PhD Theses

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Browsing PhD Theses by Author "Chacha, Nyangi"

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    Improved fermentation of pinus patula chipped wood waste pretreated by steam explosion and enzymatic hydrolysis for bioethanol production
    (University of Dar es Salaam, 2014) Chacha, Nyangi
    This study utilized Pinus patula chipped wood residue in the production of bioethanol via acid catalysed steam explosion pretretment, enzymatic hydrolysis (both commercial and crude), and fermentation processes. It also optimized fermentation process conditions to maximize bioethanol production. To estimate the cost involved in each process, techno-economic evaluation was undertaken. In pretreatment, the results showed that significant amounts of hemicelluloses were degraded from 23.2 to 5.7% in the mild and to 0.3% in the extensive steam pretreatment. The amount of cellulose significantly increased – from 37.1 to 48.3% – for mild steam pretreatment, whereby the amount of lignin increased from 28.8 to 37.1%, and that of extractives increased from 2 to 17.9%, under most extreme pretreatment conditions. In hydrolysis, commercial enzymes (Cellulaclast 1.5LTM and Novozyme 188TM) yielded more glucose (42.3 g/l) from sample pretreated at severe steam conditions (225 °C, 3% SO2) compared to crude enzymes. The fermentation experiment involved the use of E. coli KO11 (genetically modified organism - GMO) and Saccharomyces cerevisiae ATCC96581 (non-GMO). The results showed no significant difference in terms of ethanol yield when E. coli KO11 and S. cerevisiae ATCC96581 were used. The maximum ethanol obtained in test tube and bioreactor fermentation was 18.30 and 21.30 g/l for Escherichia coli KO11; and 19.41 and 19.63 g/l for S. cerevisiae ATCC96581, respectively, from samples pretreated at 225°C/ 5 min. In the fermentation process variable optimisation, the findings indicated that the optimal condition for maximum ethanol yield were found to be temperature 29.9 (°C), inocula dose of 9.9 v/v and pH 5.1 for S. cerevisiae; and pH (6-6.9) at inoculum 7.5 %v/v for E. coli. Based on the evaluation done in this study, it was found that the enzymatic hydrolysis accounts for 82% of the bioethanol production costs compared to other costed aspects such as raw materials, pretreatment, and fermentation. The study recommends optimisation of pretreatment, enzymatic hydrolysis and fermentation process variables in order to maximize the bioethanol yield. In addition a pilot plant for bioethanol production from P. patula wood chips should be developed in order to permit a detailed and comprehensive techno-economic evaluation.