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ABSTRACT

Elephant grass (Pennisetum purpureum) was evaluated for its ethanol production potential using co-cultures of Aspergillus niger and Saccharomyces cerevisiaeisolated from local sources. Proximate and lignocellulose analysis carried out on the plant sample showed that it had crude fibre, lignin, hemicellulose and cellulose contents of 31.5%, 26.78%, 18.76% and 34.16% respectively. Aspergillus niger strains were isolated from soil and bread and were further screened for both qualitative and quantitative cellulase production. Qualitative cellulase assay revealed clear zones around colonies indicative of enzyme activity on solid agar medium containing 0.1% carboxymethyl cellulose (CMC) for all the isolates. Quantitative cellulase assay showed that A. niger isolate AN-15 from soil gave highest cellulase yield of (0.1792 IU/ml/min) and was therefore selected as a co-culture with S. cerevisiae. Saccharomyces cerevisiae strains were isolated from palm wine and burukutu.Isolate PW-4 was selected for fermentation based on ethanol tolerance tests and assimilation of more sugars compared to other isolates. Fermentation of grass substrate was carried out at different concentrations ranging from 2-10% and highest ethanol yield of 1.68g/100ml was observed at an optimum substrate concentration of 6% though the yield was much less than that obtained from equal concentration of glucose (8.38g/100ml). Optimization of culture parameters for ethanol production showed maximum ethanol yield at pH 5, 35oC and agitation rate of 300 rpm. The results of the research also revealed that ethanol production by S. cerevisiae beyond the fourth day of fermentation is significantly reduced.

CHAPTER ONE

INTRODUCTION

Ethanol fuel, ethyl alcohol (CH3CH2OH), is the same type of alcohol found in alcoholic beverages. It is an oxygenated fuel with a high octane value like that of petroleum fuels known to run combustion engines at higher compression ratios and thus provides superior performance (Wheals et al., 1999). The blending of ethanol into petroleum-based automobile fuels can significantly decrease petroleum use and decrease the release of greenhouse gas emissions. Furthermore, ethanol can be a safer alternative to the common additive, methyl tertiary butyl ether (MTBE), in gasoline. Methyl tertiary butyl ether is toxic and is a known contaminant in ground water. Thus, ethanol can be a substitute to mitigate the problems associated with the rising energy demands across the world as well as a way to reduce greenhouse gas emission to as high as 85% (Perlack et al., 2005).

Ethanol may be produced either from petroleum products or from biomass substrate. Today, most of the ethanol produced comes from renewable resources (Bothast and Saha, 1997). Although, most of the ethanol currently produced from renewable resources come from sugarcane and starchy grains, significant efforts are being made to produce ethanol from lignocellulosic biomass (almost 50% of all biomass in the biosphere such as agricultural residues are lignocellulosic biomass). The technological advances in recent years are promising to produce ethanol at low cost from lignocellulosic biomass (Bothast and Saha, 1997). Bioethanol production from sugarcane and starch-rich feed stocks such as corn, potato, is considered a first generation process because it has already been developed (Joshi et al., 2011).

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