EVALUATION OF ELEPHANT GRASS (PENNISETUM PURPUREUM) AS SUBSTRATE FOR BIOETHANOL PRODUCTION USING CO-CULTURES OF ASPERGILLUS NIGER AND SACCHAROMYCES CEREVISIAE

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.