Effect of Production Factors on the Bioethanol Yield of Tropical Sawdust

Abstract

Bioethanol production from cellulosic materials is important in mitigating the concomitant displacement and exploitation of primary food crops for biofuel production and reducing carbon emissions which exacerbate climate change. The problem of reduced yield in the production and availability of yeast locally poses a barrier to market adoption and penetration of bioethanol. The study examined the effect of particle size and different yeast strains on the yield of bioethanol from waste sawdust that was sourced from a local timber processing centre. The samples of yeast were prepared from baker’s yeast (Saccharomyces cerevisiae) and palm wine yeast (Saccharomyces chevalieri). The sawdust was reduced to 212 μm, 300 μm, and 500 μm particle sizes. The samples of each particle size were pretreated and hydrolyzed with H2SO4 and fermented with S. cerevisiae or S. chevalieri yeast. The results obtained show that the weight, pH, density, viscosity, flash point, and heating value of the produced bioethanol ranged between 221.67 and 322.64 g, 6.2 and 6.6, 0.821 and 0.878 g/mL, 1.073 and 1.193, 14 and 16°C, and 20.5 and 23.1 MJ/kg, respectively, while the alcohol content of each of the samples was 69%. Furthermore, the bioethanol yield from Saccharomyces cerevisiae yeast was 213.9 mL, 193.2 mL, and 186.3 mL, for the 212 μm, 300 μm, and 500 μm particles, while for Saccharomyces chevalieri yeast, the yield was 289.8 mL, 255.3 mL, and 220.8 mL for the 212 μm, 300 μm, and 500 μm, respectively. An ANOVA on the effect of particle size on ethanol yield shows a significant difference at 5% level of significance. The study demonstrated that the use of locally produced yeast and increasing the surface area of sawdust increase bioethanol yield. Hence, it was concluded that better yeast strain use and biomass particle size reduction to a level that allows the optimal surface area for the reaction improve the yield of bioethanol. The study outcome can help in ameliorating the continued dependence on fossil fuels and the food security problems arising from displacing or utilizing food for fuel and could also encourage commercial-scale cellulosic ethanol production from waste.