Browsing by Author "Tewolde, Dawit"

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    Evaluation of Some Wood Rotting Fungi for Bagasse Pretreatment in Ethanol Production
    (Addis Ababa University, 2011-06) Tewolde, Dawit; Gessesse, Amare (PhD)
    Lignocellulosic biomass is a sustainable feedstock for ethanol production compared to other substrates. In the ethanol generation process, pretreatment makes cellulose more accessible to enzymatic hydrolysis by modification of the lignin barrier. Biological pretreatment employs selective rot fungi that preferentially degrade lignin with minimum loss of polysaccharides. The system is not well developed; but is advantageous over other pretreatments because reactions are enzymatic. These fungi produce ligninolytic enzymes, predominantly lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase (Lac) in different combinations. Studies on biological pretreatments have shown lignin weight loss and improvement in ethanol yield. However, only few well characterised white rots have been explored. The aim of this study was to evaluate the potential of 15 wood rotting fungi isolated from Ethiopia for pretreatment during 15 days solid state fermentation, using bagasse as lignocellulosic substrate. The production of ligninolytic enzymes by Fomitiporia aethiopica, F. pseudopunctata, Fomitopsis carnea and Vanderbylia vicina were reported for the first time in this study. The white rots, F. aethiopica, Perenniporia tephropora, Inonotus sp. and Pleurotus sajor-caju, were identified as relatively highly selective based on maximum and minimum productivity of ligninolytic and polysaccharide degrading enzymes, respectively. The pretreatment by the white rots caused ligninolysis and better cellulose digestibility was obtained with higher lignin loss. Among the selective degraders, P. tephropora caused the highest lignin loss (7.71%) and cellulose digestibility (29.44 %) after enzyme hydrolysis of the pretreated bagasse. This digestibility showed an improvement by 38.74 % in comparison with untreated bagasse. In addition to high MnP productivity (55.87 U/g), P. tephropora also produced high titers of Lac (79.65 U/g) in contrast to the other selective degraders that might have attributed to better lignin loss. The ethanol yield from fermentation of cellulase enzyme hydrolysed P. tephropora pretreated bagasse was 1.87 g/L, which was an improvement by 27.21 % compared with untreated bagasse (1.47 g/L). Therefore, P. tephropora pretreatment enhances ethanol production from bagasse through partial degradation of lignin, which improves the accessibility of cellulose to enzyme hydrolysis. Key words: bagasse, ethanol, ligninolytic enzymes, pretreatment, rot fungi