeast with beet molasses was tricky in both batch and fed-batch cultivation as the concentration more than 50g.l-1 in batch cultivation prevent from yeast growing.

Place, publisher, year, edition, pages
University of Borås/School of Engineering , 2008.
Series
Magisteruppsats
Keywords [en]
concentrating, lignocellulosic hydrolysate, evaporation, flocculating, yeast, fermentation, ethanol
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:hb:diva-19095Local ID: 2320/4018OAI: oai:DiVA.org:hb-19095DiVA, id: diva2:1311029
Note
Uppsatsnivå: DAvailable from: 2019-04-30 Created: 2019-04-30

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