ABSTRACT
The wide use and application of ethanol in our daily life has necessitated the need for the search of inexpensive sources for ethanol production. Research has shown that biological production of ethanol from lignocellulosic crops like sugar cane and corn is tenable but not sustainable, this is due to their other major economic values for human and livestock nutrition. Elephant grass (Pennisetum purpureum) and banana pseudostem (regarded as agricultural wastes in some regions) are rich in lignocellulose. Their relative availability in large quantities makes them ideal as less expensive feedstocks than the starchy crops of food value. Therefore, this study focused on investigating the potential use of banana pseudostem and elephant grass for the production of bioethanol.
Elephant grass (Pennisetum purpureum) and Banana (Musa acuminate) pseudo-stem were obtained from communities around University of Benin, Benin city. They were washed, dried and milled with clean commercial millers. Saccharomyces cerevisiae was isolated from palm wine, pineapple peels and baker’s yeast using standard microbiological techniques. The milled elephant grass and banana pseudostem were pre-treated with 5% H2SO4. A consecutive addition of 5% NAOH followed, to neutralize residual acids and then mild heating (40oC) to produce fermentable sugars. The resulting mixture was dissolved in 300ml of distilled water and inoculated with strains of Saccharomyces cerevisiae for fermentation. Parameters assessed during fermentation were viable plate count, pH, specific gravity, temperature, reducing sugar and alcohol content. Ethanol was recovered on the final day of fermentation by means of fractional distillation.
The pH and specific gravity of all mediums decreased as fermentation progressed from 6.32 to 2.69 and 1.67 to 0.94 respectively in elephant grass medium and from 6.69 to 2.57 and 2.03 to 0.85 in banana pseudostem medium. Temperature ranged between 26oC to 29oC during fermentation. In elephant grass medium, palm wine yeast, pineapple yeast and baker’s yeast isolates showed steady increase in growth having their highest counts on Day 5 (131±12.05x103 cfu/ml, 92±4.0 x 103 cfu/ml and 148±16.6 x 103 cfu/ml respectively); then a decline on Day 6. For banana pseudostem medium, yeast growth peaked between Day 1 and 2, decline on Day 3 (except pineapple yeast) and then increased between Day 4 and 5. This effect was also reflected in the alcohol production activity of these yeasts in banana pseudostem medium - showing a decline in production on Day 3 and an increase between Day 4 and 5 for palmwine yeast and baker’s yeast. In elephant grass and banana pseudostem media, baker’s yeast produced the highest bioethanol yields of about 72ml and 68.7ml, while pineapple yeast produced the lowest yields which was 41.8ml and 59.3ml respectively. If scaled up, banana pseudostem and elephant grass can serve as better sustainable alternatives to the expensive conventional feedstocks used in ethanol production in Africa and other regions.
