Ethanol produced from lignocellulosic biomass has the potential to become a promisingalternative to gasoline. In this work the simultaneous saccharification and fermentation (SSF)technology was applied for ethanol production from hardwood with focus on cell growth,ethanol production and contamination.The SSF was performed at PH 5.5 and 35°C for different suspended solid concentrations(8%, 10% and 12%) of pretreated birch slurry which contained 16 % total suspended solids.Two different hexose fermenting yeast strain (Ethanol Red) and pentose fermenting yeaststrain were used.Quantifying the concentration of chemical components and metabolites in the fermentationmedium demonstrated that glucose and xylose are the major fermentable sugars in the slurry.The higher load of slurry (12%) represents a higher content of carbohydrates and potentiallyhigher end concentration of ethanol. Moreover, more lactic acid is produced with the lowerload of slurry (8 % or 10 %), presumably due to a result of a less inhibitory environment forbacterial growth. In this context, acetic acid sticks out as the most important inhibitor withconcentrations of 15.2 and 12.5 and 9.7 g/l respectively in the 12 %, 10 % and 8 % (ofsuspended solids) trials. Using pentose fermenting yeast may lead to higher ethanolproduction, lower xylose uptake and lower lactic acid formation. Cell viability and cellvitality determination from fermentation media in all the trails represented a sharplydecreasing trend during the fermentation for both Ethanol Red yeast strain and the pentosefermenting strain yeast strain apparently due to cell decomposition. / Program: MSc in Resource Recovery - Industrial Biotechnology

Thesis (M.Sc. (Microbiology)) -- University of Limpopo, 2020 / Production of bioethanol from lignocellulosic biomass has gained significant attention worldwide as an alternative fuel source for the transportation sector without affecting food supply. Efficient conversion of pentose sugars (L-arabinose and D-xylose) produced during hydrolysis of hemicellulose to ethanol can enhance the economic viability. In this study, a total of 390 yeasts isolated from Marula wine, the gut of dung beetles, herbal concoctions and banana residues were screened for the ability to ferment L-arabinose and D-xylose. Fourteen yeasts were able to ferment both pentose sugars and ten strains were subjected to an adaptation process in the presence of acetic acid using L-arabinose as carbon source. Four adapted strains of Meyerozyma caribbica were able to ferment L-arabinose to ethanol and arabitol in the presence of 3 g/L acetic acid at 35 °C. Meyerozyma caribbica Mu 2.2f fermented D-xylose, L-arabinose and a mixture of D-xylose and L-arabinose to produce 1.7, 3.0 and 1.9 g/L ethanol, respectively, compared to the parental strain with 1.5, 1.0 and 1.8 g/L ethanol, respectively, in the absence of acetic acid. The adapted strain of M. caribbica Mu 2.2f produced 3.6 and 0.8 g/L ethanol from L-arabinose and D-xylose, respectively in the presence of acetic acid while the parental strain failed to grow. In the bioreactor, the adapted strain of M. caribbica Mu 2.2f produced 5.7 g/L ethanol in the presence of 3 g/L acetic acid with an ethanol yield and productivity of 0.338 g/g and 0.158 g/L/h, respectively at a KLa value of 3.3 h-1. The adapted strain produced 26.7 g/L arabitol with a yield of 0.900 g/g at a KLa value of 4.9 h-1. Meyerozyma caribbica Mu 2.2f could potentially be used to produce ethanol and arabitol under stressed conditions. / National Research Foundation (NRF)